<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ef0f5-4f2b-78ca-bec4-6b16d58da4f4,g:5365caa7-26be-4752-b5f1-8cf46cf41762-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://pelthos.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="pths-20260630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ef0f5-5176-77c2-87e7-a2330bfdbcc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ef0f5-5176-756d-b7d0-bd7bd088bb69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-77c2-87e7-a2330bfdbcc5" xlink:to="loc_us-gaap_StatementTable_019ef0f5-5176-756d-b7d0-bd7bd088bb69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f433c-15da-7e44-bbfc-2f15c8f65054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5176-756d-b7d0-bd7bd088bb69" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f433c-15da-7e44-bbfc-2f15c8f65054" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7e44-bbfc-2f15c8f65054_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f433c-15da-7e44-bbfc-2f15c8f65054" xlink:to="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7e44-bbfc-2f15c8f65054_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7463-8a0f-8dc36043f431" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f433c-15da-7e44-bbfc-2f15c8f65054" xlink:to="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7463-8a0f-8dc36043f431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019f433c-35da-7dad-9a4d-62ae5963b48e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7463-8a0f-8dc36043f431" xlink:to="loc_us-gaap_NonrelatedPartyMember_019f433c-35da-7dad-9a4d-62ae5963b48e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019f433c-5fe1-7b16-b709-a0379d9a4233" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019f433c-15da-7463-8a0f-8dc36043f431" xlink:to="loc_us-gaap_RelatedPartyMember_019f433c-5fe1-7b16-b709-a0379d9a4233" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-7cd2-9033-539b15661c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5176-756d-b7d0-bd7bd088bb69" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-7cd2-9033-539b15661c1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7cd2-9033-539b15661c1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-7cd2-9033-539b15661c1f" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7cd2-9033-539b15661c1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7517-a23e-32982490abef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-7cd2-9033-539b15661c1f" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7517-a23e-32982490abef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5176-7fe3-97cd-59b60f646251" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7517-a23e-32982490abef" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5176-7fe3-97cd-59b60f646251" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5176-7606-be1b-b5ab54e508d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7517-a23e-32982490abef" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5176-7606-be1b-b5ab54e508d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-77c2-87e7-a2330bfdbcc5" xlink:to="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ef0f5-5176-74ba-828d-56a3099b37b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ef0f5-5176-74ba-828d-56a3099b37b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_019ef0f5-5176-7e71-a178-7abe95afdce2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_RestrictedCashCurrent_019ef0f5-5176-7e71-a178-7abe95afdce2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019ef0f5-5176-729a-95ae-19ed5ff4c603" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019ef0f5-5176-729a-95ae-19ed5ff4c603" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019ef0f5-5176-7d5a-8343-cdf132ee08ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_InventoryNet_019ef0f5-5176-7d5a-8343-cdf132ee08ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019ef0f5-5176-74b5-8e06-2b649604425d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019ef0f5-5176-74b5-8e06-2b649604425d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019ef0f5-5176-7c11-8ad5-97eb9155f84c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_AssetsCurrent_019ef0f5-5176-7c11-8ad5-97eb9155f84c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ef0f5-5176-7338-a225-e3b2d5a1bc11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ef0f5-5176-7338-a225-e3b2d5a1bc11" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019ef0f5-5176-7b49-99a8-d8e632acb991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019ef0f5-5176-7b49-99a8-d8e632acb991" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5176-7605-9e57-f843f12bad74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5176-7605-9e57-f843f12bad74" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ef0f5-5176-74b0-b4ce-39d897259fe1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_Goodwill_019ef0f5-5176-74b0-b4ce-39d897259fe1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019ef0f5-5176-7ef7-a750-3e082eed2bc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ef0f5-5176-7b2e-9cc1-565056510a0b" xlink:to="loc_us-gaap_Assets_019ef0f5-5176-7ef7-a750-3e082eed2bc0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-77c2-87e7-a2330bfdbcc5" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019ef0f5-5176-77de-b48b-3371a795fa00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_AccountsPayableCurrent_019ef0f5-5176-77de-b48b-3371a795fa00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_019ef0f5-5176-7d06-883e-ffd579e1c472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_019ef0f5-5176-7d06-883e-ffd579e1c472" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019ef0f5-5176-7444-b36b-d9e54671e2f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019ef0f5-5176-7444-b36b-d9e54671e2f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_019ef0f5-5176-7327-aa6b-d6c5f9c02815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_019ef0f5-5176-7327-aa6b-d6c5f9c02815" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019ef0f5-5176-794c-ad65-b13827a18fb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019ef0f5-5176-794c-ad65-b13827a18fb7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019ef0f5-5176-7549-b217-2a363fdb6dbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019ef0f5-5176-7549-b217-2a363fdb6dbb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019ef0f5-5176-73e9-b27e-7933cc5a545a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_LiabilitiesCurrent_019ef0f5-5176-73e9-b27e-7933cc5a545a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019ef0f5-5176-78b2-817c-70f6b4e39d09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019ef0f5-5176-78b2-817c-70f6b4e39d09" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019ef0f5-5176-7747-acad-a8c5c40781b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019ef0f5-5176-7747-acad-a8c5c40781b5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_019ef0f5-5176-7e14-8da8-7ec302415605" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_019ef0f5-5176-7e14-8da8-7ec302415605" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredLongTermDebt_019ef0f5-5176-7d23-a757-24950bd046c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_SecuredLongTermDebt_019ef0f5-5176-7d23-a757-24950bd046c3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019ef0f5-5176-7a71-b17c-9dbac039a70b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019ef0f5-5176-7a71-b17c-9dbac039a70b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019ef0f5-5176-76f2-b95b-445406d75aab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_Liabilities_019ef0f5-5176-76f2-b95b-445406d75aab" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019ef0f5-5176-7245-896d-4b63f969bbd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019ef0f5-5176-7245-896d-4b63f969bbd1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019ef0f5-5176-7010-a209-70ab0fe18788" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_PreferredStockValue_019ef0f5-5176-7010-a209-70ab0fe18788" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019ef0f5-5176-751f-8eaa-d280553c82a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_CommonStockValue_019ef0f5-5176-751f-8eaa-d280553c82a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019ef0f5-5176-7d60-9549-183061dacb07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019ef0f5-5176-7d60-9549-183061dacb07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019ef0f5-5176-7b39-a5b2-7a80fc155366" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019ef0f5-5176-7b39-a5b2-7a80fc155366" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ef0f5-5176-76c4-9a63-79c75ccfcb1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ef0f5-5176-76c4-9a63-79c75ccfcb1d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ef0f5-5176-7b80-991b-a9a394a0c970" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ef0f5-5176-7416-944e-0accbe39e20a" xlink:to="loc_us-gaap_StockholdersEquity_019ef0f5-5176-7b80-991b-a9a394a0c970" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019ef0f5-5176-786a-919a-8eaba3a9b858" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ef0f5-5176-7fd2-bd82-71a2a31aea4b" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019ef0f5-5176-786a-919a-8eaba3a9b858" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="pths-20260630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ef0f5-5176-77b2-9db8-e2bfe4ad7e70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_StatementTable_019ef0f5-5176-77b2-9db8-e2bfe4ad7e70" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-78e1-9e39-f1d24d5e506a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5176-77b2-9db8-e2bfe4ad7e70" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-78e1-9e39-f1d24d5e506a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-78e1-9e39-f1d24d5e506a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-78e1-9e39-f1d24d5e506a" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-78e1-9e39-f1d24d5e506a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7a4f-a87c-9b9cbfa81a51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5176-78e1-9e39-f1d24d5e506a" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7a4f-a87c-9b9cbfa81a51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5176-7051-9ed1-c25c4ece1caa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7a4f-a87c-9b9cbfa81a51" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5176-7051-9ed1-c25c4ece1caa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5176-7663-8c55-565b2fcfc6ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5176-7a4f-a87c-9b9cbfa81a51" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5176-7663-8c55-565b2fcfc6ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ef0f5-5176-7be8-a2c1-db4c8afe6cc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ef0f5-5176-7be8-a2c1-db4c8afe6cc6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019ef0f5-5176-7a47-b7ea-c0469214e0fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019ef0f5-5176-7a47-b7ea-c0469214e0fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019ef0f5-5176-72d7-8d0d-4683d857914f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019ef0f5-5176-72d7-8d0d-4683d857914f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5176-7132-83cc-619d5f1547be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5176-7132-83cc-619d5f1547be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ef0f5-5176-74e6-9fcd-4a026ad53caa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ef0f5-5176-74e6-9fcd-4a026ad53caa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019ef0f5-5176-743b-86bd-5a6bbcd085dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019ef0f5-5176-743b-86bd-5a6bbcd085dd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019ef0f5-5176-7ef6-9771-9d1d12916256" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_CommonStockSharesIssued_019ef0f5-5176-7ef6-9771-9d1d12916256" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ef0f5-5176-7d69-a4bc-e039a6549e91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7bf3-be50-8bcdb1655ece" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ef0f5-5176-7d69-a4bc-e039a6549e91" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS" xlink:type="simple" xlink:href="pths-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ef0f5-5176-7edb-a402-a746ae2f1961" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_StatementTable_019ef0f5-5176-7edb-a402-a746ae2f1961" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ef0f5-5176-774d-a70b-81a024496409" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5176-7edb-a402-a746ae2f1961" xlink:to="loc_srt_ProductOrServiceAxis_019ef0f5-5176-774d-a70b-81a024496409" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-774d-a70b-81a024496409_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5176-774d-a70b-81a024496409" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-774d-a70b-81a024496409_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-7d14-add0-b521c4315d02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5176-774d-a70b-81a024496409" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-7d14-add0-b521c4315d02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019fddf1-cc9d-752b-8116-c777c15e591b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-7d14-add0-b521c4315d02" xlink:to="loc_us-gaap_ProductMember_019fddf1-cc9d-752b-8116-c777c15e591b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndCollaborationMember_019ef0f5-5176-7896-8e0c-6ada943b6f61" xlink:href="pths-20260630.xsd#pths_LicenseAndCollaborationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5176-7d14-add0-b521c4315d02" xlink:to="loc_pths_LicenseAndCollaborationMember_019ef0f5-5176-7896-8e0c-6ada943b6f61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019ef0f5-5176-7117-8fd8-04dfc0d800fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_RevenuesAbstract_019ef0f5-5176-7117-8fd8-04dfc0d800fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ef0f5-5176-7a11-b521-0aa4dad9659e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019ef0f5-5176-7117-8fd8-04dfc0d800fd" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ef0f5-5176-7a11-b521-0aa4dad9659e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019ef0f5-5176-7adb-a844-244b8902677a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019ef0f5-5176-7adb-a844-244b8902677a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019ef0f5-5176-719b-8a20-8848467235e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019ef0f5-5176-719b-8a20-8848467235e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ef0f5-5176-78cb-bfc9-d3334bef0c24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ef0f5-5176-78cb-bfc9-d3334bef0c24" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019ef0f5-5176-7d01-994e-a4236c3be326" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019ef0f5-5176-7d01-994e-a4236c3be326" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019ef0f5-5176-75fe-a351-915ecc118bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ef0f5-5176-7173-a67b-4658ae505761" xlink:to="loc_us-gaap_CostsAndExpenses_019ef0f5-5176-75fe-a351-915ecc118bc9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019ef0f5-5176-784b-a8d5-9e55ba7c3d19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_OperatingIncomeLoss_019ef0f5-5176-784b-a8d5-9e55ba7c3d19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019ef0f5-5176-7222-bd24-995a285b9cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019ef0f5-5176-7222-bd24-995a285b9cde" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019ef0f5-5176-774e-b672-a2a0e8aaa711" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019ef0f5-5176-7222-bd24-995a285b9cde" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019ef0f5-5176-774e-b672-a2a0e8aaa711" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ChangeInFairValueOfConvertibleDebt_019ef0f5-5176-7953-9dd6-29639e20ce15" xlink:href="pths-20260630.xsd#pths_ChangeInFairValueOfConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019ef0f5-5176-7222-bd24-995a285b9cde" xlink:to="loc_pths_ChangeInFairValueOfConvertibleDebt_019ef0f5-5176-7953-9dd6-29639e20ce15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019ef0f5-5176-7f95-b366-e6c7dcbc480e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019ef0f5-5176-7222-bd24-995a285b9cde" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019ef0f5-5176-7f95-b366-e6c7dcbc480e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019ef0f5-5176-7bb8-8868-32cfff23802e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019ef0f5-5176-7bb8-8868-32cfff23802e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019ef0f5-5176-7771-93c7-8cc5f55fa978" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019ef0f5-5176-7771-93c7-8cc5f55fa978" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ef0f5-5176-75a6-90a5-98a7efcb2a39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_NetIncomeLoss_019ef0f5-5176-75a6-90a5-98a7efcb2a39" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019ef0f5-5176-71c6-b5a2-4081bf8cf8de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019ef0f5-5176-71c6-b5a2-4081bf8cf8de" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ef0f5-5176-7615-9f74-2bc8ac8ee178" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019ef0f5-5176-71c6-b5a2-4081bf8cf8de" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ef0f5-5176-7615-9f74-2bc8ac8ee178" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ef0f5-5176-7014-bae5-e7193506c019" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019ef0f5-5176-71c6-b5a2-4081bf8cf8de" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ef0f5-5176-7014-bae5-e7193506c019" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019ef0f5-5176-73e9-9431-bfda99abbb62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_EarningsPerShareBasic_019ef0f5-5176-73e9-9431-bfda99abbb62" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019ef0f5-5176-7b35-9055-afdedcb2bdca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019ef0f5-5176-7b35-9055-afdedcb2bdca" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ef0f5-5176-706e-ad81-b0b01e41db7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ef0f5-5176-706e-ad81-b0b01e41db7c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ef0f5-5176-7e70-84fe-5308b68b3e78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5176-7756-8584-ad6636b8f716" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ef0f5-5176-7e70-84fe-5308b68b3e78" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITYDEFICIT" xlink:type="simple" xlink:href="pths-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITYDEFICIT"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITYDEFICIT" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ef0f5-5177-737d-857c-c9b8b688aeba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ef0f5-5177-7d18-b83b-6975980fb459" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5177-737d-857c-c9b8b688aeba" xlink:to="loc_us-gaap_StatementTable_019ef0f5-5177-7d18-b83b-6975980fb459" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5177-7d29-b6c5-b95b033921a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5177-7d18-b83b-6975980fb459" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5177-7d29-b6c5-b95b033921a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7d29-b6c5-b95b033921a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5177-7d29-b6c5-b95b033921a3" xlink:to="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7d29-b6c5-b95b033921a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5177-7d29-b6c5-b95b033921a3" xlink:to="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019ef0f5-5177-7b5c-ba81-4b5bc93d043b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:to="loc_us-gaap_PreferredStockMember_019ef0f5-5177-7b5c-ba81-4b5bc93d043b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ef0f5-5177-7aa1-85e2-93976574c55c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:to="loc_us-gaap_CommonStockMember_019ef0f5-5177-7aa1-85e2-93976574c55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ef0f5-5177-7205-a34e-a6f49c1a6f65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ef0f5-5177-7205-a34e-a6f49c1a6f65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ef0f5-5177-7b6b-8906-8c1797b3fdc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ef0f5-5177-7b6b-8906-8c1797b3fdc0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ef0f5-5177-735f-a03f-1b47d24c4a03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5177-7439-b4ae-b741a44aafa7" xlink:to="loc_us-gaap_RetainedEarningsMember_019ef0f5-5177-735f-a03f-1b47d24c4a03" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5177-759a-90bc-6370f00229a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ef0f5-5177-7d18-b83b-6975980fb459" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5177-759a-90bc-6370f00229a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-759a-90bc-6370f00229a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5177-759a-90bc-6370f00229a8" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-759a-90bc-6370f00229a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-7136-b5cf-cdba2c6d9aca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5177-759a-90bc-6370f00229a8" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-7136-b5cf-cdba2c6d9aca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5177-71d2-ac4d-c9b4b855b710" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-7136-b5cf-cdba2c6d9aca" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5177-71d2-ac4d-c9b4b855b710" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5177-7c17-9226-1f6df4c0e87e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5177-7136-b5cf-cdba2c6d9aca" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5177-7c17-9226-1f6df4c0e87e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ef0f5-5177-737d-857c-c9b8b688aeba" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5177-7d35-a95a-f4f1172f9e84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5177-7d35-a95a-f4f1172f9e84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ef0f5-5177-7802-8d7c-97c4af653368" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ef0f5-5177-7802-8d7c-97c4af653368" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ef0f5-5177-7311-ab6b-294a3a817b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockholdersEquity_019ef0f5-5177-7311-ab6b-294a3a817b9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ef0f5-5177-7c55-a617-3ec5b3766a93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ef0f5-5177-7c55-a617-3ec5b3766a93" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019fddf0-5b31-73aa-8bde-496507e901ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019fddf0-5b31-73aa-8bde-496507e901ad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019f664c-11b3-74f9-b385-4e93641167dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019f664c-11b3-74f9-b385-4e93641167dd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019ef0f5-5177-7279-8966-61205f7c93ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019ef0f5-5177-7279-8966-61205f7c93ea" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019ef0f5-5177-7bda-bcbb-c0fe0d19919d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019ef0f5-5177-7bda-bcbb-c0fe0d19919d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019ef0f5-5177-78d6-87a8-c677d03a4c33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019ef0f5-5177-78d6-87a8-c677d03a4c33" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockSplits_019f033c-88ea-71e6-bdb0-06d5d043b77a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockSplits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockSplits_019f033c-88ea-71e6-bdb0-06d5d043b77a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesOther_019ef0f5-5177-7e19-bb07-c3c7b490540c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesOther_019ef0f5-5177-7e19-bb07-c3c7b490540c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5177-76f6-8669-ffbf6c7e9850" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5177-76f6-8669-ffbf6c7e9850" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019ff255-f248-799b-998e-f4cf88c85bc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019ff255-f248-799b-998e-f4cf88c85bc8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ef0f5-5177-7990-8f38-2b9917d23d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ef0f5-5177-7990-8f38-2b9917d23d4e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ef0f5-5177-71a8-ae95-40c7097f95d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ef0f5-5177-7d90-b926-960108fad07c" xlink:to="loc_us-gaap_NetIncomeLoss_019ef0f5-5177-71a8-ae95-40c7097f95d3" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5177-7314-a128-a70c388be5aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ef0f5-5177-7dc4-8819-4069ace0db80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ef0f5-5177-7dab-9460-6b9d4ab39757" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ORGANIZATIONANDDESCRIPTIONOFBUSINESSNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ORGANIZATIONANDDESCRIPTIONOFBUSINESSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ORGANIZATIONANDDESCRIPTIONOFBUSINESSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-7f78-971e-5e7e6ea6b09c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5240-78bb-8411-9ecf9b0a9bd3" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-7f78-971e-5e7e6ea6b09c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_019ef0f5-5240-7a6a-9ba2-371c1745480b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-7f78-971e-5e7e6ea6b09c" xlink:to="loc_us-gaap_IPOMember_019ef0f5-5240-7a6a-9ba2-371c1745480b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SecuritiesPurchaseAgreementsMember_019ef0f5-5240-7f7a-8264-34025a504a3a" xlink:href="pths-20260630.xsd#pths_SecuritiesPurchaseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5240-7f78-971e-5e7e6ea6b09c" xlink:to="loc_pths_SecuritiesPurchaseAgreementsMember_019ef0f5-5240-7f7a-8264-34025a504a3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5240-76d3-8913-530f3b012ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5240-76d3-8913-530f3b012ad6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5240-76d3-8913-530f3b012ad6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5240-76d3-8913-530f3b012ad6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5240-76d3-8913-530f3b012ad6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5240-7c33-b9d5-6048a1ea6c04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5240-76d3-8913-530f3b012ad6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5240-7c33-b9d5-6048a1ea6c04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5240-772a-9005-b2c4a2d787db" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5240-7c33-b9d5-6048a1ea6c04" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5240-772a-9005-b2c4a2d787db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ef0f5-5240-7eb5-98c0-e9631a13dd8a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_srt_CounterpartyNameAxis_019ef0f5-5240-7eb5-98c0-e9631a13dd8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7eb5-98c0-e9631a13dd8a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5240-7eb5-98c0-e9631a13dd8a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7eb5-98c0-e9631a13dd8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5240-7eb5-98c0-e9631a13dd8a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandMember_019ef0f5-5240-7204-995a-e7ddcf6a2d02" xlink:href="pths-20260630.xsd#pths_LigandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:to="loc_pths_LigandMember_019ef0f5-5240-7204-995a-e7ddcf6a2d02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PIPEInvestorsMember_019ef0f5-5240-7c88-857f-869483f45fb7" xlink:href="pths-20260630.xsd#pths_PIPEInvestorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:to="loc_pths_PIPEInvestorsMember_019ef0f5-5240-7c88-857f-869483f45fb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CompanysSecurityHoldersPriorToMergerMember_019ef0f5-5240-7a6a-8b8c-43996bcd7f0a" xlink:href="pths-20260630.xsd#pths_CompanysSecurityHoldersPriorToMergerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:to="loc_pths_CompanysSecurityHoldersPriorToMergerMember_019ef0f5-5240-7a6a-8b8c-43996bcd7f0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCSecurityHoldersPriorToMergerMember_019ef0f5-5240-74df-850b-51d7ca8ae734" xlink:href="pths-20260630.xsd#pths_LNHCSecurityHoldersPriorToMergerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5240-7536-8653-d37a79bbba7c" xlink:to="loc_pths_LNHCSecurityHoldersPriorToMergerMember_019ef0f5-5240-74df-850b-51d7ca8ae734" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-7bbe-b899-02e4617663fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-7bbe-b899-02e4617663fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-7bbe-b899-02e4617663fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-7bbe-b899-02e4617663fd" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-7bbe-b899-02e4617663fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-79a7-b19d-55905901597a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-7bbe-b899-02e4617663fd" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-79a7-b19d-55905901597a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5240-7d65-8430-4f23dd08898b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-79a7-b19d-55905901597a" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5240-7d65-8430-4f23dd08898b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5240-7f85-8f85-ed6c29b3979c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5240-7f85-8f85-ed6c29b3979c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-7f85-8f85-ed6c29b3979c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5240-7f85-8f85-ed6c29b3979c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-7f85-8f85-ed6c29b3979c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-789d-a58d-97f5213d31e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5240-7f85-8f85-ed6c29b3979c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-789d-a58d-97f5213d31e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019ef0f5-5240-7b8a-bba2-6d9913849d18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-789d-a58d-97f5213d31e1" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019ef0f5-5240-7b8a-bba2-6d9913849d18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ef0f5-5240-75de-a8b8-914fa7bba78c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5240-789d-a58d-97f5213d31e1" xlink:to="loc_us-gaap_LineOfCreditMember_019ef0f5-5240-75de-a8b8-914fa7bba78c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ef0f5-5240-79ed-85d2-dda7e015e4be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ef0f5-5240-79ed-85d2-dda7e015e4be" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ef0f5-5240-79ed-85d2-dda7e015e4be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ef0f5-5240-79ed-85d2-dda7e015e4be" xlink:to="loc_us-gaap_RelatedPartyDomain_019ef0f5-5240-79ed-85d2-dda7e015e4be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ef0f5-5240-746e-8102-dd1eb62a8744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ef0f5-5240-79ed-85d2-dda7e015e4be" xlink:to="loc_us-gaap_RelatedPartyDomain_019ef0f5-5240-746e-8102-dd1eb62a8744" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019ef0f5-5240-7f72-81d6-d3debcadc4c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ef0f5-5240-746e-8102-dd1eb62a8744" xlink:to="loc_us-gaap_RelatedPartyMember_019ef0f5-5240-7f72-81d6-d3debcadc4c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ef0f5-5240-71be-bf41-fbc8c91786be" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_srt_RangeAxis_019ef0f5-5240-71be-bf41-fbc8c91786be" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ef0f5-5240-71be-bf41-fbc8c91786be_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ef0f5-5240-71be-bf41-fbc8c91786be" xlink:to="loc_srt_RangeMember_019ef0f5-5240-71be-bf41-fbc8c91786be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ef0f5-5240-7c7a-856a-4ec8b772ca45" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ef0f5-5240-71be-bf41-fbc8c91786be" xlink:to="loc_srt_RangeMember_019ef0f5-5240-7c7a-856a-4ec8b772ca45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ef0f5-5240-7163-b27e-e747d5aed752" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ef0f5-5240-7c7a-856a-4ec8b772ca45" xlink:to="loc_srt_MinimumMember_019ef0f5-5240-7163-b27e-e747d5aed752" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ef0f5-5240-778b-a50b-6b32d7c25b90" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ef0f5-5240-7c7a-856a-4ec8b772ca45" xlink:to="loc_srt_MaximumMember_019ef0f5-5240-778b-a50b-6b32d7c25b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5240-77e4-9b89-f205c9bbdee3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5240-77e4-9b89-f205c9bbdee3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ef0f5-5240-77e4-9b89-f205c9bbdee3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5240-77e4-9b89-f205c9bbdee3" xlink:to="loc_us-gaap_EquityComponentDomain_019ef0f5-5240-77e4-9b89-f205c9bbdee3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ef0f5-5240-7f0e-8c67-35e3c00608a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ef0f5-5240-77e4-9b89-f205c9bbdee3" xlink:to="loc_us-gaap_EquityComponentDomain_019ef0f5-5240-7f0e-8c67-35e3c00608a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ef0f5-5240-7986-b6d9-a454cda60e94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ef0f5-5240-7f0e-8c67-35e3c00608a3" xlink:to="loc_us-gaap_CommonStockMember_019ef0f5-5240-7986-b6d9-a454cda60e94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ef0f5-5240-72ef-8ffc-9e4c203930cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_CreditFacilityAxis_019ef0f5-5240-72ef-8ffc-9e4c203930cd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5240-72ef-8ffc-9e4c203930cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5240-72ef-8ffc-9e4c203930cd" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5240-72ef-8ffc-9e4c203930cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5240-782b-a773-224859d7f8e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5240-72ef-8ffc-9e4c203930cd" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5240-782b-a773-224859d7f8e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_019ef0f5-5240-7698-85d4-e760c9d43537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ef0f5-5240-782b-a773-224859d7f8e6" xlink:to="loc_us-gaap_BridgeLoanMember_019ef0f5-5240-7698-85d4-e760c9d43537" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5240-709e-a15b-d98777dcd2bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-762e-86eb-274da1f05b02" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5240-709e-a15b-d98777dcd2bc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-709e-a15b-d98777dcd2bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5240-709e-a15b-d98777dcd2bc" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-709e-a15b-d98777dcd2bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-7baa-9934-ee528f96d560" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5240-709e-a15b-d98777dcd2bc" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-7baa-9934-ee528f96d560" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandFacilityMember_019ef0f5-5240-7c19-8e19-90feaa9ef350" xlink:href="pths-20260630.xsd#pths_LigandFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-7baa-9934-ee528f96d560" xlink:to="loc_pths_LigandFacilityMember_019ef0f5-5240-7c19-8e19-90feaa9ef350" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ThirdPartyFacilityMember_019ef0f5-5240-7e9a-8c1b-d48ee31f4229" xlink:href="pths-20260630.xsd#pths_ThirdPartyFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5240-7baa-9934-ee528f96d560" xlink:to="loc_pths_ThirdPartyFacilityMember_019ef0f5-5240-7e9a-8c1b-d48ee31f4229" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NumberOfFDAApprovedProducts_019ef0f5-5240-7c9e-8e62-292484a731aa" xlink:href="pths-20260630.xsd#pths_NumberOfFDAApprovedProducts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_NumberOfFDAApprovedProducts_019ef0f5-5240-7c9e-8e62-292484a731aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NumberOfCommercialProductsActivelyPromoted_019ef0f5-5240-7a36-bc87-a64df1f778d8" xlink:href="pths-20260630.xsd#pths_NumberOfCommercialProductsActivelyPromoted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_NumberOfCommercialProductsActivelyPromoted_019ef0f5-5240-7a36-bc87-a64df1f778d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ef0f5-5240-791b-9c35-d79def1cafbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ef0f5-5240-791b-9c35-d79def1cafbe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019ef0f5-5240-75b9-9337-f80ac5989636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019ef0f5-5240-75b9-9337-f80ac5989636" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_019ef0f5-5240-7523-a84b-1e0cfa2516ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_019ef0f5-5240-7523-a84b-1e0cfa2516ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseOfferingCost_019ef0f5-5240-7da1-b56c-c85b38555c42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpenseOfferingCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_NoninterestExpenseOfferingCost_019ef0f5-5240-7da1-b56c-c85b38555c42" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019ef0f5-5240-7644-bad5-77045e486334" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019ef0f5-5240-7644-bad5-77045e486334" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5240-7af3-8d17-deeee95ef0b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5240-7af3-8d17-deeee95ef0b4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ef0f5-5240-76fd-822e-cd629b99b931" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ef0f5-5240-76fd-822e-cd629b99b931" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ProceedsFromPIPEGross_019ef0f5-5240-7a41-96b4-ce59183d5521" xlink:href="pths-20260630.xsd#pths_ProceedsFromPIPEGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_ProceedsFromPIPEGross_019ef0f5-5240-7a41-96b4-ce59183d5521" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ef0f5-5240-7e35-82ee-3f5f9389bb29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ef0f5-5240-7e35-82ee-3f5f9389bb29" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentAmount1_019ef0f5-5240-7ffa-850d-3c9bbd3ac188" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentAmount1_019ef0f5-5240-7ffa-850d-3c9bbd3ac188" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NumberOfAdditionalPIPEInvestors_019ef0f5-5240-7b10-ab38-5fb0abc48ac3" xlink:href="pths-20260630.xsd#pths_NumberOfAdditionalPIPEInvestors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_NumberOfAdditionalPIPEInvestors_019ef0f5-5240-7b10-ab38-5fb0abc48ac3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_019ef0f5-5240-7438-a588-734f27e81a98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_019ef0f5-5240-7438-a588-734f27e81a98" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionPrice_019fdddd-009e-789a-9b9f-3b116c4f9487" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionPrice_019fdddd-009e-789a-9b9f-3b116c4f9487" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PreferredStockConversionMaximumOwnershipPercentage_019ef0f5-5240-71cd-9843-1c12595ac39e" xlink:href="pths-20260630.xsd#pths_PreferredStockConversionMaximumOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_PreferredStockConversionMaximumOwnershipPercentage_019ef0f5-5240-71cd-9843-1c12595ac39e" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PreferredStockChangeToMaximumPercentageOwnershipNoticePeriod_019ef0f5-5240-79ed-a24e-84f87267499d" xlink:href="pths-20260630.xsd#pths_PreferredStockChangeToMaximumPercentageOwnershipNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_PreferredStockChangeToMaximumPercentageOwnershipNoticePeriod_019ef0f5-5240-79ed-a24e-84f87267499d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5240-747b-b8a5-57e444c25809" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5240-747b-b8a5-57e444c25809" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019ef0f5-5240-7c15-9d94-31e5dafb21df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019ef0f5-5240-7c15-9d94-31e5dafb21df" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5240-710a-b1f3-cfc0fdbdd996" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5240-710a-b1f3-cfc0fdbdd996" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessAcquisitionPercentageOfBusinessOwnedAfterMerger_019ef0f5-5240-74ef-b11d-0f7efcdfaa28" xlink:href="pths-20260630.xsd#pths_BusinessAcquisitionPercentageOfBusinessOwnedAfterMerger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_BusinessAcquisitionPercentageOfBusinessOwnedAfterMerger_019ef0f5-5240-74ef-b11d-0f7efcdfaa28" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ef0f5-5240-7ad3-9de8-789d71bcac6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ef0f5-5240-7ad3-9de8-789d71bcac6a" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019ef0f5-5240-7635-aa8e-8425776bc6d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_us-gaap_LongTermDebtCurrent_019ef0f5-5240-7635-aa8e-8425776bc6d9" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtConversionToEquityValue_019ef0f5-5240-7107-8281-f5e56532d096" xlink:href="pths-20260630.xsd#pths_DebtConversionToEquityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_DebtConversionToEquityValue_019ef0f5-5240-7107-8281-f5e56532d096" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityNumberOfThirdPartyLenders_019ef0f5-5240-77af-af6f-ce9b3540f80b" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityNumberOfThirdPartyLenders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_LineOfCreditFacilityNumberOfThirdPartyLenders_019ef0f5-5240-77af-af6f-ce9b3540f80b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationConsiderationTransferredLiabilitiesSettled_019ef0f5-5240-7c50-938a-2243f46ac54e" xlink:href="pths-20260630.xsd#pths_BusinessCombinationConsiderationTransferredLiabilitiesSettled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-7b15-97bc-0b336c7f0200" xlink:to="loc_pths_BusinessCombinationConsiderationTransferredLiabilitiesSettled_019ef0f5-5240-7c50-938a-2243f46ac54e" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ORGANIZATIONANDDESCRIPTIONOFBUSINESSScheduleofMergerandPIPEFinancingActivitiesDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ORGANIZATIONANDDESCRIPTIONOFBUSINESSScheduleofMergerandPIPEFinancingActivitiesDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ORGANIZATIONANDDESCRIPTIONOFBUSINESSScheduleofMergerandPIPEFinancingActivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-70ae-975e-c0e932c718b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-70ae-975e-c0e932c718b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-79f6-9f7a-36f19b199141" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5240-70ae-975e-c0e932c718b5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-79f6-9f7a-36f19b199141" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-79f6-9f7a-36f19b199141_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-79f6-9f7a-36f19b199141" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-79f6-9f7a-36f19b199141_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-797c-aced-cf21256bdd95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5240-79f6-9f7a-36f19b199141" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-797c-aced-cf21256bdd95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5240-73d4-a5af-365f533fe18d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5240-797c-aced-cf21256bdd95" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5240-73d4-a5af-365f533fe18d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:href="pths-20260630.xsd#pths_PreferredASharesIssuedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5240-73a7-a5f9-fa08889d44cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5240-73a7-a5f9-fa08889d44cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019ef0f5-5240-77d7-873d-b31ce0408706" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019ef0f5-5240-77d7-873d-b31ce0408706" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019ef0f5-5240-7f78-ae9e-e1ea8322c6b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019ef0f5-5240-7f78-ae9e-e1ea8322c6b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5240-7be3-a6bf-989aea950e67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_PreferredASharesIssuedRollForward_019ef0f5-5240-7230-ab75-1e63b564f26e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019ef0f5-5240-7be3-a6bf-989aea950e67" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ef0f5-5240-744e-bc7a-bafd3e69c1a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ProceedsFromPIPEGross_019ef0f5-5240-7a0c-8a36-f6224e085c9e" xlink:href="pths-20260630.xsd#pths_ProceedsFromPIPEGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_pths_ProceedsFromPIPEGross_019ef0f5-5240-7a0c-8a36-f6224e085c9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PIPEProceedsAllocatedToDebtPayable_019ef0f5-5240-7ad3-93ec-a4f848b658ef" xlink:href="pths-20260630.xsd#pths_PIPEProceedsAllocatedToDebtPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_pths_PIPEProceedsAllocatedToDebtPayable_019ef0f5-5240-7ad3-93ec-a4f848b658ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PIPEProceedsAllocatedToFeesAccountsPayable_019ef0f5-5240-75cc-84b7-2e591a37e3c9" xlink:href="pths-20260630.xsd#pths_PIPEProceedsAllocatedToFeesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_pths_PIPEProceedsAllocatedToFeesAccountsPayable_019ef0f5-5240-75cc-84b7-2e591a37e3c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ProceedsFromPIPENet_019ef0f5-5240-7a7f-9b01-862281fd1771" xlink:href="pths-20260630.xsd#pths_ProceedsFromPIPENet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5240-75c3-8ac4-40491eb14ede" xlink:to="loc_pths_ProceedsFromPIPENet_019ef0f5-5240-7a7f-9b01-862281fd1771" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd778-c503-7c9b-89e1-4cabe4c65f3e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_srt_ProductOrServiceAxis_019fd778-c503-7c9b-89e1-4cabe4c65f3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd778-c503-7c9b-89e1-4cabe4c65f3e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd778-c503-7c9b-89e1-4cabe4c65f3e" xlink:to="loc_srt_ProductsAndServicesDomain_019fd778-c503-7c9b-89e1-4cabe4c65f3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd778-c503-79fb-8d8d-4b3d25634012" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd778-c503-7c9b-89e1-4cabe4c65f3e" xlink:to="loc_srt_ProductsAndServicesDomain_019fd778-c503-79fb-8d8d-4b3d25634012" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019fddf2-9a29-7916-9d65-1be9b3f5a0e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd778-c503-79fb-8d8d-4b3d25634012" xlink:to="loc_us-gaap_ProductMember_019fddf2-9a29-7916-9d65-1be9b3f5a0e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZelsuvmiMember_019fd779-080a-7adc-92f0-e2e23dcb2cfe" xlink:href="pths-20260630.xsd#pths_ZelsuvmiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd778-c503-79fb-8d8d-4b3d25634012" xlink:to="loc_pths_ZelsuvmiMember_019fd779-080a-7adc-92f0-e2e23dcb2cfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019fd778-c503-765f-a5ae-c9579e94d99a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_us-gaap_CreditFacilityAxis_019fd778-c503-765f-a5ae-c9579e94d99a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019fd778-c503-765f-a5ae-c9579e94d99a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019fd778-c503-765f-a5ae-c9579e94d99a" xlink:to="loc_us-gaap_CreditFacilityDomain_019fd778-c503-765f-a5ae-c9579e94d99a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019fd778-c503-7725-9a85-23100e50bff3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019fd778-c503-765f-a5ae-c9579e94d99a" xlink:to="loc_us-gaap_CreditFacilityDomain_019fd778-c503-7725-9a85-23100e50bff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019fd778-c503-743e-b9f3-f95d5adc7a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019fd778-c503-7725-9a85-23100e50bff3" xlink:to="loc_us-gaap_SecuredDebtMember_019fd778-c503-743e-b9f3-f95d5adc7a71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd778-c503-7af8-953b-a2bba48cd660" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd778-c503-7af8-953b-a2bba48cd660" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-7af8-953b-a2bba48cd660_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd778-c503-7af8-953b-a2bba48cd660" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-7af8-953b-a2bba48cd660_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-725f-8643-64258abe540a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd778-c503-7af8-953b-a2bba48cd660" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-725f-8643-64258abe540a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019fd778-c503-72fd-846a-1ea9451b8a7f" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-725f-8643-64258abe540a" xlink:to="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019fd778-c503-72fd-846a-1ea9451b8a7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019fd779-080a-704b-b198-146952bf2e6f" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd778-c503-725f-8643-64258abe540a" xlink:to="loc_pths_ConvertibleNotesMember_019fd779-080a-704b-b198-146952bf2e6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd778-c503-7ae6-90d4-50b5021a7425" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd778-c503-7ae6-90d4-50b5021a7425" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-7ae6-90d4-50b5021a7425_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd778-c503-7ae6-90d4-50b5021a7425" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-7ae6-90d4-50b5021a7425_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-70dc-b4d6-dc37e73a6abb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd778-c503-7ae6-90d4-50b5021a7425" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-70dc-b4d6-dc37e73a6abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019fd778-c503-744f-9222-c62e936c49e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-70dc-b4d6-dc37e73a6abb" xlink:to="loc_us-gaap_LineOfCreditMember_019fd778-c503-744f-9222-c62e936c49e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd779-080a-7b5f-829a-31a25dfd6920" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd778-c503-70dc-b4d6-dc37e73a6abb" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd779-080a-7b5f-829a-31a25dfd6920" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019fd779-080a-7237-a2ea-73225df4e695" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_srt_StatementScenarioAxis_019fd779-080a-7237-a2ea-73225df4e695" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019fd779-080a-7237-a2ea-73225df4e695_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019fd779-080a-7237-a2ea-73225df4e695" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019fd779-080a-7237-a2ea-73225df4e695_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019fd779-080a-7c7d-8b9d-e0b3826e5245" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019fd779-080a-7237-a2ea-73225df4e695" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019fd779-080a-7c7d-8b9d-e0b3826e5245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019fd779-080a-73b1-891e-0e6efff456d6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019fd779-080a-7c7d-8b9d-e0b3826e5245" xlink:to="loc_srt_ScenarioForecastMember_019fd779-080a-73b1-891e-0e6efff456d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019fd779-52a6-7762-9d75-6ca2cdc4c3ce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_srt_MajorCustomersAxis_019fd779-52a6-7762-9d75-6ca2cdc4c3ce" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-7762-9d75-6ca2cdc4c3ce_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019fd779-52a6-7762-9d75-6ca2cdc4c3ce" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-7762-9d75-6ca2cdc4c3ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019fd779-52a6-7762-9d75-6ca2cdc4c3ce" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ThreeCustomersMember_019fd779-52a6-7dce-ade9-333b7e05c02b" xlink:href="pths-20260630.xsd#pths_ThreeCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:to="loc_pths_ThreeCustomersMember_019fd779-52a6-7dce-ade9-333b7e05c02b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CustomerOneMember_019fd779-52a6-79bc-8c8a-befd02205971" xlink:href="pths-20260630.xsd#pths_CustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:to="loc_pths_CustomerOneMember_019fd779-52a6-79bc-8c8a-befd02205971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CustomerTwoMember_019fd779-52a6-74e9-9ffd-1e26ea8c8808" xlink:href="pths-20260630.xsd#pths_CustomerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:to="loc_pths_CustomerTwoMember_019fd779-52a6-74e9-9ffd-1e26ea8c8808" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CustomerThreeMember_019fd779-52a6-715b-a39d-1695c5eab4b3" xlink:href="pths-20260630.xsd#pths_CustomerThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fd779-52a6-73f5-abc3-82c073df6b72" xlink:to="loc_pths_CustomerThreeMember_019fd779-52a6-715b-a39d-1695c5eab4b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd779-52a6-7fe3-ab5e-8234f0f5992c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd779-52a6-7fe3-ab5e-8234f0f5992c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7fe3-ab5e-8234f0f5992c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd779-52a6-7fe3-ab5e-8234f0f5992c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7fe3-ab5e-8234f0f5992c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7339-9714-cb00a37a6bda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd779-52a6-7fe3-ab5e-8234f0f5992c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7339-9714-cb00a37a6bda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019fd779-52a6-7ac2-a385-798917866736" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7339-9714-cb00a37a6bda" xlink:to="loc_us-gaap_AccountsReceivableMember_019fd779-52a6-7ac2-a385-798917866736" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_019fd779-52a6-7568-bc47-e41328bdfbec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd779-52a6-7339-9714-cb00a37a6bda" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_019fd779-52a6-7568-bc47-e41328bdfbec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd779-52a6-7198-a332-bf38dd8250fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd779-52a6-7198-a332-bf38dd8250fa" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd779-52a6-7198-a332-bf38dd8250fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd779-52a6-7198-a332-bf38dd8250fa" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd779-52a6-7198-a332-bf38dd8250fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd779-52a6-7eba-a8ab-469559e35172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd779-52a6-7198-a332-bf38dd8250fa" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd779-52a6-7eba-a8ab-469559e35172" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019fd779-52a6-791e-8011-8223071248ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fd779-52a6-7eba-a8ab-469559e35172" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019fd779-52a6-791e-8011-8223071248ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fdd46-b073-7a63-b0c0-05202eeedbed" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5241-75f0-914f-3470f8157fdd" xlink:to="loc_srt_CounterpartyNameAxis_019fdd46-b073-7a63-b0c0-05202eeedbed" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fdd46-b073-7a63-b0c0-05202eeedbed_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fdd46-b073-7a63-b0c0-05202eeedbed" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fdd46-b073-7a63-b0c0-05202eeedbed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fdd46-b073-7c18-96d3-ec6a68d6ad98" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fdd46-b073-7a63-b0c0-05202eeedbed" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fdd46-b073-7c18-96d3-ec6a68d6ad98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandMember_019fdd46-d0b1-7b57-a023-609bb44f4503" xlink:href="pths-20260630.xsd#pths_LigandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fdd46-b073-7c18-96d3-ec6a68d6ad98" xlink:to="loc_pths_LigandMember_019fdd46-d0b1-7b57-a023-609bb44f4503" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019fd778-c503-7c62-88a8-2d4a4adc7a18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019fd778-c503-7c62-88a8-2d4a4adc7a18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd778-c503-766b-8ca9-5f7ee8139883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd778-c503-766b-8ca9-5f7ee8139883" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WorkingCapital_019fd778-c503-79d7-829d-a791a9918907" xlink:href="pths-20260630.xsd#pths_WorkingCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_WorkingCapital_019fd778-c503-79d7-829d-a791a9918907" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd778-c503-7004-877d-6da819f964ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd778-c503-7004-877d-6da819f964ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerExcludingAssessedTaxQuarterlyGrowthPercentage_019fd778-c503-7cbb-b9fe-a3965a7eab90" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerExcludingAssessedTaxQuarterlyGrowthPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_RevenueFromContractWithCustomerExcludingAssessedTaxQuarterlyGrowthPercentage_019fd778-c503-7cbb-b9fe-a3965a7eab90" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_019fd779-080a-77f1-b582-18f9155e1556" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_019fd779-080a-77f1-b582-18f9155e1556" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd778-c503-7533-af68-7f3d2b11733d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd778-c503-7533-af68-7f3d2b11733d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019fd778-c503-7e16-a4ef-b883fec36aa0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019fd778-c503-7e16-a4ef-b883fec36aa0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019fd779-080a-7163-a747-632149ba6b1b" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019fd779-080a-7163-a747-632149ba6b1b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement_019ff0ee-f943-79ff-9801-b36780492404" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement_019ff0ee-f943-79ff-9801-b36780492404" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementNumberOfMilestonePaymentsDue_019fd779-080a-7378-b9ea-704a0566a49b" xlink:href="pths-20260630.xsd#pths_LicenseAgreementNumberOfMilestonePaymentsDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_LicenseAgreementNumberOfMilestonePaymentsDue_019fd779-080a-7378-b9ea-704a0566a49b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementAccruedMilestonePaymentsCurrent_019fd779-080a-770f-bdb4-feb70a35a8ec" xlink:href="pths-20260630.xsd#pths_LicenseAgreementAccruedMilestonePaymentsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_LicenseAgreementAccruedMilestonePaymentsCurrent_019fd779-080a-770f-bdb4-feb70a35a8ec" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_019fd779-080a-7a35-b94a-d36435483d5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_ConvertibleDebt_019fd779-080a-7a35-b94a-d36435483d5e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_019fd779-080a-7927-a370-5a9f2f155b55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_019fd779-080a-7927-a370-5a9f2f155b55" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fd779-52a6-74aa-8af3-d8f52bb47ed1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fd779-52a6-74aa-8af3-d8f52bb47ed1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWriteDown_019fd779-b1c0-7850-b0d0-c59ab2fccce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWriteDown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_us-gaap_InventoryWriteDown_019fd779-b1c0-7850-b0d0-c59ab2fccce9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_InventoryWriteOffNumberOfBatches_019fd779-b1c0-7001-9c39-d902951c94f7" xlink:href="pths-20260630.xsd#pths_InventoryWriteOffNumberOfBatches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5241-79be-9fe6-240ea3510050" xlink:to="loc_pths_InventoryWriteOffNumberOfBatches_019fd779-b1c0-7001-9c39-d902951c94f7" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofReclassificationsMadetoPriorPeriodFinancialStatementsDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofReclassificationsMadetoPriorPeriodFinancialStatementsDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofReclassificationsMadetoPriorPeriodFinancialStatementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_019fa919-ba33-745a-af53-0298ca228341" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_019fa919-ba33-745a-af53-0298ca228341" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_019fa91a-54bb-7ef0-b5df-49ff48567090" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_019fa919-ba33-745a-af53-0298ca228341" xlink:to="loc_srt_RestatementAxis_019fa91a-54bb-7ef0-b5df-49ff48567090" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019fa91a-54bb-7ef0-b5df-49ff48567090_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_019fa91a-54bb-7ef0-b5df-49ff48567090" xlink:to="loc_srt_RestatementDomain_019fa91a-54bb-7ef0-b5df-49ff48567090_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019fa91a-54bb-774c-8cb6-8a01f4e8556d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_019fa91a-54bb-7ef0-b5df-49ff48567090" xlink:to="loc_srt_RestatementDomain_019fa91a-54bb-774c-8cb6-8a01f4e8556d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_019fa91a-54bb-710b-ab15-3243f6deb523" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_019fa91a-54bb-774c-8cb6-8a01f4e8556d" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_019fa91a-54bb-710b-ab15-3243f6deb523" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_019fa91a-54bb-7286-8e84-f7276cb875fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_ProfessionalFees_019fa91a-54bb-7286-8e84-f7276cb875fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019fa91a-54bb-7f34-8334-631368e5c0a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019fa91a-54bb-7f34-8334-631368e5c0a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fa91a-54bb-786b-a696-438b89fdeb31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fa91a-54bb-786b-a696-438b89fdeb31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_019fa91a-54bb-749b-a260-108a252991d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_019fa91a-54bb-749b-a260-108a252991d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities_019fa91a-54bb-79c4-a26f-9c032d356c73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities_019fa91a-54bb-79c4-a26f-9c032d356c73" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019fa91a-54bb-7db7-a401-b4a99de32095" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019fa91a-54bb-7db7-a401-b4a99de32095" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_019fa91a-54bb-7652-9b6f-1a84d6cadef7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_019fa919-fdb0-7d4d-bc0a-57516733b5cb" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_019fa91a-54bb-7652-9b6f-1a84d6cadef7" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ef0f5-5241-7844-9dcb-7e3bf24d7ac4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ef0f5-5241-726b-ad90-66706f5bf5ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ef0f5-5241-7844-9dcb-7e3bf24d7ac4" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ef0f5-5241-726b-ad90-66706f5bf5ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ef0f5-5241-7917-b3d3-5eda9c1e5954" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ef0f5-5241-726b-ad90-66706f5bf5ea" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ef0f5-5241-7917-b3d3-5eda9c1e5954" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-7917-b3d3-5eda9c1e5954_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ef0f5-5241-7917-b3d3-5eda9c1e5954" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-7917-b3d3-5eda9c1e5954_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ef0f5-5241-7917-b3d3-5eda9c1e5954" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_019ef0f5-5241-756b-9c66-7bbe19a31377" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_019ef0f5-5241-756b-9c66-7bbe19a31377" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-7644-9ee8-3b763d9f8af2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-7644-9ee8-3b763d9f8af2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5241-7a57-b3d2-513bf8b1417f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019ef0f5-5241-7a57-b3d2-513bf8b1417f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019ef0f5-5241-77d4-996d-96eb906f41b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_WarrantMember_019ef0f5-5241-77d4-996d-96eb906f41b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5241-7e16-b4f3-54dee1bdc38f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5241-7e16-b4f3-54dee1bdc38f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5241-7215-aa7c-bb18a94e278b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ef0f5-5241-70c1-8fa0-79a5aa5c20d2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5241-7215-aa7c-bb18a94e278b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ef0f5-5241-7746-86bb-949dcf02d086" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ef0f5-5241-7844-9dcb-7e3bf24d7ac4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ef0f5-5241-7746-86bb-949dcf02d086" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofRelatedPartyLiabilitiesDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofRelatedPartyLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofRelatedPartyLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fc866-9029-7082-b53d-d3853cc5765e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fc866-9029-7082-b53d-d3853cc5765e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fc867-1f4a-73be-b2d9-10e67227485d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fc866-9029-7082-b53d-d3853cc5765e" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fc867-1f4a-73be-b2d9-10e67227485d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fc867-1f4a-73be-b2d9-10e67227485d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fc867-1f4a-73be-b2d9-10e67227485d" xlink:to="loc_us-gaap_RelatedPartyDomain_019fc867-1f4a-73be-b2d9-10e67227485d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fc867-1f4a-7433-94c2-3549f444c152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fc867-1f4a-73be-b2d9-10e67227485d" xlink:to="loc_us-gaap_RelatedPartyDomain_019fc867-1f4a-7433-94c2-3549f444c152" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019fc867-1f4a-7453-b522-887388049a16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fc867-1f4a-7433-94c2-3549f444c152" xlink:to="loc_us-gaap_RelatedPartyMember_019fc867-1f4a-7453-b522-887388049a16" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_019fc867-1f4a-7e7a-8488-d8d98c3f0cc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_019fc867-1f4a-7e7a-8488-d8d98c3f0cc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_InterestPayableNoncurrent_019fc867-1f4a-7b4e-a2a8-7286224c47e7" xlink:href="pths-20260630.xsd#pths_InterestPayableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:to="loc_pths_InterestPayableNoncurrent_019fc867-1f4a-7b4e-a2a8-7286224c47e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligation_019fc867-1f4a-7745-bcf6-6875c90d069c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:to="loc_us-gaap_ContractualObligation_019fc867-1f4a-7745-bcf6-6875c90d069c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019fc867-1f4a-793f-8aaf-2c2e00c40452" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fc866-cc74-782f-8fcd-b473185c717d" xlink:to="loc_us-gaap_Liabilities_019fc867-1f4a-793f-8aaf-2c2e00c40452" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ACQUISITIONOFLNHCINCNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ACQUISITIONOFLNHCINCNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ACQUISITIONOFLNHCINCNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7a67-8f2e-8708279406d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7a67-8f2e-8708279406d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7a67-8f2e-8708279406d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7a67-8f2e-8708279406d5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7a67-8f2e-8708279406d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7f4a-9b91-852ed0402260" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7a67-8f2e-8708279406d5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7f4a-9b91-852ed0402260" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5241-750e-8c77-1f64dbfd78ab" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7f4a-9b91-852ed0402260" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5241-750e-8c77-1f64dbfd78ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7ddd-bd33-196f8927f32a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7ddd-bd33-196f8927f32a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7ddd-bd33-196f8927f32a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7ddd-bd33-196f8927f32a" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7ddd-bd33-196f8927f32a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7877-acdc-47783e237736" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7ddd-bd33-196f8927f32a" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7877-acdc-47783e237736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-70be-9819-c2f773cfcc73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7877-acdc-47783e237736" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-70be-9819-c2f773cfcc73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7cfe-a986-22c889649c5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7cfe-a986-22c889649c5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7cfe-a986-22c889649c5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7cfe-a986-22c889649c5e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7cfe-a986-22c889649c5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7318-be56-ba82244f66e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7cfe-a986-22c889649c5e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7318-be56-ba82244f66e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-74e3-ac3d-500f910dc112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7318-be56-ba82244f66e4" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-74e3-ac3d-500f910dc112" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-7247-b9a3-53f50474d7a6" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7318-be56-ba82244f66e4" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-7247-b9a3-53f50474d7a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7775-b3a0-55ad64390528" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7474-b5a1-1b3a70af10f1" xlink:to="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7775-b3a0-55ad64390528" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7775-b3a0-55ad64390528_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7775-b3a0-55ad64390528" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7775-b3a0-55ad64390528_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7342-84d6-9b750949bf3b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7775-b3a0-55ad64390528" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7342-84d6-9b750949bf3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekMember_019ef0f5-5241-7031-b3dc-534b06e57a7b" xlink:href="pths-20260630.xsd#pths_ReedyCreekMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7342-84d6-9b750949bf3b" xlink:to="loc_pths_ReedyCreekMember_019ef0f5-5241-7031-b3dc-534b06e57a7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5241-70dc-9e5d-f7acba01ca99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5241-70dc-9e5d-f7acba01ca99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019ef0f5-5241-7112-8fb2-21a0371f0c3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019ef0f5-5241-7112-8fb2-21a0371f0c3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiability_019ef0f5-5241-7aee-89a1-7acf063207d9" xlink:href="pths-20260630.xsd#pths_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_pths_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiability_019ef0f5-5241-7aee-89a1-7acf063207d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019ef0f5-5241-7ad3-993d-c16aff4ae938" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019ef0f5-5241-7ad3-993d-c16aff4ae938" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019ef0f5-5241-7dd1-93b7-85d605287333" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019ef0f5-5241-7dd1-93b7-85d605287333" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019ef0f5-5241-7584-96d9-2af3291c2fe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019ef0f5-5241-7584-96d9-2af3291c2fe5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-70bb-a3f9-5c90f651a1c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-75a8-bd6c-85bda0066ea6" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-70bb-a3f9-5c90f651a1c5" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofConsiderationinMergerDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ACQUISITIONOFLNHCINCScheduleofConsiderationinMergerDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofConsiderationinMergerDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7462-a30d-68440fc7d09b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7462-a30d-68440fc7d09b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7771-94a4-06baa9a0c4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7462-a30d-68440fc7d09b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7771-94a4-06baa9a0c4f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7771-94a4-06baa9a0c4f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7771-94a4-06baa9a0c4f8" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7771-94a4-06baa9a0c4f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7629-89ee-f55958899d8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ef0f5-5241-7771-94a4-06baa9a0c4f8" xlink:to="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7629-89ee-f55958899d8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-730a-961f-e74043fab277" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ef0f5-5241-7629-89ee-f55958899d8b" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019ef0f5-5241-730a-961f-e74043fab277" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7fbe-bb32-18e5242fde98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ef0f5-5241-7462-a30d-68440fc7d09b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7fbe-bb32-18e5242fde98" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7fbe-bb32-18e5242fde98_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7fbe-bb32-18e5242fde98" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7fbe-bb32-18e5242fde98_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7720-874e-ea39a5aed33d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7fbe-bb32-18e5242fde98" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7720-874e-ea39a5aed33d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5241-765f-864a-3d96982d1f1c" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7720-874e-ea39a5aed33d" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5241-765f-864a-3d96982d1f1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5241-7080-ad6f-079efad442d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ef0f5-5241-7080-ad6f-079efad442d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationConsiderationTransferredEquityInterestPricePerShare_019ef0f5-5241-7d9a-aa1d-860a508937a4" xlink:href="pths-20260630.xsd#pths_BusinessCombinationConsiderationTransferredEquityInterestPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:to="loc_pths_BusinessCombinationConsiderationTransferredEquityInterestPricePerShare_019ef0f5-5241-7d9a-aa1d-860a508937a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019ef0f5-5241-721e-85ad-0ee99549601d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019ef0f5-5241-721e-85ad-0ee99549601d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionRatio_019ef0f5-5241-7231-ac25-627ae0ba47e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ef0f5-5241-7f9a-8539-9e0448a0655a" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionRatio_019ef0f5-5241-7231-ac25-627ae0ba47e8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofTangibleandIntangibleAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ACQUISITIONOFLNHCINCScheduleofTangibleandIntangibleAssetsAcquiredandLiabilitiesAssumedDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofTangibleandIntangibleAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-7d44-8b4b-2b27d283f7ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-7d44-8b4b-2b27d283f7ce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-721a-99a8-e1ff51a27c8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-7d44-8b4b-2b27d283f7ce" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-721a-99a8-e1ff51a27c8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-721a-99a8-e1ff51a27c8f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-721a-99a8-e1ff51a27c8f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-721a-99a8-e1ff51a27c8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7cbf-a4d7-ea1e1377cc9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-721a-99a8-e1ff51a27c8f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7cbf-a4d7-ea1e1377cc9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5241-71d3-a464-da146cadea0c" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7cbf-a4d7-ea1e1377cc9a" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5241-71d3-a464-da146cadea0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019ef0f5-5241-7e6e-8d15-5fa53ba7ba92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019ef0f5-5241-7e6e-8d15-5fa53ba7ba92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019ef0f5-5241-7102-86ac-0b2e9c189622" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019ef0f5-5241-7102-86ac-0b2e9c189622" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019ef0f5-5241-75c1-8f39-f23c5c902fce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019ef0f5-5241-75c1-8f39-f23c5c902fce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019ef0f5-5241-754d-a69e-cb36d1e4d784" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019ef0f5-5241-754d-a69e-cb36d1e4d784" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019ef0f5-5241-7586-b2ef-043e3807901c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019ef0f5-5241-7586-b2ef-043e3807901c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019ef0f5-5241-72f9-ad0f-976a248bb429" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019ef0f5-5241-72f9-ad0f-976a248bb429" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAssets_019ef0f5-5241-7e07-9925-0b7d081ea50c" xlink:href="pths-20260630.xsd#pths_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_pths_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAssets_019ef0f5-5241-7e07-9925-0b7d081ea50c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019ef0f5-5241-76ef-9135-dc686611f187" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019ef0f5-5241-76ef-9135-dc686611f187" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019ef0f5-5241-7fda-8e9d-c1bc23ad69bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019ef0f5-5241-7fda-8e9d-c1bc23ad69bc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesCurrent_019ef0f5-5241-7e7a-a644-70974f517cc8" xlink:href="pths-20260630.xsd#pths_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_pths_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesCurrent_019ef0f5-5241-7e7a-a644-70974f517cc8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt_019ef0f5-5241-7205-9320-5b9f295ca002" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt_019ef0f5-5241-7205-9320-5b9f295ca002" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019ef0f5-5241-7410-9aa7-9c1ab99ca698" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019ef0f5-5241-7410-9aa7-9c1ab99ca698" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesCurrent_019ef0f5-5241-71d8-91e5-57dc853df947" xlink:href="pths-20260630.xsd#pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesCurrent_019ef0f5-5241-71d8-91e5-57dc853df947" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationRecognizedLiabilityAssumedDeferredRevenueLongTermPortion_019ef0f5-5241-71ce-b458-1f07362c9575" xlink:href="pths-20260630.xsd#pths_BusinessCombinationRecognizedLiabilityAssumedDeferredRevenueLongTermPortion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_pths_BusinessCombinationRecognizedLiabilityAssumedDeferredRevenueLongTermPortion_019ef0f5-5241-71ce-b458-1f07362c9575" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesNoncurrent_019ef0f5-5241-7271-85bf-428cb5c26641" xlink:href="pths-20260630.xsd#pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_pths_BusinessCombinationRecognizedLiabilityAssumedOperatingLeaseLiabilitiesNoncurrent_019ef0f5-5241-7271-85bf-428cb5c26641" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019ef0f5-5241-7d4d-9c7e-6f5d6c84ef6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019ef0f5-5241-7d4d-9c7e-6f5d6c84ef6a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-758c-ba31-21e52002aaa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-758c-ba31-21e52002aaa2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_019ef0f5-5241-765e-b041-5c227d967166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_019ef0f5-5241-765e-b041-5c227d967166" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ef0f5-5241-762f-8aa9-3c2ec1b8b1b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_Goodwill_019ef0f5-5241-762f-8aa9-3c2ec1b8b1b4" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019ef0f5-5241-7625-a802-82b6da941d74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7d98-b242-da565403fe76" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019ef0f5-5241-7625-a802-82b6da941d74" xlink:type="arc" order="19"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofProFormaInformationDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#ACQUISITIONOFLNHCINCScheduleofProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/ACQUISITIONOFLNHCINCScheduleofProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7f8b-891b-0761f9ae9e22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-748b-baf9-7f64ac886e73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7f8b-891b-0761f9ae9e22" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-748b-baf9-7f64ac886e73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7d08-8f32-08da38f6b4c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ef0f5-5241-748b-baf9-7f64ac886e73" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7d08-8f32-08da38f6b4c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7d08-8f32-08da38f6b4c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7d08-8f32-08da38f6b4c8" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7d08-8f32-08da38f6b4c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7718-9388-bbb859a1432a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-7d08-8f32-08da38f6b4c8" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7718-9388-bbb859a1432a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5241-7dcb-919a-4226e7b74ce4" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-7718-9388-bbb859a1432a" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5241-7dcb-919a-4226e7b74ce4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019ef0f5-5241-7af1-b7db-1e725347a438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7f8b-891b-0761f9ae9e22" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019ef0f5-5241-7af1-b7db-1e725347a438" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019ef0f5-5241-7d68-9e50-d8edb55501ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ef0f5-5241-7f8b-891b-0761f9ae9e22" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019ef0f5-5241-7d68-9e50-d8edb55501ac" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BALANCESHEETACCOUNTDETAILSScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ef0f5-5241-75b9-8562-879a4a08da7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ef0f5-5241-7b72-a08a-3342906991b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ef0f5-5241-75b9-8562-879a4a08da7d" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ef0f5-5241-7b72-a08a-3342906991b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ef0f5-5241-73af-bca9-f563842721ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ef0f5-5241-7b72-a08a-3342906991b5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ef0f5-5241-73af-bca9-f563842721ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-73af-bca9-f563842721ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ef0f5-5241-73af-bca9-f563842721ba" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-73af-bca9-f563842721ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ef0f5-5241-73af-bca9-f563842721ba" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ManufacturingAndLaboratoryEquipmentMember_019ef0f5-5241-7341-b4af-c4c1d1bcde2c" xlink:href="pths-20260630.xsd#pths_ManufacturingAndLaboratoryEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_pths_ManufacturingAndLaboratoryEquipmentMember_019ef0f5-5241-7341-b4af-c4c1d1bcde2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwarePurchasedMember_019fddda-4426-781e-995c-5ee517e43344" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwarePurchasedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_us-gaap_SoftwarePurchasedMember_019fddda-4426-781e-995c-5ee517e43344" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019ef0f5-5241-7864-ab1f-bad209bb50e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019ef0f5-5241-7864-ab1f-bad209bb50e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019ef0f5-5241-7863-9fe3-249ca18a5548" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_us-gaap_ComputerEquipmentMember_019ef0f5-5241-7863-9fe3-249ca18a5548" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019ef0f5-5241-75e0-b7aa-59134ac5329b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019ef0f5-5241-75e0-b7aa-59134ac5329b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019ef0f5-5241-77f3-9182-08195ea36e24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ef0f5-5241-7b8f-b7b0-feb2537f5dbe" xlink:to="loc_us-gaap_ConstructionInProgressMember_019ef0f5-5241-77f3-9182-08195ea36e24" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019ef0f5-5241-7bfd-9bc1-0d22caf8c455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ef0f5-5241-75b9-8562-879a4a08da7d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019ef0f5-5241-7bfd-9bc1-0d22caf8c455" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ef0f5-5241-7b74-ae1e-d541669937d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ef0f5-5241-75b9-8562-879a4a08da7d" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ef0f5-5241-7b74-ae1e-d541669937d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ef0f5-5241-7eb4-9fb6-3dfed36137a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ef0f5-5241-75b9-8562-879a4a08da7d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ef0f5-5241-7eb4-9fb6-3dfed36137a0" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BALANCESHEETACCOUNTDETAILSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pths_BalanceSheetRelatedDisclosuresLineItems_019fd786-ab99-781c-afba-03b003b0645a" xlink:href="pths-20260630.xsd#pths_BalanceSheetRelatedDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BalanceSheetRelatedDisclosuresTable_019fd786-863e-778a-b475-0b71495cb5b0" xlink:href="pths-20260630.xsd#pths_BalanceSheetRelatedDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pths_BalanceSheetRelatedDisclosuresLineItems_019fd786-ab99-781c-afba-03b003b0645a" xlink:to="loc_pths_BalanceSheetRelatedDisclosuresTable_019fd786-863e-778a-b475-0b71495cb5b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd787-6cb1-77e6-8594-bba0c7a27867" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pths_BalanceSheetRelatedDisclosuresTable_019fd786-863e-778a-b475-0b71495cb5b0" xlink:to="loc_srt_ProductOrServiceAxis_019fd787-6cb1-77e6-8594-bba0c7a27867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd787-6cb1-77e6-8594-bba0c7a27867_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd787-6cb1-77e6-8594-bba0c7a27867" xlink:to="loc_srt_ProductsAndServicesDomain_019fd787-6cb1-77e6-8594-bba0c7a27867_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd787-6cb1-7d9a-bebe-3449ed5f4cea" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd787-6cb1-77e6-8594-bba0c7a27867" xlink:to="loc_srt_ProductsAndServicesDomain_019fd787-6cb1-7d9a-bebe-3449ed5f4cea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZelsuvmiMember_019fd787-6cb1-7221-b076-eafba6968054" xlink:href="pths-20260630.xsd#pths_ZelsuvmiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd787-6cb1-7d9a-bebe-3449ed5f4cea" xlink:to="loc_pths_ZelsuvmiMember_019fd787-6cb1-7221-b076-eafba6968054" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019fd787-366f-7425-babb-ab8270436782" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_BalanceSheetRelatedDisclosuresLineItems_019fd786-ab99-781c-afba-03b003b0645a" xlink:to="loc_us-gaap_Depreciation_019fd787-366f-7425-babb-ab8270436782" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementNumberOfMilestonePaymentsDue_019fd787-6cb1-7680-808b-d2d62fe6320a" xlink:href="pths-20260630.xsd#pths_LicenseAgreementNumberOfMilestonePaymentsDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_BalanceSheetRelatedDisclosuresLineItems_019fd786-ab99-781c-afba-03b003b0645a" xlink:to="loc_pths_LicenseAgreementNumberOfMilestonePaymentsDue_019fd787-6cb1-7680-808b-d2d62fe6320a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementAccruedMilestonePaymentsCurrent_019fd787-6cb1-7e1d-a435-734b243f4461" xlink:href="pths-20260630.xsd#pths_LicenseAgreementAccruedMilestonePaymentsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_BalanceSheetRelatedDisclosuresLineItems_019fd786-ab99-781c-afba-03b003b0645a" xlink:to="loc_pths_LicenseAgreementAccruedMilestonePaymentsCurrent_019fd787-6cb1-7e1d-a435-734b243f4461" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofIntangibleAssetsandGoodwillDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BALANCESHEETACCOUNTDETAILSScheduleofIntangibleAssetsandGoodwillDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofIntangibleAssetsandGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7e21-acc9-8a995ecd95ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7e21-acc9-8a995ecd95ae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7e38-9f31-6fabbd2aa598" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7e21-acc9-8a995ecd95ae" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7e38-9f31-6fabbd2aa598" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7e38-9f31-6fabbd2aa598_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7e38-9f31-6fabbd2aa598" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7e38-9f31-6fabbd2aa598_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-749a-af51-18c626dc5b7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7e38-9f31-6fabbd2aa598" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-749a-af51-18c626dc5b7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-749a-af51-18c626dc5b7b" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseNetOfImpairmentMember_019ef0f5-5241-758e-8232-a12be1c001ea" xlink:href="pths-20260630.xsd#pths_SatoLicenseNetOfImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:to="loc_pths_SatoLicenseNetOfImpairmentMember_019ef0f5-5241-758e-8232-a12be1c001ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-78fe-a6b2-8270a998d1b4" xlink:href="pths-20260630.xsd#pths_XepiTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:to="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-78fe-a6b2-8270a998d1b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7e8c-adf9-54f25a0f2e90" xlink:href="pths-20260630.xsd#pths_XeglyzeTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:to="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7e8c-adf9-54f25a0f2e90" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7cfb-b90d-ff63462b34a9" xlink:href="pths-20260630.xsd#pths_WebsiteDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7234-984e-b1d96d16b6f5" xlink:to="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7cfb-b90d-ff63462b34a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ef0f5-5241-7d9e-a48c-52967fd08001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:to="loc_us-gaap_Goodwill_019ef0f5-5241-7d9e-a48c-52967fd08001" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ef0f5-5241-70c2-8b37-08fa742edb58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ef0f5-5241-70c2-8b37-08fa742edb58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ef0f5-5241-71fd-a8d4-9f2120eda54b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ef0f5-5241-71fd-a8d4-9f2120eda54b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7ee0-aaf8-f304c9e7fef5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7c03-bfaa-3ffb614072c0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7ee0-aaf8-f304c9e7fef5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofOtherLiabilitiesandOtherLongtermLiabilitiesDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#BALANCESHEETACCOUNTDETAILSScheduleofOtherLiabilitiesandOtherLongtermLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/BALANCESHEETACCOUNTDETAILSScheduleofOtherLiabilitiesandOtherLongtermLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7904-8e56-e8a9f6b2eb3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7904-8e56-e8a9f6b2eb3e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79e3-87c5-5e36b3ba0836" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7904-8e56-e8a9f6b2eb3e" xlink:to="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79e3-87c5-5e36b3ba0836" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-79e3-87c5-5e36b3ba0836_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79e3-87c5-5e36b3ba0836" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-79e3-87c5-5e36b3ba0836_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79e3-87c5-5e36b3ba0836" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-7475-a57f-3a6d7c51427d" xlink:href="pths-20260630.xsd#pths_ReedyCreekLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:to="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-7475-a57f-3a6d7c51427d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-72e7-a94d-3fc403a4e12a" xlink:href="pths-20260630.xsd#pths_ZELSUVMILicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:to="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-72e7-a94d-3fc403a4e12a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiLicenseMember_019ef0f5-5241-73e9-888f-c982d938cb31" xlink:href="pths-20260630.xsd#pths_XepiLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:to="loc_pths_XepiLicenseMember_019ef0f5-5241-73e9-888f-c982d938cb31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-779b-a081-fe58d035e5d4" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7bbb-92ab-a817f8fb66c5" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-779b-a081-fe58d035e5d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019faf93-729f-78ee-ab0d-ab3178d87716" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7904-8e56-e8a9f6b2eb3e" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019faf93-729f-78ee-ab0d-ab3178d87716" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019faf93-729f-78ee-ab0d-ab3178d87716_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019faf93-729f-78ee-ab0d-ab3178d87716" xlink:to="loc_us-gaap_RelatedPartyDomain_019faf93-729f-78ee-ab0d-ab3178d87716_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019faf93-729f-71f9-b66e-edd9e7f3e232" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019faf93-729f-78ee-ab0d-ab3178d87716" xlink:to="loc_us-gaap_RelatedPartyDomain_019faf93-729f-71f9-b66e-edd9e7f3e232" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019faf93-8c53-733b-a29b-e4af49c92bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019faf93-729f-71f9-b66e-edd9e7f3e232" xlink:to="loc_us-gaap_NonrelatedPartyMember_019faf93-8c53-733b-a29b-e4af49c92bb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019faf93-a9b3-7d1c-800f-0bcb133d8abe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019faf93-729f-71f9-b66e-edd9e7f3e232" xlink:to="loc_us-gaap_RelatedPartyMember_019faf93-a9b3-7d1c-800f-0bcb133d8abe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationCurrent_019ff225-3b3b-767f-a31f-9f5f9aa58623" xlink:href="pths-20260630.xsd#pths_ContractualObligationCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_pths_ContractualObligationCurrent_019ff225-3b3b-767f-a31f-9f5f9aa58623" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019ef0f5-5241-79be-8ee3-a4fac91898f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019ef0f5-5241-79be-8ee3-a4fac91898f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationNoncurrent_019ef0f5-5241-73b4-868f-96991fb9cae9" xlink:href="pths-20260630.xsd#pths_ContractualObligationNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_pths_ContractualObligationNoncurrent_019ef0f5-5241-73b4-868f-96991fb9cae9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_InterestPayableNoncurrent_019ef0f5-5241-71b9-988d-8a9d8c3628ba" xlink:href="pths-20260630.xsd#pths_InterestPayableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_pths_InterestPayableNoncurrent_019ef0f5-5241-71b9-988d-8a9d8c3628ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019ef0f5-5241-79db-9bfa-9ab045afed1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-719d-8aa8-5146e729def4" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019ef0f5-5241-79db-9bfa-9ab045afed1f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#GOODWILLANDINTANGIBLEASSETSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fa947-a7a7-7cd2-8af9-ed4193ca1226" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fa947-a7a7-7cd2-8af9-ed4193ca1226" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa947-a7a7-7cd2-8af9-ed4193ca1226_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fa947-a7a7-7cd2-8af9-ed4193ca1226" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa947-a7a7-7cd2-8af9-ed4193ca1226_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa947-a7a7-70ec-8d99-f57dac7b1606" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fa947-a7a7-7cd2-8af9-ed4193ca1226" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa947-a7a7-70ec-8d99-f57dac7b1606" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019fa947-a7a7-7d8f-814b-433896911320" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa947-a7a7-70ec-8d99-f57dac7b1606" xlink:to="loc_pths_LNHCInc.Member_019fa947-a7a7-7d8f-814b-433896911320" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fa947-ceca-72d0-98c8-83cfb95345d3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_srt_RangeAxis_019fa947-ceca-72d0-98c8-83cfb95345d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fa947-ceca-72d0-98c8-83cfb95345d3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fa947-ceca-72d0-98c8-83cfb95345d3" xlink:to="loc_srt_RangeMember_019fa947-ceca-72d0-98c8-83cfb95345d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fa947-ceca-722a-afc5-005dcbbea72a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fa947-ceca-72d0-98c8-83cfb95345d3" xlink:to="loc_srt_RangeMember_019fa947-ceca-722a-afc5-005dcbbea72a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fa947-ceca-7a28-95ff-982e85d18ddb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fa947-ceca-722a-afc5-005dcbbea72a" xlink:to="loc_srt_MaximumMember_019fa947-ceca-7a28-95ff-982e85d18ddb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019fa947-ceca-7913-8324-8bcc333201f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019fa947-ceca-7913-8324-8bcc333201f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-7913-8324-8bcc333201f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019fa947-ceca-7913-8324-8bcc333201f2" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-7913-8324-8bcc333201f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-700a-80dc-4663b30035d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019fa947-ceca-7913-8324-8bcc333201f2" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-700a-80dc-4663b30035d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BiofronteraInc.Member_019fa947-ceca-7459-89cf-c485e09ba973" xlink:href="pths-20260630.xsd#pths_BiofronteraInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-700a-80dc-4663b30035d0" xlink:to="loc_pths_BiofronteraInc.Member_019fa947-ceca-7459-89cf-c485e09ba973" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionMember_019fa948-215a-74a4-9605-bc7919e5f389" xlink:href="pths-20260630.xsd#pths_XepiTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-700a-80dc-4663b30035d0" xlink:to="loc_pths_XepiTransactionMember_019fa948-215a-74a4-9605-bc7919e5f389" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XeglyzeAssetPurchaseAgreementMember_019fa948-59ad-7d1f-a042-cba9b2e7c0f5" xlink:href="pths-20260630.xsd#pths_XeglyzeAssetPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019fa947-ceca-700a-80dc-4663b30035d0" xlink:to="loc_pths_XeglyzeAssetPurchaseAgreementMember_019fa948-59ad-7d1f-a042-cba9b2e7c0f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019fa947-ceca-74dd-9b9e-eb2852bab7e9" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019fa947-ceca-74dd-9b9e-eb2852bab7e9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-74dd-9b9e-eb2852bab7e9_default" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019fa947-ceca-74dd-9b9e-eb2852bab7e9" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-74dd-9b9e-eb2852bab7e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-7d85-9a98-4143a4f7b32d" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019fa947-ceca-74dd-9b9e-eb2852bab7e9" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-7d85-9a98-4143a4f7b32d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember_019fa947-ceca-7fa1-ad0c-fd4abc2b077a" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-7d85-9a98-4143a4f7b32d" xlink:to="loc_pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember_019fa947-ceca-7fa1-ad0c-fd4abc2b077a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember_019fa947-ceca-7bab-8668-1385faf071b2" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-7d85-9a98-4143a4f7b32d" xlink:to="loc_pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember_019fa947-ceca-7bab-8668-1385faf071b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember_019fa948-215a-78a2-bd45-c58fbe19ea44" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019fa947-ceca-7d85-9a98-4143a4f7b32d" xlink:to="loc_pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember_019fa948-215a-78a2-bd45-c58fbe19ea44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fa947-ceca-7bd8-9850-566dfc9556da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_srt_CounterpartyNameAxis_019fa947-ceca-7bd8-9850-566dfc9556da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7bd8-9850-566dfc9556da_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fa947-ceca-7bd8-9850-566dfc9556da" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7bd8-9850-566dfc9556da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7014-ac55-87162b060387" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fa947-ceca-7bd8-9850-566dfc9556da" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7014-ac55-87162b060387" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FerrerInternacionalS.A.AndInterquimS.A.U.Member_019fa947-ceca-7d31-9974-90e35c174889" xlink:href="pths-20260630.xsd#pths_FerrerInternacionalS.A.AndInterquimS.A.U.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7014-ac55-87162b060387" xlink:to="loc_pths_FerrerInternacionalS.A.AndInterquimS.A.U.Member_019fa947-ceca-7d31-9974-90e35c174889" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FerrerMember_019fa948-215a-73d9-87f0-70c99f67c73e" xlink:href="pths-20260630.xsd#pths_FerrerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa947-ceca-7014-ac55-87162b060387" xlink:to="loc_pths_FerrerMember_019fa948-215a-73d9-87f0-70c99f67c73e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fa947-ceca-7460-945b-aca7afc18a6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fa947-ceca-7460-945b-aca7afc18a6b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa947-ceca-7460-945b-aca7afc18a6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fa947-ceca-7460-945b-aca7afc18a6b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa947-ceca-7460-945b-aca7afc18a6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa947-ceca-7316-87f8-d042f5bcba2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fa947-ceca-7460-945b-aca7afc18a6b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa947-ceca-7316-87f8-d042f5bcba2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FerrerLicenseAgreementMember_019fa947-ceca-7bdd-b4ee-10d8082897fe" xlink:href="pths-20260630.xsd#pths_FerrerLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa947-ceca-7316-87f8-d042f5bcba2d" xlink:to="loc_pths_FerrerLicenseAgreementMember_019fa947-ceca-7bdd-b4ee-10d8082897fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa948-215a-72fc-a025-953c2a72b67b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa948-215a-72fc-a025-953c2a72b67b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-72fc-a025-953c2a72b67b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa948-215a-72fc-a025-953c2a72b67b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-72fc-a025-953c2a72b67b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-7a88-b56a-56d6f2b38778" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa948-215a-72fc-a025-953c2a72b67b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-7a88-b56a-56d6f2b38778" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionIntangibleAssetMember_019fa948-215a-70d3-b7ff-26a1e03d356c" xlink:href="pths-20260630.xsd#pths_XepiTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-7a88-b56a-56d6f2b38778" xlink:to="loc_pths_XepiTransactionIntangibleAssetMember_019fa948-215a-70d3-b7ff-26a1e03d356c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_019fa948-59ad-7685-8d82-8bd602c7b3d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-7a88-b56a-56d6f2b38778" xlink:to="loc_us-gaap_IntellectualPropertyMember_019fa948-59ad-7685-8d82-8bd602c7b3d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019fa948-9715-7f5d-9459-a339bae46c9c" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa948-215a-7a88-b56a-56d6f2b38778" xlink:to="loc_pths_SatoLicenseMember_019fa948-9715-7f5d-9459-a339bae46c9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeAxis_019fa948-215a-79bf-8350-b21c0eb01103" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-7c44-9147-fe6d3b6599a2" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeAxis_019fa948-215a-79bf-8350-b21c0eb01103" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeDomain_019fa948-215a-79bf-8350-b21c0eb01103_default" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeAxis_019fa948-215a-79bf-8350-b21c0eb01103" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeDomain_019fa948-215a-79bf-8350-b21c0eb01103_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeDomain_019fa948-215a-7fff-b294-a2df2004d8f8" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeAxis_019fa948-215a-79bf-8350-b21c0eb01103" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeDomain_019fa948-215a-7fff-b294-a2df2004d8f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContractualAmountMember_019fa948-215a-7caf-8813-389eaccecd45" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContractualAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeDomain_019fa948-215a-7fff-b294-a2df2004d8f8" xlink:to="loc_pths_AssetAcquisitionContractualAmountMember_019fa948-215a-7caf-8813-389eaccecd45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fa947-a7a7-7c5a-b95b-05bbb8dd52cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_Goodwill_019fa947-a7a7-7c5a-b95b-05bbb8dd52cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019fa947-a7a7-7299-8251-decf45b77ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019fa947-a7a7-7299-8251-decf45b77ce4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionPriceOfAcquisitionExpected_019fa947-ceca-7269-a9fa-b6968b226e5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionPriceOfAcquisitionExpected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AssetAcquisitionPriceOfAcquisitionExpected_019fa947-ceca-7269-a9fa-b6968b226e5f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_019fa947-ceca-7efd-aee8-c023561659a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_019fa947-ceca-7efd-aee8-c023561659a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration_019fa947-ceca-701f-bdde-f1ecd02dc377" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration_019fa947-ceca-701f-bdde-f1ecd02dc377" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionNumberOfContingentMilestones_019fa947-ceca-7a3e-8031-97a3d459ce9c" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionNumberOfContingentMilestones"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_AssetAcquisitionNumberOfContingentMilestones_019fa947-ceca-7a3e-8031-97a3d459ce9c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationNumberOfNetSalesAchievements_019fa947-ceca-7ec5-a6a7-8d1ddf78422a" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationNumberOfNetSalesAchievements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationNumberOfNetSalesAchievements_019fa947-ceca-7ec5-a6a7-8d1ddf78422a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementPurchaseObligationForecastPeriod_019fa947-ceca-7ad6-9228-974ac2009d0f" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementPurchaseObligationForecastPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementPurchaseObligationForecastPeriod_019fa947-ceca-7ad6-9228-974ac2009d0f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementPurchaseObligationBindingForecastPeriod_019fa947-ceca-7292-8a00-a5acbf2e5863" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementPurchaseObligationBindingForecastPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementPurchaseObligationBindingForecastPeriod_019fa947-ceca-7292-8a00-a5acbf2e5863" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementPurchaseRequirementPercentage_019fa947-ceca-7a37-bc8d-8d9ea120b89d" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementPurchaseRequirementPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementPurchaseRequirementPercentage_019fa947-ceca-7a37-bc8d-8d9ea120b89d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementInitialTerm_019fa947-ed2d-7dfb-bf6c-b2f2c19357b4" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementInitialTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementInitialTerm_019fa947-ed2d-7dfb-bf6c-b2f2c19357b4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementRenewalTerm_019fa947-ed2d-75a7-8fd9-32ba78f94a29" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementRenewalTerm_019fa947-ed2d-75a7-8fd9-32ba78f94a29" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementNoticeOfTerminationMinimumPeriodBeforeEndOfTerm_019fa947-ed2d-7ded-a9b1-cb526e32e8d1" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementNoticeOfTerminationMinimumPeriodBeforeEndOfTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementNoticeOfTerminationMinimumPeriodBeforeEndOfTerm_019fa947-ed2d-7ded-a9b1-cb526e32e8d1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019ff103-39eb-756c-9679-f09d1e851e3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019ff103-39eb-756c-9679-f09d1e851e3c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementUpfrontPaymentPayable_019fa947-ed2d-7bbb-8c4f-204a16dc56d4" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementUpfrontPaymentPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementUpfrontPaymentPayable_019fa947-ed2d-7bbb-8c4f-204a16dc56d4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementPaymentsForUpfrontPayment_019fc8aa-93da-724d-9a78-097fc87a4c10" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementPaymentsForUpfrontPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementPaymentsForUpfrontPayment_019fc8aa-93da-724d-9a78-097fc87a4c10" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementPaymentsForInitialSupply_019fddf7-30fc-7d55-b537-7c985b61b60e" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementPaymentsForInitialSupply"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementPaymentsForInitialSupply_019fddf7-30fc-7d55-b537-7c985b61b60e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementRoyaltyBasedOnNetSalesPercent_019fa947-ed2d-74b4-afd7-66d9f9fa64a2" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementRoyaltyBasedOnNetSalesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementRoyaltyBasedOnNetSalesPercent_019fa947-ed2d-74b4-afd7-66d9f9fa64a2" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAndSupplyAgreementInitialSupplyAmount_019fa947-ed2d-72c5-99f9-e45117cde180" xlink:href="pths-20260630.xsd#pths_LicenseAndSupplyAgreementInitialSupplyAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_LicenseAndSupplyAgreementInitialSupplyAmount_019fa947-ed2d-72c5-99f9-e45117cde180" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fa948-215a-7d46-a65d-ca3f5e166aae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fa948-215a-7d46-a65d-ca3f5e166aae" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationToBeTransferredContingentConsideration_019ff0f3-624b-7578-a1f0-2ea1f860f313" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationToBeTransferredContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_pths_AssetAcquisitionConsiderationToBeTransferredContingentConsideration_019ff0f3-624b-7578-a1f0-2ea1f860f313" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019fa948-59ad-7dba-9ecb-862982a1f88c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019fa948-59ad-7dba-9ecb-862982a1f88c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost_019fa948-59ad-742d-ba4b-9030fdafbdb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost_019fa948-59ad-742d-ba4b-9030fdafbdb1" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fa948-7465-71e2-b2c5-b83733c12554" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fa948-7465-71e2-b2c5-b83733c12554" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fa948-9715-7ab4-b44c-0be7c825691c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fa948-9715-7ab4-b44c-0be7c825691c" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_019fa948-9715-7b1d-a401-6baa3dc2cde2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-786b-8e20-dc0979db215a" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_019fa948-9715-7b1d-a401-6baa3dc2cde2" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofConsiderationForAssetAcquisitionDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#GOODWILLANDINTANGIBLEASSETSScheduleofConsiderationForAssetAcquisitionDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofConsiderationForAssetAcquisitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeAxis_019ef0f5-5241-76e3-b6a4-4261a4720682" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeAxis_019ef0f5-5241-76e3-b6a4-4261a4720682" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-76e3-b6a4-4261a4720682_default" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeAxis_019ef0f5-5241-76e3-b6a4-4261a4720682" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-76e3-b6a4-4261a4720682_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-737a-9d9e-e4b83a9f290a" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeAxis_019ef0f5-5241-76e3-b6a4-4261a4720682" xlink:to="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-737a-9d9e-e4b83a9f290a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContractualAmountMember_019ef0f5-5241-7e00-9f38-b0e13edf06e8" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContractualAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-737a-9d9e-e4b83a9f290a" xlink:to="loc_pths_AssetAcquisitionContractualAmountMember_019ef0f5-5241-7e00-9f38-b0e13edf06e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionAllocatedPurchasePriceMember_019ef0f5-5241-7027-9076-8ae40bb021bb" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionAllocatedPurchasePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionConsiderationTypeDomain_019ef0f5-5241-737a-9d9e-e4b83a9f290a" xlink:to="loc_pths_AssetAcquisitionAllocatedPurchasePriceMember_019ef0f5-5241-7027-9076-8ae40bb021bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ef0f5-5241-70ab-8b53-5c1f2bfd9410" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:to="loc_srt_CounterpartyNameAxis_019ef0f5-5241-70ab-8b53-5c1f2bfd9410" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-70ab-8b53-5c1f2bfd9410_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-70ab-8b53-5c1f2bfd9410" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-70ab-8b53-5c1f2bfd9410_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7165-939c-86a9e0cce425" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-70ab-8b53-5c1f2bfd9410" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7165-939c-86a9e0cce425" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_BiofronteraInc.Member_019ef0f5-5241-7689-a620-393cba060627" xlink:href="pths-20260630.xsd#pths_BiofronteraInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7165-939c-86a9e0cce425" xlink:to="loc_pths_BiofronteraInc.Member_019ef0f5-5241-7689-a620-393cba060627" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FerrerMember_019ef0f5-5241-79c6-bc32-63557a88acf2" xlink:href="pths-20260630.xsd#pths_FerrerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7165-939c-86a9e0cce425" xlink:to="loc_pths_FerrerMember_019ef0f5-5241-79c6-bc32-63557a88acf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VariousMember_019ef0f5-5241-7e1e-96a9-ad554fe5b9cf" xlink:href="pths-20260630.xsd#pths_VariousMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7165-939c-86a9e0cce425" xlink:to="loc_pths_VariousMember_019ef0f5-5241-7e1e-96a9-ad554fe5b9cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019ef0f5-5241-7388-b7a0-abe8406a9733" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019ef0f5-5241-7388-b7a0-abe8406a9733" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019ef0f5-5241-7388-b7a0-abe8406a9733_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019ef0f5-5241-7388-b7a0-abe8406a9733" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019ef0f5-5241-7388-b7a0-abe8406a9733_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019ef0f5-5241-7061-935d-8f229b02ab88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019ef0f5-5241-7388-b7a0-abe8406a9733" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019ef0f5-5241-7061-935d-8f229b02ab88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionMember_019ef0f5-5241-708d-afa3-1fdbf7ad032f" xlink:href="pths-20260630.xsd#pths_XepiTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019ef0f5-5241-7061-935d-8f229b02ab88" xlink:to="loc_pths_XepiTransactionMember_019ef0f5-5241-708d-afa3-1fdbf7ad032f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019ef0f5-5241-7b76-83d2-7c238de2ee00" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_019ef0f5-5241-7b84-9952-41f8e6c62f70" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019ef0f5-5241-7b76-83d2-7c238de2ee00" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7b76-83d2-7c238de2ee00_default" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019ef0f5-5241-7b76-83d2-7c238de2ee00" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7b76-83d2-7c238de2ee00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7300-be6b-050c440affd8" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeAxis_019ef0f5-5241-7b76-83d2-7c238de2ee00" xlink:to="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7300-be6b-050c440affd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember_019ef0f5-5241-72c1-aa86-b90cf4ae52bf" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7300-be6b-050c440affd8" xlink:to="loc_pths_ContingentConsiderationAchievementOfCommercialQuantitiesMember_019ef0f5-5241-72c1-aa86-b90cf4ae52bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember_019ef0f5-5241-79f4-a5fa-5c9c67e88caa" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7300-be6b-050c440affd8" xlink:to="loc_pths_ContingentConsiderationAchievementOfSalesBasedMilestonesMember_019ef0f5-5241-79f4-a5fa-5c9c67e88caa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember_019ef0f5-5241-7887-8bcb-ce92ca99db3e" xlink:href="pths-20260630.xsd#pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_AssetAcquisitionContingentConsiderationTypeDomain_019ef0f5-5241-7300-be6b-050c440affd8" xlink:to="loc_pths_ContingentConsiderationAcceptanceOfInitialAPIPurchaseMember_019ef0f5-5241-7887-8bcb-ce92ca99db3e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_019ef0f5-5241-7f8c-9bb1-e749eb73c2a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_019ef0f5-5241-7f8c-9bb1-e749eb73c2a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration_019ef0f5-5241-77cb-9d23-f51488679c71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferredContingentConsideration_019ef0f5-5241-77cb-9d23-f51488679c71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost_019ef0f5-5241-7b27-81f0-51627a93cb21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost_019ef0f5-5241-7b27-81f0-51627a93cb21" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019ef0f5-5241-7bf3-ae09-f8610b0fdcbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019ef0f5-5241-7bf3-ae09-f8610b0fdcbc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetAcquisitionRoyaltyPaymentOnNetSalesPercent_019ef0f5-5241-73f7-a2ff-4536876ad185" xlink:href="pths-20260630.xsd#pths_AssetAcquisitionRoyaltyPaymentOnNetSalesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_019ef0f5-5241-7e60-85b1-708874224243" xlink:to="loc_pths_AssetAcquisitionRoyaltyPaymentOnNetSalesPercent_019ef0f5-5241-73f7-a2ff-4536876ad185" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofDefiniteandIndefiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#GOODWILLANDINTANGIBLEASSETSScheduleofDefiniteandIndefiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofDefiniteandIndefiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7837-ba77-353124976764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7837-ba77-353124976764" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7450-8a44-0ef74bd2d8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019ef0f5-5241-7837-ba77-353124976764" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7450-8a44-0ef74bd2d8ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7450-8a44-0ef74bd2d8ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7450-8a44-0ef74bd2d8ce" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7450-8a44-0ef74bd2d8ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7450-8a44-0ef74bd2d8ce" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7ec8-b3ca-da54e6ea51b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019ef0f5-5241-7ec8-b3ca-da54e6ea51b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-7b7b-a629-789a63baef1e" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-7b7b-a629-789a63baef1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-7b20-a29c-730eedd860d1" xlink:href="pths-20260630.xsd#pths_XepiTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:to="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-7b20-a29c-730eedd860d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7350-9c5f-0e52757ef50c" xlink:href="pths-20260630.xsd#pths_XeglyzeTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:to="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7350-9c5f-0e52757ef50c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7c91-8930-a2b275e31964" xlink:href="pths-20260630.xsd#pths_WebsiteDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-707d-ac7c-4b240b923794" xlink:to="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7c91-8930-a2b275e31964" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ef0f5-5241-7580-ac23-e7298d6193fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ef0f5-5241-7580-ac23-e7298d6193fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ef0f5-5241-772b-b3e0-4bef582c53a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ef0f5-5241-7580-ac23-e7298d6193fc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ef0f5-5241-772b-b3e0-4bef582c53a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ef0f5-5241-7005-b516-f5121dba787e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ef0f5-5241-7580-ac23-e7298d6193fc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ef0f5-5241-7005-b516-f5121dba787e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7d22-b48b-00395e05c7ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ef0f5-5241-7580-ac23-e7298d6193fc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7d22-b48b-00395e05c7ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLossAbstract_019ef0f5-5241-7c61-9371-345683b2b11d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLossAbstract_019ef0f5-5241-7c61-9371-345683b2b11d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_019ef0f5-5241-740f-8d1b-e3b2a4b8ceb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLossAbstract_019ef0f5-5241-7c61-9371-345683b2b11d" xlink:to="loc_us-gaap_GoodwillGross_019ef0f5-5241-740f-8d1b-e3b2a4b8ceb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ef0f5-5241-7ebc-b87c-561cb615d59c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLossAbstract_019ef0f5-5241-7c61-9371-345683b2b11d" xlink:to="loc_us-gaap_Goodwill_019ef0f5-5241-7ebc-b87c-561cb615d59c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetIncludingGoodwillAbstract_019ef0f5-5241-7015-aa9c-787cac1fcd9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetIncludingGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:to="loc_us-gaap_IntangibleAssetsNetIncludingGoodwillAbstract_019ef0f5-5241-7015-aa9c-787cac1fcd9d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ef0f5-5241-79a5-859f-56176f605259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019ef0f5-5241-7b48-b23f-eceb6089c9b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-7090-abf6-f24e8cfa0aee" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019ef0f5-5241-7b48-b23f-eceb6089c9b8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofAmortizationExpenseExpectedtobeRecognizedDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#GOODWILLANDINTANGIBLEASSETSScheduleofAmortizationExpenseExpectedtobeRecognizedDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofAmortizationExpenseExpectedtobeRecognizedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-78d7-b20e-0753e34ebf30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-78d7-b20e-0753e34ebf30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7220-a72e-5988067453cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredIndefiniteLivedIntangibleAssetsByMajorClassTable_019ef0f5-5241-78d7-b20e-0753e34ebf30" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7220-a72e-5988067453cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7220-a72e-5988067453cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7220-a72e-5988067453cb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-7220-a72e-5988067453cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ef0f5-5241-7220-a72e-5988067453cb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DevelopedTechnologyMember_019ef0f5-5241-705a-8817-393951b4a9c1" xlink:href="pths-20260630.xsd#pths_DevelopedTechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:to="loc_pths_DevelopedTechnologyMember_019ef0f5-5241-705a-8817-393951b4a9c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-75e1-b4d4-692d0d55aedc" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-75e1-b4d4-692d0d55aedc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-7405-a595-fd7fad3b5492" xlink:href="pths-20260630.xsd#pths_XepiTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:to="loc_pths_XepiTransactionIntangibleAssetMember_019ef0f5-5241-7405-a595-fd7fad3b5492" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7851-b3b1-28b0e10bc43e" xlink:href="pths-20260630.xsd#pths_XeglyzeTransactionIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:to="loc_pths_XeglyzeTransactionIntangibleAssetMember_019ef0f5-5241-7851-b3b1-28b0e10bc43e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7d05-94be-2313f0a3a507" xlink:href="pths-20260630.xsd#pths_WebsiteDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ef0f5-5241-721e-ad4e-04cc3c8e9fa3" xlink:to="loc_pths_WebsiteDevelopmentMember_019ef0f5-5241-7d05-94be-2313f0a3a507" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019ef0f5-5241-7333-a1dd-891a7a0d6724" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019ef0f5-5241-7333-a1dd-891a7a0d6724" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019ef0f5-5241-71c9-a4b8-1c0855140d13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019ef0f5-5241-71c9-a4b8-1c0855140d13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019ef0f5-5241-7bfe-81a4-bd5bfd69a032" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019ef0f5-5241-7bfe-81a4-bd5bfd69a032" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019ef0f5-5241-7fea-b4c8-89ea5086bbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019ef0f5-5241-7fea-b4c8-89ea5086bbc8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019ef0f5-5241-7a52-8351-f97620561f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019ef0f5-5241-7a52-8351-f97620561f38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019ef0f5-5241-7f1f-a13f-571f29d45176" xlink:href="pths-20260630.xsd#pths_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_pths_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019ef0f5-5241-7f1f-a13f-571f29d45176" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7d29-86a6-ea07a0a67f2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_019ef0f5-5241-79c0-a66c-1206ff77c2fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ef0f5-5241-7d29-86a6-ea07a0a67f2e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/SATOAGREEMENTDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#SATOAGREEMENTDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/SATOAGREEMENTDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:to="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoMember_019ef0f5-5241-71ef-8809-e22b20bd74ba" xlink:href="pths-20260630.xsd#pths_SatoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:to="loc_pths_SatoMember_019ef0f5-5241-71ef-8809-e22b20bd74ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019ef0f5-5241-74df-a71c-beffc3dcec24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019ef0f5-5241-74df-a71c-beffc3dcec24" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerRenewalPeriod_019ef0f5-5241-77a4-950e-8f4e20bbdbf3" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerRenewalPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerRenewalPeriod_019ef0f5-5241-77a4-950e-8f4e20bbdbf3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019ef0f5-5241-729b-8d90-006aaaaac3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019ef0f5-5241-729b-8d90-006aaaaac3e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ef0f5-5241-7adf-88a3-25967df08207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ef0f5-5241-7adf-88a3-25967df08207" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod_019ef0f5-5241-7425-9bf6-8a56d29bdd00" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod_019ef0f5-5241-7425-9bf6-8a56d29bdd00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod_019ef0f5-5241-7f30-99f6-60bd1d7ac443" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod_019ef0f5-5241-7f30-99f6-60bd1d7ac443" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/SATOAGREEMENTDetails_1" xlink:type="simple" xlink:href="pths-20260630.xsd#SATOAGREEMENTDetails_1"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/SATOAGREEMENTDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-73e6-b9b9-8815d6c3a77a" xlink:to="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019ef0f5-5241-7e60-8cd6-f1f834a2a1fa" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoMember_019ef0f5-5241-71ef-8809-e22b20bd74ba" xlink:href="pths-20260630.xsd#pths_SatoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ef0f5-5241-723d-9b13-6b0789c9a6f7" xlink:to="loc_pths_SatoMember_019ef0f5-5241-71ef-8809-e22b20bd74ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerRenewalPeriod_019ef0f5-5241-77a4-950e-8f4e20bbdbf3" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerRenewalPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerRenewalPeriod_019ef0f5-5241-77a4-950e-8f4e20bbdbf3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019ef0f5-5241-729b-8d90-006aaaaac3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019ef0f5-5241-729b-8d90-006aaaaac3e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ef0f5-5241-7adf-88a3-25967df08207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ef0f5-5241-7adf-88a3-25967df08207" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod_019ef0f5-5241-7425-9bf6-8a56d29bdd00" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerContractTerminationWithoutCauseAdvanceWrittenNoticePeriod_019ef0f5-5241-7425-9bf6-8a56d29bdd00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod_019ef0f5-5241-7f30-99f6-60bd1d7ac443" xlink:href="pths-20260630.xsd#pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-7ba8-8979-35c0f2994187" xlink:to="loc_pths_RevenueFromContractWithCustomerContractTerminationMaterialBreachAdvanceWrittenNoticePeriod_019ef0f5-5241-7f30-99f6-60bd1d7ac443" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLENarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLENarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLENarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019fa980-2206-7b0c-8068-eeae471ca831" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_CreditFacilityAxis_019fa980-2206-7b0c-8068-eeae471ca831" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019fa980-2206-7b0c-8068-eeae471ca831_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019fa980-2206-7b0c-8068-eeae471ca831" xlink:to="loc_us-gaap_CreditFacilityDomain_019fa980-2206-7b0c-8068-eeae471ca831_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019fa980-2206-779a-8035-7fa48a219d8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019fa980-2206-7b0c-8068-eeae471ca831" xlink:to="loc_us-gaap_CreditFacilityDomain_019fa980-2206-779a-8035-7fa48a219d8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019fa980-2206-7bed-a12b-722f687780dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019fa980-2206-779a-8035-7fa48a219d8c" xlink:to="loc_us-gaap_SecuredDebtMember_019fa980-2206-7bed-a12b-722f687780dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fa980-2206-791e-b23f-c1572ac6176e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fa980-2206-791e-b23f-c1572ac6176e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-791e-b23f-c1572ac6176e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fa980-2206-791e-b23f-c1572ac6176e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-791e-b23f-c1572ac6176e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-744b-84d0-3f5fdf6ef828" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fa980-2206-791e-b23f-c1572ac6176e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-744b-84d0-3f5fdf6ef828" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019fa980-2206-7d75-806a-004830691af0" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-744b-84d0-3f5fdf6ef828" xlink:to="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019fa980-2206-7d75-806a-004830691af0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019fa980-7754-73ed-b910-ab1df9ce3282" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fa980-2206-744b-84d0-3f5fdf6ef828" xlink:to="loc_pths_ConvertibleNotesMember_019fa980-7754-73ed-b910-ab1df9ce3282" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fa980-2206-760f-9e34-5c68582ae794" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fa980-2206-760f-9e34-5c68582ae794" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-760f-9e34-5c68582ae794_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fa980-2206-760f-9e34-5c68582ae794" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-760f-9e34-5c68582ae794_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-7214-840d-577bc42c8691" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fa980-2206-760f-9e34-5c68582ae794" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-7214-840d-577bc42c8691" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019fa980-2206-7e5c-915d-42b4352f7605" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-7214-840d-577bc42c8691" xlink:to="loc_us-gaap_LineOfCreditMember_019fa980-2206-7e5c-915d-42b4352f7605" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fa980-7754-7c60-a3da-7c547ec8a619" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-7214-840d-577bc42c8691" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fa980-7754-7c60-a3da-7c547ec8a619" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssetBasedLoanFacilityMember_019fa980-7754-7d60-b228-085c0a677b84" xlink:href="pths-20260630.xsd#pths_AssetBasedLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fa980-2206-7214-840d-577bc42c8691" xlink:to="loc_pths_AssetBasedLoanFacilityMember_019fa980-7754-7d60-b228-085c0a677b84" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fa980-adff-745a-90f1-383e8cbc9203" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_srt_ProductOrServiceAxis_019fa980-adff-745a-90f1-383e8cbc9203" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fa980-adff-745a-90f1-383e8cbc9203_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fa980-adff-745a-90f1-383e8cbc9203" xlink:to="loc_srt_ProductsAndServicesDomain_019fa980-adff-745a-90f1-383e8cbc9203_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fa980-adff-743b-bd9f-cfc5c017361b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fa980-adff-745a-90f1-383e8cbc9203" xlink:to="loc_srt_ProductsAndServicesDomain_019fa980-adff-743b-bd9f-cfc5c017361b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiMember_019fa980-adff-763c-bf84-dc4dd3f87d0a" xlink:href="pths-20260630.xsd#pths_XepiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fa980-adff-743b-bd9f-cfc5c017361b" xlink:to="loc_pths_XepiMember_019fa980-adff-763c-bf84-dc4dd3f87d0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZelsuvmiMember_019fa980-adff-7641-87fa-5561bddd3dd2" xlink:href="pths-20260630.xsd#pths_ZelsuvmiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fa980-adff-743b-bd9f-cfc5c017361b" xlink:to="loc_pths_ZelsuvmiMember_019fa980-adff-7641-87fa-5561bddd3dd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019ff25f-0cf2-7cd0-8109-c96ee92e1e1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fa980-adff-743b-bd9f-cfc5c017361b" xlink:to="loc_us-gaap_ProductMember_019ff25f-0cf2-7cd0-8109-c96ee92e1e1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodAxis_019fa980-2206-71d3-98f4-7ce6a5a3f832" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodAxis_019fa980-2206-71d3-98f4-7ce6a5a3f832" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-71d3-98f4-7ce6a5a3f832_default" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_DebtInstrumentRepaymentPeriodAxis_019fa980-2206-71d3-98f4-7ce6a5a3f832" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-71d3-98f4-7ce6a5a3f832_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-76c7-ac33-c04da7c8fca9" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_DebtInstrumentRepaymentPeriodAxis_019fa980-2206-71d3-98f4-7ce6a5a3f832" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-76c7-ac33-c04da7c8fca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodOneMember_019fa980-2206-766f-ab97-5b778349a6c2" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-76c7-ac33-c04da7c8fca9" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodOneMember_019fa980-2206-766f-ab97-5b778349a6c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodTwoMember_019fa980-2206-7cf0-8148-78bd7d217937" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-76c7-ac33-c04da7c8fca9" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodTwoMember_019fa980-2206-7cf0-8148-78bd7d217937" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentPeriodThreeMember_019fa980-4e0e-7478-a362-0c77781a08c5" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_DebtInstrumentRepaymentPeriodDomain_019fa980-2206-76c7-ac33-c04da7c8fca9" xlink:to="loc_pths_DebtInstrumentRepaymentPeriodThreeMember_019fa980-4e0e-7478-a362-0c77781a08c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fa980-2206-7fcc-937c-1be028e6ebdd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_srt_RangeAxis_019fa980-2206-7fcc-937c-1be028e6ebdd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fa980-2206-7fcc-937c-1be028e6ebdd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fa980-2206-7fcc-937c-1be028e6ebdd" xlink:to="loc_srt_RangeMember_019fa980-2206-7fcc-937c-1be028e6ebdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fa980-2206-74c3-9aa5-ca43b8cb1243" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fa980-2206-7fcc-937c-1be028e6ebdd" xlink:to="loc_srt_RangeMember_019fa980-2206-74c3-9aa5-ca43b8cb1243" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fa980-2206-7ac8-8610-77c02c20c7e0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fa980-2206-74c3-9aa5-ca43b8cb1243" xlink:to="loc_srt_MinimumMember_019fa980-2206-7ac8-8610-77c02c20c7e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fa980-adff-75aa-bf86-d7b04d4a4fa5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fa980-2206-74c3-9aa5-ca43b8cb1243" xlink:to="loc_srt_MaximumMember_019fa980-adff-75aa-bf86-d7b04d4a4fa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa980-4e0e-79f7-aff4-5629730a8c19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa980-4e0e-79f7-aff4-5629730a8c19" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa980-4e0e-79f7-aff4-5629730a8c19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa980-4e0e-79f7-aff4-5629730a8c19" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa980-4e0e-79f7-aff4-5629730a8c19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa980-4e0e-764b-ac96-9c8e03d54f2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa980-4e0e-79f7-aff4-5629730a8c19" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa980-4e0e-764b-ac96-9c8e03d54f2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_HorizonWarrantsMember_019fa980-4e0e-711f-8d7e-dbb8c2c88396" xlink:href="pths-20260630.xsd#pths_HorizonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa980-4e0e-764b-ac96-9c8e03d54f2a" xlink:to="loc_pths_HorizonWarrantsMember_019fa980-4e0e-711f-8d7e-dbb8c2c88396" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fa980-adff-754b-9a02-97058d4f69fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_srt_CounterpartyNameAxis_019fa980-adff-754b-9a02-97058d4f69fe" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-754b-9a02-97058d4f69fe_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fa980-adff-754b-9a02-97058d4f69fe" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-754b-9a02-97058d4f69fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-709b-9e16-819d4b57d3c9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fa980-adff-754b-9a02-97058d4f69fe" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-709b-9e16-819d4b57d3c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandMember_019fa980-adff-709a-a9de-e71e2ebebfb6" xlink:href="pths-20260630.xsd#pths_LigandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-709b-9e16-819d4b57d3c9" xlink:to="loc_pths_LigandMember_019fa980-adff-709a-a9de-e71e2ebebfb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleInvestorsMember_019fa980-adff-7d89-9187-375679050e25" xlink:href="pths-20260630.xsd#pths_ConvertibleInvestorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fa980-adff-709b-9e16-819d4b57d3c9" xlink:to="loc_pths_ConvertibleInvestorsMember_019fa980-adff-7d89-9187-375679050e25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019fa981-0f40-794a-832a-aa8774d53a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019fa981-0f40-794a-832a-aa8774d53a9b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-794a-832a-aa8774d53a9b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019fa981-0f40-794a-832a-aa8774d53a9b" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-794a-832a-aa8774d53a9b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-7f50-ba21-0d47a4caadf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019fa981-0f40-794a-832a-aa8774d53a9b" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-7f50-ba21-0d47a4caadf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_019fa981-0f40-77b1-8b41-146dc2aa7f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-7f50-ba21-0d47a4caadf7" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_019fa981-0f40-77b1-8b41-146dc2aa7f7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_019fa981-0f40-7375-b58a-3391112fea5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019fa981-0f40-7f50-ba21-0d47a4caadf7" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_019fa981-0f40-7375-b58a-3391112fea5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7ab2-b1b8-a1ca75e3a494" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa981-7eed-734d-ac5a-05cd6d9bf935" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fa981-7eed-7b2f-8bf1-fdd1f85bef3f" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa981-7eed-734d-ac5a-05cd6d9bf935" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FerrerLicenseAgreementMember_019fa981-7eed-7fa5-a4f9-801b07dfcb3f" xlink:href="pths-20260630.xsd#pths_FerrerLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fa981-7eed-734d-ac5a-05cd6d9bf935" xlink:to="loc_pths_FerrerLicenseAgreementMember_019fa981-7eed-7fa5-a4f9-801b07dfcb3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fa980-2206-7016-99f5-2dc946862007" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fa980-2206-7016-99f5-2dc946862007" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NumberOfProductsAcquired_019fa980-2206-7c4e-a878-415a507367be" xlink:href="pths-20260630.xsd#pths_NumberOfProductsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_NumberOfProductsAcquired_019fa980-2206-7c4e-a878-415a507367be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_019ff203-5ad0-7701-a0db-0e78af98b2d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_019ff203-5ad0-7701-a0db-0e78af98b2d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019fa980-2206-7c7a-9b0c-885edb28b490" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019fa980-2206-7c7a-9b0c-885edb28b490" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd708-02d9-78d9-a659-31bae68e3a85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd708-02d9-78d9-a659-31bae68e3a85" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019fd708-02d9-758a-bbf0-a76168d42f2a" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019fd708-02d9-758a-bbf0-a76168d42f2a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement_019ff205-cab8-7f24-854d-6c217d8e7f95" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_LineOfCreditFacilityRemainingBorrowingCapacityPortionSubjectToMilestoneAchievement_019ff205-cab8-7f24-854d-6c217d8e7f95" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fa980-2206-73c2-ab36-b62208d8e5f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fa980-2206-73c2-ab36-b62208d8e5f1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentVariableRateFloor_019fa980-2206-7772-8ab7-d0f1485cdb02" xlink:href="pths-20260630.xsd#pths_DebtInstrumentVariableRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentVariableRateFloor_019fa980-2206-7772-8ab7-d0f1485cdb02" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fa980-2206-7d96-bc49-2d70fb4e32e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fa980-2206-7d96-bc49-2d70fb4e32e3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentNumberOfMonthlyPayments_019fa980-2206-71fa-b13f-61f892b7e780" xlink:href="pths-20260630.xsd#pths_DebtInstrumentNumberOfMonthlyPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentNumberOfMonthlyPayments_019fa980-2206-71fa-b13f-61f892b7e780" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentMilestoneTrailing12MonthNetRevenueMinimum_019fa980-2206-744f-bac1-deaa2987573a" xlink:href="pths-20260630.xsd#pths_DebtInstrumentMilestoneTrailing12MonthNetRevenueMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentMilestoneTrailing12MonthNetRevenueMinimum_019fa980-2206-744f-bac1-deaa2987573a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_019fa980-2206-7853-825c-e6e7d44e13a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_019fa980-2206-7853-825c-e6e7d44e13a9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019fa980-2206-7584-af74-24cea8a8ce00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019fa980-2206-7584-af74-24cea8a8ce00" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LineOfCreditFacilityCommitmentFeePercentageFinalPayment_019fa980-2206-787c-8ee2-61235db51b91" xlink:href="pths-20260630.xsd#pths_LineOfCreditFacilityCommitmentFeePercentageFinalPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_LineOfCreditFacilityCommitmentFeePercentageFinalPayment_019fa980-2206-787c-8ee2-61235db51b91" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentPrepaymentPremiumPercent_019fa980-4e0e-717a-bbe2-3b3efdd3eac7" xlink:href="pths-20260630.xsd#pths_DebtInstrumentPrepaymentPremiumPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentPrepaymentPremiumPercent_019fa980-4e0e-717a-bbe2-3b3efdd3eac7" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fa980-4e0e-731b-a132-88173b4d882c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fa980-4e0e-731b-a132-88173b4d882c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fa980-4e0e-7f79-9a60-97d9e4f113ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fa980-4e0e-7f79-9a60-97d9e4f113ac" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fa980-4e0e-7679-ac82-b0e8f5d583d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fa980-4e0e-7679-ac82-b0e8f5d583d5" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019fa980-4e0e-7752-8faa-2000c9ceb9fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019fa980-4e0e-7752-8faa-2000c9ceb9fe" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ClassOfWarrantOrRightWarrantsIssuablePercentOfDebtDividedByExercisePrice_019fa980-4e0e-7b51-83a2-ee34cddd941e" xlink:href="pths-20260630.xsd#pths_ClassOfWarrantOrRightWarrantsIssuablePercentOfDebtDividedByExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_ClassOfWarrantOrRightWarrantsIssuablePercentOfDebtDividedByExercisePrice_019fa980-4e0e-7b51-83a2-ee34cddd941e" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentEventOfDefaultPotentialIncreaseInInterestRate_019fa980-7754-7296-b8f3-b507d23c3ad1" xlink:href="pths-20260630.xsd#pths_DebtInstrumentEventOfDefaultPotentialIncreaseInInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentEventOfDefaultPotentialIncreaseInInterestRate_019fa980-7754-7296-b8f3-b507d23c3ad1" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_019fa980-7754-7a22-a8c8-07d302bb757d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_019fa980-7754-7a22-a8c8-07d302bb757d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentSeniorRankIndebtednessMaximum_019fa980-7754-7981-b8b5-a61ec7589db4" xlink:href="pths-20260630.xsd#pths_DebtInstrumentSeniorRankIndebtednessMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentSeniorRankIndebtednessMaximum_019fa980-7754-7981-b8b5-a61ec7589db4" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fa980-7754-7d9c-b38e-91e24bab56f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fa980-7754-7d9c-b38e-91e24bab56f2" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentInterestRateDefault_019fa980-7754-7e86-8556-557c83276347" xlink:href="pths-20260630.xsd#pths_DebtInstrumentInterestRateDefault"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentInterestRateDefault_019fa980-7754-7e86-8556-557c83276347" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019fa980-adff-7d56-956f-3f8897b38fe4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019fa980-adff-7d56-956f-3f8897b38fe4" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019fa980-adff-73d1-ac7e-5c733221dc47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019fa980-adff-73d1-ac7e-5c733221dc47" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConvertiblePercentOfSharesOwnedAfterConversionMaximum_019fa980-adff-77e5-8da5-bf680a9939ba" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConvertiblePercentOfSharesOwnedAfterConversionMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentConvertiblePercentOfSharesOwnedAfterConversionMaximum_019fa980-adff-77e5-8da5-bf680a9939ba" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConvertiblePercentOfSharesOwnedModificationNoticePeriod_019fa980-adff-7d00-a959-a025a1bbe796" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConvertiblePercentOfSharesOwnedModificationNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentConvertiblePercentOfSharesOwnedModificationNoticePeriod_019fa980-adff-7d00-a959-a025a1bbe796" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales_019fa980-adff-75b6-adec-52fa116b7b5a" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales_019fa980-adff-75b6-adec-52fa116b7b5a" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany_019fa980-adff-77b5-af83-b9154c7091ff" xlink:href="pths-20260630.xsd#pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany_019fa980-adff-77b5-af83-b9154c7091ff" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019fa981-0f40-78b7-b95b-13ebc7e303f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019fa981-0f40-78b7-b95b-13ebc7e303f7" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019fa981-0f40-77d2-8041-9dcae821d0ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019fa981-0f40-77d2-8041-9dcae821d0ad" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConvertibleDaysPriorToConsummationOfChangeOfControl_019fa981-0f40-751a-aa46-743bbb0dc76a" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConvertibleDaysPriorToConsummationOfChangeOfControl"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentConvertibleDaysPriorToConsummationOfChangeOfControl_019fa981-0f40-751a-aa46-743bbb0dc76a" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentRepaymentProhibitionLiftedPeriodFollowingRepaymentOfOtherDebt_019feb8d-439f-70a6-9969-3928b0dfc862" xlink:href="pths-20260630.xsd#pths_DebtInstrumentRepaymentProhibitionLiftedPeriodFollowingRepaymentOfOtherDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_DebtInstrumentRepaymentProhibitionLiftedPeriodFollowingRepaymentOfOtherDebt_019feb8d-439f-70a6-9969-3928b0dfc862" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_019fa981-5007-744c-a360-669624b32c5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_us-gaap_ConvertibleDebt_019fa981-5007-744c-a360-669624b32c5b" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PledgeAgreementPercentageOfAggregateNetSalesOfEndProduct_019fa981-7eed-700a-8c5a-db5239c65a02" xlink:href="pths-20260630.xsd#pths_PledgeAgreementPercentageOfAggregateNetSalesOfEndProduct"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_PledgeAgreementPercentageOfAggregateNetSalesOfEndProduct_019fa981-7eed-700a-8c5a-db5239c65a02" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PledgeAgreementAccruedLiabilitiesForPaymentsMaximum_019fa981-7eed-7f1c-92fa-e484e9d1b17e" xlink:href="pths-20260630.xsd#pths_PledgeAgreementAccruedLiabilitiesForPaymentsMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7779-b45b-0c19aede53cc" xlink:to="loc_pths_PledgeAgreementAccruedLiabilitiesForPaymentsMaximum_019fa981-7eed-7f1c-92fa-e484e9d1b17e" xlink:type="arc" order="38"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofAllocationofFairValueDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofAllocationofFairValueDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofAllocationofFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-71af-959e-bb8d443d00ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-71af-959e-bb8d443d00ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-71af-959e-bb8d443d00ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-71af-959e-bb8d443d00ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-71af-959e-bb8d443d00ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7dc8-8dc0-61715c147847" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-71af-959e-bb8d443d00ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7dc8-8dc0-61715c147847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019ef0f5-5241-74a9-a990-3c8219866335" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7dc8-8dc0-61715c147847" xlink:to="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019ef0f5-5241-74a9-a990-3c8219866335" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b91-850c-e3ba882ba312" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b91-850c-e3ba882ba312" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7b91-850c-e3ba882ba312_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b91-850c-e3ba882ba312" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7b91-850c-e3ba882ba312_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7781-9258-9fe2997a0533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b91-850c-e3ba882ba312" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7781-9258-9fe2997a0533" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7071-b963-8f8789221ce5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7781-9258-9fe2997a0533" xlink:to="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7071-b963-8f8789221ce5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7d03-a873-e62e98d79776" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7d03-a873-e62e98d79776" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7d03-a873-e62e98d79776_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7d03-a873-e62e98d79776" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7d03-a873-e62e98d79776_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-74df-ae1a-bd03f0709852" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7d03-a873-e62e98d79776" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-74df-ae1a-bd03f0709852" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_HorizonWarrantsMember_019ef0f5-5241-752f-b81a-47e4311b2db3" xlink:href="pths-20260630.xsd#pths_HorizonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-74df-ae1a-bd03f0709852" xlink:to="loc_pths_HorizonWarrantsMember_019ef0f5-5241-752f-b81a-47e4311b2db3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-728c-946c-8efa833004db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-77ed-988e-0b7098e3398e" xlink:to="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-728c-946c-8efa833004db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-728c-946c-8efa833004db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-728c-946c-8efa833004db" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-728c-946c-8efa833004db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7b4a-9274-10c631a65bb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-728c-946c-8efa833004db" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7b4a-9274-10c631a65bb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7d0a-9caf-8ded469f3460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7b4a-9274-10c631a65bb7" xlink:to="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7d0a-9caf-8ded469f3460" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LongTermDebtFairValueAllocationAmount_019ef0f5-5241-73ac-81e9-7d1b6f4ac99b" xlink:href="pths-20260630.xsd#pths_LongTermDebtFairValueAllocationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_LongTermDebtFairValueAllocationAmount_019ef0f5-5241-73ac-81e9-7d1b6f4ac99b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WarrantLiabilityFairValueAllocationAmount_019ef0f5-5241-7a79-a8e8-a9eb1a31c557" xlink:href="pths-20260630.xsd#pths_WarrantLiabilityFairValueAllocationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_WarrantLiabilityFairValueAllocationAmount_019ef0f5-5241-7a79-a8e8-a9eb1a31c557" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentsAndWarrantsFairValueAllocationAmount_019ef0f5-5241-78fd-a6f4-2d9c67a659d1" xlink:href="pths-20260630.xsd#pths_DebtInstrumentsAndWarrantsFairValueAllocationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_DebtInstrumentsAndWarrantsFairValueAllocationAmount_019ef0f5-5241-78fd-a6f4-2d9c67a659d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFeeAmount_019ef0f5-5241-7079-90d3-e1096b2b84ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_us-gaap_DebtInstrumentFeeAmount_019ef0f5-5241-7079-90d3-e1096b2b84ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentThirdPartyFeeAmount_019ef0f5-5241-786d-8bd8-5390e9a25ac7" xlink:href="pths-20260630.xsd#pths_DebtInstrumentThirdPartyFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_DebtInstrumentThirdPartyFeeAmount_019ef0f5-5241-786d-8bd8-5390e9a25ac7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LongTermDebtFairValueAllocationNet_019ef0f5-5241-7b8a-83fb-97009f68f94c" xlink:href="pths-20260630.xsd#pths_LongTermDebtFairValueAllocationNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_LongTermDebtFairValueAllocationNet_019ef0f5-5241-7b8a-83fb-97009f68f94c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_WarrantLiabilityFairValueAllocationNet_019ef0f5-5241-788e-8209-95e2f5c3375a" xlink:href="pths-20260630.xsd#pths_WarrantLiabilityFairValueAllocationNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_WarrantLiabilityFairValueAllocationNet_019ef0f5-5241-788e-8209-95e2f5c3375a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentsAndWarrantsFairValueAllocationNet_019ef0f5-5241-7c8a-a49b-fda6c4fb09fe" xlink:href="pths-20260630.xsd#pths_DebtInstrumentsAndWarrantsFairValueAllocationNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-74fa-88eb-b1875fb8e491" xlink:to="loc_pths_DebtInstrumentsAndWarrantsFairValueAllocationNet_019ef0f5-5241-7c8a-a49b-fda6c4fb09fe" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofChangeinFairValueasDeterminedbyLevel3InputsfortheConvertibleNotesDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofChangeinFairValueasDeterminedbyLevel3InputsfortheConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofChangeinFairValueasDeterminedbyLevel3InputsfortheConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019ef0f5-5241-7adf-ac65-9ccc759e0e24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ef0f5-5241-7cad-9c07-f84cea52056c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019ef0f5-5241-7adf-ac65-9ccc759e0e24" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ef0f5-5241-7cad-9c07-f84cea52056c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019ef0f5-5241-799f-aed4-84cc13a20c4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ef0f5-5241-7cad-9c07-f84cea52056c" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019ef0f5-5241-799f-aed4-84cc13a20c4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019ef0f5-5241-799f-aed4-84cc13a20c4a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019ef0f5-5241-799f-aed4-84cc13a20c4a" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019ef0f5-5241-799f-aed4-84cc13a20c4a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019ef0f5-5241-7b6e-a005-393adeacb3df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019ef0f5-5241-799f-aed4-84cc13a20c4a" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019ef0f5-5241-7b6e-a005-393adeacb3df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-7878-8b65-af975aec186f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019ef0f5-5241-7b6e-a005-393adeacb3df" xlink:to="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-7878-8b65-af975aec186f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019ef0f5-5241-7adf-ac65-9ccc759e0e24" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019ef0f5-5241-7bae-ace9-c16f489dc515" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019ef0f5-5241-7bae-ace9-c16f489dc515" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPaymentInKind_019ef0f5-5241-7092-a670-2719df66a377" xlink:href="pths-20260630.xsd#pths_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPaymentInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:to="loc_pths_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPaymentInKind_019ef0f5-5241-7092-a670-2719df66a377" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019ef0f5-5241-77fb-afa4-be2f6ef9d544" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019ef0f5-5241-77fb-afa4-be2f6ef9d544" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019ef0f5-5241-7a88-bde8-1716cfb3457b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ef0f5-5241-7c75-bcca-de0d9e6dea41" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019ef0f5-5241-7a88-bde8-1716cfb3457b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019ef0f5-5241-743c-abbd-40dc9c6da6c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofSignificantInputsandValuationMethodologiesUsedDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofSignificantInputsandValuationMethodologiesUsedDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofSignificantInputsandValuationMethodologiesUsedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019ef0f5-5241-7160-8697-fe241316aee0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019ef0f5-5241-7160-8697-fe241316aee0" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7bb2-8aad-53265a49061d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7bb2-8aad-53265a49061d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7bb2-8aad-53265a49061d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7bb2-8aad-53265a49061d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7bb2-8aad-53265a49061d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7661-a13d-3931a36ae193" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5241-7bb2-8aad-53265a49061d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7661-a13d-3931a36ae193" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_HorizonWarrantsMember_019ef0f5-5241-7a98-9c49-00f994d5994b" xlink:href="pths-20260630.xsd#pths_HorizonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5241-7661-a13d-3931a36ae193" xlink:to="loc_pths_HorizonWarrantsMember_019ef0f5-5241-7a98-9c49-00f994d5994b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7a8d-82e2-07715ec81032" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7a8d-82e2-07715ec81032" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7a8d-82e2-07715ec81032_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7a8d-82e2-07715ec81032" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7a8d-82e2-07715ec81032_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7caa-872e-4a809f38b208" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7a8d-82e2-07715ec81032" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7caa-872e-4a809f38b208" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-7dfb-9da9-f3b744eb9fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7caa-872e-4a809f38b208" xlink:to="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-7dfb-9da9-f3b744eb9fa2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7f7d-afc8-ca1dd0d7854e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7caa-872e-4a809f38b208" xlink:to="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7f7d-afc8-ca1dd0d7854e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7983-9a16-16097bb60c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7983-9a16-16097bb60c1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7983-9a16-16097bb60c1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7983-9a16-16097bb60c1f" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7983-9a16-16097bb60c1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7983-9a16-16097bb60c1f" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_MeasurementInputPaidInKindPeriodMember_019ef0f5-5241-7f9a-b46b-8947f9319c5d" xlink:href="pths-20260630.xsd#pths_MeasurementInputPaidInKindPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_pths_MeasurementInputPaidInKindPeriodMember_019ef0f5-5241-7f9a-b46b-8947f9319c5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019ef0f5-5241-70ad-8622-3dd3931c94be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019ef0f5-5241-70ad-8622-3dd3931c94be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputConversionPriceMember_019ef0f5-5241-7c80-bc7c-e6eb15c01c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputConversionPriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputConversionPriceMember_019ef0f5-5241-7c80-bc7c-e6eb15c01c2e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019ef0f5-5241-7e57-886c-7e765d13d5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019ef0f5-5241-7e57-886c-7e765d13d5ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019ef0f5-5241-7ebc-a3da-cb2b5a9f393e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019ef0f5-5241-7ebc-a3da-cb2b5a9f393e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019ef0f5-5241-70c8-819f-e482a6b35d5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019ef0f5-5241-70c8-819f-e482a6b35d5c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019ef0f5-5241-7b2d-b080-e4400b00151c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019ef0f5-5241-7b2d-b080-e4400b00151c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_MeasurementInputWeightedAverageFairValuePerOptionMember_019ef0f5-5241-7954-b82b-a626fb178ba4" xlink:href="pths-20260630.xsd#pths_MeasurementInputWeightedAverageFairValuePerOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-783a-98ff-1efd99ceae4f" xlink:to="loc_pths_MeasurementInputWeightedAverageFairValuePerOptionMember_019ef0f5-5241-7954-b82b-a626fb178ba4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-73a3-a98b-ae714dd3c015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-73a3-a98b-ae714dd3c015" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73a3-a98b-ae714dd3c015_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-73a3-a98b-ae714dd3c015" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73a3-a98b-ae714dd3c015_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7997-a90e-df32a030f941" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-73a3-a98b-ae714dd3c015" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7997-a90e-df32a030f941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019ef0f5-5241-785e-8895-3ba53f5471a5" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7997-a90e-df32a030f941" xlink:to="loc_pths_ConvertibleNotesMember_019ef0f5-5241-785e-8895-3ba53f5471a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019ef0f5-5241-7484-a364-8ace8c685403" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7677-8a50-d81fd294b324" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019fddcc-ebc0-7d12-92b0-8a1473ed5a5f" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7677-8a50-d81fd294b324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019ff0f0-e02f-7e7b-8c35-6761e1f82b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7677-8a50-d81fd294b324" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019ff0f0-e02f-7e7b-8c35-6761e1f82b5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BlackScholesMertonModelMember_019ff0f1-2a7c-76bf-86a4-901fa0dd797b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BlackScholesMertonModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019fddcc-ebc0-7677-8a50-d81fd294b324" xlink:to="loc_us-gaap_BlackScholesMertonModelMember_019ff0f1-2a7c-76bf-86a4-901fa0dd797b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019ef0f5-5241-724c-9d53-eac120bedffb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019ef0f5-5241-7160-8697-fe241316aee0" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019ef0f5-5241-724c-9d53-eac120bedffb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentMeasurementInput_019ef0f5-5241-76c6-b7dd-cf39aec7656e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019ef0f5-5241-7160-8697-fe241316aee0" xlink:to="loc_us-gaap_DebtInstrumentMeasurementInput_019ef0f5-5241-76c6-b7dd-cf39aec7656e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofCarryingValueofLoanDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofCarryingValueofLoanDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofCarryingValueofLoanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7d43-9880-725ae478c2bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-76a4-a928-418c4ea609e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7d43-9880-725ae478c2bb" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-76a4-a928-418c4ea609e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-76b4-a103-b4242de7edfa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-76a4-a928-418c4ea609e8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-76b4-a103-b4242de7edfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-76b4-a103-b4242de7edfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-76b4-a103-b4242de7edfa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-76b4-a103-b4242de7edfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73ff-9dba-04934a22443a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-76b4-a103-b4242de7edfa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73ff-9dba-04934a22443a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019ef0f5-5241-7e78-a991-01b359c0957a" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73ff-9dba-04934a22443a" xlink:to="loc_pths_VentureLoanAndSecurityAgreementTermLoansMember_019ef0f5-5241-7e78-a991-01b359c0957a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementTermLoansFinalPaymentMember_019ef0f5-5241-7dd9-829d-2c98e79af321" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementTermLoansFinalPaymentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73ff-9dba-04934a22443a" xlink:to="loc_pths_VentureLoanAndSecurityAgreementTermLoansFinalPaymentMember_019ef0f5-5241-7dd9-829d-2c98e79af321" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementMember_019ef0f5-5241-76d6-a0a1-f3e79bfd9c56" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-73ff-9dba-04934a22443a" xlink:to="loc_pths_VentureLoanAndSecurityAgreementMember_019ef0f5-5241-76d6-a0a1-f3e79bfd9c56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-76a4-a928-418c4ea609e8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-72e2-9359-6fb23878592b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-7b1b-9b82-d36a5fd27b0a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-72e2-9359-6fb23878592b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-77c1-a738-2e6db30ac8f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-72e2-9359-6fb23878592b" xlink:to="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-77c1-a738-2e6db30ac8f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-7c96-a87c-17add18fb83f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-76a4-a928-418c4ea609e8" xlink:to="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-7c96-a87c-17add18fb83f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7c96-a87c-17add18fb83f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-7c96-a87c-17add18fb83f" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7c96-a87c-17add18fb83f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-720e-9f8d-49842d4e550f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-7c96-a87c-17add18fb83f" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-720e-9f8d-49842d4e550f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7178-a2b8-3a337ce74ec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-720e-9f8d-49842d4e550f" xlink:to="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7178-a2b8-3a337ce74ec7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019ef0f5-5241-790a-8e13-7ff3ea4d9c19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7d43-9880-725ae478c2bb" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019ef0f5-5241-790a-8e13-7ff3ea4d9c19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019ef0f5-5241-7cec-bc79-a9cf0a45f7bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7d43-9880-725ae478c2bb" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019ef0f5-5241-7cec-bc79-a9cf0a45f7bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019ef0f5-5241-7a6f-95e7-3aadfdbdd895" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7d43-9880-725ae478c2bb" xlink:to="loc_us-gaap_LongTermDebt_019ef0f5-5241-7a6f-95e7-3aadfdbdd895" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofDebtDiscountRateDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofDebtDiscountRateDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofDebtDiscountRateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7583-8a90-c44440e38590" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:to="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7583-8a90-c44440e38590" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fa989-4ab2-788d-9fe5-99f92508b318" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7583-8a90-c44440e38590" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fa989-4ab2-788d-9fe5-99f92508b318" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fa989-4ab2-788d-9fe5-99f92508b318_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fa989-4ab2-788d-9fe5-99f92508b318" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fa989-4ab2-788d-9fe5-99f92508b318_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fa989-4ab2-7676-8a43-dcbd0c4c3d98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fa989-4ab2-788d-9fe5-99f92508b318" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fa989-4ab2-7676-8a43-dcbd0c4c3d98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019fa989-4ab2-70d9-a0aa-9159e15e98b1" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fa989-4ab2-7676-8a43-dcbd0c4c3d98" xlink:to="loc_pths_ConvertibleNotesMember_019fa989-4ab2-70d9-a0aa-9159e15e98b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fa989-4ab2-79a1-aa77-82c9248d3ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ef0f5-5241-7583-8a90-c44440e38590" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fa989-4ab2-79a1-aa77-82c9248d3ab2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fa989-4ab2-79a1-aa77-82c9248d3ab2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fa989-4ab2-79a1-aa77-82c9248d3ab2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fa989-4ab2-79a1-aa77-82c9248d3ab2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fa989-4ab2-7293-902f-a117bdb7adc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fa989-4ab2-79a1-aa77-82c9248d3ab2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fa989-4ab2-7293-902f-a117bdb7adc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fa989-4ab2-7b64-9d95-c69dfbb0b983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fa989-4ab2-7293-902f-a117bdb7adc4" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fa989-4ab2-7b64-9d95-c69dfbb0b983" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentSubordinationPremiumPercent_019ff668-1afb-7429-b8f9-5e509a481cdc" xlink:href="pths-20260630.xsd#pths_DebtInstrumentSubordinationPremiumPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:to="loc_pths_DebtInstrumentSubordinationPremiumPercent_019ff668-1afb-7429-b8f9-5e509a481cdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentCompanySpecificRiskPremiumPercent_019fa989-4ab2-7c19-a3f2-7fa9ae318b49" xlink:href="pths-20260630.xsd#pths_DebtInstrumentCompanySpecificRiskPremiumPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:to="loc_pths_DebtInstrumentCompanySpecificRiskPremiumPercent_019fa989-4ab2-7c19-a3f2-7fa9ae318b49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentBloombergBYieldCurvePercent_019fa989-4ab2-7917-b997-29b22a37343d" xlink:href="pths-20260630.xsd#pths_DebtInstrumentBloombergBYieldCurvePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:to="loc_pths_DebtInstrumentBloombergBYieldCurvePercent_019fa989-4ab2-7917-b997-29b22a37343d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentDiscountRatePercent_019fa989-4ab2-7229-b20c-d68adb94a6b1" xlink:href="pths-20260630.xsd#pths_DebtInstrumentDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ef0f5-5241-7f14-abfe-4c12a439f1e5" xlink:to="loc_pths_DebtInstrumentDiscountRatePercent_019fa989-4ab2-7229-b20c-d68adb94a6b1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/NOTESPAYABLEScheduleofMaturitiesofLongTermDebtDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#NOTESPAYABLEScheduleofMaturitiesofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/NOTESPAYABLEScheduleofMaturitiesofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-7bdc-b5df-6b9b1c2b4745" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-7bdc-b5df-6b9b1c2b4745" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-79b6-b66b-9454a3201820" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-7bdc-b5df-6b9b1c2b4745" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-79b6-b66b-9454a3201820" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-79b6-b66b-9454a3201820_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-79b6-b66b-9454a3201820" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-79b6-b66b-9454a3201820_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7bc2-a8ec-5fc9d43ac66f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-79b6-b66b-9454a3201820" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7bc2-a8ec-5fc9d43ac66f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_VentureLoanAndSecurityAgreementMember_019ef0f5-5241-7367-929a-c6b0e91cf2a7" xlink:href="pths-20260630.xsd#pths_VentureLoanAndSecurityAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7bc2-a8ec-5fc9d43ac66f" xlink:to="loc_pths_VentureLoanAndSecurityAgreementMember_019ef0f5-5241-7367-929a-c6b0e91cf2a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019ef0f5-5241-765c-ba6a-511d77e319a7" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7bc2-a8ec-5fc9d43ac66f" xlink:to="loc_pths_ConvertibleNotesMember_019ef0f5-5241-765c-ba6a-511d77e319a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-765a-84a6-53728cf0363d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-7bdc-b5df-6b9b1c2b4745" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-765a-84a6-53728cf0363d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-765a-84a6-53728cf0363d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-765a-84a6-53728cf0363d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-765a-84a6-53728cf0363d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7645-9dea-b48a26143bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-765a-84a6-53728cf0363d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7645-9dea-b48a26143bfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7c21-9172-da54ea6feeb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7645-9dea-b48a26143bfe" xlink:to="loc_us-gaap_LineOfCreditMember_019ef0f5-5241-7c21-9172-da54ea6feeb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-731f-9207-b916b5e65d98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7645-9dea-b48a26143bfe" xlink:to="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-731f-9207-b916b5e65d98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-75f1-af90-077e2a09e043" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ef0f5-5241-7bdc-b5df-6b9b1c2b4745" xlink:to="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-75f1-af90-077e2a09e043" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-75f1-af90-077e2a09e043_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-75f1-af90-077e2a09e043" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-75f1-af90-077e2a09e043_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7870-89d2-fd38ac95ae63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ef0f5-5241-75f1-af90-077e2a09e043" xlink:to="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7870-89d2-fd38ac95ae63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7f92-ab48-c17c75b9ca5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ef0f5-5241-7870-89d2-fd38ac95ae63" xlink:to="loc_us-gaap_SecuredDebtMember_019ef0f5-5241-7f92-ab48-c17c75b9ca5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019ef0f5-5241-7728-9812-bfb7ff2f7d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019ef0f5-5241-7728-9812-bfb7ff2f7d1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019ef0f5-5241-7d63-b338-438d933049d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019ef0f5-5241-7d63-b338-438d933049d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019ef0f5-5241-7086-8716-af0e353aea13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019ef0f5-5241-7086-8716-af0e353aea13" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019ef0f5-5241-7007-9e5e-0b4b804c8e1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019ef0f5-5241-7007-9e5e-0b4b804c8e1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019ef0f5-5241-75d9-a546-baf420d3c9be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019ef0f5-5241-75d9-a546-baf420d3c9be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LongTermDebtMaturityYearFiveAndThereafter_019ef0f5-5241-7a18-976b-59a87a0add94" xlink:href="pths-20260630.xsd#pths_LongTermDebtMaturityYearFiveAndThereafter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_pths_LongTermDebtMaturityYearFiveAndThereafter_019ef0f5-5241-7a18-976b-59a87a0add94" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019ef0f5-5241-7349-af1f-6f240511f13b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ef0f5-5241-7400-a974-772c77b6f2f7" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019ef0f5-5241-7349-af1f-6f240511f13b" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/REEDYCREEKLIABILITYDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#REEDYCREEKLIABILITYDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/REEDYCREEKLIABILITYDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ef0f5-5241-78b0-80a1-127b52b80ca9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:to="loc_srt_CounterpartyNameAxis_019ef0f5-5241-78b0-80a1-127b52b80ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-78b0-80a1-127b52b80ca9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-78b0-80a1-127b52b80ca9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-78b0-80a1-127b52b80ca9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-74a2-b3e7-7eb82dee858e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-78b0-80a1-127b52b80ca9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-74a2-b3e7-7eb82dee858e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekMember_019ef0f5-5241-7b79-bebc-8b60c565038e" xlink:href="pths-20260630.xsd#pths_ReedyCreekMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-74a2-b3e7-7eb82dee858e" xlink:to="loc_pths_ReedyCreekMember_019ef0f5-5241-7b79-bebc-8b60c565038e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_019ef0f5-5241-776c-a7b6-e1bc1de16538" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_019ef0f5-5241-776c-a7b6-e1bc1de16538" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_019ef0f5-5241-776c-a7b6-e1bc1de16538_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_019ef0f5-5241-776c-a7b6-e1bc1de16538" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_019ef0f5-5241-776c-a7b6-e1bc1de16538_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_019ef0f5-5241-7acc-a60f-00e978602583" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_019ef0f5-5241-776c-a7b6-e1bc1de16538" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_019ef0f5-5241-7acc-a60f-00e978602583" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekPurchaseAgreementMember_019ef0f5-5241-770a-a153-8bab8224c7bc" xlink:href="pths-20260630.xsd#pths_ReedyCreekPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_019ef0f5-5241-7acc-a60f-00e978602583" xlink:to="loc_pths_ReedyCreekPurchaseAgreementMember_019ef0f5-5241-770a-a153-8bab8224c7bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ef0f5-5241-72c5-a058-8755afc50530" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:to="loc_dei_LegalEntityAxis_019ef0f5-5241-72c5-a058-8755afc50530" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ef0f5-5241-72c5-a058-8755afc50530_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ef0f5-5241-72c5-a058-8755afc50530" xlink:to="loc_dei_EntityDomain_019ef0f5-5241-72c5-a058-8755afc50530_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ef0f5-5241-7011-b971-23e18993a0dc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ef0f5-5241-72c5-a058-8755afc50530" xlink:to="loc_dei_EntityDomain_019ef0f5-5241-7011-b971-23e18993a0dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NovanMember_019ef0f5-5241-77b3-b58b-a5556b50eba4" xlink:href="pths-20260630.xsd#pths_NovanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ef0f5-5241-7011-b971-23e18993a0dc" xlink:to="loc_pths_NovanMember_019ef0f5-5241-77b3-b58b-a5556b50eba4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ef0f5-5241-78e8-a7e4-718527f13e49" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:to="loc_srt_RangeAxis_019ef0f5-5241-78e8-a7e4-718527f13e49" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ef0f5-5241-78e8-a7e4-718527f13e49_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ef0f5-5241-78e8-a7e4-718527f13e49" xlink:to="loc_srt_RangeMember_019ef0f5-5241-78e8-a7e4-718527f13e49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ef0f5-5241-7a5a-9185-3d3dbf08b729" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ef0f5-5241-78e8-a7e4-718527f13e49" xlink:to="loc_srt_RangeMember_019ef0f5-5241-7a5a-9185-3d3dbf08b729" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ef0f5-5241-72bc-a4c0-a70397bdd1f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ef0f5-5241-7a5a-9185-3d3dbf08b729" xlink:to="loc_srt_MinimumMember_019ef0f5-5241-72bc-a4c0-a70397bdd1f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ef0f5-5241-7925-bc5c-afdb1209edfa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ef0f5-5241-7a5a-9185-3d3dbf08b729" xlink:to="loc_srt_MaximumMember_019ef0f5-5241-7925-bc5c-afdb1209edfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-743e-9b7d-3d3b3507462a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7365-a454-543f5a8777a0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-743e-9b7d-3d3b3507462a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-743e-9b7d-3d3b3507462a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-743e-9b7d-3d3b3507462a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-743e-9b7d-3d3b3507462a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-78c3-9497-0731f61202c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ef0f5-5241-743e-9b7d-3d3b3507462a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-78c3-9497-0731f61202c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LNHCInc.Member_019ef0f5-5241-7b70-a0b2-38de9e99b478" xlink:href="pths-20260630.xsd#pths_LNHCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ef0f5-5241-78c3-9497-0731f61202c1" xlink:to="loc_pths_LNHCInc.Member_019ef0f5-5241-7b70-a0b2-38de9e99b478" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentArrangementFundingReceived_019ef0f5-5241-7b5e-be6b-3cd295dcc5f0" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentArrangementFundingReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:to="loc_pths_ResearchAndDevelopmentArrangementFundingReceived_019ef0f5-5241-7b5e-be6b-3cd295dcc5f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentPercentage_019ef0f5-5241-7c4a-b75e-d09b548bf056" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:to="loc_pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentPercentage_019ef0f5-5241-7c4a-b75e-d09b548bf056" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentFeesOrMilestonePaymentsPercentage_019ef0f5-5241-7b51-9028-5c39a84c7566" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentFeesOrMilestonePaymentsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:to="loc_pths_ResearchAndDevelopmentArrangementOngoingQuarterlyPaymentFeesOrMilestonePaymentsPercentage_019ef0f5-5241-7b51-9028-5c39a84c7566" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-7e1c-91e2-27c05ce2a880" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7b43-85ae-7558cf9133ee" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019ef0f5-5241-7e1c-91e2-27c05ce2a880" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#LICENSEANDOTHERAGREEMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ef0f5-5241-773f-a859-40fbe2ae9db0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_srt_ProductOrServiceAxis_019ef0f5-5241-773f-a859-40fbe2ae9db0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-773f-a859-40fbe2ae9db0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-773f-a859-40fbe2ae9db0" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-773f-a859-40fbe2ae9db0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-773f-a859-40fbe2ae9db0" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_U.S.PatentsCoveringZELSUVMIMember_019ef0f5-5241-7c7a-80f4-1a1a12e980d6" xlink:href="pths-20260630.xsd#pths_U.S.PatentsCoveringZELSUVMIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_U.S.PatentsCoveringZELSUVMIMember_019ef0f5-5241-7c7a-80f4-1a1a12e980d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiMember_019ef0f5-5241-7546-9635-96c0e2def800" xlink:href="pths-20260630.xsd#pths_XepiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_XepiMember_019ef0f5-5241-7546-9635-96c0e2def800" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZelsuvmiMember_019ef0f5-5241-7463-9d2d-d36094f5e135" xlink:href="pths-20260630.xsd#pths_ZelsuvmiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_ZelsuvmiMember_019ef0f5-5241-7463-9d2d-d36094f5e135" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-7e85-bdb7-84b17f2af1e4" xlink:href="pths-20260630.xsd#pths_ZELSUVMILicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-7e85-bdb7-84b17f2af1e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_UNCLicenseMember_019ef0f5-5241-797a-9899-e5d6c52f25fd" xlink:href="pths-20260630.xsd#pths_UNCLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_UNCLicenseMember_019ef0f5-5241-797a-9899-e5d6c52f25fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ChannelCoveredProductsLicenseMember_019ef0f5-5241-7893-ad71-3c2112baedce" xlink:href="pths-20260630.xsd#pths_ChannelCoveredProductsLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-70e7-87c1-6b4069323ef5" xlink:to="loc_pths_ChannelCoveredProductsLicenseMember_019ef0f5-5241-7893-ad71-3c2112baedce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7fef-b164-9b3dd2571b54" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7fef-b164-9b3dd2571b54" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7fef-b164-9b3dd2571b54_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7fef-b164-9b3dd2571b54" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7fef-b164-9b3dd2571b54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ef0f5-5241-7fef-b164-9b3dd2571b54" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandMember_019ef0f5-5241-7c41-84f4-ed660aa6bfcf" xlink:href="pths-20260630.xsd#pths_LigandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:to="loc_pths_LigandMember_019ef0f5-5241-7c41-84f4-ed660aa6bfcf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_UNCMember_019ef0f5-5241-74b2-8b77-56dfa515e7c4" xlink:href="pths-20260630.xsd#pths_UNCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:to="loc_pths_UNCMember_019ef0f5-5241-74b2-8b77-56dfa515e7c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NomisRoyaltyVestLCMember_019ef0f5-5241-7d30-a371-6315626d0f65" xlink:href="pths-20260630.xsd#pths_NomisRoyaltyVestLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:to="loc_pths_NomisRoyaltyVestLCMember_019ef0f5-5241-7d30-a371-6315626d0f65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NRVLigandMadisonMember_019ef0f5-5241-7baf-baa0-5ccb9866e823" xlink:href="pths-20260630.xsd#pths_NRVLigandMadisonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:to="loc_pths_NRVLigandMadisonMember_019ef0f5-5241-7baf-baa0-5ccb9866e823" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_MadisonMember_019ef0f5-5241-7106-b967-f917667c62a3" xlink:href="pths-20260630.xsd#pths_MadisonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ef0f5-5241-7e0b-9e7a-4efd8c979682" xlink:to="loc_pths_MadisonMember_019ef0f5-5241-7106-b967-f917667c62a3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ef0f5-5241-7c77-acb7-617f050c3f13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ef0f5-5241-7c77-acb7-617f050c3f13" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7c77-acb7-617f050c3f13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ef0f5-5241-7c77-acb7-617f050c3f13" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7c77-acb7-617f050c3f13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ef0f5-5241-7c77-acb7-617f050c3f13" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandAssignmentAgreementAmendmentMember_019ef0f5-5241-7315-9f8b-85dfa73313ee" xlink:href="pths-20260630.xsd#pths_LigandAssignmentAgreementAmendmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:to="loc_pths_LigandAssignmentAgreementAmendmentMember_019ef0f5-5241-7315-9f8b-85dfa73313ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LigandRoyaltyAgreementMember_019ef0f5-5241-7215-8cbf-0acc34c4412c" xlink:href="pths-20260630.xsd#pths_LigandRoyaltyAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:to="loc_pths_LigandRoyaltyAgreementMember_019ef0f5-5241-7215-8cbf-0acc34c4412c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_UNCLicenseAgreementMember_019ef0f5-5241-700f-84f2-41f255c5c684" xlink:href="pths-20260630.xsd#pths_UNCLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:to="loc_pths_UNCLicenseAgreementMember_019ef0f5-5241-700f-84f2-41f255c5c684" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZELSUVMIRoyaltyAgreementMember_019ef0f5-5241-7f48-894c-3f89f2bcdc29" xlink:href="pths-20260630.xsd#pths_ZELSUVMIRoyaltyAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:to="loc_pths_ZELSUVMIRoyaltyAgreementMember_019ef0f5-5241-7f48-894c-3f89f2bcdc29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ChannelProductsRoyaltyAgreementMember_019ef0f5-5241-750e-b462-4435eccc8d14" xlink:href="pths-20260630.xsd#pths_ChannelProductsRoyaltyAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ef0f5-5241-7988-b0db-2999c53f7fc1" xlink:to="loc_pths_ChannelProductsRoyaltyAgreementMember_019ef0f5-5241-750e-b462-4435eccc8d14" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-7c09-976f-aed8f3bb1244" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-7c09-976f-aed8f3bb1244" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7c09-976f-aed8f3bb1244_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-7c09-976f-aed8f3bb1244" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-7c09-976f-aed8f3bb1244_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-758f-ba74-62ca0f3c0836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ef0f5-5241-7c09-976f-aed8f3bb1244" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-758f-ba74-62ca0f3c0836" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019ef0f5-5241-7376-bfdc-0e884608135c" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ef0f5-5241-758f-ba74-62ca0f3c0836" xlink:to="loc_pths_ConvertibleNotesMember_019ef0f5-5241-7376-bfdc-0e884608135c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-77f9-afb6-a6d758f4e2fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-77f9-afb6-a6d758f4e2fc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-77f9-afb6-a6d758f4e2fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-77f9-afb6-a6d758f4e2fc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-77f9-afb6-a6d758f4e2fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7ffd-8da0-7f6424ccd569" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ef0f5-5241-77f9-afb6-a6d758f4e2fc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7ffd-8da0-7f6424ccd569" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-735e-a245-e841cabf98cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ef0f5-5241-7ffd-8da0-7f6424ccd569" xlink:to="loc_us-gaap_ConvertibleDebtMember_019ef0f5-5241-735e-a245-e841cabf98cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyEventAxis_019ef0f5-5241-7f87-99fc-aee742e4b7d4" xlink:href="pths-20260630.xsd#pths_RoyaltyEventAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ef0f5-5241-7ebe-81da-3f580bcda83f" xlink:to="loc_pths_RoyaltyEventAxis_019ef0f5-5241-7f87-99fc-aee742e4b7d4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyEventDomain_019ef0f5-5241-7f87-99fc-aee742e4b7d4_default" xlink:href="pths-20260630.xsd#pths_RoyaltyEventDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pths_RoyaltyEventAxis_019ef0f5-5241-7f87-99fc-aee742e4b7d4" xlink:to="loc_pths_RoyaltyEventDomain_019ef0f5-5241-7f87-99fc-aee742e4b7d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:href="pths-20260630.xsd#pths_RoyaltyEventDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pths_RoyaltyEventAxis_019ef0f5-5241-7f87-99fc-aee742e4b7d4" xlink:to="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PriorToTheExpirationOfInitialRoyaltyTermMember_019ef0f5-5241-7d30-93a1-6d91b64b3e75" xlink:href="pths-20260630.xsd#pths_PriorToTheExpirationOfInitialRoyaltyTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:to="loc_pths_PriorToTheExpirationOfInitialRoyaltyTermMember_019ef0f5-5241-7d30-93a1-6d91b64b3e75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AfterTheExpirationOfInitialRoyaltyTermMember_019ef0f5-5241-7293-871f-98b70a40a949" xlink:href="pths-20260630.xsd#pths_AfterTheExpirationOfInitialRoyaltyTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:to="loc_pths_AfterTheExpirationOfInitialRoyaltyTermMember_019ef0f5-5241-7293-871f-98b70a40a949" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FirstCommercialSaleMember_019ef0f5-5241-7d6c-b59f-187838dcbadf" xlink:href="pths-20260630.xsd#pths_FirstCommercialSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:to="loc_pths_FirstCommercialSaleMember_019ef0f5-5241-7d6c-b59f-187838dcbadf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_OccurrenceOfObtaining35000ThresholdInNetSalesForFourConsecutiveQuartersMember_019ef0f5-5241-72b0-9824-f0a874b836aa" xlink:href="pths-20260630.xsd#pths_OccurrenceOfObtaining35000ThresholdInNetSalesForFourConsecutiveQuartersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_RoyaltyEventDomain_019ef0f5-5241-76c8-8747-418c2149556b" xlink:to="loc_pths_OccurrenceOfObtaining35000ThresholdInNetSalesForFourConsecutiveQuartersMember_019ef0f5-5241-72b0-9824-f0a874b836aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_NumberOfPatentsObtained_019ef0f5-5241-7c33-9b19-5e2b36d7a447" xlink:href="pths-20260630.xsd#pths_NumberOfPatentsObtained"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_NumberOfPatentsObtained_019ef0f5-5241-7c33-9b19-5e2b36d7a447" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_FiniteLivedIntangibleAssetsTermExtension_019ef0f5-5241-70b9-84dc-818233e1d8cf" xlink:href="pths-20260630.xsd#pths_FiniteLivedIntangibleAssetsTermExtension"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_FiniteLivedIntangibleAssetsTermExtension_019ef0f5-5241-70b9-84dc-818233e1d8cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssignmentAgreementPercentageOfMilestonePaymentsPayable_019ef0f5-5241-78a9-9ee9-1d65c6cee738" xlink:href="pths-20260630.xsd#pths_AssignmentAgreementPercentageOfMilestonePaymentsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_AssignmentAgreementPercentageOfMilestonePaymentsPayable_019ef0f5-5241-78a9-9ee9-1d65c6cee738" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_AssignmentAgreementPercentageOfOtherAmountsReceivedPayable_019ef0f5-5241-75c3-ac04-87761d869458" xlink:href="pths-20260630.xsd#pths_AssignmentAgreementPercentageOfOtherAmountsReceivedPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_AssignmentAgreementPercentageOfOtherAmountsReceivedPayable_019ef0f5-5241-75c3-ac04-87761d869458" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales_019ef0f5-5241-7a1a-a622-24cad84638c7" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_DebtInstrumentConsiderationToInvestorsPercentRoyaltyOnNetSales_019ef0f5-5241-7a1a-a622-24cad84638c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany_019ef0f5-5241-7d0c-b32d-cd3f965c5b1b" xlink:href="pths-20260630.xsd#pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_DebtInstrumentPercentageOfMilestonePaymentRetainedByCompany_019ef0f5-5241-7d0c-b32d-cd3f965c5b1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyAgreementVariableConsiderationPercentOfNetSales_019ef0f5-5241-7c70-9367-a9d6df679d4c" xlink:href="pths-20260630.xsd#pths_RoyaltyAgreementVariableConsiderationPercentOfNetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RoyaltyAgreementVariableConsiderationPercentOfNetSales_019ef0f5-5241-7c70-9367-a9d6df679d4c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationAmount_019ef0f5-5241-75d7-b524-4c96952e2ccb" xlink:href="pths-20260630.xsd#pths_RevenueRemainingPerformanceObligationVariableConsiderationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationAmount_019ef0f5-5241-75d7-b524-4c96952e2ccb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationNetSalesThreshold_019ef0f5-5241-7670-8395-9f12f7966255" xlink:href="pths-20260630.xsd#pths_RevenueRemainingPerformanceObligationVariableConsiderationNetSalesThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationNetSalesThreshold_019ef0f5-5241-7670-8395-9f12f7966255" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationPercentOfNonRoyaltySublicenseIncome_019ef0f5-5241-7789-b0f1-8aa652de4f49" xlink:href="pths-20260630.xsd#pths_RevenueRemainingPerformanceObligationVariableConsiderationPercentOfNonRoyaltySublicenseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RevenueRemainingPerformanceObligationVariableConsiderationPercentOfNonRoyaltySublicenseIncome_019ef0f5-5241-7789-b0f1-8aa652de4f49" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyAgreementTerminationNoticePeriod_019ef0f5-5241-7ff6-a6d8-eff2c8b2f2f2" xlink:href="pths-20260630.xsd#pths_RoyaltyAgreementTerminationNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RoyaltyAgreementTerminationNoticePeriod_019ef0f5-5241-7ff6-a6d8-eff2c8b2f2f2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyAgreementDevelopmentRightsPeriod_019ef0f5-5241-79cb-9acc-0dd4a60cb965" xlink:href="pths-20260630.xsd#pths_RoyaltyAgreementDevelopmentRightsPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RoyaltyAgreementDevelopmentRightsPeriod_019ef0f5-5241-79cb-9acc-0dd4a60cb965" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementRequiredRegulatoryAndCommercialMilestonePaymentsMaximum_019ef0f5-5241-7a97-8ca5-5451dc87103b" xlink:href="pths-20260630.xsd#pths_LicenseAgreementRequiredRegulatoryAndCommercialMilestonePaymentsMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_LicenseAgreementRequiredRegulatoryAndCommercialMilestonePaymentsMaximum_019ef0f5-5241-7a97-8ca5-5451dc87103b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementCommercialMilestonePayments_019fa930-f809-73e8-92f4-b45b8db97619" xlink:href="pths-20260630.xsd#pths_LicenseAgreementCommercialMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_LicenseAgreementCommercialMilestonePayments_019fa930-f809-73e8-92f4-b45b8db97619" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementMaterialBreachUncuredPeriod_019ef0f5-5241-760c-a98f-3043d36fca26" xlink:href="pths-20260630.xsd#pths_LicenseAgreementMaterialBreachUncuredPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_LicenseAgreementMaterialBreachUncuredPeriod_019ef0f5-5241-760c-a98f-3043d36fca26" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LicenseAgreementWrittenNoticeForBankruptcyOrInsolvencyEventsPeriod_019ef0f5-5241-7ec5-a5b2-31440ee0c0ba" xlink:href="pths-20260630.xsd#pths_LicenseAgreementWrittenNoticeForBankruptcyOrInsolvencyEventsPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_LicenseAgreementWrittenNoticeForBankruptcyOrInsolvencyEventsPeriod_019ef0f5-5241-7ec5-a5b2-31440ee0c0ba" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyAgreementPurchasePrice_019ef0f5-5241-748e-8d62-08dc2be2399c" xlink:href="pths-20260630.xsd#pths_RoyaltyAgreementPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RoyaltyAgreementPurchasePrice_019ef0f5-5241-748e-8d62-08dc2be2399c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RoyaltyAgreementVariableConsiderationPercentOfNonRoyaltySublicensingPayments_019ef0f5-5241-7ca9-8b4e-279606e706ef" xlink:href="pths-20260630.xsd#pths_RoyaltyAgreementVariableConsiderationPercentOfNonRoyaltySublicensingPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_pths_RoyaltyAgreementVariableConsiderationPercentOfNonRoyaltySublicensingPayments_019ef0f5-5241-7ca9-8b4e-279606e706ef" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRoyalties_019ef0f5-5241-7e59-8514-69e71ef4d216" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ef0f5-5241-7893-bbe6-9a345cbc91a3" xlink:to="loc_us-gaap_PaymentsForRoyalties_019ef0f5-5241-7e59-8514-69e71ef4d216" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSScheduleofSignificantAssumptionsusedinDeterminingFairValueofFinancingDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#LICENSEANDOTHERAGREEMENTSScheduleofSignificantAssumptionsusedinDeterminingFairValueofFinancingDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSScheduleofSignificantAssumptionsusedinDeterminingFairValueofFinancingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-77dc-b413-2650ffd5a8be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-713b-bcd9-4e17ed8fea5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-77dc-b413-2650ffd5a8be" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-713b-bcd9-4e17ed8fea5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7087-b443-f2be190eff43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-713b-bcd9-4e17ed8fea5e" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7087-b443-f2be190eff43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7087-b443-f2be190eff43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7087-b443-f2be190eff43" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7087-b443-f2be190eff43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7da7-9d09-6bbd89c92dda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019ef0f5-5241-7087-b443-f2be190eff43" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7da7-9d09-6bbd89c92dda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019ef0f5-5241-78bd-ba6d-a094b027ab8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7da7-9d09-6bbd89c92dda" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019ef0f5-5241-78bd-ba6d-a094b027ab8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_MeasurementInputProbabilityOfSuccessMember_019ef0f5-5241-7552-9167-49460fbe562a" xlink:href="pths-20260630.xsd#pths_MeasurementInputProbabilityOfSuccessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019ef0f5-5241-7da7-9d09-6bbd89c92dda" xlink:to="loc_pths_MeasurementInputProbabilityOfSuccessMember_019ef0f5-5241-7552-9167-49460fbe562a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ef0f5-5241-762a-b445-9a3e4cb79d8c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019ef0f5-5241-713b-bcd9-4e17ed8fea5e" xlink:to="loc_srt_ProductOrServiceAxis_019ef0f5-5241-762a-b445-9a3e4cb79d8c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-762a-b445-9a3e4cb79d8c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-762a-b445-9a3e4cb79d8c" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-762a-b445-9a3e4cb79d8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-762a-b445-9a3e4cb79d8c" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-70eb-8283-a266eb030eb1" xlink:href="pths-20260630.xsd#pths_ReedyCreekLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:to="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-70eb-8283-a266eb030eb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-716a-bd9b-669f103d7ce8" xlink:href="pths-20260630.xsd#pths_ZELSUVMILicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:to="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-716a-bd9b-669f103d7ce8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ChannelCoveredProductsLicenseMember_019ef0f5-5241-72dd-8e7d-4181f9bd54f1" xlink:href="pths-20260630.xsd#pths_ChannelCoveredProductsLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:to="loc_pths_ChannelCoveredProductsLicenseMember_019ef0f5-5241-72dd-8e7d-4181f9bd54f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiLicenseMember_019ef0f5-5241-7d9e-886d-dffd34f5b3db" xlink:href="pths-20260630.xsd#pths_XepiLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:to="loc_pths_XepiLicenseMember_019ef0f5-5241-7d9e-886d-dffd34f5b3db" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-7fc2-bc0b-4b9f8fdb2b07" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-7b69-897e-897b92f0062b" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-7fc2-bc0b-4b9f8fdb2b07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationMeasurementInput_019ef0f5-5241-73e0-9841-83b10a166f31" xlink:href="pths-20260630.xsd#pths_ContractualObligationMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019ef0f5-5241-77dc-b413-2650ffd5a8be" xlink:to="loc_pths_ContractualObligationMeasurementInput_019ef0f5-5241-73e0-9841-83b10a166f31" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSScheduleofActivityinFinancingforRoyaltyAgreementsDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#LICENSEANDOTHERAGREEMENTSScheduleofActivityinFinancingforRoyaltyAgreementsDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/LICENSEANDOTHERAGREEMENTSScheduleofActivityinFinancingforRoyaltyAgreementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019ef0f5-5241-7ec4-8998-64cfabee5428" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019ef0f5-5241-7ec4-8998-64cfabee5428" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79b4-a42a-1f63ac92681a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ef0f5-5241-7ec4-8998-64cfabee5428" xlink:to="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79b4-a42a-1f63ac92681a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-79b4-a42a-1f63ac92681a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79b4-a42a-1f63ac92681a" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-79b4-a42a-1f63ac92681a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-71d9-aabd-446671d94799" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ef0f5-5241-79b4-a42a-1f63ac92681a" xlink:to="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-71d9-aabd-446671d94799" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ef0f5-5241-71d9-aabd-446671d94799" xlink:to="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-7a93-8d04-383680f3ff33" xlink:href="pths-20260630.xsd#pths_ReedyCreekLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:to="loc_pths_ReedyCreekLicenseMember_019ef0f5-5241-7a93-8d04-383680f3ff33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-7426-83a5-88b6ed2b760a" xlink:href="pths-20260630.xsd#pths_ZELSUVMILicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:to="loc_pths_ZELSUVMILicenseMember_019ef0f5-5241-7426-83a5-88b6ed2b760a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_XepiLicenseMember_019ef0f5-5241-7b9b-8145-4351f42f4f6d" xlink:href="pths-20260630.xsd#pths_XepiLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:to="loc_pths_XepiLicenseMember_019ef0f5-5241-7b9b-8145-4351f42f4f6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SatoLicenseMember_019ef0f5-5241-7ba7-ae3d-3a6b6d22f9cb" xlink:href="pths-20260630.xsd#pths_SatoLicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LicenseMember_019ef0f5-5241-761e-b516-54e649afae10" xlink:to="loc_pths_SatoLicenseMember_019ef0f5-5241-7ba7-ae3d-3a6b6d22f9cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationRollForward_019ef0f5-5241-7aed-9123-61ff65e15305" xlink:href="pths-20260630.xsd#pths_ContractualObligationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_pths_ContractualObligationRollForward_019ef0f5-5241-7aed-9123-61ff65e15305" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligation_019ef0f5-5241-7a9c-b219-ac5203593211" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_ContractualObligationRollForward_019ef0f5-5241-7aed-9123-61ff65e15305" xlink:to="loc_us-gaap_ContractualObligation_019ef0f5-5241-7a9c-b219-ac5203593211" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationLiabilityInterestAccretion_019ef0f5-5305-7407-8f83-0937689b5485" xlink:href="pths-20260630.xsd#pths_ContractualObligationLiabilityInterestAccretion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_ContractualObligationRollForward_019ef0f5-5241-7aed-9123-61ff65e15305" xlink:to="loc_pths_ContractualObligationLiabilityInterestAccretion_019ef0f5-5305-7407-8f83-0937689b5485" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationLiabilityPaymentsAccrued_019ef0f5-5305-75a9-9b61-e106b32f2e8d" xlink:href="pths-20260630.xsd#pths_ContractualObligationLiabilityPaymentsAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pths_ContractualObligationRollForward_019ef0f5-5241-7aed-9123-61ff65e15305" xlink:to="loc_pths_ContractualObligationLiabilityPaymentsAccrued_019ef0f5-5305-75a9-9b61-e106b32f2e8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligation_019ef0f5-5305-7630-b37d-54db5bdd596b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligation"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationCurrent_019ef0f5-5305-7f90-9650-ab945e4b0a98" xlink:href="pths-20260630.xsd#pths_ContractualObligationCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_pths_ContractualObligationCurrent_019ef0f5-5305-7f90-9650-ab945e4b0a98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationLiabilityConvertibleFeesAllocatedToRoyalty_019ef0f5-5305-7019-ac14-f691caff465c" xlink:href="pths-20260630.xsd#pths_ContractualObligationLiabilityConvertibleFeesAllocatedToRoyalty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_pths_ContractualObligationLiabilityConvertibleFeesAllocatedToRoyalty_019ef0f5-5305-7019-ac14-f691caff465c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationNoncurrent_019ef0f5-5305-7941-b84d-c0b035f94024" xlink:href="pths-20260630.xsd#pths_ContractualObligationNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_pths_ContractualObligationNoncurrent_019ef0f5-5305-7941-b84d-c0b035f94024" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ContractualObligationLiabilityEffectiveAnnualDiscountRate_019ef0f5-5305-7e96-a231-73f943c1fc89" xlink:href="pths-20260630.xsd#pths_ContractualObligationLiabilityEffectiveAnnualDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ef0f5-5241-766b-9043-7d538f8fb9dc" xlink:to="loc_pths_ContractualObligationLiabilityEffectiveAnnualDiscountRate_019ef0f5-5305-7e96-a231-73f943c1fc89" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYNarrativeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5305-7d72-a6c9-349b3c5b7896" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5305-7d72-a6c9-349b3c5b7896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7d72-a6c9-349b3c5b7896_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5305-7d72-a6c9-349b3c5b7896" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7d72-a6c9-349b3c5b7896_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7ee5-b26f-bbfbf30f7400" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ef0f5-5305-7d72-a6c9-349b3c5b7896" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7ee5-b26f-bbfbf30f7400" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_019ef0f5-5305-79b5-9c55-c9a0c0026c29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7ee5-b26f-bbfbf30f7400" xlink:to="loc_us-gaap_IPOMember_019ef0f5-5305-79b5-9c55-c9a0c0026c29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CEFPurchaseAgreementMember_019ef0f5-5305-7b85-9f7b-bf9aefdd6606" xlink:href="pths-20260630.xsd#pths_CEFPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ef0f5-5305-7ee5-b26f-bbfbf30f7400" xlink:to="loc_pths_CEFPurchaseAgreementMember_019ef0f5-5305-7b85-9f7b-bf9aefdd6606" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5305-78d2-839a-11eeafbee558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5305-78d2-839a-11eeafbee558" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-78d2-839a-11eeafbee558_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5305-78d2-839a-11eeafbee558" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-78d2-839a-11eeafbee558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-7a6d-afc2-6b42a5340aca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ef0f5-5305-78d2-839a-11eeafbee558" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-7a6d-afc2-6b42a5340aca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_UnderwriterWarrantsMember_019ff0f8-d6a0-7300-adc1-5e5c4ad1c053" xlink:href="pths-20260630.xsd#pths_UnderwriterWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-7a6d-afc2-6b42a5340aca" xlink:to="loc_pths_UnderwriterWarrantsMember_019ff0f8-d6a0-7300-adc1-5e5c4ad1c053" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_HorizonWarrantsMember_019ef0f5-5305-77fc-8662-0fcb3c57d951" xlink:href="pths-20260630.xsd#pths_HorizonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ef0f5-5305-7a6d-afc2-6b42a5340aca" xlink:to="loc_pths_HorizonWarrantsMember_019ef0f5-5305-77fc-8662-0fcb3c57d951" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7136-afc9-ffe5c52430a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:to="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7136-afc9-ffe5c52430a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7136-afc9-ffe5c52430a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7136-afc9-ffe5c52430a5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7136-afc9-ffe5c52430a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7665-a6b8-f1e74ce1e671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7136-afc9-ffe5c52430a5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7665-a6b8-f1e74ce1e671" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-77bf-8425-c2899b44e34e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7665-a6b8-f1e74ce1e671" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-77bf-8425-c2899b44e34e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019faf92-3800-7ae7-9e89-ad8610da4c03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7665-a6b8-f1e74ce1e671" xlink:to="loc_us-gaap_PerformanceSharesMember_019faf92-3800-7ae7-9e89-ad8610da4c03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019ef0f5-5305-72bf-bfa5-f33aa355607b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:to="loc_us-gaap_PlanNameAxis_019ef0f5-5305-72bf-bfa5-f33aa355607b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ef0f5-5305-72bf-bfa5-f33aa355607b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019ef0f5-5305-72bf-bfa5-f33aa355607b" xlink:to="loc_us-gaap_PlanNameDomain_019ef0f5-5305-72bf-bfa5-f33aa355607b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ef0f5-5305-7724-b972-b7f79e98b489" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019ef0f5-5305-72bf-bfa5-f33aa355607b" xlink:to="loc_us-gaap_PlanNameDomain_019ef0f5-5305-7724-b972-b7f79e98b489" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_TwoThousandTwentyThreePlanMember_019ef0f5-5305-720c-8497-62deb7f9ea1d" xlink:href="pths-20260630.xsd#pths_TwoThousandTwentyThreePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ef0f5-5305-7724-b972-b7f79e98b489" xlink:to="loc_pths_TwoThousandTwentyThreePlanMember_019ef0f5-5305-720c-8497-62deb7f9ea1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019faf87-0e7f-7aba-9830-3d6350dc301f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7d38-9bc5-4d3777378272" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019faf87-0e7f-7aba-9830-3d6350dc301f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf87-0e7f-7aba-9830-3d6350dc301f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019faf87-0e7f-7aba-9830-3d6350dc301f" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf87-0e7f-7aba-9830-3d6350dc301f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf87-0e7f-71a2-befe-7b8f29a6ebd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019faf87-0e7f-7aba-9830-3d6350dc301f" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf87-0e7f-71a2-befe-7b8f29a6ebd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019faf87-2cb6-7c80-bbe3-d12a9311b805" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019faf87-0e7f-71a2-befe-7b8f29a6ebd2" xlink:to="loc_us-gaap_SubsequentEventMember_019faf87-2cb6-7c80-bbe3-d12a9311b805" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ef0f5-5305-7290-845b-1d933b418374" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ef0f5-5305-7290-845b-1d933b418374" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019ef0f5-5305-7d20-972f-c4612183a208" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019ef0f5-5305-7d20-972f-c4612183a208" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_019ef0f5-5305-7418-85e4-43b9398015b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_019ef0f5-5305-7418-85e4-43b9398015b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseOfferingCost_019ef0f5-5305-7ef4-8084-3ea675852239" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpenseOfferingCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_NoninterestExpenseOfferingCost_019ef0f5-5305-7ef4-8084-3ea675852239" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_019ef0f5-5305-77fb-9b5f-3af9d10bb1ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_019ef0f5-5305-77fb-9b5f-3af9d10bb1ed" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CommonStockIncreaseDecreaseInCapitalSharesReservedForFutureIssuance_019ef0f5-5305-7624-bada-793b76361af7" xlink:href="pths-20260630.xsd#pths_CommonStockIncreaseDecreaseInCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_pths_CommonStockIncreaseDecreaseInCapitalSharesReservedForFutureIssuance_019ef0f5-5305-7624-bada-793b76361af7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019ff258-187c-7a36-806a-9151afb0fd42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019ff258-187c-7a36-806a-9151afb0fd42" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ff5f4-45f8-7d07-b5f9-361330eb9bd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ff5f4-45f8-7d07-b5f9-361330eb9bd7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019ef0f5-5305-7f4f-81f5-ca3f1fb635c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019ef0f5-5305-7f4f-81f5-ca3f1fb635c7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019ef0f5-5305-7544-9253-3e1a558ec9f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019ef0f5-5305-7544-9253-3e1a558ec9f8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ClassOfWarrantOrRightPeriodFollowingCommencementDateExercisable_019ef0f5-5305-798f-b598-3d4143f3e132" xlink:href="pths-20260630.xsd#pths_ClassOfWarrantOrRightPeriodFollowingCommencementDateExercisable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_pths_ClassOfWarrantOrRightPeriodFollowingCommencementDateExercisable_019ef0f5-5305-798f-b598-3d4143f3e132" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_019ef0f5-5305-7fb8-a806-69f9dccea9ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAdjustmentOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_019ef0f5-5305-7fb8-a806-69f9dccea9ce" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ef0f5-5305-756b-aac4-1415aa1a37ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ef0f5-5305-756b-aac4-1415aa1a37ca" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019ef0f5-5305-7c67-9c0d-62e2e76f1335" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019ef0f5-5305-7c67-9c0d-62e2e76f1335" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SaleOfStockAuthorizedAmount_019ef0f5-5305-7539-b077-1caddf5b407e" xlink:href="pths-20260630.xsd#pths_SaleOfStockAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_pths_SaleOfStockAuthorizedAmount_019ef0f5-5305-7539-b077-1caddf5b407e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ef0f5-5305-7084-aabf-6736c58ce8d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ef0f5-5305-7084-aabf-6736c58ce8d5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019ef0f5-5305-7ac6-88ef-f9952bba8602" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019ef0f5-5305-7ac6-88ef-f9952bba8602" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019faf86-e8e4-7153-847c-f1e2769c238c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7bd3-b3e4-0fc59e2853df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019faf86-e8e4-7153-847c-f1e2769c238c" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingSecuritiesandIssuableCommonSharesDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYOutstandingSecuritiesandIssuableCommonSharesDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingSecuritiesandIssuableCommonSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019faf69-8ede-706d-a86f-54ba43a499aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019faf69-8ede-706d-a86f-54ba43a499aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019faf69-cb55-7992-9ca7-5fce8de46992" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019faf69-8ede-706d-a86f-54ba43a499aa" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019faf69-cb55-7992-9ca7-5fce8de46992" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7992-9ca7-5fce8de46992_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019faf69-cb55-7992-9ca7-5fce8de46992" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7992-9ca7-5fce8de46992_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7a1f-92ee-d58569c51ebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019faf69-cb55-7992-9ca7-5fce8de46992" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7a1f-92ee-d58569c51ebe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_UnderwriterWarrantsMember_019faf6a-0174-723e-a9d9-91347f77a683" xlink:href="pths-20260630.xsd#pths_UnderwriterWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7a1f-92ee-d58569c51ebe" xlink:to="loc_pths_UnderwriterWarrantsMember_019faf6a-0174-723e-a9d9-91347f77a683" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_HorizonWarrantsMember_019faf6a-1c3f-7c76-9d3e-99ba92a0c18f" xlink:href="pths-20260630.xsd#pths_HorizonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019faf69-cb55-7a1f-92ee-d58569c51ebe" xlink:to="loc_pths_HorizonWarrantsMember_019faf6a-1c3f-7c76-9d3e-99ba92a0c18f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019faf6e-d01d-78fe-bc27-2ac5c817a2b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019faf69-8ede-706d-a86f-54ba43a499aa" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019faf6e-d01d-78fe-bc27-2ac5c817a2b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019faf6e-d01d-78fe-bc27-2ac5c817a2b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019faf6e-d01d-78fe-bc27-2ac5c817a2b0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019faf6e-d01d-78fe-bc27-2ac5c817a2b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019faf6e-d01d-7d2e-b214-6ccdb37b899d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019faf6e-d01d-78fe-bc27-2ac5c817a2b0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019faf6e-d01d-7d2e-b214-6ccdb37b899d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019faf6e-e576-7b8a-a375-78e32c6af317" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019faf6e-d01d-7d2e-b214-6ccdb37b899d" xlink:to="loc_us-gaap_ConvertibleDebtMember_019faf6e-e576-7b8a-a375-78e32c6af317" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019faf6e-faf8-7f92-a448-4e62c011148d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019faf69-8ede-706d-a86f-54ba43a499aa" xlink:to="loc_us-gaap_DebtInstrumentAxis_019faf6e-faf8-7f92-a448-4e62c011148d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019faf6e-faf8-7f92-a448-4e62c011148d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019faf6e-faf8-7f92-a448-4e62c011148d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019faf6e-faf8-7f92-a448-4e62c011148d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019faf6e-faf8-7804-a52f-71464208bbba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019faf6e-faf8-7f92-a448-4e62c011148d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019faf6e-faf8-7804-a52f-71464208bbba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ConvertibleNotesMember_019faf6f-170c-7eb2-9f4d-2095c437eb31" xlink:href="pths-20260630.xsd#pths_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019faf6e-faf8-7804-a52f-71464208bbba" xlink:to="loc_pths_ConvertibleNotesMember_019faf6f-170c-7eb2-9f4d-2095c437eb31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019faf6c-11a9-74c4-b405-5a64c8f8415f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019faf6c-11a9-74c4-b405-5a64c8f8415f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments_019faf6d-ad63-7b51-bc6a-8e9785d586e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments_019faf6d-ad63-7b51-bc6a-8e9785d586e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019faf6b-98f3-746b-bf5c-914e2db04829" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019faf6b-98f3-746b-bf5c-914e2db04829" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019faf6a-b27a-73b9-b2ab-d0d5392df6ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019faf6a-b27a-73b9-b2ab-d0d5392df6ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019faf69-8ede-7a4f-a8cd-5c7def31e267" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019faf69-8ede-7a4f-a8cd-5c7def31e267" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_019ff0f9-d108-790f-a144-d1bdc1f7f221" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_ConvertibleDebt_019ff0f9-d108-790f-a144-d1bdc1f7f221" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019faf70-f585-724e-ba94-fd248842cd31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_us-gaap_InterestExpenseDebt_019faf70-f585-724e-ba94-fd248842cd31" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DebtInstrumentConvertibleSharesIssuableUponFinalConversion_019faf71-d2b5-769d-b8c0-e3a74facda79" xlink:href="pths-20260630.xsd#pths_DebtInstrumentConvertibleSharesIssuableUponFinalConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf69-8ede-79e3-8065-732d3630e548" xlink:to="loc_pths_DebtInstrumentConvertibleSharesIssuableUponFinalConversion_019faf71-d2b5-769d-b8c0-e3a74facda79" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingCommonandPreferredStockDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYOutstandingCommonandPreferredStockDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingCommonandPreferredStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019faf7b-aee6-7a85-9cf9-7bd8348f01b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019faf7b-aee6-7a85-9cf9-7bd8348f01b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019faf7b-aee6-7561-97a7-ef318e6fb768" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019faf7b-aee6-7a85-9cf9-7bd8348f01b4" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019faf7b-aee6-7561-97a7-ef318e6fb768" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7561-97a7-ef318e6fb768_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019faf7b-aee6-7561-97a7-ef318e6fb768" xlink:to="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7561-97a7-ef318e6fb768_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7ea5-87f8-c32a5ccde280" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019faf7b-aee6-7561-97a7-ef318e6fb768" xlink:to="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7ea5-87f8-c32a5ccde280" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019faf7d-82dc-739f-8a91-fb42603ad5dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7ea5-87f8-c32a5ccde280" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019faf7d-82dc-739f-8a91-fb42603ad5dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019faf7d-b6e9-792c-a1d5-1df838cd6e7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019faf7b-aee6-7ea5-87f8-c32a5ccde280" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019faf7d-b6e9-792c-a1d5-1df838cd6e7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ff25e-6126-72eb-b674-4f0be01358b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019faf7b-aee6-7a85-9cf9-7bd8348f01b4" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ff25e-6126-72eb-b674-4f0be01358b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ff25e-6126-72eb-b674-4f0be01358b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ff25e-6126-72eb-b674-4f0be01358b4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ff25e-6126-72eb-b674-4f0be01358b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ff25e-6126-7a85-9b26-e24ac35ebc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ff25e-6126-72eb-b674-4f0be01358b4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ff25e-6126-7a85-9b26-e24ac35ebc6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SecuritiesPurchaseAgreementsMember_019ff25e-6126-7628-9245-f4dea170bbce" xlink:href="pths-20260630.xsd#pths_SecuritiesPurchaseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ff25e-6126-7a85-9b26-e24ac35ebc6d" xlink:to="loc_pths_SecuritiesPurchaseAgreementsMember_019ff25e-6126-7628-9245-f4dea170bbce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019faf7b-aee6-744b-b969-ad8545f8bc5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019faf7b-aee6-744b-b969-ad8545f8bc5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019faf7c-974c-7b9a-8c6d-ec46fe86d2f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019faf7c-974c-7b9a-8c6d-ec46fe86d2f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleSharesIssuable_019faf7d-1b10-7038-86e2-e972f38139a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleSharesIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_PreferredStockConvertibleSharesIssuable_019faf7d-1b10-7038-86e2-e972f38139a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019ff25e-6126-7eca-9616-a9814d6a5acf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019ff25e-6126-7eca-9616-a9814d6a5acf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionRatio_019fddd4-d410-7459-8bf4-bb99371017ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionRatio_019fddd4-d410-7459-8bf4-bb99371017ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_PreferredStockConvertiblePercentageOfIPOPrice_019faf7f-e401-7c4e-907e-aa3a365c6fcd" xlink:href="pths-20260630.xsd#pths_PreferredStockConvertiblePercentageOfIPOPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019faf7b-aee6-7bf6-85bd-2d203e3c93a3" xlink:to="loc_pths_PreferredStockConvertiblePercentageOfIPOPrice_019faf7f-e401-7c4e-907e-aa3a365c6fcd" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingStockBasedCompensationAwardsDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYOutstandingStockBasedCompensationAwardsDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYOutstandingStockBasedCompensationAwardsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019faf82-705e-7992-b6f3-0f0d7c698798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019faf82-705e-7992-b6f3-0f0d7c698798" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019faf82-705f-7759-a699-eb4fde35ec5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019faf82-705e-7992-b6f3-0f0d7c698798" xlink:to="loc_us-gaap_AwardTypeAxis_019faf82-705f-7759-a699-eb4fde35ec5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7759-a699-eb4fde35ec5a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019faf82-705f-7759-a699-eb4fde35ec5a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7759-a699-eb4fde35ec5a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7d17-8831-7d80b486cf48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019faf82-705f-7759-a699-eb4fde35ec5a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7d17-8831-7d80b486cf48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019faf82-705f-7ebb-beb9-b428a3140e46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7d17-8831-7d80b486cf48" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019faf82-705f-7ebb-beb9-b428a3140e46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019faf82-705f-7f26-b2e8-1a2aa2973e5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019faf82-705f-7d17-8831-7d80b486cf48" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019faf82-705f-7f26-b2e8-1a2aa2973e5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019faf82-705f-7010-a647-070672415e3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019faf82-705f-7010-a647-070672415e3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019faf82-705f-79d3-854e-2da1ff97cea1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019faf82-705f-79d3-854e-2da1ff97cea1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019faf82-705f-7c53-a0ba-71ecfe5a9735" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019faf82-705f-7c53-a0ba-71ecfe5a9735" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019faf84-918b-7c25-bc81-0a6469c42402" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019faf82-705f-7011-b019-17d6211c072e" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019faf84-918b-7c25-bc81-0a6469c42402" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7371-b1d8-61547837abff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7371-b1d8-61547837abff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019ef0f5-5305-7a21-b59a-08157ad94316" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7371-b1d8-61547837abff" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019ef0f5-5305-7a21-b59a-08157ad94316" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-77b0-87cc-df76b33e3528" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-77b0-87cc-df76b33e3528" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7371-b1d8-61547837abff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ef0f5-5305-7371-b1d8-61547837abff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-77b0-87cc-df76b33e3528" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ef0f5-5305-7895-898d-6d5b86b8bb62" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-77b0-87cc-df76b33e3528" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofShareBasedCompensationExpensebyAwardTypeDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofShareBasedCompensationExpensebyAwardTypeDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofShareBasedCompensationExpensebyAwardTypeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7051-9273-863b23bf5767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d7d-8de8-a59047a42ba0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7051-9273-863b23bf5767" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d7d-8de8-a59047a42ba0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7ff3-8300-66d37cf5d82f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d7d-8de8-a59047a42ba0" xlink:to="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7ff3-8300-66d37cf5d82f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7ff3-8300-66d37cf5d82f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7ff3-8300-66d37cf5d82f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7ff3-8300-66d37cf5d82f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7d77-ba99-040db725ebf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-7ff3-8300-66d37cf5d82f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7d77-ba99-040db725ebf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-7931-bea1-b5c31c1ae745" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7d77-ba99-040db725ebf4" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-7931-bea1-b5c31c1ae745" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5305-7a5b-a137-c829557f9935" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7d77-ba99-040db725ebf4" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5305-7a5b-a137-c829557f9935" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-7874-ab4d-ba6a62f6cab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7051-9273-863b23bf5767" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ef0f5-5305-7874-ab4d-ba6a62f6cab1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofUnrecognizedShareBasedPaymentExpenseDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofUnrecognizedShareBasedPaymentExpenseDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofUnrecognizedShareBasedPaymentExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-76bb-9058-e734272966b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7f78-80bb-16a5ec29df41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-76bb-9058-e734272966b3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7f78-80bb-16a5ec29df41" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-75b4-b1db-cd046906ad31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7f78-80bb-16a5ec29df41" xlink:to="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-75b4-b1db-cd046906ad31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-75b4-b1db-cd046906ad31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-75b4-b1db-cd046906ad31" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-75b4-b1db-cd046906ad31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7f88-9618-8d010060543e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-75b4-b1db-cd046906ad31" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7f88-9618-8d010060543e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-720b-8bfe-966429f8c4f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7f88-9618-8d010060543e" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-720b-8bfe-966429f8c4f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5305-715d-90d8-8f5a20c339b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7f88-9618-8d010060543e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5305-715d-90d8-8f5a20c339b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ef0f5-5305-7215-9904-042398f79b81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-76bb-9058-e734272966b3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ef0f5-5305-7215-9904-042398f79b81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ef0f5-5305-7e0f-a49f-227cf620490b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-76bb-9058-e734272966b3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ef0f5-5305-7e0f-a49f-227cf620490b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofFairValueAssumptionsDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofFairValueAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofFairValueAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d58-bb1e-d43b91b05be5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d58-bb1e-d43b91b05be5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-743a-950f-3d0294d227e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5305-7d58-bb1e-d43b91b05be5" xlink:to="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-743a-950f-3d0294d227e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-743a-950f-3d0294d227e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-743a-950f-3d0294d227e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-743a-950f-3d0294d227e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7062-b225-e5f59632e034" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5305-743a-950f-3d0294d227e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7062-b225-e5f59632e034" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-7112-aa6b-9b59a96d1128" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5305-7062-b225-e5f59632e034" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ef0f5-5305-7112-aa6b-9b59a96d1128" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_019ef0f5-5305-7b81-a4c7-d59f3f9da3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_019ef0f5-5305-7b81-a4c7-d59f3f9da3fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019ef0f5-5305-7997-97af-5f237b587ff0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019ef0f5-5305-7997-97af-5f237b587ff0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ef0f5-5305-72f4-a7dd-ed8b6d2d1472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ef0f5-5305-72f4-a7dd-ed8b6d2d1472" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ef0f5-5306-721d-9264-6f13b16fc45b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ef0f5-5306-721d-9264-6f13b16fc45b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-750a-bcab-b69c01728653" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5305-7dd1-95bf-620ca0307645" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-750a-bcab-b69c01728653" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofRestrictedStockUnitActivityDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#STOCKHOLDERSEQUITYScheduleofRestrictedStockUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/STOCKHOLDERSEQUITYScheduleofRestrictedStockUnitActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5306-78f5-9d79-53b2082e495e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5306-76a9-80bb-c9b74690c76d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5306-78f5-9d79-53b2082e495e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5306-76a9-80bb-c9b74690c76d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ef0f5-5306-77af-97cc-68f37a1bb79d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ef0f5-5306-76a9-80bb-c9b74690c76d" xlink:to="loc_us-gaap_AwardTypeAxis_019ef0f5-5306-77af-97cc-68f37a1bb79d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5306-77af-97cc-68f37a1bb79d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5306-77af-97cc-68f37a1bb79d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5306-77af-97cc-68f37a1bb79d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5306-782b-a219-8a6b738b8896" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ef0f5-5306-77af-97cc-68f37a1bb79d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5306-782b-a219-8a6b738b8896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5306-772e-8f51-b39d35002893" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ef0f5-5306-782b-a219-8a6b738b8896" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ef0f5-5306-772e-8f51-b39d35002893" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5306-78f5-9d79-53b2082e495e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ef0f5-5306-772a-98a8-b77b473166be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ef0f5-5306-772a-98a8-b77b473166be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ef0f5-5306-791b-a780-d8e6a2fdd396" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ef0f5-5306-791b-a780-d8e6a2fdd396" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ef0f5-5306-763f-9813-36ec27bab8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ef0f5-5306-763f-9813-36ec27bab8d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ef0f5-5306-78f7-b330-dd4a8f3780dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ef0f5-5306-766d-b970-0c1aa1f82bad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ef0f5-5306-78f7-b330-dd4a8f3780dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ef0f5-5306-7458-b437-b9eb8b3b168b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ef0f5-5306-78f5-9d79-53b2082e495e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ef0f5-5306-7be8-a50d-456e34bb02bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ef0f5-5306-7be8-a50d-456e34bb02bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-79e7-9ae1-15233366867e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-79e7-9ae1-15233366867e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-73b6-9550-8b69cc267f3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ef0f5-5306-73b6-9550-8b69cc267f3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ef0f5-5306-732f-9b3a-70826738281f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ef0f5-5306-7b29-928b-0446aeef6555" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ef0f5-5306-732f-9b3a-70826738281f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ef0f5-5306-7214-b560-7bc0aa1c55ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#COMMITMENTSANDCONTINGENCIESDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019fa9a1-f750-76f4-8561-65ba5fac3b8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019fa9a1-d04a-7fe3-ac5f-1a0bd5a203b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fa9a1-f750-76f4-8561-65ba5fac3b8b" xlink:to="loc_us-gaap_LossContingenciesTable_019fa9a1-d04a-7fe3-ac5f-1a0bd5a203b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019fa9a2-243c-7c19-9a44-0c54618a7bb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fa9a1-d04a-7fe3-ac5f-1a0bd5a203b7" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019fa9a2-243c-7c19-9a44-0c54618a7bb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019fa9a2-243c-7c19-9a44-0c54618a7bb8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019fa9a2-243c-7c19-9a44-0c54618a7bb8" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019fa9a2-243c-7c19-9a44-0c54618a7bb8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019fa9a2-243c-7dc3-8ab8-4b6efa3d7a16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019fa9a2-243c-7c19-9a44-0c54618a7bb8" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019fa9a2-243c-7dc3-8ab8-4b6efa3d7a16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_LiquidatedDamagesMember_019ff0ff-c979-7bea-97b8-db66cc0cbbb5" xlink:href="pths-20260630.xsd#pths_LiquidatedDamagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019fa9a2-243c-7dc3-8ab8-4b6efa3d7a16" xlink:to="loc_pths_LiquidatedDamagesMember_019ff0ff-c979-7bea-97b8-db66cc0cbbb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fa9a1-d04a-7fe3-ac5f-1a0bd5a203b7" xlink:to="loc_srt_LitigationCaseAxis_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65" xlink:to="loc_srt_LitigationCaseTypeDomain_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019ff0ff-0c4a-710e-91ea-f86dfa03d0e6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019ff0ff-0c4a-71f3-96c3-7c28d77aaa65" xlink:to="loc_srt_LitigationCaseTypeDomain_019ff0ff-0c4a-710e-91ea-f86dfa03d0e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_DrLangEmploymentContractMember_019fa9a2-243c-7918-bb10-1ca2c49f7837" xlink:href="pths-20260630.xsd#pths_DrLangEmploymentContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019ff0ff-0c4a-710e-91ea-f86dfa03d0e6" xlink:to="loc_pths_DrLangEmploymentContractMember_019fa9a2-243c-7918-bb10-1ca2c49f7837" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyDamagesSoughtValue_019ff0fd-e34d-7923-8553-c1e13210d446" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyDamagesSoughtValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fa9a1-f750-76f4-8561-65ba5fac3b8b" xlink:to="loc_us-gaap_LossContingencyDamagesSoughtValue_019ff0fd-e34d-7923-8553-c1e13210d446" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_019fc8dd-5320-79c0-9782-b676742220b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fa9a1-f750-76f4-8561-65ba5fac3b8b" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_019fc8dd-5320-79c0-9782-b676742220b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019fc8dd-b8fd-7500-ab8c-30daf4267a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fa9a1-f750-76f4-8561-65ba5fac3b8b" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019fc8dd-b8fd-7500-ab8c-30daf4267a0a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019ef0f5-5306-7653-a1da-1405ec984acc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ef0f5-5306-71ec-8359-4216def91b29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ef0f5-5306-7653-a1da-1405ec984acc" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ef0f5-5306-71ec-8359-4216def91b29" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ef0f5-5306-7cf9-8466-5d1b33ec90f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ef0f5-5306-71ec-8359-4216def91b29" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ef0f5-5306-7cf9-8466-5d1b33ec90f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ef0f5-5306-7cf9-8466-5d1b33ec90f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ef0f5-5306-7cf9-8466-5d1b33ec90f5" xlink:to="loc_us-gaap_SegmentDomain_019ef0f5-5306-7cf9-8466-5d1b33ec90f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ef0f5-5306-7f78-a7b4-da559a291ca8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ef0f5-5306-7cf9-8466-5d1b33ec90f5" xlink:to="loc_us-gaap_SegmentDomain_019ef0f5-5306-7f78-a7b4-da559a291ca8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CommercialOperationsSegmentMember_019ef0f5-5306-75c6-8bcb-890240dcf031" xlink:href="pths-20260630.xsd#pths_CommercialOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ef0f5-5306-7f78-a7b4-da559a291ca8" xlink:to="loc_pths_CommercialOperationsSegmentMember_019ef0f5-5306-75c6-8bcb-890240dcf031" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019ef0f5-5306-793f-ac3b-7dafe3dbb12f" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ef0f5-5306-7f78-a7b4-da559a291ca8" xlink:to="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019ef0f5-5306-793f-ac3b-7dafe3dbb12f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ef0f5-5306-76ca-b8ca-d88d901a3869" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ef0f5-5306-7653-a1da-1405ec984acc" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ef0f5-5306-76ca-b8ca-d88d901a3869" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ef0f5-5306-7f46-99bf-4afea1eae5b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ef0f5-5306-7653-a1da-1405ec984acc" xlink:to="loc_us-gaap_NetIncomeLoss_019ef0f5-5306-7f46-99bf-4afea1eae5b9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofRevenueDetails" xlink:type="simple" xlink:href="pths-20260630.xsd#SEGMENTINFORMATIONScheduleofRevenueDetails"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9bb-47c7-7059-9854-8845ef90e66f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9bb-47c7-7059-9854-8845ef90e66f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9bb-47c7-7c0b-b073-c392e078afd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9bb-47c7-7059-9854-8845ef90e66f" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9bb-47c7-7c0b-b073-c392e078afd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fa9bb-47c7-7c0b-b073-c392e078afd5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9bb-47c7-7c0b-b073-c392e078afd5" xlink:to="loc_us-gaap_SegmentDomain_019fa9bb-47c7-7c0b-b073-c392e078afd5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fa9bb-47c7-713f-b79a-dd1147bcaf25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9bb-47c7-7c0b-b073-c392e078afd5" xlink:to="loc_us-gaap_SegmentDomain_019fa9bb-47c7-713f-b79a-dd1147bcaf25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CommercialOperationsSegmentMember_019fa9bb-47c7-73d3-abd5-e903f2b7c5b6" xlink:href="pths-20260630.xsd#pths_CommercialOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fa9bb-47c7-713f-b79a-dd1147bcaf25" xlink:to="loc_pths_CommercialOperationsSegmentMember_019fa9bb-47c7-73d3-abd5-e903f2b7c5b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019fa9bb-47c7-71bb-8ec5-467d22df11e7" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fa9bb-47c7-713f-b79a-dd1147bcaf25" xlink:to="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019fa9bb-47c7-71bb-8ec5-467d22df11e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fa9bc-4be6-722d-8bbd-a387d2934533" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9bb-47c7-7059-9854-8845ef90e66f" xlink:to="loc_srt_ConsolidationItemsAxis_019fa9bc-4be6-722d-8bbd-a387d2934533" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fa9bc-4be6-722d-8bbd-a387d2934533_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fa9bc-4be6-722d-8bbd-a387d2934533" xlink:to="loc_srt_ConsolidationItemsDomain_019fa9bc-4be6-722d-8bbd-a387d2934533_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fa9bc-4be6-7e8c-99fd-26ddea106cac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fa9bc-4be6-722d-8bbd-a387d2934533" xlink:to="loc_srt_ConsolidationItemsDomain_019fa9bc-4be6-7e8c-99fd-26ddea106cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fa9bc-4be6-7ee5-a1e1-60ad113a27d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fa9bc-4be6-7e8c-99fd-26ddea106cac" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fa9bc-4be6-7ee5-a1e1-60ad113a27d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fa9bc-4be6-7469-9615-4e71e6b20165" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fa9bc-4be6-7469-9615-4e71e6b20165" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019fa9bc-4be6-7268-a8f2-07e6b0d3a994" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019fa9bc-4be6-7268-a8f2-07e6b0d3a994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fa9bc-4be6-7ba9-8339-de426100bf92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fa9bc-4be6-7ba9-8339-de426100bf92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019fa9bc-4be6-7ec9-9e4e-003373fcc38a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019fa9bc-4be6-7ec9-9e4e-003373fcc38a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fa9bc-4be6-78f3-9532-13e58a014b29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fa9bc-4be6-78f3-9532-13e58a014b29" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019fa9bc-4be6-71ee-9881-afef06835516" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019fa9bc-4be6-71ee-9881-afef06835516" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ChangeInFairValueOfConvertibleDebt_019fa9bc-4be6-77a8-b9d0-42754db23381" xlink:href="pths-20260630.xsd#pths_ChangeInFairValueOfConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_pths_ChangeInFairValueOfConvertibleDebt_019fa9bc-4be6-77a8-b9d0-42754db23381" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fa9bc-4be6-7945-b91a-cae2347451b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9bb-47c7-7a5e-bbf2-f3d213acfd4f" xlink:to="loc_us-gaap_NetIncomeLoss_019fa9bc-4be6-7945-b91a-cae2347451b2" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails_1" xlink:type="simple" xlink:href="pths-20260630.xsd#SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails_1"/>
  <link:definitionLink xlink:role="http://pelthos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fa9be-2180-7650-a35e-d70a4c89d8fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9be-2180-71c1-90be-c3deab577de0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9be-2180-7650-a35e-d70a4c89d8fa" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9be-2180-71c1-90be-c3deab577de0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9be-2180-7f94-a199-465e735733e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa9be-2180-71c1-90be-c3deab577de0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9be-2180-7f94-a199-465e735733e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fa9be-2180-7f94-a199-465e735733e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9be-2180-7f94-a199-465e735733e3" xlink:to="loc_us-gaap_SegmentDomain_019fa9be-2180-7f94-a199-465e735733e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fa9be-2180-7c04-8912-e393ae6f90c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fa9be-2180-7f94-a199-465e735733e3" xlink:to="loc_us-gaap_SegmentDomain_019fa9be-2180-7c04-8912-e393ae6f90c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_CommercialOperationsSegmentMember_019fa9be-2180-7a5a-9e37-b32c8c99e9f9" xlink:href="pths-20260630.xsd#pths_CommercialOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fa9be-2180-7c04-8912-e393ae6f90c1" xlink:to="loc_pths_CommercialOperationsSegmentMember_019fa9be-2180-7a5a-9e37-b32c8c99e9f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019fa9be-2180-7740-a243-978bf5f50c6f" xlink:href="pths-20260630.xsd#pths_ResearchAndDevelopmentOperationsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fa9be-2180-7c04-8912-e393ae6f90c1" xlink:to="loc_pths_ResearchAndDevelopmentOperationsSegmentMember_019fa9be-2180-7740-a243-978bf5f50c6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019fa9be-2180-766a-a2b7-6d81de4dca08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa9be-2180-7650-a35e-d70a4c89d8fa" xlink:to="loc_us-gaap_Assets_019fa9be-2180-766a-a2b7-6d81de4dca08" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_RichardMalamutMember_019fa9cd-40fc-73c6-bfad-796a473f35e8" xlink:href="pths-20260630.xsd#pths_RichardMalamutMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pths_RichardMalamutMember_019fa9cd-40fc-73c6-bfad-796a473f35e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_ScottPleshaMember_019fa9ce-1cbd-79af-a0fc-42714bcb07d5" xlink:href="pths-20260630.xsd#pths_ScottPleshaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pths_ScottPleshaMember_019fa9ce-1cbd-79af-a0fc-42714bcb07d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_JohnM.GayMember_019fa9ce-5022-76b9-b288-8bb41008e1a8" xlink:href="pths-20260630.xsd#pths_JohnM.GayMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pths_JohnM.GayMember_019fa9ce-5022-76b9-b288-8bb41008e1a8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pths_SaiRangaraoMember_019fa9ce-8b14-7d36-bde0-ff8cce27c315" xlink:href="pths-20260630.xsd#pths_SaiRangaraoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pths_SaiRangaraoMember_019fa9ce-8b14-7d36-bde0-ff8cce27c315" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
