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  <xs:element id="ardx_AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" abstract="false" name="AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" abstract="false" name="FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_KnightTherapeuticsIncMember" abstract="true" name="KnightTherapeuticsIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFeesFirstInstallment" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFeesFirstInstallment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_HealthCareRoyaltyPartnersIVLPMember" abstract="true" name="HealthCareRoyaltyPartnersIVLPMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToCreditsOrDeductionsIssued" abstract="false" name="ContractWithCustomerGrossToCreditsOrDeductionsIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsAbstract" abstract="true" name="CollaborationAndLicensingAgreementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_CostOfRevenueAggregateAmountRecognized" abstract="false" name="CostOfRevenueAggregateAmountRecognized" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PercentageOfNonRoyaltyRevenue" abstract="false" name="PercentageOfNonRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_DerivativeIssued" abstract="false" name="DerivativeIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AstrazenecaMember" abstract="true" name="AstrazenecaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeTerm" abstract="false" name="LoanAgreementExitFeeTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_ExitFee2022Member" abstract="true" name="ExitFee2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_StrezsakVersusArdelyxIncMember" abstract="true" name="StrezsakVersusArdelyxIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LoanAgreementFutureObligationUponFundingOrOtherEvents" abstract="false" name="LoanAgreementFutureObligationUponFundingOrOtherEvents" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_GrossToNetSalesAccrualAndReserveClassificationAxis" abstract="true" name="GrossToNetSalesAccrualAndReserveClassificationAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_SaleOfStockWeightedAveragePricePerShare" abstract="false" name="SaleOfStockWeightedAveragePricePerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccrualRollForward" abstract="true" name="ContractWithCustomerGrossToNetSalesAccrualRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" abstract="false" name="LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_CardinalHealthMember" abstract="true" name="CardinalHealthMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerProductSalesGrossToNetAccruals" abstract="false" name="ContractWithCustomerProductSalesGrossToNetAccruals" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_IncreaseDecreaseInPrepaidCommercialManufacturingExpense" abstract="false" name="IncreaseDecreaseInPrepaidCommercialManufacturingExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_OpenMarketSalesAgreement2021AtTheMarketOfferingMember" abstract="true" name="OpenMarketSalesAgreement2021AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ResearchCollaborationAndOptionAgreementMember" abstract="true" name="ResearchCollaborationAndOptionAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_KyowaKirinCo.LtdMember" abstract="true" name="KyowaKirinCo.LtdMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_AstraZenecaTerminationAgreementMember" abstract="true" name="AstraZenecaTerminationAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
