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  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_RemainingFundingBasedOnConditionalMilestoneAchievement" abstract="false" name="RemainingFundingBasedOnConditionalMilestoneAchievement" 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_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_DebtInstrumentClosingFee" abstract="false" name="DebtInstrumentClosingFee" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <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_AvailableForSaleSecuritiesDebtSecuritiesNoncurrentContractualMaturitiesMinimum" abstract="false" name="AvailableForSaleSecuritiesDebtSecuritiesNoncurrentContractualMaturitiesMinimum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_DeferredTaxLiabilitiesRightOfUseAsset" abstract="false" name="DeferredTaxLiabilitiesRightOfUseAsset" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_OperatingLossCarryforwardsWithoutExpiration" abstract="false" name="OperatingLossCarryforwardsWithoutExpiration" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_IncomeTaxDisclosureLineItems" abstract="true" name="IncomeTaxDisclosureLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <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_LongTermInvestmentsAmortizedCost" abstract="false" name="LongTermInvestmentsAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <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_IncomeTaxDisclosureTable" abstract="true" name="IncomeTaxDisclosureTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_DebtInstrumentInterestPaymentExtensionTerm" abstract="false" name="DebtInstrumentInterestPaymentExtensionTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_DebtInstrumentPrepaymentFeePercentage" abstract="false" name="DebtInstrumentPrepaymentFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_DebtInstrumentClosingFeeAmount" abstract="false" name="DebtInstrumentClosingFeeAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PriorPeriodErrorsPolicyTextBlock" abstract="false" name="PriorPeriodErrorsPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_WorkforceRealignmentMember" abstract="true" name="WorkforceRealignmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_PotentialCommonSharesAntiDilutiveEffectOnSecurities" abstract="false" name="PotentialCommonSharesAntiDilutiveEffectOnSecurities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToGrantedInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToGrantedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" abstract="true" name="ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentFinalFeePayment" abstract="false" name="DebtInstrumentFinalFeePayment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ThresholdPercentageOfSalesForTieredRoyalties" abstract="false" name="ThresholdPercentageOfSalesForTieredRoyalties" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_LongTermInvestmentsFairValue" abstract="false" name="LongTermInvestmentsFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" 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_TermLoan2022AMember" abstract="true" name="TermLoan2022AMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeesStockPurchasePlanPurchasedNumber" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeesStockPurchasePlanPurchasedNumber" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_CollaborationPartnershipConcentrationRiskMember" abstract="true" name="CollaborationPartnershipConcentrationRiskMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <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_CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LongTermInvestmentsAccumulatedGrossUnrealizedLoss" abstract="false" name="LongTermInvestmentsAccumulatedGrossUnrealizedLoss" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentVariableRateBaseOption" abstract="false" name="DebtInstrumentVariableRateBaseOption" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_UnchargedLicenseFeeReclassifiedToAccountsPayable" abstract="false" name="UnchargedLicenseFeeReclassifiedToAccountsPayable" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_FacilityTwoWalthamMassachusettsMember" abstract="true" name="FacilityTwoWalthamMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToStockIssuedForServicesInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToStockIssuedForServicesInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_UnderwrittenPublicOfferingDecember2019Member" abstract="true" name="UnderwrittenPublicOfferingDecember2019Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AstraZenecaTerminationAgreementMember" abstract="true" name="AstraZenecaTerminationAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TermOfPaymentOfLicenseFeeFirstInstallment" abstract="false" name="TermOfPaymentOfLicenseFeeFirstInstallment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_RestructuringAndRelatedCostImpactedEmployeesTermForCashPaymentsAndBenefits" abstract="false" name="RestructuringAndRelatedCostImpactedEmployeesTermForCashPaymentsAndBenefits" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <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_TermLoan2022BMember" abstract="true" name="TermLoan2022BMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" abstract="false" name="IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_LeaseArrangementsAxis" abstract="true" name="LeaseArrangementsAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialDevelopmentMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TwoThousandEightStockIncentivePlanMember" abstract="true" name="TwoThousandEightStockIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_PercentageOfRoyaltyRevenue" abstract="false" name="PercentageOfRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_FacilityMilwaukeeWisconsinMember" abstract="true" name="FacilityMilwaukeeWisconsinMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LesseeOperatingLeaseNumberOfRenewalOptions" abstract="false" name="LesseeOperatingLeaseNumberOfRenewalOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_FosunMember" abstract="true" name="FosunMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_UnchargedLicenseFeeCurrent" abstract="false" name="UnchargedLicenseFeeCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccruedContractManufacturingCosts" abstract="false" name="AccruedContractManufacturingCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermLoan2022Member" abstract="true" name="TermLoan2022Member" 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_AccruedProfessionalAndConsultantFeesCurrent" abstract="false" name="AccruedProfessionalAndConsultantFeesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <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_UnderwritingDiscountsAndCommissions" abstract="false" name="UnderwritingDiscountsAndCommissions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_RestructuringAndRelatedCostPlannedNumberOfPositionsEliminatedPeriodPercent" abstract="false" name="RestructuringAndRelatedCostPlannedNumberOfPositionsEliminatedPeriodPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_NumberOfOperatingLeaseArrangements" abstract="false" name="NumberOfOperatingLeaseArrangements" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" abstract="false" name="ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_StockIssuanceCostCommissionPercent" abstract="false" name="StockIssuanceCostCommissionPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_DeferredTaxAssetsAmortizationAndDepreciation" abstract="false" name="DeferredTaxAssetsAmortizationAndDepreciation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToCanceledInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToCanceledInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_PaymentsOfUnchargedLicenseFees" abstract="false" name="PaymentsOfUnchargedLicenseFees" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_FacilityFremontCaliforniaMember" abstract="true" name="FacilityFremontCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFeesSecondInstallment" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFeesSecondInstallment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PaymentsOfUnchargedLicenseFeesAggregateAmountPaid" abstract="false" name="PaymentsOfUnchargedLicenseFeesAggregateAmountPaid" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LaboratoryEquipmentMember" abstract="true" name="LaboratoryEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TaxAuthorityStatesOtherThanCaliforniaMember" abstract="true" name="TaxAuthorityStatesOtherThanCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_InvestmentsAndCashAmortizedCost" abstract="false" name="InvestmentsAndCashAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" abstract="false" name="LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_OfficeEquipmentAndFurnitureMember" abstract="true" name="OfficeEquipmentAndFurnitureMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ExitFeePercentage" abstract="false" name="ExitFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityIncreaseDueToUnbilledPrepaymentsRecorded" abstract="false" name="ContractWithCustomerLiabilityIncreaseDueToUnbilledPrepaymentsRecorded" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentInterestRateOnDefaultPercentage" abstract="false" name="DebtInstrumentInterestRateOnDefaultPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanSharesAvailableRollForward" abstract="true" name="EmployeeStockPurchasePlanSharesAvailableRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_AccruedClinicalExpenses" abstract="false" name="AccruedClinicalExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashReceived" abstract="false" name="ContractWithCustomerLiabilityRevenueRecognizedCashReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CostOfRevenueTableTextBlock" abstract="false" name="CostOfRevenueTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_UnderwrittenPublicOfferingIncludingOverallotmentDecember2019Member" abstract="true" name="UnderwrittenPublicOfferingIncludingOverallotmentDecember2019Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ProductSupplyRevenueMember" abstract="true" name="ProductSupplyRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <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_CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" abstract="false" name="CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_IncreaseDecreaseInUnbilledRevenue" abstract="false" name="IncreaseDecreaseInUnbilledRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsInitialTransactionPrice" abstract="false" name="CollaborationAndLicensingAgreementsInitialTransactionPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_XuanzhuMember" abstract="true" name="XuanzhuMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsSecondMilestonePayment" abstract="false" name="CollaborationAndLicensingAgreementsSecondMilestonePayment" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeTerm" abstract="false" name="LoanAgreementExitFeeTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisTenPercentChangeInProbabilityOfOccurrenceEffectOnValuation" abstract="false" name="FairValueSensitivityAnalysisTenPercentChangeInProbabilityOfOccurrenceEffectOnValuation" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityIncreaseForCashReceived" abstract="false" name="ContractWithCustomerLiabilityIncreaseForCashReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" abstract="false" name="AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_XuanzhuHKBiopharmaceuticalLimitedMember" abstract="true" name="XuanzhuHKBiopharmaceuticalLimitedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_CostOfRevenueAdjustmentUponAdoptionOfAccountingStandard" abstract="false" name="CostOfRevenueAdjustmentUponAdoptionOfAccountingStandard" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsLicenseFee" abstract="false" name="CollaborationAndLicensingAgreementsLicenseFee" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LongTermInvestmentsAccumulatedGrossUnrealizedGain" abstract="false" name="LongTermInvestmentsAccumulatedGrossUnrealizedGain" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccruedResearchAndDevelopmentExpensesPolicyPolicyTextBlock" abstract="false" name="AccruedResearchAndDevelopmentExpensesPolicyPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <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_LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_StockOptionsAggregateIntrinsicValueAbstract" abstract="true" name="StockOptionsAggregateIntrinsicValueAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_MinimumTaxCreditCarryforwardMember" abstract="true" name="MinimumTaxCreditCarryforwardMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_RestructuringAndRelatedCostNumberOfPreviouslyEliminatedPositionsRetained" abstract="false" name="RestructuringAndRelatedCostNumberOfPreviouslyEliminatedPositionsRetained" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_DerivativeLiabilityForExitFee" abstract="false" name="DerivativeLiabilityForExitFee" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialCommercializationMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_SaleOfStockOverAllotmentOptionOptionPeriod" abstract="false" name="SaleOfStockOverAllotmentOptionOptionPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_PerformanceBasedRestrictedStockUnitsMember" abstract="true" name="PerformanceBasedRestrictedStockUnitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <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_AstrazenecaMember" abstract="true" name="AstrazenecaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
