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Permeability Classification of Highly Variable Drugs

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Permeability Classification of Highly Variable Drugs Vatsala Naageshwaran Associate Director, Scientific Operations Oral Drug Absorption Bioequivalence (BE): Absence of a significant difference in the rate and extent of drug absorption between test and RLD. Fa is the fraction of the drug that is absorbed from the intestinal lumen to the intestinal enterocytes. Fg is the fraction of the unmetabolized drug in the enterocytes. Fa Fg reaches the portal vein. Fh is the fraction of the unmetabolized drug in the liver.Fa Fg Fhreaches systemic circulation. Bioavailability (F%) = the rate and extent to which an active moiety becomes available in the systemic circulation. Absorptive Flux

=Cint Pwall Absorptive Flux (J) If two drug products, containing the same drug, have the same concentration time profile at the intestinal membrane surface then they will have the same rate and extent of absorption Amidon.G et. al. A Theoretical Basis for a Biopharmaceutics Drug Classification:The Correlation of in Vitro Drug Product Dissolution and in Vivo Bioavailability, Pharm Res (12) No. 3, 1995. Which implies Pwall = effectiveor BCS permeabilityCint =concentration in lumen Absorptive Flux

=Cint Pwall Absorptive Flux (J) When in vitro testing can demonstrate the same GI concentration time profile under all luminal conditions.it can serve as a reliable surrogate for judging therapeutic equivalence of pharmaceutically equivalent drug products Which further implies Pwall = effectiveor BCS permeabilityCint =concentration in lumen Progression of IR Solid Oral Dosage Form Release RatePermeabilitySolubility Dissolution Absorption Formulated Drug Solubilized Drug Factors Drug in Enterocyte Solubility Determinants Dosed form must be stable in the intestinal lumen. Correlation between Dissolution and AbsorptionDefined by three dimensionless numbers Dose NumberDissolution NumberAbsorption Number Mo = dose (MW) Vo = 250 mL Cs = equilibrium solubility Tres = GI residence time Tabs = absorption time for drug substance Tres = GI residence time TDiss = time requiredfor dissolution of product Comparison of equilibrium solubilityto highest dose concentration Comparison of mean residence time to time required forabsorption Comparison of mean residence time to time required for complete dissolution Do= (Mo/Vo) Cs An= Tres Tabs Dn= Tres TDiss BCS Classification Class IIIClass IV High High Permeability Low Class II Class I Solubility Low BCS Class ILow Do High An High Dn TDiss due toDR Rapid dissolutionin relation togastric emptying and therefore not rate limiting Tabs due toP High permeability ensures complete absorption within transit time Mo orCs High solubility does not limit dissolution and, therefore, absorption In Agreement with Statement If two drug products, containing the same drug, have the same concentration time profile at the intestinal membrane surface then they will have the same rate and extent of absorption Amidon.G et. al. A Theoretical Basis for a Biopharmaceutics Drug Classification:The Correlation of in Vitro Drug Product Dissolution and in Vivo Bioavailability, Pharm Res (12) No. 3, 1995. FDA and EMA Agree Low Do Low An High Dn BCS Class III if two drug products, containing the same drug, have the same concentration time profile at the intestinal membrane surface then they will have the same rate and extent of absorption further implies that the two drug products have the same in vivo dissolution profile under all luminal conditions then they will have the same rate and extent of drug absorption Low Do Low An High Dn BCS Class III if two drug products, containing the same drug, have the same concentration time profile at the intestinal membrane surface then they will have the same rate and extent of absorption EMA agrees In Vitro TestsPermeability Published Literature Experimental Approved Label (RLD) Published Clinical Data Non-Clinical Data Human PK Non-Clinical Techniques Solubility Dissolution pH 1.0-7.5 or 1.2-6.8Experimental Experimental0.1 N HCl, pH 4.5 & 6.8 FDA Guidance In Other Words High BCS (human in vivo) permeabilit y= High Fabs High in vitro Papp = Always high BCS permeability Therefore: High in vitro Papp = Always high Fabs FDA is not aware of any cases wherein vitro permeability affects the rank order relationship with the human extent of absorption Lawrence Yu, Director for Science, OGD. PPB Open Forum, 2010. FIP PSWC/AAPS Annual Meeting However,High BCS permeability not always = high in vitro Papp Residence time, Barrier differences, transporter expression etc YES! QuestionFor a rapidly dissolving IR product with High permeabilityHigh solubility Adequate stability Will absorption always be complete? 17 FDA Experience with Biowaivers Mehta, Sept. 2010; AAPS Webinar: Application of Biopharmaceutical Classification System (BCS) in Regulatory Submissions Davit, June 2011, BCS Classification Workshop, Canadian Society for Pharmaceutical Sciences FDA Experience with Biopharmaceutics Classification System (BCS) Biowaivers New Drugs vs. Generics Between 2003 June, 2011, 54 drugproducts submitted to FDA for classification 18 FDA Experience: Generics Communicated via Individual Product Recommendations (IPRs) Special Population Special Population with Reference Scaled Approach Fed/FastedParent and Metabolite19 FDA Experience: Generics All Therapeutic Classes ConsideredMethods for Permeability Classification Direct Human intestinal perfusion Indirect Human PK: Absolute BA or mass balance Rat intestinal perfusion Epithelial cell monolayers Excised human or animal intestinal tissues Caco-2 Cell Monolayers Permeability and P-gp function: Days in culture: 21-28 Passage number: 58-76 Donor pH: 6.5 and 7.4 Multiple operators How did you validate your test system? Apical Chamber Cell Monolayer Filter Basolateral Chamber Test System ReproducibilityHigh Permeability Internal Standard (HPIS) Common Issues with HPIS: High Papp Variations with donor pH Inaccurate classification How did you choose your high permeability internal standard? HPISAB Papp pH 6.5AB PapppH 7.4%F Antipyrine63.44 11.5462.54 15.28100 Metoprolol11.65 1.7027.88 2.8095 Improved HPIS Caco-2 Papp (x 10-6 cm/s) Antipyrine: Papp ~63 Metoprolol: Papp ~28 Pindolol:Papp ~17 Minoxidil:Papp ~4 Selection of a high permeability internal standardwith permeability in close proximity to thelow/high permeability class boundary may facilitate classification of a test drug substance. Papp Recovery Test Compound11.892.5% Pindolol13.996.1% Atenolol0.2193.1% Concentration Papp Test Compound 1.0 M0.95 50 M7.90 Dose Strength 3239 MN/A Benefits: Accuracy Absolute BA is 98%Pindolol is Inadequate StandardBiowaiver Recommendation in IPR Benefits: Covariance Benefits: Normalization Benefits: Regulatory Approval At least 95% fraction absorbed> 90% metabolized Passive transport No known food effects or DDI No pH effect How do you justify using minoxidil as your high permeability internal standard? Multiple Validated pH Levels Donor pH 6.5 or 7.4 Obtaining Quality Permeability Data Mass balance Replicates Time points Relevant concentrations Lack of interactions between test compoundand co-dosed controlsMass Balance Underestimated Papp Exaggerated efflux ratio FDA expects >80% recovery 0/C AV dt dCPr rapp ) () (B A appA B appPPRCaco-2 Papp (x 10-6 cm/s) Provide intracellular accumulation data to demonstrate mass balance Time Points Replicates Test Compound A-to-B Papp

Minoxidil A-to-B Papp

Study 15.895.87 Study 24.475.51 34 Relevant Concentration Range Test Compound Concentration Efflux Ratio Permeability Classification 10 M6.2Similar32 M1.9High 100 M1.2High 320 M0.9High Consider: Highest dose per administration vs. highest dose strength Tolerability Monolayer Integrity pH Verification Analytical sensitivity Lack of Interaction with Internal Standards Phase 1A: Test compoundcodosed with controls Phase 1B: Test compound without controls PEDS Phase 2 (GLP): Unidirectional codosed with controls Bidirectional without controls Does the test compound impact permeability of internal standards and vice versa? 36 Correlation: Caco-2 Papp vs. Human Fabs

Quadrant4: In Vitro Limitations Transporter expression Residence time Barrier differences Inaccurate HPIS NSB of drug substance Why Quadrant2? Davit et al. AAPS Journal2008, Vol 10, No 1 148-156 Highly VariableDrugs RMSE > 0.3 Consistently Inconsistent(drug substance related) Extensive pre-systemicmetabolism Inconsistently Inconsistent (drug product related) Drug release rate Prevalence of HVDs Therapeutic Class Independent 180 Different DrugsANDA Applications from 2003-2005 57 Drugs are HVDs 22 Inconsistently Inconsistent35 Consistently Inconsistent(83% pre-systemic metabolism)23% Metabolism 123 less variable drugs BE Issues Biostudy Davit et al. AAPS Journal2008, Vol 10, No 1 148-156 Flat Dose Response Curve SubjectsApproach Highly Variable Drugs 55 min. RSARTR Less Variable Drugs 32 max. Two treatment crossover Applying BCS for HVDs Fa is the fraction of the drug that is absorbed from the intestinal lumen to the intestinal enterocytes. Fg is the fraction of the unmetabolized drug in the enterocytes. Fa Fg reaches the portal vein. Fh is the fraction of the unmetabolized drug in the liver.Fa Fg Fhreaches systemic circulation. Bioavailability (F%) = the rate and extent to which an active moiety becomes available in the systemic circulation. Rapid absorption Extensive metabolism 29-63% in urine 18-38% in feces Plasma concentrations of unchanged drug very low and highly variable (Cmax 1 to 6 ng/mL, tmax 40-90 min) HVD: Extensive Metabolism, High Variability BCS Permeability Data Papp 33.6 Minoxidil4.33 Atenolol0.26 Efflux Ratio1.1 Recovery89% Individual Product Recommendation (IPR) Source: FDA WebsiteHVD: Analysis of Parent and Metabolite Rapid absorpti