Studies commonly done through the course of drug development to estimate fCL and fm

StageStudy TypeInformation GatheredPros and Cons
Pre-FIH/ Preclinical Development• Preclinical Species PK/ADME• NME cleared via metabolism or excretion in animalsPros:
(in vivo)• Major metabolic pathways in animals•Confidence from IVIVC in animals
• Preclinical Species CLint + metabolite profiling (in vitro)• Metabolic pathway in vitro similar to that in vivo in animalsCons:
• Human routes of metabolism maybe quite different from animals
• Human CLint + metabolite profiling (in vitro)• Major metabolic pathways in humans in vitroPros:
• P450 and other DME identification (in vitro human matrices)• Relative contribution of oxidation versus Conjugation• Preliminary estimates of P450-mediated DDI risk
• Relative contribution of P450 enzymesCons:
• Metabolism involve single or multiple enzymes• In vitro pathways may not be major pathways in vivo
FIH (SAD /MAD)• Detailed reaction phenotyping (in vitro)• fm of P450 or other major enzyme involved (in vitro)Pros:
• Metabolite profiling in plasma and urine in human usually available; in certain cases in bile (Entero-Test)• First look into major metabolic pathways in humans(commonly in plasma and urine; sometimes in bile)• Usually metabolite monitoring in in vitro phenotyping studies
• Crude estimate of fCL,renal (if NME substantially cleared renally); quantitative metabolite information in plasma and urine in certain cases (e.g., with quantitative NMR)• First look in humans—are metabolic pathways similar in vivo versus in vitro? Any human unique pathway not captured in vitro
• PK linearity (understand saturable processes)Cons:
• All qualitative estimates; quantitative estimate in plasma and urine possible if using quantitative NMR which allows minimum estimate of fm
• Missing metabolites info in feces
Definitive Human StudiesHuman radiolabel ADME study• Route of CL in humans (fCL)Pros:
• Quantitative metabolite profiling• fCL,metabolism + fCL,renal + fCL,biliary quantitatively determined
• Metabolites determined in feces
• Learn if fCL pathways predicted earlier is consistent with observed human fCL pathways
• fCL,biliary challenging after oral dose when substantial unchanged NME in feces
• In case of poor mass balance fCL pathways still not well defined
DDI with potent and selective enzyme inhibitor• Contribution of a DME toward overall NME metabolic clearance (fm) (assumption that inhibitor completely inhibits only enzyme of interest and for orally administered drugs, maximal intestinal inhibition is achieved)Pros:
• fm quantitatively determined
• Wide range of fm values when variability of PK, which can have significant impact on DDI magnitude
PK in genotyped population• Contribution of a polymorphic drug metabolizing enzyme toward overall NME metabolic clearance (fm) (assumption that in null phenotype (PM), polymorphic enzyme pathway is completely absent)Pros:
• fm quantitatively determined
• Inaccurate fm if residual activity of polymorphic enzyme in PM
  • FIH, first in human; PK, pharmacokinetics; NME, new molecular entity; ADME, absorption distribution metabolism excretion; CLint, intrinsic clearance; CL, clearance; IVIVC, in vitro-in vivo correlation; P450, cytochrome P450; DDI, drug-drug interactions; fCL, fraction of clearance; fm, fraction metabolized; NMR, nuclear magnetic resonance; PM, poor metabolizer.