Resolving parameter non-identifiability through hypothesis testing with PBPK simulations: identifying gut metabolism (reference 43). PBPK physiologically based pharmacokinetics, NCE new chemical entity, CYP cytochrome P450, IV intravenous, PK pharmacokinetics, SAD single ascending dose, MAD multiple ascending dose, DDI drug–drug inhibition, Fg gut bioavailability, CLint intrinsic clearance, P-gp P-glycoprotein, Kp tissue partition coefficient