Construction and Verification of Physiologically Based Pharmacokinetic Models for Four Drugs Majorly Cleared by Glucuronidation: Lorazepam, Oxazepam, Naloxone, and Zidovudine.

Physiologically based pharmacokinetic (PBPK) modeling is less well established for substrates of UDP-glucuronosyltransferases (UGT) than for cytochrome P450 (CYP) metabolized drugs and more verification of simulations is necessary to increase confidence. To address specific challenges of UGT substrates, we developed PBPK models for four drugs cleared majorly via glucuronidation (lorazepam, oxazepam, naloxone, and zidovudine). In vitro to in vivo scaling of intrinsic clearance generated with co-cultured human hepatocytes was applied for hepatic metabolism and extra-hepatic clearance was extrapolated based on relative expression of UGT isoforms in the liver, kidney, and intestine. Non-metabolic clearance and the contributions of individual UGT isoforms to glucuronidation were based on in vitro and in vivo studies taken from the literature and simulations were verified and evaluated with a broad set of clinical pharmacokinetic data. Model evaluation showed systemic clearance predictions within 1.5-fold for all drugs and all simulated parameters were within 2-fold of observed. However, during the verification step, top-down model fitting was necessary to adjust for under-prediction of zidovudine V