In vitro-in vivo extrapolation of hepatic clearance involving active uptake: theoretical and experimental aspects.

The importance of hepatic uptake transporters in drug clearance is well recognized. The subject is reviewed with the intention of providing an overview of the concepts in order to link the increasing knowledge of transporter-mediated uptake into established models of hepatic clearance. In order to understand and quantify their impact, models of hepatic elimination that incorporate permeability barriers are required. Models that include both active and passive uptake into hepatocytes are discussed and simulations of the influence of active uptake and passive diffusion on hepatic clearance are presented. The advantages and weaknesses of a number of in vitro assays of hepatic uptake are described, and their ability to predict hepatic clearance is reviewed.