Abstract

We investigated hepatic in vitro intrinsic clearance (CL_{int,in vitro}) in freshly isolated or cryopreserved hepatocytes and compared with CL_{int,in vivo} by using nine model compounds, FK1052, FK480, diazepam, diltiazem, troglitazone, quinotolast, FK079, zidovudine, and acetaminophen, in rats and humans. The compounds showed a broad range of in vivo hepatic extraction ratios (rat, 0.05–0.93; humans, 0.03–0.76) and were metabolized by hepatic P450, UDP-glucuronosyltransferase, sulfotransferase, and/or esterase. CL_{int,in vitro} was determined from substrate disappearance rate at 1 μM in hepatocytes. CL_{int,in vivo}was calculated from in vivo pharmacokinetic data using two frequently used mathematical models (the well stirred and dispersion models). When estimating rat CL_{int,in vitro} in freshly isolated hepatocytes, the rat scaling factor values (CL_{int,in vivo}/CL_{int,in vitro}) showed marked difference among the model compounds (0.2–73.1-fold). The rat CL_{int,in vitro} values in freshly isolated hepatocytes were in good agreement with these in cryopreserved hepatocytes. Human CL_{int,in vitro} were determined by use of cryopreserved hepatocytes. When human CL_{int,in vitro} was regarded as the predicted CL_{int,in vivo}, the observed and predicted CL_{int,in vivo} for FK1052, FK480, troglitazone, and FK079 differed markedly (12.4–199.0-fold). In contrast, using human CL_{int,in vitro} corrected with the rat scaling factors yielded better predictions of CL_{int,in vivo} that were mostly within 5-fold of the actual values. These results make the evaluation using hepatocytes more useful and provide a basis for predicting hepatic clearance using hepatocytes.