Vol. 31, Issue 5, 580-588, May 2003

Utility of Hepatocytes in Predicting Drug Metabolism: Comparison of Hepatic Intrinsic Clearance in Rats and Humans in Vivo and in Vitro

Yoichi Naritomi, Shigeyuki Terashita, Akira Kagayama, and Yuichi Sugiyama

Biopharmaceutical and Pharmacokinetic Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan (Y.N., S.T., A.K.); and Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan (Y.S.)

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.