Utility of hepatocytes in predicting drug metabolism: Comparison of hepatic intrinsic clearance in rats and humans in vivo and in vitro

We investigated hepatic in vitro intrinsic clearance (CLint, in vitro) in freshly isolated or cryopreserved hepatocytes and compared with CLint, 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. CLint, in vitro was determined from substrate disappearance rate at 1 muM in hepatocytes. CLint, in vivo was calculated from in vivo pharmacokinetic data using two frequently used mathematical models ( the well stirred and dispersion models). When estimating rat CLint, in vitro in freshly isolated hepatocytes, the rat scaling factor values (CLint, in vivo/CLint, in vitro) showed marked difference among the model compounds (0.2-73.1-fold). The rat CLint, in vitro values in freshly isolated hepatocytes were in good agreement with these in cryopreserved hepatocytes. Human CLint, in vitro were determined by use of cryopreserved hepatocytes. When human CLint, in vitro was regarded as the predicted CLint, in vivo, the observed and predicted CLint, in vivo for FK1052, FK480, troglitazone, and FK079 differed markedly (12.4-199.0-fold). In contrast, using human CLint, in vitro corrected with the rat scaling factors yielded better predictions of CLint, 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.