Prediction of in vivo hepatic clearance of selected compounds using the isolated perfused rat liver, precision-cut liver slices and hepatocytes

Abstract

The overall objective of this dissertation was to estimate the in vivo hepatic clearance (CL(H)) of compounds using in vitro methods of drug metabolism. The isolated perfused rat liver, precision-cut liver slices and hepatocyte were used to estimate in vitro CL(H) and compared to in vivo CL(H) Two compounds, benzoic acid and tolbutamide were chosen as model compounds. An isolated perfused rat liver (IPRL) apparatus was developed to measure hepatic extraction ratio. Three compounds, antipyrine, ethanol and lidocaine were used to characterize the apparatus. The ability of the IPRL to utilize oxygen was also investigated. Antipyrine extraction ratio was independent of perfusate flow rate, while the extraction of ethanol and lidocaine were flow-dependent. The extraction ratios of benzoic acid and tolbutamide were determined. The CL(H) of benzoic acid and tolbutamide was 4.43 ± 0.84 mL/min and 1.52 ± 0.59 mL/min, respectively. The intrinsic clearance of benzoic acid and tolbutamide was determined in precision-cut liver slices and scaled to the whole liver using total protein. The CL(H) of benzoic acid in rat liver slices was 2.13 ± 0.71 mL/min, while the intrinsic clearance in humans was 270 mL/min. The CL(H) of tolbutamide in rat and human liver slices was 0.019 mL/min and 3.16 mL/min, respectively. The intrinsic clearance of benzoic acid and tolbutamide was determined in rat hepatocytes and scaled to the whole liver using total number of cells in the rat liver. The CL(H) of benzoic acid and tolbutamide in rat hepatocytes was 3.55 ± 1.29 mL/min and 0.57 ± 0.16 mL/min, respectively. The CL(H) of benzoic acid and tolbutamide on intravenous dosing in the rat was 8.02 ± 1.01mL/min and 0.49 ± 0.06 mL/min, respectively. Precision cut liver slices under-estimated the CL(H) of benzoic acid and tolbutamide. The under-estimation is probably due to the inability of the drug to permeate the liver slice over the short time course of the initial rate experiments. The CL(H) of benzoic acid and tolbutamide in rats was better predicted by the IPRL and hepatocytes.