PT  - JOURNAL ARTICLE
AU  - Peter J. Kilford
AU  - Rowan Stringer
AU  - Bindi Sohal
AU  - J. Brian Houston
AU  - Aleksandra Galetin
TI  - Prediction of Drug Clearance by Glucuronidation from in Vitro Data: Use of Combined Cytochrome P450 and UDP-Glucuronosyltransferase Cofactors in Alamethicin-Activated Human Liver Microsomes
AID  - 10.1124/dmd.108.023853
DP  - 2009 Jan 01
TA  - Drug Metabolism and Disposition
PG  - 82--89
VI  - 37
IP  - 1
4099  - http://dmd.aspetjournals.org/content/37/1/82.short
4100  - http://dmd.aspetjournals.org/content/37/1/82.full
SO  - Drug Metab Dispos2009 Jan 01; 37
AB  - Glucuronidation via UDP-glucuronosyltransferase (UGT) is an increasingly important clearance pathway. In this study intrinsic clearance (CLint) values for buprenorphine, carvedilol, codeine, diclofenac, gemfibrozil, ketoprofen, midazolam, naloxone, raloxifene, and zidovudine were determined in pooled human liver microsomes using the substrate depletion approach. The in vitro clearance data indicated a varying contribution of glucuronidation to the clearance of the compounds studied, ranging from 6 to 79% for midazolam and gemfibrozil, respectively. The CLint was ob tained using either individual or combined cofactors for cytochrome P450 (P450) and UGT enzymes with alamethicin activation and in the presence and absence of 2% bovine serum albumin (BSA). In the presence of combined P450 and UGT cofactors, CLint ranged from 2.8 to 688 μl/min/mg for zidovudine and buprenorphine, respectively; the clearance was approximately equal to the sum of the CLint values obtained in the presence of individual cofactors. The unbound intrinsic clearance (CLint, u) was scaled to provide an in vivo predicted CLint; the data obtained in the presence of combined cofactors resulted in 5-fold underprediction on average. Addition of 2% BSA to the incubation with both P450 and UGT cofactors reduced the bias in the clearance prediction, with 8 of 10 compounds predicted within 2-fold of in vivo values with the exception of raloxifene and gemfibrozil. The current study indicates the applicability of combined cofactor conditions in the assessment of clearance for compounds with a differential contribution of P450 and UGT enzymes to their elimination. In addition, improved predictability of microsomal data is observed in the presence of BSA, in particular for UGT2B7 substrates. The American Society for Pharmacology and Experimental Therapeutics