Predicting drug pharmacokinetics in humans from in vitro metabolism studies

The pharmaceutical industry is committed to market safer drugs with fewer side effects, pre-dictable pharmacokinetic properties and quanti-fiable drug–drug interactions. There is an increasing need to develop robust, enhanced-throughput in vitro assays, which accurately ex-trapolate to humans. The major drug metabolizing human hepatic cytochrome P450s (CYPs; CYP1A2, 2C9, 2C19, 2D6 and 3A4) have been co-expressed functionally in Escherichia coli with human NADPH-cytochrome P450 reductase and validated as surrogates to their counterparts in human liver microsomes (HLM) with respect to their kinetic and inhibition properties. Using these recombinant enzymes, fully automated in vitro assays to assess CYP inhibition and determine the enzymology of drug oxidation have been devel-oped and validated. IC values determined for a series of test compounds in HLM and recom-binant CYPs were similar (r#fl0.9, P!0.001). There was a good correlation between the sum of individual CYP intrinsic clearance (C