RT Journal Article SR Electronic T1 (–)-N-3-Benzylphenobarbital Is Superior to Omeprazole and (+)-N-3-Benzylnirvanol as a CYP2C19 Inhibitor in Suspended Human Hepatocytes JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1121 OP 1128 DO 10.1124/dmd.120.000089 VO 48 IS 11 A1 Marie-Lynn Cuypers A1 Hugues Chanteux A1 Eric Gillent A1 Pierre Bonnaillie A1 Kenneth Saunders A1 Claire Beckers A1 Claude Delatour A1 Sylvie Dell’Aiera A1 Anna-Lena Ungell A1 Johan Nicolaï YR 2020 UL http://dmd.aspetjournals.org/content/48/11/1121.abstract AB Early assessment of metabolism pathways of new chemical entities guides the understanding of drug-drug interactions. Selective enzyme inhibitors are indispensable in CYP reaction phenotyping. The most commonly applied CYP2C19 inhibitor, omeprazole, lacks selectivity. Two promising alternatives, (+)-N-3-benzylnirvanol and (−)-N-3-benzylphenobarbital, are already used as CYP2C19 inhibitors in some in vitro studies with suspended human hepatocytes. However, a full validation proving their suitability in terms of CYP and non-CYP selectivity has not been presented in literature. The present study provides a thorough comparison between omeprazole, (+)-N-3-benzylnirvanol, and (−)-N-3-benzylphenobarbital in terms of potency and selectivity and shows the superiority of (−)-N-3-benzylphenobarbital as a CYP2C19 inhibitor in suspended human hepatocytes. Furthermore, we evaluated the application of (−)-N-3-benzylphenobarbital to predict the in vivo contribution of CYP2C19 to drug metabolism [fraction metabolized (fm) of CYP2C19, fmCYP2C19]. A set of 10 clinically used CYP2C19 substrates with reported in vivo fmCYP2C19 data was evaluated. fmCYP2C19, which was predicted using data from suspended human hepatocyte incubations, underestimated the in vivo fmCYP2C19. The use of a different hepatocyte batch with a different CYP3A4/CYP2C19 activity ratio showed the impact of intrinsic CYP activities on the determination of fmCYP2C19. Overall, this study confirms the selective CYP2C19 inhibition by (−)-N-3-benzylphenobarbital over other CYP isoforms (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP3A4) and clinically relevant non-CYP enzymes [aldehyde oxidase, flavin-containing monooxygenase 3, N-acetyltransferase 2, uridine diphosphate glucuronosyltransferase (UGT) 1A1, UGT1A4, UGT2B7, UGT2B15] in suspended human hepatocytes. (−)-N-3-benzylphenobarbital is therefore the preferred CYP2C19 inhibitor to assess fmCYP2C19 in suspended human hepatocytes in comparison with omeprazole and (+)-N-3-benzylnirvanol.SIGNIFICANCE STATEMENT (−)-N-3-Benzylphenobarbital is a more potent and selective inhibitor of CYP2C19 in suspended human hepatocytes than omeprazole and (+)-N-3-benzylnirvanol. (−)-N-3-Benzylphenobarbital can be used to predict the fraction metabolized by CYP2C19 in suspended human hepatocytes.