This work was previously presented in part as follows: Paris BL, Yerino P, Ogilvie BW, and Parkinson A (2008) The proton pump inhibitors (PPIs) omeprazole and rabeprazole, but not lansoprazole, are in vitro time-dependent inhibitors of CYP2C19. 10th European Regional ISSX Meeting; 2008 May 18–21; Vienna, Austria. International Society for the Study of Xenobiotics, Washington, DC. Drug Metab Rev 40 (Suppl 1): 89–90; Parkinson A, Kazmi F, Buckley DB, Yerino P, Ogilvie BW, and Paris BL (2010) System-dependent outcomes during the evaluation of drug candidates as inhibitors of cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) enzymes: human hepatocytes versus liver microsomes versus recombinant enzymes. Drug Metab Pharmacokinet 25:16–27; Parkinson A (2011) Irreversible inhibition of CYP2C19 by some but not all proton pump inhibitors and its relevance to the anti-platelet effect of clopidogrel (Plavix). North Jersey ACS Drug Metabolism Discussion Group (http://www.njacs.org/drugmet.html); 2011 Apr 13; Somerset, NJ.