Interindividual variability of CYP2C19-catalyzed drug metabolism due to differences in gene diplotypes and cytochrome P450 oxidoreductase content.

Large interindividual variability has been observed in the metabolism of CYP2C19 substrates in vivo. The study aimed to evaluate sources of this variability in CYP2C19 activity, focusing on CYP2C19 diplotypes and the cytochrome P450 oxidoreductase (POR). CYP2C19 gene analysis was carried out on 347 human liver samples. CYP2C19 activity assayed using human liver microsomes confirmed a significant a priori predicted rank order for (S)-mephenytoin hydroxylase activity of CYP2C19*17/*17 > *1B/*17 > *1B/*1B > *2A/*17 > *1B/*2A > 2A/2A diplotypes. In a multivariate analysis, the CYP2C192A allele and POR protein content were associated with CYP2C19 activity. Further analysis indicated a strong effect of the CYP2C192A, but not the *17, allele on both metabolic steps in the conversion of clopidogrel to its active metabolite. The present study demonstrates that interindividual variability in CYP2C19 activity is due to differences in both CYP2C19 protein content associated with gene diplotypes and the POR concentration.The Pharmacogenomics Journal advance online publication, 1 September 2015; doi:10.1038/tpj.2015.58.