PT - JOURNAL ARTICLE AU - Adam J. Claessens AU - Linda J. Risler AU - Sara Eyal AU - Danny D. Shen AU - Thomas R. Easterling AU - Mary F. Hebert TI - CYP2D6 Mediates 4-Hydroxylation of Clonidine In Vitro: Implication for Pregnancy-Induced Changes in Clonidine Clearance AID - 10.1124/dmd.110.033878 DP - 2010 Sep 01 TA - Drug Metabolism and Disposition PG - 1393--1396 VI - 38 IP - 9 4099 - http://dmd.aspetjournals.org/content/38/9/1393.short 4100 - http://dmd.aspetjournals.org/content/38/9/1393.full SO - Drug Metab Dispos2010 Sep 01; 38 AB - Clonidine is a centrally acting, α-2 adrenergic agonist used for the treatment of hypertension during pregnancy. The metabolic pathways of clonidine are poorly understood, and the quantitative contribution of specific human cytochrome P450 (P450) isoforms has not been systematically assessed. In this study, 17 cDNA-expressed P450 enzymes, in addition to pooled human liver microsomes, were evaluated for clonidine 4-hydroxylation activity in vitro. Five P450 enzymes—CYP2D6, 1A2, 3A4, 1A1, and 3A5—catalyzed measurable formation of 4-hydroxyclonidine. Selective inhibition studies in human liver microsomes confirmed that these isoforms are jointly responsible for 4-hydroxylation of clonidine in vitro, and CYP2D6 accounted for approximately two-thirds of the activity. The major role of CYP2D6 in clonidine metabolism might explain the increase in its nonrenal clearance during pregnancy.