title: Gemfibrozil is a potent inhibitor of human cytochrome P450 2C9.
abstract: The in vitro inhibitory effects of gemfibrozil on cytochrome P450 (CYP) 1A2 (phenacetin O-deethylation), CYP2A6 (coumarin 7-hydroxylation), CYP2C9 (tolbutamide hydroxylation), CYP2C19 (S-mephenytoin 4'-hydroxylation), CYP2D6 (dextromethorphan O-deethylation), CYP2E1 (chlorzoxazone 6-hydroxylation), and CYP3A4 (midazolam 1'-hydroxylation) activities were examined using pooled human liver microsomes. The in vivo drug interactions of gemfibrozil were predicted in vitro using the [I]/([I] + K(i)) values. Gemfibrozil strongly and competitively inhibited CYP2C9 activity, with a K(i) (IC(50)) value of 5.8 (9.6) microM. In addition, gemfibrozil exhibited somewhat smaller inhibitory effects on CYP2C19 and CYP1A2 activities, with K(i) (IC(50)) values of 24 (47) microM and 82 (136) microM, respectively. With concentrations up to 250 microM, gemfibrozil showed no appreciable effect on CYP2A6, CYP2D6, CYP2E1, and CYP3A4 activities. Based on [I]/([I] + K(i)) values calculated using peak total (or unbound) plasma concentration of gemfibrozil, 96% (56%), 86% (24%), and 64% (8%) inhibition of the clearance of CYP2C9, CYP2C19, and CYP1A2 substrates could be expected, respectively. In conclusion, gemfibrozil inhibits the activity of CYP2C9 at clinically relevant concentrations, and this is the likely mechanism by which gemfibrozil interacts with CYP2C9 substrate drugs, such as warfarin and glyburide. Gemfibrozil may also impair clearance of CYP2C19 and CYP1A2 substrates, but inhibition of other CYP isoforms is unlikely.
authors.affiliation: Department of Clinical Pharmacology, University of Helsinki, Haartmaninkatu 4, FIN-00290 Helsinki, Finland.
authors.forename: X
authors.initials: X
authors.lastname: Wen
authors.forename: J S
authors.initials: JS
authors.lastname: Wang
authors.forename: J T
authors.initials: JT
authors.lastname: Backman
authors.forename: K T
authors.initials: KT
authors.lastname: Kivistö
authors.forename: P J
authors.initials: PJ
authors.lastname: Neuvonen
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065637:Cytochrome P-450 CYP2A6; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D015248:Gemfibrozil / Q000494:pharmacology*; D006801:Humans; D000960:Hypolipidemic Agents / Q000494:pharmacology*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D000960:Hypolipidemic Agents; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C585710:CYP2A6 protein, human; C045793:CYP2C19 protein, human; C104464:CYP3A protein, human; D019388:Cytochrome P-450 CYP1A2; D065637:Cytochrome P-450 CYP2A6; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; D039181:Steroid 16-alpha-Hydroxylase; C510163:CYP3A4 protein, human; D015248:Gemfibrozil