PT  - JOURNAL ARTICLE
AU  - Johanna Honkalammi
AU  - Mikko Niemi
AU  - Pertti J. Neuvonen
AU  - Janne T. Backman
TI  - Dose-Dependent Interaction between Gemfibrozil and Repaglinide in Humans: Strong Inhibition of CYP2C8 with Subtherapeutic Gemfibrozil Doses
AID  - 10.1124/dmd.111.040931
DP  - 2011 Oct 01
TA  - Drug Metabolism and Disposition
PG  - 1977--1986
VI  - 39
IP  - 10
4099  - http://dmd.aspetjournals.org/content/39/10/1977.short
4100  - http://dmd.aspetjournals.org/content/39/10/1977.full
SO  - Drug Metab Dispos2011 Oct 01; 39
AB  - Gemfibrozil 1-O-β-glucuronide inactivates CYP2C8 irreversibly. We investigated the effect of gemfibrozil dose on CYP2C8 activity in humans using repaglinide as a probe drug. In a randomized, five-phase crossover study, 10 healthy volunteers ingested 0.25 mg of repaglinide 1 h after different doses of gemfibrozil or placebo. Concentrations of plasma repaglinide, gemfibrozil, their metabolites, and blood glucose were measured. A single gemfibrozil dose of 30, 100, 300, and 900 mg increased the area under the concentration-time curve of repaglinide 1.8-, 4.5-, 6.7-, and 8.3-fold (P < 0.001), and its peak concentration 1.4-, 1.7-, 2.1-, and 2.4-fold (P < 0.05), compared with placebo, respectively. Gemfibrozil pharmacokinetics was characterized by a slightly more than dose-proportional increase in the area under the curve of gemfibrozil and its glucuronide. The gemfibrozil-repaglinide interaction could be mainly explained by gemfibrozil 1-O-β-glucuronide concentration-dependent, mechanism-based inhibition of CYP2C8, with a minor contribution by competitive inhibition of organic anion-transporting polypeptide 1B1 at the highest gemfibrozil dose. The findings are consistent with ∼50% inhibition of CYP2C8 already with a single 30-mg dose of gemfibrozil and >95% inhibition with 900 mg. In clinical drug-drug interaction studies, a single 900-mg dose of gemfibrozil can be used to achieve nearly complete inactivation of CYP2C8.