The cytochrome P4503A4 inhibitor clarithromycin increases the plasma concentrations and effects of repaglinide

Objective: Our objective was to study the effects of the macrolide antibiotic clarithromycin on the pharmacokinetics and pharmacodynamics of repaglinide, a novel short-acting antidiabetic drug. Methods: In a randomized, double-blind, 2-phase crossover study, 9 healthy volunteers were treated for 4 days with 250 mg oral clarithromycin or placebo twice daily. On day 5 they received a single dose of 250 mg clarithromycin or placebo, and 1 hour later a single dose of 0.25 mg repaglinide was given orally. Plasma repaglinide, serum insulin, and blood glucose concentrations were measured up to 7 hours. Results: Clarithromycin increased the mean total area under the concentration-time curve of repaglinide by 40% (P < .0001) and the peak plasma concentration by 67% (P < .005) compared with placebo. The mean elimination half-life of repaglinide was prolonged from 1.4 to 1.7 hours (P < .05) by clarithromycin. Clarithromycin increased the mean incremental area under the concentration-time curve from 0 to 3 hours of serum insulin by 51% (P < .05) and the maximum increase in the serum insulin concentration by 61% (P < .01) compared with placebo. No statistically significant differences were found in the blood glucose concentrations between the placebo and clarithromycin phases. Conclusions: Even low doses of the cytochrome P4503A4 (CYP3A4) inhibitor clarithromycin increase the plasma concentrations and effects of repaglinide. Concomitant use of clarithromycin or other potent inhibitors of CYP3A4 with repaglinide may enhance its blood glucose-lowering effect and increase the risk of hypoglycemia.