No abstract

Itraconazole, gemfibrozil and their combination markedly raise the plasma concentrations of loperamide. Although not seen in the psychomotor tests used, an increased risk of adverse effects should be considered during concomitant use of loperamide with itraconazole, gemfibrozil and especially their combination.

What is already known about this subject • Severe hypoglycaemia has been reported after concomitant use of clarithromycin and glibenclamide. • Glibenclamide is a substrate for the transporters P‐glycoprotein and OATP2B1. • Clarithromycin inhibits P‐glycoprotein and grapefruit juice inhibits OATP2B1. What this study adds • Clarithromycin increases the plasma concentration of glibenclamide. • A pharmacokinetic interaction may explain reported hypoglycaemia during simultaneous administration of clarithromycin and glibenclamide. • Grapefruit juice has no effect on the pharmacokinetics of glibenclamide. Aims Case reports suggest that clarithromycin can increase the glucose‐lowering effect of glibenclamide which is metabolized mainly by CYP2C9 and is a substrate for P‐glycoprotein and OATP2B1. Our objective was to evaluate whether the P‐glycoprotein inhibitor, clarithromycin, increases and the putative OATP2B1 inhibitor, grapefruit juice, decreases plasma concentrations of glibenclamide. Methods In a randomized three‐phase crossover study, 12 subjects ingested 250 mg clarithromycin or placebo twice daily or 200 ml grapefruit juice three times daily for 2 days. On day 3, they ingested 0.875 mg glibenclamide with sugar water or grapefruit juice. Concentrations of glibenclamide and clarithromycin in plasma, glucose in blood, and excretion of hydroxyglibenclamide into urine were measured up to 12 h. Results Clarithromycin increased the peak concentration (Cmax) of glibenclamide to 1.25‐fold (95% confidence interval (CI) 1.12, 1.40; P < 0.01) and the area under the plasma concentration‐time curve to 1.35‐fold (95% CI 1.21, 1.50; P < 0.01) compared with the placebo phase. The time to Cmax, the half‐life of glibenclamide, and the amount of hydroxyglibenclamide excreted into urine remained unaltered. Grapefruit juice did not change the pharmacokinetics of glibenclamide. Clarithromycin concentrations implied a good compliance. Blood glucose did not deviate between the phases. Conclusions Clarithromycin increased plasma concentrations of glibenclamide, possibly by inhibiting P‐glycoprotein in the intestinal wall. Although not seen with the present study design, clarithromycin may enhance the effect of glibenclamide by increasing plasma glibenclamide concentrations, which warrants close monitoring of blood glucose during their co‐administration. Grapefruit juice had no effect on glibenclamide pharmacokinetics.