Effects of single and multiple doses of itraconazole on the pharmacokinetics of fexofenadine, a substrate of P-glycoprotein

Aims We determined whether or not the extent of drug interaction of fexofenadine by itraconazole is time-dependent. Methods In a randomized two-phase crossover study, itraconazole was administered orally for 6 days, and, on days 1, 3 and 6, fexofenadine was administered simultaneously. On another occasion, fexofenadine was administered alone. Results Itraconazole increased fexofenadine AUC(0, infinity), and the % change for difference was 178% (95% CI 1235, 3379), 205% (95% CI 1539, 3319) and 169% (95% CI 1128, 2987) on days 1, 3 and 6 of the 6 day treatment, respectively. Conclusions The extent of drug interaction by itraconazole was not time-dependent.