Co‐administration of ketoconazole with H1‐antagonists ebastine and loratadine in healthy subjects: pharmacokinetic and pharmacodynamic effects

AIMS: Two studies were conducted to evaluate the effects of coadministration of ketoconazole with two nonsedating antihistamines, ebastine and loratadine, on the QTc interval and on the pharmacokinetics of the antihistamines. METHODS: In both studies healthy male subjects (55 in one study and 62 in the other) were assigned to receive 5 days of antihistamine (ebastine 20 mg qd in one study, and loratadine 10 mg qd in the other) or placebo alone using a predetermined randomization schedule, followed by 8 days of concomitant ketoconazole 450 mg qd/antihistamine or ketoconazole 400 mg qd/placebo. Serial ECGs and blood sampling for drug analysis were performed at baseline and on study days 5 (at the end of monotherapy) and 13 (at the end of combination therapy). QT intervals were corrected for heart rate using the formula QTc = QT/RR(alpha) with special emphasis on individualized alpha values derived from each subject's own QT/RR relationship at baseline. RESULTS: No significant changes in QTc interval from baseline were observed after 5 days administration of ebastine, loratadine or placebo. Ketoconazole/placebo increased the mean QTc (95% CI) by 6.96 (3.31-10.62) ms in the ebastine study and by 7.52 (4.15-10.89) ms in the loratadine study. Mean QTc was statistically significantly increased during both ebastine/ketoconazole administration (12.21 ms; 7.39-17.03 ms) and loratadine/ketoconazole administration (10.68 ms; 6.15-15.21 ms) but these changes were not statistically significantly different from the increases seen with placebo/ketoconazole (6.96 ms; 3.31-10.62 ms), P = 0.08 ebastine study, (7.52 ms; 4.15-10.89 ms), P = 0.26 loratadine study). After the addition of ketoconazole, the mean area under the plasma concentration-time curve (AUC) for ebastine increased by 42.5 fold, and that of its metabolite carebastine by 1.4 fold. The mean AUC for loratadine increased by 4.5 fold and that of its metabolite desloratadine by 1.9 fold following administration of ketoconazole. No subjects were withdrawn because of ECG changes or drug-related adverse events. CONCLUSIONS: Ketoconazole altered the pharmacokinetic profiles of both ebastine and loratadine although the effect was greater for the former drug. The coadministration of ebastine with ketoconazole resulted in a non significant mean increase of 5.25 ms (-0.65 to 11.15 ms) over ketoconazole with placebo (6.96 ms) while ketoconazole plus loratadine resulted in a nonsignificant mean increase of 3.16 ms (-2.73 to 8.68 ms) over ketoconazole plus placebo (7.52 ms). Changes in uncorrected QT intervals for both antihistamines were not statistically different from those observed with ketoconazole alone. The greater effect of ketoconazole on the pharmacokinetics of ebastine was not accompanied by a correspondingly greater pharmacodynamic effect on cardiac repolarization.