Author(s): Yamada S, YasuiFurukori N, Akamine Y, Kaneko S, Uno T
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Abstract The aim of this study was to evaluate the possible effects of carbamazepine, a P-glycoprotein inducer, on fexofenadine pharmacokinetics. Twelve healthy Japanese volunteers (nine males and three females) were enrolled in this study after giving written informed consent. This randomized open-label study consisted of two phases (control and 7-day treatment) with a 2-week washout period. In the control phase, volunteers received 60 mg fexofenadine hydrochloride after an overnight fast. In the treatment phase, carbamazepine was dosed 100 mg three times daily (for a total daily dose of 300 mg) for 7 days, and on Day 7, a single 60-mg dose of fexofenadine was coadministered with a 100-mg dose of carbamazepine. The plasma concentrations and urinary excretion of fexofenadine were measured for 24 hours after dosing. Carbamazepine pretreatment significantly altered fexofenadine pharmacokinetics, decreasing the mean (+/- standard deviation) peak plasma concentration from 176.6 (+/- 82.1) ng/mL to 103.2 (+/- 33.6) ng/mL (P < 0.01) and the area under the plasma concentration-time curve from 1058.4 (+/- 528.7) ng/h/mL to 604.8 (+/- 255.9) ng/h/mL (P < 0.01) without changing the elimination half-life. Relatively, carbamazepine significantly reduced the amount of fexofenadine excreted into the urine from 8.1 (+/- 2.1) mg to 4.5 (+/- 1.4) mg (P < 0.001), although the renal clearance of fexofenadine remained constant between the two study phases. Thus, this study indicates that carbamazepine significantly decreases fexofenadine plasma concentrations, probably as a result of P-glycoprotein induction in the small intestine. Carbamazepine treatment, therefore, is of moderate clinical significance for patients receiving fexofenadine.
This article was published in Ther Drug Monit
and referenced in Journal of Bioequivalence & Bioavailability