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  • Title: Enantioselective disposition of fexofenadine with the P-glycoprotein inhibitor verapamil.
    Author: Sakugawa T, Miura M, Hokama N, Suzuki T, Tateishi T, Uno T.
    Journal: Br J Clin Pharmacol; 2009 May; 67(5):535-40. PubMed ID: 19552748.
    Abstract:
    AIMS: The aim was to compare possible effects of verapamil, as a P-glycoprotein (P-gp) inhibitor, on the pharmacokinetics of each fexofenadine enantiomer, as a P-gp substrate. METHODS: Thirteen healthy Japanese volunteers (10 male and three female) were enrolled. In a randomized, two-phase, crossover design, verapamil was dosed 80 mg three times daily (with total daily doses of 240 mg) for 6 days, and on day 6, a single 120-mg dose of fexofenadine was administered along with an 80-mg dose of verapamil. Subsequently, fexofenadine was administered alone after a 2-week wash-out period. The plasma concentrations of fexofenadine enantiomers were measured up to 24 h after dosing. RESULTS: During the control phase, the mean AUC(0-infinity) of S(-)- and R(+)-fexofenadine was 700 ng h(-1) ml(-1)[95% confidence interval (CI) 577, 823] and 1202 ng h(-1) ml(-1) (95% CI 1007, 1396), respectively, with a significant difference (P < 0.001). Verapamil had a greater effect on the pharmacokinetic parameters of S(-)-fexofenadine compared with those of the R(+)-enantiomer, and increased AUC(0-infinity) of S(-)-fexofenadine and R(+)-fexofenadine by 3.5-fold (95% CI of differences 1.9, 5.1; P < 0.001) and by 2.2-fold (95% CI of differences 1.7, 3.0; P < 0.001), respectively. The R/S ratio for the AUC(0-infinity) was reduced from 1.76 to 1.32 (P < 0.001) by verapamil treatments. CONCLUSION: This study indicates that P-gp plays a key role in the stereoselectivity of fexofenadine pharmacokinetics, since the pharmacokinetics of fexofenadine enantiomers were altered by the P-gp inhibitor verapamil, and this effect was greater for S-fexofenadine compared with R-fexofenadine.
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