Role of Cytochrome P450 Isoenzymes 3A and 2D6 in the In Vivo Metabolism of Mirabegron, a β3-Adrenoceptor Agonist
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Background Mirabegron is a β3b>-adrenoceptor agonist for the treatment of overactive bladder. There has been little information published or presented about the involvement of cytochrome P450 (CYP) isoenzymes 3A and 2D6 in the metabolism of mirabegron in humans; in vitro data indicate that oxidative metabolism is primarily mediated by CYP3A with a minor role for CYP2D6. Objective To determine to what extent CYP3A and CYP2D6 isoenzymes are involved in mirabegron metabolism. Methods Two open-label, randomized, one-sequence crossover drug–drug interaction studies in healthy subjects were conducted to assess the effect of ketoconazole and rifampicin on the pharmacokinetics of mirabegron and two parallel-group studies in healthy subjects with either known confirmed or predicted CYP2D6 phenotype. Results Co-administration of multiple dosages of 400?mg/day ketoconazole with a single 100?mg mirabegron oral controlled absorption system (OCAS) dose increased mirabegron maximum concentration (C maxb>) and area under the curve extrapolated to infinity (AUC?/sub>) to 145?% (90?% confidence interval [CI] 123-72?%] and 181?% (90?% CI 163-01?%), respectively. Co-administration of multiple dosages of 600?mg/day rifampicin with a single 100?mg mirabegron OCAS dose decreased mirabegron C maxb> and AUC?/sub> to 65?% (90?% CI 50-6?%) and 56?% (90?% CI 49-5?%), respectively, without an effect on terminal elimination half-life (t ?b>). The urinary excretion of mirabegron was increased by ketoconazole and decreased by rifampicin, reflecting the AUC changes, whereas renal clearance was not affected. Ketoconazole decreased mirabegron t ?b> from 50.9 to 37.6?h suggesting that volume of distribution as well as first-pass effect decreased. Rifampicin did not affect mirabegron t ?b>, suggesting that it affects first pass through the intestinal wall or liver. Rifampicin greatly increased the ratio to parent drug of the presumed CYP-mediated mirabegron metabolites M8 and M15 by 777 and 646?%. Steady-state mirabegron pharmacokinetic parameters (50 and 100?mg mirabegron OCAS) were similar in 13 CYP2D6 poor, 40 intermediate, and 99 extensive metabolizers, whereas C maxb> and AUC under the dosing interval τ of 24?h (AUCτb>) were 30-7?% lower in 10 ultrarapid metabolizers. After administration of 160?mg mirabegron immediate release, C maxb> was 14?% and AUC?/sub> 19?% higher in eight poor metabolizers than in eight extensive metabolizers (phenotyped) with similar t ?b>. All treatments were well tolerated. Conclusions Mirabegron is metabolized by CYP3A and to a minor extent by CYP2D6 in humans. Mirabegron is not considered a sensitive substrate of CYP3A in vivo, as ketoconazole increased mirabegron exposure by less than 2-fold. The effect of CYP2D6 phenotype on mirabegron exposure is small and likely of limited clinical importance.

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