Author(s): Shin SC, Choi JS, Li X
Abstract Share this page
Abstract Orally administered tamoxifen undergoes a first-pass metabolism and substrates for multidrug resistance (MDR) transporters efflux in the liver and intestines, which obstructs its systemic exposure. This study investigated the effect of quercetin, a dual inhibitor of CYP3A4 and P-gp, on the bioavailability and pharmacokinetics of tamoxifen and one of its metabolites, 4-hydroxytamoxifen, in rats. The pharmacokinetic parameters of tamoxifen and 4-hydroxytamoxifen in plasma were determined after orally administering tamoxifen (10 mg/kg) with or without quercetin (2.5, 7.5 and 15 mg/kg). The coadministration of quercetin (2.5 and 7.5 mg/kg) significantly (p < 0.05) increased the absorption rate constant (K(a)), peak concentration (C(max)) and the areas under the plasma concentration-time curve (AUC) of tamoxifen. The absolute bioavailability (AB\%) of tamoxifen with 2.5 and 7.5 mg/kg quercetin ranged from 18.0\% to 24.1\%, which was significantly higher than the control group, 15.0\% (p < 0.05). The relative bioavailability (RB\%) of tamoxifen coadministered with quercetin was 1.20-1.61 times higher than the control group. The coadministration of quercetin caused no significant changes in the terminal half-life (t(1/2)) and the time to reach the peak concentration (T(max)) of tamoxifen. Compared with the control group, the coadministration of 7.5 mg/kg quercetin significantly (p < 0.05) increased the AUC of 4-hydroxytamoxifen. However, the metabolite ratios (MR; AUC of 4-hydroxytamoxifen to tamoxifen) were significantly lower (p < 0.05). This suggests that quercetin inhibits the both MDR transporters efflux and first-pass metabolism of tamoxifen. The enhanced bioavailability of tamoxifen as a result of its coadministration with quercetin might be due to the effect of quercetin promoting the intestinal absorption and reducing the first-pass metabolism of tamoxifen. If the results are further confirmed in the clinical trials, the tamoxifen dosage should be adjusted when tamoxifen is administered with quercetin or quercetin-containing dietary supplements in order to avoid potential drug interactions.
This article was published in Int J Pharm
and referenced in Journal of Bioengineering & Biomedical Science