Effects of morin on the bioavailability of tamoxifen and its main metabolite, 4-hydroxytamoxifen, in rats.

This study examined the effect of morin on the bioavailability and pharmacokinetics of tamoxifen and its metabolite, 4-hydroxytamoxifen, in rats. A single dose of tamoxifen was administered to rats intravenously (2 mg/kg) or orally (10 mg/kg), with or without morin (3 or 10 mg/kg). The presence of morin significantly altered the pharmacokinetics of the orally administered tamoxifen. Compared with the oral control group (given tamoxifen alone), the total body clearance (CL/F) of tamoxifen in the presence of morin was significantly reduced (by 35.9-40.8%, p<0.01). The area under the plasma concentration-time curve (AUC(0-infinity)) and the peak plasma concentration (Cmax) of tamoxifen significantly (p<0.05 for 3 mg/kg of morin, p<0.01 for 10 mg/kg of morin) increased by 50.6-68.9% and 65.1-80.9%, respectively. Consequently, the absolute bioavailability (AB) of tamoxifen in the presence of morin was 37.4-40.5%, which was enhanced significantly (p<0.05) compared with the oral control group (23.9%). The relative bioavailability (RB) of tamoxifen was 1.56 to 1.68 times higher than the control group. The increased bioavailability of tamoxifen is likely to be due to the decrease in the first-pass metabilism by the intestines and liver. Morin at a dose of 10 mg/kg significant increased the AUC(0-infinity), of 4-hydroxytamoxifen (by 50.9%, p<0.05) but the metabolite:parent ratio (MR) of 4-hydroxytamoxifen was not altered significantly, suggesting that the formation of 4-hydroxytamoxifen is not affected considerably by morin. The increased bioavailability of tamoxifen in the presence of morin should be taken into consideration for dosage regimens due to potential drug interaction.