Herb-drug interaction of Epimedium extract on the pharmacokinetic of dapoxetine in rats.

The aim of study is to develop a high performance liquid chromatography tandem mass spectrometry (LC-MS/MS) method to investigate the pharmacokinetic interaction of Epimedium extract on the dapoxetine in rats. Experimental rats were divided into the following four parallel groups: (1) dapoxetine alone (10mg/kg, i.v.); (2) oral administration of Epimedium extract (2g/kg) for 3 consecutive days and on the fourth day dapoxetine was administered (10mg/kg, i.v.); (3) dapoxetine alone (10mg/kg, p.o.); (4) oral administration of Epimedium extract (2g/kg) for 3 consecutive days and on the fourth day dapoxetine was administered (10mg/kg, p.o.). The calibration curves of dapoxetine were acquired over a concentration ranges from 1 to 500ng/mL with the R(2)=0.999. The mean matrix effects and extraction recoveries of dapoxetine at three different concentrations (1, 10, 500ng/mL) ranged from 107.3 to 110.9% and from 25.5 to 28.2% respectively. The interday and intraday relative standard deviation were both <6% while the bias were both <14%. The pharmacokinetic results demonstrated that pretreated with/without Epimedium extract for three consecutive days did not significant alter the pharmacokinetics of dapoxetine in rats. The oral bioavailability of dapoxetine was about 75% in rats.

Pharmacokinetics of ractopamine and its organ distribution in rats.

Ractopamine, a ß-agonist, is used to increase the proportion of lean meat in livestock. However, due to potential cardiovascular risks, ractopamine has been banned for use in food-producing animals in many countries. Nevertheless, pharmacokinetic studies of ractopamine have not been completed. The aim of this study was to develop a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for the determination of ractopamine. This validated method was used to investigate the pharmacokinetics and organ distribution of ractopamine in rats. The validation results complied with the U.S. Food and Drug Administration's standards. The oral bioavailability of ractopamine was 2.99%. After intravenous administration, ractopamine concentrations varied as follows: kidney > lung > spleen > heart > liver > muscle > plasma > brain. Nonlinear pharmacokinetics and strong partitioning into tissues were observed after intravenous administration of ractopamine. These effects may be due to nonlinear elimination via the kidney.