Effect of Wuziyanzong pill on metabolism of dapoxetine in vivo and in vitro.

In vitro incubation of rat liver microsomes with 30 µL of 100 µmol·L-1 dapoxetine and 30 µL of 10, 100, 250, 500, 1000, 2500, or 5000 µg·mL-1 Wuziyanzong pill was performed at 37 °C for 60 min. Dapoxetine concentration was analyzed by high performance liquid chromatography (HPLC). The half maximal inhibitory concentration (IC50) of Wuziyanzong pill on metabolism of dapoxetine was 296.10 µg mL-1in vitro. Twelve SD rats were randomly divided into 2 groups: Control group and Wuziyanzong pill group. The two groups were administrated with 10 mL·kg-1 saline (Control group) or 10 mL·kg-1 Wuziyanzong pill solution (Experimental group, solution contained 200 mg mL-1 Wuziyanzong pill) for 15 consecutive days. Following administration of saline or Wuziyanzong pill on the 15th day, 20 mg kg-1 dapoxetine was administered to all rats. Blood was collected from the tail vein (0.3 mL) at multiple time points, and ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) was used to determine the concentration of dapoxetine and its main metabolites, dapoxetine-N-oxide and desmethyldapoxetine in rats. Pharmacokinetic analysis of dapoxetine showed that area under the concentration-time curve (AUC) and mean maximum plasma concentration (Cmax) of the Wuziyanzong pill group were decreased, while plasma clearance (CLz) was increased compared with control group (P < 0.01). The HPLC method for determination of dapoxetine in vitro was accurate and specific. The UHPLC-MS/MS method established for determination of dapoxetine and its major metabolites in rat plasma was rapid and specific, which met the requirements of pharmacokinetic guidelines. Wuziyanzong pill had a weak inhibitory effect on metabolism of dapoxetine in vitro, but had a very strong induction effect in vivo, suggesting the dosage of dapoxetine should be increased when administered in combination with Wuziyanzong pill.