Pharmacokinetics of paeoniflorin microemulsion after repeated dosing in rats with adjuvant arthritis.

An investigation was designed and conducted to detect pharmacokinetic differences between paeoniflorin (Pae) microemulsion and Pae saline. Pae microemulsion (25, 50,100 mg x kg(-1)) was administered to three groups of rats with adjuvant arthritis (AA) while Pae (25, 50,100 mg x kg(-1)) was given to another three groups of rats both for ten days. A HPLC assay was developed to determine the plasma concentrations of Pae. The plasma concentrations of Pae groups (25, 50 mg x kg(-1)) were undetectable. Furthermore, compared with pharmacokinetic parameters of Pae group (100 mg x kg(-1)), maximum concentration (C(max)), the area under the plasma concentration-time curve (AUC(0-t)), and mean retention time MRT(0-infinity))(h) of Pae microemulsion (100 mg x kg(-1)) increased apparently, while volume of distribution (Vd) and clearance rate (CL/F) decreased. These results indicate that a microemulsion significantly improves the absorption of Pae in AA rats.