HPLC analyses and pharmacokinetic studies of baicalin and oxymatrine in rabbits.

In the present study two simple RP-HPLC methods were developed to determine baicalin and oxymatrine in rabbit serum. Separation was performed on a Diamonsil C18 column (200 mm x 4.6 mm I.D., 5 microm) with UV detector at 277 nm for baicalin and 220 nm for oxymatrine. The mobile phase was methanol-water-phosphoric acid 50:50:0.2 v/v for baicalin and acetonitrile-water (20:80, v/v, 5 mmol/L sodium octanesulfonate was contained and pH was adjusted to 3.2 with phosphoric acid for oxymatrine. p-Nitrobenzoic acid and phenacetin were used as internal standards for baicalin and oxymatrine, respectively. The standard curves were linear from 0.5 to 200.0 mg/L for baicalin and from 0.5 to 100.0 mg/L for oxymatrine with correlation coefficients of 0.9994 and 0.9965, respectively. The intra-day and inter-day RSD were less than 5.4% and 7.2% for baicalin and 6.6% and 13.8% for oxymatrine. The mean recoveries were 100.1% for baicalin and 99.1% for oxymatrine. The methods were applied to a pharmacokinetic study of baicalin and oxymatrine in rabbits. The pharmacokinetic parameters were determined after intravenous injections of baicalin and oxymatrine (40 mg/kg) separately and together to rabbits. They all fit to the two-compartment open model. Student's t test shows that there is no significant difference in the main pharmacokinetic parameters including AUC(0-infinity), when alpha and beta, when baicalin and oxymatrine were administered separately or together.