HPLC with electrochemical detection to examine the pharmacokinetics of baicalin and baicalein in rat plasma after oral administration of a Kampo medicine.

A highly sensitive method for determining baicalin and baicalein in rat plasma was developed using micro HPLC with electrochemical detection (muHPLC-ED). Peak heights for baicalin and baicalein were found to be linearly related to the amounts injected, ranging from 2.2 pg to 4.5 ng (r = 0.997) and from 1.4 pg to 2.7 ng (r = 0.997), respectively. The detection limits (signal/noise ratio = 3) of the current method for baicalin and baicalein were 0.89 and 0.54 pg, respectively. The concentrations of baicalin, baicalein, and their conjugates in rat plasma after oral administration of 2.0 mg/kg of Saiko-keishi-to (TJ-10) were determined. The glucuronide and sulfate forms of baicalin and baicalein in plasma were hydrolyzed enzymatically using beta-glucuronidase and sulfatase, respectively, and the hydrolyzed solutions were extracted with a 0.1-mol/L phosphoric acid-ethyl acetate mixture (1:1, v/v). Based on the time courses of the concentrations of the free and conjugated forms of baicalin and baicalein in rat plasma after oral administration of Saiko-keishi-to, the pharmacokinetic parameters of C(max), t(max), and AUC(0-6 h) were obtained.