Comparative pharmacokinetics of baicalin and wogonoside by liquid chromatography–mass spectrometry after oral administration of Xiaochaihu Tang and Radix scutellariae extract to rats

The aim of this study was to compare the pharmacokinetics of baicalin and wogonoside in rats following oral administration of Xiaochaihu Tang (Minor Radix Bupleuri Decoction) and Radix scutellariae extract. Thus, a specific LC–MS method was developed and validated for the determination of these flavonoids in the plasma of rats after oral administration Xiaochaihu Tang and Radix scutellariae extract. Chromatographic separation was performed on a Zorbax SB C18 column (150 mm × 4.6 mm, i.d.: 5 μm) with 0.1% formic acid in water and acetonitrile by linear gradient elution. Baicalin, wogonoside and carbamazepine (internal standard, I.S.) were detected in select-ion-monitoring (SIM) mode with a positive electrospray ionization (ESI) interface. The following ions: m/z 447 for baicalin, m/z 461 for wogonoside and m/z 237 for the I.S. were used for quantitative determination. The calibration curves were linear over the concentration ranges from 0.1231 to 6.156 μg mL−1 for baicalin and 0.08832 to 4.416 μg mL−1 for wogonoside. The lower limit of detection (LLOD) based on a signal-to-noise ratio of 2 was 0.06155 μg mL−1 for baicalin and 0.04416 μg mL−1 for wogonoside. Intra-day and inter-day precisions (RSD%) were within 10% and accuracy (RE%) ranged from −6.4 to 4.4%. The extraction recovery at three QC concentrations ranged from 74.7 to 86.0% for baicalin and from 71.3 to 83.7% for wogonoside. The plasma concentrations of baicalin and wogonoside in rats at designated time periods after oral administration were successfully determined using the validated method, pharmacokinetic parameters were estimated by a non-compartment model. Following oral administration of Xiaochaihu Tang and Radix scutellariae extract, the t1/2 of baicalin was 3.60 ± 0.90 and 5.64 ± 1.67, the Cmax1 was 1.64 ± 0.99 and 5.66 ± 2.02, the tmax1 was 0.13 ± 0.05 and 0.20 ± 0.07, the Cmax2 was 2.43 ± 0.46 and 3.18 ± 1.66, and the tmax2 were 6.40 ± 1.67 and 5.66 ± 2.02, respectively. Following oral administration of Xiaochaihu Tang and Radix scutellariae extract, the t1/2 of wogonoside was 4.97 ± 1.68 and 7.71 ± 1.55, the Cmax1 was 1.39 ± 0.83 and 1.45 ± 0.37, the tmax1 was 0.21 ± 0.20 and 0.17 ± 0.01, the Cmax2 was 1.90 ± 0.55 and 1.42 ± 0.70, and the tmax2 was 5.60 ± 1.67 and 5.20 ± 1.79, respectively. A significant difference (p < 0.05) was observed for t1/2, and the elimination of baicalin and wogonoside in Xiaochaihu Tang was increased.