ABSTRACT
To study the pharmacokinetics of flavonoids from Xiexin decoction in rats. SD rats were given a single ig dose of Xiexin decoction 12 g x kg(-1), plasma and urine were collected before and after dosing. Flavonoids components in plasma and urine were measured by HPLC. Pharmacokinetic parameters were determined from the plasma concentration-time data and urinary excretion-time data with the DAS software package. Baicalin was incubated with the rat renal homogenate to investigate its metabolism in vitro. After oral administration of Xiexin decoction baicalin and wogonoside were quickly absorbed and exhibited double peak phenomena in their plasma concentrations. The first peaks in plasma concentrations of baicalin and wogonoside reached Cmax1 of (10 +/- 8) and (1.5 +/- 0.5) mg x L(-1) at Tmax1 of (0.27 +/- 0.09) and (0.17 +/- 0.00) h, while the second peaks reached Cmax2 of (3. 9 0. 5) and (0. 74 +/- 0.11) mg x L(-1) at Tmax2 of (7.6 +/- 2.6) and (16.0 +/- 0.0) h, respectively. The T(1/2) of baicalin and wogonoside were (7 +/- 3) and (6.4 +/- 2.1) h, AUC(0-infinity) were (57 +/- 12) and (15 +/- 3) mg x h x L(-1), respectively. After oral administration of Xiexin decoction, not only baicalin and wogonoside but also baicalein and wogonin can be detected in the urine. The amounts of baicalin, wogonoside, baicalein and wogonin excreted from urine during 0-72 h were (1.4 +/- 0.3), (3.4 +/- 1.3), (2.2 +/- 0.97), (10 +/- 4)% of dose given in rats, respectively. The excretion T(1/2) of the four flavonoids were (6.9 +/- 2.1), (9 +/- 4) , (8.2 +/- 2.0) and (7.2 +/- 1.8) h, respectively. Baicalin was metabolized into baicalein in the rat renal homogenate in vitro, and the kinetic parameters were measured as Vmax = 702 nmol x min(-1) x g(-1) (protein) and Km=135 micromol x L(-1). After oral administration of Xiexin decoction, flavonoids can be absorbed quickly. Only a small quantity of baicalin, wogonoside, baicalein and wogonin were excreted from urine. Baicalin may be metabolized into baicalein in the rat kidney.