Dissolution and pharmacokinetics of baicalin-polyvinylpyrrolidone coprecipitate

Baicalin-polyvinylpyrrolidone coprecipitate was prepared with the aim of improving the dissolution and bioavailability of the baicalin.

The dissolution of the coprecipitate in capsule form was tested and compared with baicalin active pharmaceutical ingredient (API) capsules. A sensitive high-performance liquid chromatography-ultraviolet detection method was established to determine the concentration of baicalin in plasma. The liquid-liquid extraction and solid phase extraction methods were used to pretreat the baicalin plasma sample. The pharmacokinetics of the coprecipitate capsules were tested and compared with the API capsules in six beagle dogs after crossover oral administration.

The results of the dissolution demonstrated that the dissolution of the coprecipitate capsules was 21.02, 2.02 and 3.29 times that of the API capsules in 0.1 mol/l HCl solution, pH 4.5 solution and water, respectively, but it was slightly lower than that of the API capsules in a pH 6.8 solution. The calibration curve showed a good linearity at concentrations between 3.648 ng/mL and 364.8 ng/mL (r = 0.998). The baicalin plasma sample was successfully pretreated, with endogenous impurities almost completely removed. The pharmacokinetics of the coprecipitate capsules and the API capsules indicated that the mean values of Cmax were 127.04 ± 10.6 and 27.49 ± 36 μg/l, and those of AUC(0-24h) were 1080.23 ± 336.43 and 337.84 ± 127.64 μg/l × h, respectively. Compared with the baicalin API capsules, the relative bioavailability of the coprecipitate capsules was 338.2% ± 93.2%.

From these observations of improved dissolution and pharmacokinetic behaviours, a good relationship was found in vitro and in vivo, indicating that the coprecipitate could be a promising formulation strategy for insoluble baicalin.