Objective: To study in situ intestinal absorption kinetics of baicalin contained in Tiangou Jiangya capsules, and the effect of different intestinal segments, pH value, drug concentration and P-gp inhibitor on the absorption.
Method: The in situ intestinal perfusion test was adopted, and HPLC method was used to determine the content of baicalin in samples at different time points. Ultra-violet (UV) spectrophotometry was used to determine the content of phenol red in samples at different time points.
Result: When pH value was at 5. 0, 6. 5, 7. 4, the absorption of baicalin was not impacted. P-gp inhibitor verapamil could enhance the absorption of baicalin. When the quality concentration of the test solution ranged between 5-20 g L -1 , the linearity of the absorption amount of baicalin increased. The absorption kinetic equation of baicalin was Y = -0. 073 7X +0. 118 7 (r = 0. 994 8) , K. 0. 073 7 h -1 , t1/2 9. 40 h.
Conclusion: Baicalin is mainly absorbed in colon. The absorption of baicalin shows the first-order kinetics process, with the absorption mechanism of passive diffusion. Baicalin is a substrate for P-gp.