Pharmacokinetics of Baicalin in Rats and its Interactions with Cyclosporin A, Quinidine and SKF-525A: A Microdialysis Study

Baicalin, a flavone glucuronide derived mainly from the root of Scutellaria baicalensis, has been used in traditional Chinese medicine as an anti-inflammatory and anti-viral agent. To explore whether the disposition of baicalin is related to multidrug resistance P-glycoprotein (P-gp), baicalin (3, 10 and 30 mg kg(-1); i. v.) was injected to rats for a pharmacokinetic study using microdialysis coupled with HPLC. The results indicate that baicalin goes through hepatobiliary excretion against a concentration gradient based on the blood-to-bile distribution ratio (AUCbile/AUCblood), but that AUCblood or AUCbile did not show any dose-related increase in the range from 3 to 30 mg kg(-1). Coadministration of cyclosporin A (CsA) or quinidine (both are P-gp inhibitors) was used to delineate the role of P-gp on baicalin disposition, while SKF-525A (a cytochrome P450 inhibitor) could specifically inhibit the cytochrome P450 catalysis of baicalin without crossing with P-gp function. Both CsA and quinidine promoted the active transport of baicalin into bile and reduced its level in blood, and this result was the same as that obtained by treating with SKF-525A. Hence, the association of the involvement of P-gp in active baicalin efflux into bile seems to be excluded since CsA and quinidine are also cytochrome P450 inhibitors. In addition, baicalin was not detected in the brain striatum after treating with baicalin alone in the present study. Also, neither CsA nor quinidine co-administered with baicalin is able to induce measurable levels of baicalin in rat brain, which suggests that baicalin might not be able to pass through the blood-brain barrier (BBB).