Comparative pharmacokinetics of baicalin after oral administration of pure baicalin, Radix scutellariae extract and Huang-Lian-Jie-Du-Tang to rats

Huang-Lian-Jie-Du-Tang (HLJDT) is an important “heat-clearing” multiherb remedy of traditional Chinese medicine, and Radix scutellariae (Scutellaria baicalensis Georgi, Labiatae) is a key ingredient herb in it. Baicalin and wogonoside are two main effective ingredients enriched in Radix scutellariae. In the present study, pharmacokinetic differences of baicalin following oral administration of pure baicalin, Radix scutellariae extract, baicalin co-administrated with extract of the other three herbs of HLJDT and HLJDT were investigated in male S.D. rats with approximately the same dose of 200 mg/kg baicalin. The pharmacokinetic comparison of wogonoside was conducted only in Radix scutellariae extract and HLJDT. Plasma concentrations of baicalin and wogonoside were determined using HPLC method. Unpaired Student's t-test was used for statistical comparison. The results indicated that baicalin and wogonoside demonstrated bimodal phenomenon in the plasma profile. Some ingredients in the other three herbs of HLJDT, not in Radix scutellariae itself, had pharmacokinetic interaction with baicalin and wogonoside and hence decreased their systematic exposure level (p < 0.01). The absorption site of baicalin was preliminary evaluated in rat using in situ absorption in stomach and different intestinal segments and results revealed the existence of double-site absorption of baicalin. The first absorption site was in upper intestinal, probably via directly absorption of baicalin; while the second absorption site was in colon in the form of aglygon.