Determination of sweroside in rat plasma and bile for oral bioavailability and hepatobiliary excretion.

Sweroside is an active ingredient of iridoid glycoside isolated from the flower buds of Lonicera japonica THUNB. A quantitative HPLC-UV method was developed for monitoring sweroside in rat plasma, urine, feces and bile. The method was successfully applied for a basic pharmacokinetic study. The obtained data of pharmacokinetics were applied to evaluate the oral bioavailabilities of sweroside and the active ingredients of purified herbal extracts (IGEs-1). The absolute bioavailability was estimated to F(sweroside) 0.31% and F(IGEs-1) 0.67%. The majority of sweroside excreted to feces revealed one reason of the low oral bioavailability. The values of F(IGEs-1) much higher than that of F(sweroside) reveals that ingredients in IGEs-1 such as loganin, secoxyloganin and some phenolic acids may promote the absorption of sweroside. The study of hepatobiliary excretion was achieved by an in vivo microdialysis sampling method after intravenous administration of sweroside. The percentage of accumulation of free form sweroside in bile duct was 31.2+/-7.2% of the total dosage. It may be one reason why sweroside possesses strong hepatoprotective effect.