A Chinese traditional medicine, Sho-saiko-to (Xiao-Chaihu-Tang), reduces the bioavailability of tolbutamide after oral administration in rats

The effects of Sho-saiko-to on the pharmacokinetics of tolbutamide were inv estigated in rats. After intravenous administration of tolbutamide (5 mg/kg ), no significant change in the pharmacokinetics of tolbutamide was observe d in both groups of single and multiple (7 days) pre-administration of Sho- saiko-to (500 mg/kg). In the study of single oral administration of tolbuta mide (50 mg/kg), co-administration of Sho-saiko-to tended to accelerate the initial absorption rate of tolbutamide. The area under the plasma concentr ation-time curve of tolbutamide after oral administration was significantly reduced by Sho-saiko-to. Subsequently, a significant decrease was observed in the oral bioavailability of this drug when Sho-saiko-to was given conco mitantly. These findings suggest that Sho-saiko-to reduces the bioavailabil ity of tolbutamide after oral administration in rats, and that this change is not related to hepatic metabolism.