Impaired insulin secretion. Reduced antidiabetic effect of acarbose, acetohexamide, chlorpropamide, glipizide, glyburide, metformin, miglitol, pioglitazone, repaglinide, rosiglitazone, glimepiride, tolbutamide, troglitazone. Reduced effect of doxorubicin, etoposide, teniposide. Potentiated anticoagulant effects of warfarin.