Additive effect w/ sulfonylureas. Thiazide diuretics, corticosteroids, phenothiazines, OC, sympathomimetics, niacin, Ca channel blockers and isoniazid may exacerbate loss of glycaemic control. ACE inhibitors may reduce fasting blood glucose concentrations. May increase serum level w/ cimetidine.
Potentially Fatal: Concurrent use w/ iodinated contrast agents may increase the risk of metformin-induced lactic acidosis.