Metformin hydrochloride is an oral antihyperglycemic drug not chemically or pharmacologically related to thiazolidinediones. Metformin is a biguanide, which has been shown to be effective in improving glycemic control in diabetic patients. Metformin inhibits hepatic glucose production, most likely through an inhibition of gluconeogenesis, and its use is associated with an improvement in tissue sensitivity to insulin. In accordance with published algorithms for the use of combination therapy for the treatment of type 2 diabetes, physicians have traditionally combined metformin with other antidiabetic agents.