Metformin and Heart Failure

Abstract

Throughout the world and for many years, metformin has been a mainstay of therapy for patients with type 2 diabetes. This highly effective and usually well-tolerated oral agent is, to date, the only one demonstrated to reduce cardiovascular disease (CVD) complications in newly diagnosed type 2 diabetic patients (1). It's precise mechanism of action remains enigmatic, although it clearly results in a reduction of endogenous glucose production, primarily hepatic gluconeogenesis, most likely involving the stimulation of AMP-activated protein kinase activity (2). A peripheral insulin-sensitizing effect in skeletal muscle has also been demonstrated by some, but not all, investigators (3). In small studies, metformin appears to exert benefit on various other fundamental biological processes that influence atherogenesis, such as lipid metabolism, inflammation, and vascular endothelial function (4). Another insulin sensitizer category, the thiazolidinediones (TZDs), has also been proposed to reduce CVD risk, but that class carries with it concerns of weight gain and fluid retention. As a result, TZDs remain more popular in combination therapy regimens. Perhaps of greatest import to clinicians is the recognition that metformin is the only oral antidiabetic agent associated with weight loss. Accordingly, metformin remains, in the eyes of many authorities, the optimal initial drug choice in most type 2 diabetic patients if diet and exercise have not succeeded in adequately reducing blood glucose levels (5). Approval of metformin in the U.S. was delayed because of previous experience with phenformin, which was associated with lactic acidosis. Although the risk of such metabolic decompensation with metformin was known to be significantly lower than with the earlier biguanide, a fair amount of debate occurred during the approval process (6). The Food and Drug Administration (FDA) eventually sanctioned metformin's use, with the stipulation that strong warnings be included in the package insert regarding potential risks (7). Since metformin …