Metformin is an insulin-sensitizing agent that has been in use for more than 50 years. Chemically, metformin is a biguanide. Its main action is to increase peripheral glucose utilization and decrease hepatic glucose release. In overweight patients with Type 2 diabetes, metformin has been shown to lower cardiovascular and diabetes-related deaths and has been considered the oral hypoglycemic agent of choice. It is also indicated to treat the insulin resistance of polycystic ovary syndrome. Metformin is excreted renally and has a half-life of 1.5 to 5 hours. Metformin is available as the branded drugs Glucophage, Glucophage XR tablets, Fortamet tablets, and Riomet liquid. It is also a component of three combination drugs: Glucovance, Metaglip, and Avandamet.

Lactic acidosis is a high-anion-gap acidosis. Lactate is produced by anaerobic glycolysis, and the development of lactic acidosis requires over-production, slowed breakdown, or both. At high blood levels, metformin produces severe refractory lactic acidosis by the uncoupling of oxidative glycolysis, thus driving cellular mechanisms toward anaerobic metabolism.