Metformin (dimethylbiguanide) is an orally administered drug used to lower blood glucose concentrations in patients with type II diabetes mellitus (DM). Metformin lowers blood glucose concentration by improving insulin sensitivity and decreasing insulin resistance. Other mechanisms of action that may contribute to lower blood glucose concentrations are decreased basal hepatic glucose output, increased intestinal use of glucose and decreased fatty-acid oxidation.
Lactic acidosis is a rare but serious complication of metformin therapy, with an incidence in Canada of nine cases per 100,000 people per year . In most patients it occurs because one or more contraindications were overlooked, most commonly renal failure . Renal failure leads to high plasma metformin concentrations. Other factors that contribute to increased blood lactate concentrations are hypotension with low tissue perfusion, hypoxia, liver disease and alcohol abuse. Mortality in metformin-associated lactic acidosis is 50% . In practice, metformin-associated lactic acidosis is not regarded as a major problem when the exclusion criteria are adhered to. A case of severe metformin-associated lactic acidosis in the context of acute renal failure, without underlying chronic renal insufficiency, is described.