[Overdose of metformin secondary to acute renal insufficiency: a report of six cases].

Metformin is a biguanide used in the treatment of obese adults with type 2 diabetes mellitus; metformin decreases mortality by 36% in comparison to conventional treatment. Metformin administration has certain contraindications that, when ignored, especially in the case of acute renal insufficiency, leads to the accumulation of the drug and consequent lactic acidosis that can be fatal. We present 6 patients with acute renal insufficiency that experienced extreme acute metabolic acidosis (pH <6.90 and bicarbonate <5 mEq/l) and increased anion gap while receiving metformin for the treatment of diabetes. Serum lactic acid, only evaluated in the 4 patients that survived, was high. Two patients died after cardiac arrest that could have been avoided. In conclusion, lactic acidosis appearing during metformin treatment for diabetes requires rapid diagnosis and treatment to enable the drug to be withdrawn and prolonged continuous hemofiltration or hemodialysis with bicarbonate to be initiated.