Metformin-associated lactic acidosis mistaken for alcohol-related acidosis in a patient abstinent for three months

Metformin-associated lactic acidosis is an uncommon but potentially fatal complication that develops when this renally eliminated drug accumulates during an acute illness, and it reaches the emergency department as an undifferentiated high anion gap metabolic acidosis with altered consciousness, exactly as alcoholic ketoacidosis, ethanol intoxication and toxic alcohol ingestion do. A documented history of alcohol use is therefore a powerful and potentially misleading diagnostic cue. We report a 62-year-old man with type 2 diabetes mellitus taking a fixed-dose vildagliptin and metformin combination who was found unconscious at home. His relatives could give no usable history beyond long-standing heavy drinking, and alcoholic ketoacidosis and methanol ingestion were pursued as the leading diagnoses. Arterial pH was below the measurable range of the analyser at the referring hospital and, six hours later on arrival at our intensive care unit, 6.60, with a bicarbonate of 1.2 mmol/L, a lactate of 16.9 mmol/L, an anion gap of 42 mmol/L and a creatinine of 7.21 mg/dL. Serum ethanol was undetectable, neuroimaging showed no lesion suggestive of methanol toxicity, and he was hypoglycaemic at both hospitals despite a glycated haemoglobin of 13.9%. He was treated with vasoactive support, sodium bicarbonate, mechanical ventilation, intermittent haemodialysis and 40 hours of continuous renal replacement therapy, and was extubated on the fourth day. Only then, when a history could be taken directly from him, did the decisive facts emerge: ten days of diarrhoea with minimal oral intake throughout which he had continued metformin, and three months of complete abstinence from alcohol. He was discharged neurologically intact and independent of renal replacement therapy. A drinking history can dominate the assessment months after the last drink; in metformin-treated patients it should widen the differential rather than close it, particularly when no reliable collateral history is available.