Metformin overdose with a resultant serum pH of 6.59: survival without sequalae

Metformin, widely used in the treatment of diabetes mellitus, is known to cause lactic acidosis in both therapeutic use and after an overdose. We report the case of a 40-year-old woman who claimed to have ingested between 75 and 100 grams of metformin and subsequently developed severe lactic acidosis. She eventually developed a peak serum lactate level of 40.0 mmol/L and a serum pH nadir of 6.59 and became obtunded, hypotensive, and hypothermic. After aggressive supportive therapy with mechanical ventilation, vasopressor agents, sodium bicarbonate, and hemodialysis, her metabolic derangements steadily improved and she made a complete recovery without any residual sequelae. Her admission serum metformin concentration was later determined to be 160 microg/mL (therapeutic range is 1-2 microg/mL). There are several case reports and case series describing lactic acidosis secondary to metformin ingestion, although the exact mechanism remains unclear. The overall management of metformin overdose is reviewed. This case represents the largest reported amount of ingested metformin, the lowest serum pH, and the highest serum lactate concentration in any intentional metformin overdose survivor in the literature. Despite potentially lethal metabolic derangements, such patients can survive with aggressive supportive care.