Experiences of a poison center with metformin-associated lactic acidosis

Metformin is widely used in the treatment of type 2 diabetes, though it is recognized to be associated with the risk of lactic acidosis. A case of pronounced lactic acidosis with cardiac arrest (pH 6.60, lactate 17.5 mmol/l, base excess - 30, standard bicarbonate 2.5 mmol/l, core body temperature 27.8 degrees C) is presented in a 61-year-old woman under metformin therapy. The key laboratory abnormalities observed during the intensive care treatment including repeated hemodialysis are described. The patient showed a complete recovery with residually reduced mental capabilities. Furthermore, an explorative data analysis of our poison center database from 1995 until 2003 concerning metformin was performed. In 109 inquiries for metformin a lactic acidosis (mean pH 6.87 +/- 0.11, mean lactate 20.9 +/- 8.1 mmol/l) was present in 14 cases (9 female, 5 male, average age 57.7 years) with 8 patients under regular metformin therapy and 6 patients who ingested large amounts of metformin to attempt suicide. 4 patients did not survive the severe metabolic disturbance. The present report demonstrates that metformin-associated lactic acidosis is a rare but critical complication of metformin therapy of type 2 diabetes as well as in acute suicidal ingestion of metformin. Early diagnosis and rapid correction of the metabolic acidosis using hemodialysis provides the possibility of a positive outcome even in severe cases. If metformin-associated lactic acidosis is suspected we recommend early involvement of a poison center.