Phenformin and lactic acidosis

All patients admitted with severe lactic acidosis to a university teaching hospital during a 17-month period were taking phenformin hydrochloride. Serum phenformin concentration was measured in one patient and found to be four to nine times the usual therapeutic concentration. Prerenal azotemia was present at the time of admission in all but one of these patients, but renal function was normal at the time of discharge in those patients with phenformin-associated lactic acidosis who survived. Phenformin-associated lactic acidosis accounted for 7% of the episodes of metabolic acidosis and 27% of deaths due to metabolic acidosis in diabetics.