[Metformin-related lactic acidosis in an 85-year-old woman]

An 85-year-old woman presented at the emergency ward. She had had shortness of breath for several days and no bowel movements for 3 days. On the day ofhospitalisation she experienced sudden abdominal pain and collapsed as she went to the toilet. She was being treated for multiple conditions, including type-2 diabetes. She appeared to have lactic acidosis. At first, the symptoms were not attributed to metformin because she was receiving a low dose and serum-creatinine concentrations were within the normal range (98 micromol/l). Bowel ischaemia was suspected and surgery was performed but no defects were found. She was subsequently treated for metformin-related lactic acidosis but died shortly thereafter due in part to postoperative complications. Lactic acidosis is a rare side effect of metformin. In this patient, the retrospectively calculated glomerular filtration rate (GFR) was extremely low (23 ml/min). The serum-creatinine concentration was normal because the patient's body weight was low (40 kg). Impaired renal function is a risk factor for metformin-related lactic acidosis. Renal function can appear to be normal when measured by serum-creatinine concentration in older patients with reduced muscle mass, but calculation of GFR often reveals impairment. Metformin is contraindicated in patients with poor renal function. The increasing use of metformin in older patients for the treatment of diabetes mellitus warrants renewed attention to this severe side effect.