Metformin-associated nonketotic metabolic acidosis

OBJECTIVE: TO document a case of anion gap, nonketotic metabolic acidosis occurring in a patient with acute renal failure who was receiving metformin. CASE SUMMARY: A 67-year-old white man presented with a 9-day history of weakness, nausea, dizziness, and difficulty moving; he had also not eaten during the previous 2 days. The patient had numerous abnormalities on his serum chemistry panel and arterial blood gases, including a pH of 7.1 and an anion gap of 21 mEq/L. No ketones were detected in the urine. The patient was treated with intravenous fluids, sodium bicarbonate, insulin, and hemodialysis. All medications were discontinued. The acidosis resolved shortly after hemodialysis. The hospital course was complicated by the onset of atrial fibrillation occurring on day 2 that did not respond to chemical cardioversion. On day 6 the patient was discharged home with resolving acute renal failure and normal serum pH. CONCLUSIONS: The mortality rate of biguanide-induced lactic acidosis is approximately 50%; thus, early recognition and treatment are essential. Suspicion of lactic acidosis should be high when diabetic patients who are taking a biguanide present with acidosis. The majority of cases of metformin-induced lactic acidosis have occurred in patients with contraindications to the drug (i.e., renal dysfunction). Thus, it is important to maintain strict adherence to these contraindications and monitor patients for deteriorating renal function.