Atypical Presentation of Metformin-associated Lactic Acidosis: A Case Report

Metformin, a first-line type two diabetes medication, is generally considered safe and effective. However, it is rarely associated with life-threatening lactic acidosis. This generally presents in patients with gastrointestinal upset as a primary complaint. It is most common in patients with underlying chronic kidney disease. Prevention of associated mortality requires early diagnosis and intervention with fluids, bicarbonate, vasopressors, and hemodialysis.

This is a notable presentation of metformin toxicity, as the 68-year-old male patient presented with an atypical chief complaint of dyspnea and no history of kidney disease. Physical exam was notable for tachypnea and clear breath sounds. Labs revealed anion gap metabolic acidosis from an accumulation of lactic acid and acute renal failure. Other causes of lactic acid metabolic acidosis were considered and ruled out. Nephrology was consulted and pharmacological therapies started as the patient transitioned to the intensive care unit for emergent hemodialysis. He eventually regained renal function and was discharged. His metformin level returned several weeks later significantly elevated.

Emergency physicians should maintain metformin toxicity on the differential for patients on metformin presenting with dyspnea and anion gap metabolic acidosis with elevated serum lactic acid concentrations. Other sources of lactic acidosis should be ruled out, and corrective therapies, including renal replacement therapies, should be started immediately. Additionally, it is essential to determine a patient's kidney function before being prescribed metformin and to have the patient serially monitored as an outpatient.