A Rare Case of Metformin Associated Lactic Acidosis in a Type 2 Diabetic Patient With No Known Contraindications for Metformin Prescription - a Diagnostic Conundrum!

Introduction: Metformin is a biguanide drug primarily inhibits hepatic gluconeogenesis and improves insulin sensitivity. Lactic acidosis is a rare complication of metformin. The incidence of Metformin-associated lactic acidosis (MALA) is 6.3 per 100,000 patient-years. Metformin raises lactate levels by inhibiting the conversion of lactate and pyruvate into glucose, shunting towards anaerobic glycolysis. Although, MALA is a reported side effect, metformin is still identified as the drug of choice for Type 2 DM. Here we present a case of MALA in a Type 2 Diabetic patient to shed light on this controversial dilemma. Case Presentation: A 56-year-old African-American male with Type 2 DM and diabetic retinopathy presented after a fall and generalized weakness. Upon arrival, his blood sugar was 22 mg/dL. Patient was vitally stable with signs of dehydration. Home medications includes Metformin 1000 mg twice daily and Glipizide. Laboratory results showed an anion gap metabolic acidosis of 18 mmol/L, Lactic acid was 6.5 mmol/L with repeat of 7.6 mmol/L. Creatinine was 6.0 mg/dL with a BUN of 89 mg/dL. Baseline creatinine from 1 year prior was 1.3–1.5 mg/dL with GFR of 52 mL/min. Hemoglobin A1c was 5.9%. Sodium bicarbonate infusion in 5% dextrose in water. The patient clinically improved with closure of the anion gap and resolution of the metabolic acidosis. Metformin level was 10 mcg/mL. He was discharged on basal insulin and discontinued Metformin and Glipizide. Discussion: Metformin is the first line treatment of Type 2 DM due to its safety. The most common adverse events of Metformin include nausea, bloating, and diarrhea. MALA is a rare, yet serious side effect with a reported mortality of 45%. Higher mortality was associated with increased age, lower arterial pH, and need for mechanical ventilation and vasopressor medicationsThe following criteria should raise concern for MALA in patients with history of Metformin use; elevated lactate level, high anion gap, severe acidosis, low serum bicarbonate level and a history of renal insufficiency. Our patient met the above criteria. The treatment approach for MALA includes adequate supportive measures and correction of acidosis with the acceleration of lactic acid metabolism. Ultimately, if there is no improvement with the aforementioned strategies, then the next step is elimination of the offending agent by renal excretion or dialysis. Fortunately our patient improved with intravenous hydration and did not require advanced intervention. This case highlights the importance of the early recognition of MALA in a patient with unexplained anion gap acidosis and history of Metformin use as even with no risk factors, an episode of gastroenteritis can be enough to impair renal function which increases the risk of MALA. More importantly, it is crucial to educate patients to withhold Metformin in the setting of acute illness and volume contraction to prevent MALA.