METFORMIN-ASSOCIATED LACTIC ACIDOSIS—IS THIS ON YOUR RADAR?

Background Metformin is a biguanide hyperglycemic agent used to manage non-insulin-dependent diabetes mellitus. Adverse reactions mainly include mild gastrointestinal side effects, but severe complications such as metformin-associated lactic acidosis (MALA) can occur. Metformin is renally excreted, and therefore, not recommended in patients with renal impairment. The reported incidence of metformin-associated lactic acidosis (MALA) was 3 cases per 100,000 patient years.1,2 Case Report A 79-year-old female with a complex medical history, including end-stage renal disease (ESRD) on dialysis and type 2 diabetes presented to the emergency department (ED) for altered mental status. Prior to arrival, she was found to be hypoglycemic. Her laboratory results were significant for creatinine 6.56 mg/dL and an anion gap of 52 mmol/L. The venous blood gas revealed venous pH 6.857 (7.32-7.43), pCO2 15.9 (40.6-60) mm Hg, HCO3 2.7 (21-30) mmol/L; lactate 27 (0.5-2mmol/L) and ammonia of 233 umol/L. The patient was emergently dialyzed in the ED with repeat labs showing blood urea nitrogen of 10 mg/dL; creatinine 1.65 mg/dL; carbon dioxide 26 mmol/L; and anion gap of 13 mmol/L. The repeat ammonia was 16 umol/L. The patient's metabolic encephalopathy resolved, and she was discharged home on hospital day three. Why Should an Emergency Physician Be Aware of this? Metformin-associated lactic acidosis has a high mortality rate (36%). Laboratory markers have not been shown to be a reliable predictor of mortality. Sodium bicarbonate is controversial, but a pH of <7.15 indicates consideration of its use. A pH <7.1 and a lactate level >20 mmol/L indicates the need for emergent hemodialysis. Prompt ED recognition and management with early hemodialysis can result in good patient outcomes with a return to their baseline function despite severe laboratory findings.