Metformin Toxicity Leading to Severe Refractory Hyperkalemia and Metabolic Acidosis: A Case Report

Metformin is a widely prescribed, oral, anti-diabetic agent for the treatment of type 2 diabetes mellitus (DM2). While generally well-tolerated, metformin can accumulate in patients with acute kidney injury (AKI) or chronic kidney disease (CKD), leading to potentially life-threatening complications such as metformin-associated lactic acidosis (MALA). Severe hyperkalemia is a rare but serious manifestation of metformin toxicity. We report a case of a 74-year-old African American man with DM2, hypertension, and CKD stage 3a, who presented with nausea, vomiting, lethargy, and diarrhea. Laboratory findings revealed severe AKI with a creatinine level of 8 mg/dL (baseline 1.7 mg/dL) and a potassium level of 7.8 mEq/L. The patient developed refractory hyperkalemia requiring multiple interventions and eventually continuous renal replacement therapy. Further evaluation revealed metformin-induced severe lactic acidosis with a metformin level of 21 mcg/mL (therapeutic range <5 mcg/mL). This case highlights the importance of recognizing metformin toxicity as a potential cause of severe, refractory hyperkalemia and metabolic acidosis in patients with AKI or CKD. Early recognition and prompt discontinuation of metformin, along with appropriate management of electrolyte disturbances and metabolic derangements, are crucial in preventing life-threatening complications.