Hepatotoxicity Associated with Metformin Therapy in Treatment of Type 2 Diabetes Mellitus with Nonalcoholic Fatty Liver Disease

Objective: To report a case of idiosyncratic hepatotoxicity associated with metformin in the treatment of type 2 diabetes with nonalcoholic fatty liver disease (NAFLD). Case Summary: A 61-year-old obese man presented with jaundice, nausea, fatigue, and an unintentional weight loss 2 weeks following initiation of metformin. Laboratory findings revealed aminotransferase values 10–15 times the upper limit of normal. Potential causative agents, including metformin, simvastatin, and Niaspan (extended-release niacin), were discontinued. Two months later, the patient's signs and symptoms had resolved and aminotransferase values returned to normal. An objective causality assessment revealed that the adverse reaction was probably associated with metformin. Discussion: Since numerous medications and disease states can cause abnormalities in liver enzymes, it is important for providers to be able to distinguish the cause(s) and take appropriate actions. This can take a great deal of time and effort in patients with multiple medications and comorbidities. In this patient's case, viral hepatitis, worsening NAFLD, and the concomitant drugs were highly suspected. As hydroxymethylglutaryl coenzyme A reductase inhibitors offer substantial cardiovascular benefits and as metformin is a first-line agent in helping to lower blood glucose concentrations and to normalize the metabolic profile in type 2 diabetes, reintroduction of metformin and simvastatin would likely be beneficial. Conclusions: This is a case report of metformin-induced hepatotoxicity. As the prevalence of type 2 diabetes and subsequent metabolic effects increases in the US, metformin use will likewise increase. As potential for increased idiosyncratic hepatotoxicity associated with metformin use is likely to occur, clinicians should be vigilant.