Methimazole induced hepatotoxicity: A rare adverse reaction

Methimazole (MMI) is a commonly used medication in the treatment of hyperthyroidism. The side effect profile is extensive and includes the rare but serious side effect of drug associated liver injury. We report the case of a 51-year-old female who presented with painless jaundice several weeks after initiating MMI therapy for treatment of hyperthyroidism complicated by Graves’ orbitopathy. Liver function tests on presentation showed alanine aminotransferase (ALT) 1366 IU/L, aspartate aminotransferase (AST) 853 IU/L, total bilirubin 26.2 mg/dl, alkaline phosphatase 954 IU/L. Workup of structural, infectious, and autoimmune causes of hepatic injury was negative. The patient was therefore found to have MMI associated liver injury. MMI was discontinued and the patient was started on ursodiol, resulting in resolution of her jaundice and improvement of her liver function tests.