Abstract
BACKGROUND Hyperthyroidism is an overproduction of thyroid hormones. Carbimazole is an anti-thyroid medication used to treat hyperthyroidism in adults and children. It is a thionamide associated with rare adverse effects such as neutropenia, leukopenia, agranulocytosis, and hepatotoxicity. Severe neutropenia is a life-threatening event characterized by a sharp drop in absolute neutrophil count. Severe neutropenia can be treated by discontinuation of the precipitating medication. Administration of granulocyte colony-stimulating factor provides longer protection against neutropenia. Elevated liver enzymes indicate hepatotoxicity, which usually normalize after discontinuation of the offending medication. CASE REPORT A 17-year-old girl was treated with carbimazole since the age of 15 for hyperthyroidism secondary to Graves' disease. She initially received 10 mg of carbimazole orally twice daily. After 3 months, the patient's thyroid function reflected residual hyperthyroidism and was then up-titrated to 15 mg orally in the morning and 10 mg orally in the evening. She presented to the emergency department reporting fever, body aches, headache, nausea, and abdominal pain for 3 days. She was diagnosed with severe neutropenia and hepatotoxicity induced by carbimazole after 18 months of dose modification. CONCLUSIONS In hyperthyroidism, it is important to maintain patients in a euthyroid state for a long period to minimize the autoimmunity and hyperthyroid relapse, which often requires long-term use of carbimazole. However, severe neutropenia and hepatotoxicity are rare and serious adverse effects of carbimazole. Clinicians should be aware of the importance to discontinuation of carbimazole, administration of granulocyte colony-stimulating factors, and supportive treatment to reverse the consequences.