Use of antihistamines after serious allergic reaction to methimazole in pediatric Graves' disease.

Antithyroid drugs are usually considered first-line therapy for management of pediatric Graves' disease because they avoid permanent hypothyroidism, provide a chance for remission, and are less invasive than the alternatives of thyroidectomy or radioactive iodine. Methimazole (MMI) is the only antithyroid drug recommended in pediatrics due to the risk of propylthiouracil-induced liver toxicity. Allergic reactions with MMI occur in up to 10% of patients and, when mild, can be managed with concurrent antihistamine therapy. Guidelines recommend discontinuation of MMI with serious allergic reactions. We present the case of an adolescent girl with Graves' disease and a serious allergic reaction after starting MMI whose family refused radioactive iodine and was reluctant to proceed to surgery. Antihistamine therapy was successfully used to allow continued treatment with MMI. This case demonstrates extension of management guidelines for minor cutaneous allergic reactions to MMI, through the use of antihistamines for a serious allergic reaction, allowing us to continue MMI and provide treatment consistent with the family's preferences and values.