Methimazole-induced cutaneous eruptions

Methimazole-induced cutaneous eruptions represent the most frequent side effect of thionamide therapy, ranging from minor rashes to life-threatening systemic syndromes. These reactions occur when the drug acts as a hapten, binding to proteins to trigger complex immune responses involving T-cell activation or antibody-mediated damage. While genetic factors and higher dosages increase susceptibility, clinicians must distinguish between mild cases manageable with antihistamines and severe reactions requiring immediate drug cessation. Because of the high risk of immunologic cross-reactivity between different thionamides, switching medications is often discouraged in favor of alternative treatments. For patients who cannot tolerate the drug, management shifts toward definitive solutions like radioactive iodine or surgical thyroid removal to control thyroid dysfunction safely.