Beneath the Cure Lies the Risk: Carbimazole-Induced Angioedema in Graves' Disease

Carbimazole is a widely used antithyroid medication for the treatment of hyperthyroidism and is generally well tolerated. Most adverse effects are mild and limited to cutaneous reactions. However, angioedema is a rare but potentially serious hypersensitivity response that may occur shortly after drug initiation. We describe a patient who developed acute facial angioedema soon after starting carbimazole therapy. The patient presented with sudden periorbital and lip swelling accompanied by mild difficulty in swallowing, without any respiratory compromise. There was no history of allergies, autoimmune disease, or exposure to other new medications. Clinical examination revealed non-pitting edema of the eyelids and lips without associated urticaria. Given the close temporal relationship between carbimazole initiation and symptom onset, the drug was considered the most likely cause. Carbimazole was promptly discontinued, and treatment with antihistamines and corticosteroids resulted in complete resolution of symptoms within two days. No recurrence was observed following drug withdrawal, and the patient later underwent definitive treatment for hyperthyroidism. This case adds to the limited literature on carbimazole-induced angioedema and highlights the importance of early recognition of rare hypersensitivity reactions to antithyroid drugs. Prompt drug discontinuation and appropriate management can prevent progression to life-threatening airway involvement. Increased awareness of this uncommon adverse effect may improve patient safety and clinical outcomes during antithyroid therapy.