Uses

Carbimazole is an antithyroid drug used to treat hyperthyroidism, including Graves' disease and toxic multinodular goitre, and as preoperative preparation before thyroidectomy or radioiodine therapy.

Do not use if

Contraindicated in hypersensitivity to carbimazole or thionamide antithyroid drugs, and in patients with pre-existing agranulocytosis. Use with caution in hepatic impairment.

Side effects

Common side effects include rash, urticaria, nausea, and headache. Serious adverse effects include agranulocytosis (rare but potentially life-threatening), hepatotoxicity, and vasculitis.

Warnings

Patients should be instructed to seek immediate medical attention for sore throat, fever, or mouth ulcers, which may indicate agranulocytosis. Monitor thyroid function and full blood count. Use in pregnancy (particularly first trimester) requires careful risk-benefit assessment.

How it works

Carbimazole is a prodrug rapidly converted in the body to methimazole. Methimazole inhibits thyroid peroxidase, the enzyme responsible for oxidation and organification of iodide, thereby reducing the synthesis of thyroid hormones T3 and T4.

Storage

Store at room temperature (15–25°C), protected from moisture and light.