Carbimazole

Key points

• Only consider ultrasound in adults with thyrotoxicosis if there is a palpable thyroid nodule; investigate any suspicious thyroid nodule according to the thyroid-cancer pathway, including FNAC when indicated.
• Intravenous glucocorticoids are used for active moderate-to-severe Graves' orbitopathy.
• Carbimazole adverse effects: agranulocytosis, rash and hepatotoxicity. Stop antithyroid treatment and obtain an urgent full blood count if agranulocytosis is suspected, particularly with fever, sore throat or mouth ulcers.
• Carbimazole and acute pancreatitis: stop immediately and permanently if acute pancreatitis develops; do not re-expose the patient.
• Pregnancy: carbimazole is associated with congenital malformations, particularly with first-trimester exposure; women of childbearing potential should use effective contraception.
• PTU is preferred to carbimazole in pregnancy when an antithyroid drug is required, particularly during the first trimester; use the lowest effective dose.
• When antithyroid-drug treatment is chosen for Graves’ disease, carbimazole is generally given for 12–18 months.