Indications: Hyperthyroidism; thyrotoxicosis.

Cautions: same as for carbimazole. Also hepatic and renal impairment.

Side Effects: same as for carbimazole: also leucopenia, rarely cutaneous vasculitis, thrombocytopenia, aplastic anaemia, hypoprothrombinemia, hepatitis, encephalopathy, hepatic necrosis, nephritis, lupus erythematous like syndrome.

Dose: 100-200mg 3 times daily. Maintenance dose, 50-150 mg daily. Propylthiouracil is given in a dose of 200 to 400 mg daily in adults and this dose is maintained until the patient becomes euthyroid; the dose may then be gradually reduced to a maintenance dose of 50 to 150 mg daily.

Antithyroid drugs only need to be given once daily because of their prolonged effect on the thyroid. Over- treatment can result in the rapid development of hypothyroidism and should be avoided particularly during pregnancy because it can cause fetal goitre.