Initial dosage regimens

Antithyroid drug therapy is used to correct hyperthyroidism and relieve symptoms of thyrotoxicosis.

Carbimazole is the first-line drug for initial treatment of hyperthyroidism. Propylthiouracil has been associated with severe liver injury; it is only indicated if carbimazole is not tolerated, for maintenance therapy before conception and in the first trimester of pregnancy, and for thyroid storm.

Start antithyroid therapy with an initial dose that is likely to control the hyperthyroidism. The initial dose is based on symptom severity, size of the gland, degree of biochemical thyrotoxicosis, and medical urgency.

In an adult with significant symptoms (eg atrial fibrillation, heart failure, marked weight loss, proximal myopathy), or biochemically severe hyperthyroidism (eg serum free triiodothyronine [T3] or free thyroxine [T4] concentrations more than 2.5 times the upper limit of normal), use:

1 carbimazole 30 to 45 mg orally, daily in 2 or 3 divided doses. Adjust the dose at 4- to 6-weekly intervals as required (see Dose titration) hyperthyroidism, severe (adult) carbimazole carbimazole carbimazole

OR

2 propylthiouracil 300 to 450 mg orally, daily in 2 or 3 divided doses. Adjust the dose at 4- to 6-weekly intervals as required (see Dose titration). hyperthyroidism, severe (adult) propylthiouracil propylthiouracil propylthiouracil

In an adult with mild symptoms, or biochemically mild to moderate hyperthyroidism without symptoms, use:

1 carbimazole 10 to 20 mg orally, daily in 2 or 3 divided doses. Adjust the dose at 4- to 6-weekly intervals as required (see Dose titration) hyperthyroidism, mild to moderate (adult) carbimazole carbimazole carbimazole

OR

2 propylthiouracil 100 to 200 mg orally, daily in 2 or 3 divided doses. Adjust the dose at 4- to 6-weekly intervals as required (see Dose titration). hyperthyroidism, mild to moderate (adult) propylthiouracil propylthiouracil propylthiouracil

Thyrotoxicosis in a child should be managed by a specialist—antithyroid starting doses vary widely and dose titration can be difficult. Propylthiouracil is contraindicated in children as it can cause severe liver injury. A typical regimen is:

carbimazole 0.2 to 0.3 mg/kg orally, 3 times daily, titrated down as control is achieved to a maintenance dose of 2.5 to 5 mg up to 3 times daily. hyperthyroidism (child) carbimazole