Antithyroid drugs

Antithyroid drugs are used in the treatment of thyrotoxicosis. The most commonly used compound in the UK is carbimazole, though sometimes, propylthiouracil is used.

These drugs work by inhibiting the formation of thyroid hormones, and hormone synthesis is actually reduced very quickly. However, the long half life of thyroxine - about 7 days - means that clinical effects of treatment are not seen for between 10 and 20 days.

Medical treatment is indicated in children, during pregnancy, for mild hyperthyroidism with a small goitre, and for patients who are unsuitable for surgery.

Antithyroid drugs are used in two ways:

• Drugs may be given at maximum dose for 18 months along with thyroxine replacement. Those who use this regimen argue that it avoids under or overtreatment. For carbimazole, this regime also better exploits the drug's immunosuppressive action which may be useful in the treatment of immune-mediated thyroid disease.
• Alternatively the dose of drug may be titrated to the TSH levels. In this way the dose is gradually reduced to nothing over about 18 months. About half of patients relapse within two years of stopping the drug.
• similar long-term remission rates are achieved with the two regimens

Beta-blockers may be used to provide rapid symptomatic control.