carbimazole

Carbimazole is an antithyroid medication used to treat hyperthyroidism. It is a thionamide that is rapidly converted to the active metabolite methimazole and acts by inhibiting thyroid peroxidase, the enzyme required for the production of thyroid hormones. By reducing iodination of thyroglobulin and the coupling of iodotyrosines, carbimazole lowers the synthesis of thyroxine (T4) and triiodothyronine (T3).

Carbimazole is prescribed for conditions such as Graves’ disease and other forms of hyperthyroidism, including toxic multinodular goitre. It may be used to achieve a euthyroid state before thyroidectomy or radioactive iodine therapy and as a longer-term oral therapy when appropriate.

The medication is taken by mouth. In adults, dosing is commonly in the range of 5 to 40 mg per day, given as one or two divided doses and adjusted according to thyroid function tests. Treatment is continued until euthyroidism is achieved, with tapering to the lowest effective dose to maintain normal thyroid levels. Response is typically seen within weeks.

Common adverse effects include rash and pruritus; more serious but rare effects include agranulocytosis and hepatotoxicity. Hypersensitivity reactions and liver injury require stopping the drug. Regular monitoring of thyroid function and, if feasible, blood counts is recommended during therapy. Patients should be advised to report fever, sore throat, or signs of infection promptly.

In pregnancy, carbimazole is associated with congenital abnormalities when used in the first trimester and is generally avoided in early pregnancy; propylthiouracil is often preferred during the first trimester, with consideration of switching to methimazole/carbimazole later in pregnancy if needed. In breastfeeding, small amounts can pass into breast milk; if used, infants should be monitored for adverse effects.