ATC Group: H03B Antithyroid preparations

Carbimazole, a thionamide, is a pro-drug which undergoes rapid and virtually complete metabolism to the active metabolite, thiamazole, also known as methimazole. The method of action is believed to be inhibition of the organification of iodide and the coupling of iodothyronine residues which in turn suppress the synthesis of thyroid hormones.

Propylthiouracil is an antithyroid drug that depresses the formation of thyroid hormone. This is effected by interference both with the incorporation of iodine into tyrosyl residues and the coupling of such residues to form iodothyronines. Propylthiouracil achieves these actions by the inhibition of the enzyme peroxidase.

Perchlorate competitively inhibits the thyroid’s iodine uptake mechanism, iodination and affects iodisation by flushing the thyroid of iodide that is accumulating but has not yet been incorporated into a thyroglobulin molecule. Re-utilisation of iodide released outside the thyroid during deiodination of thyroid hormone is also inhibited. The antithyroid effect is based on the occurrence of iodine depletion.

Thiamazole inhibits dose-dependently the incorporation of iodine into tyrosine and thereby the neosynthesis of thyroid hormones. This property permits symptomatic therapy of hyperthyroidism regardless of its cause.