Thyrostatic treatment and its adverse effects

: Antithyroid drugs are relatively simple molecules known as thionamides, which contain a sulfhydryl group and a thiourea moiety within a heterocyclic structure. Propylthiouracil (6- propyl 2- sulfanylidene 1,2,3,4- tetrahydropyrimidin4- one) and methimazole (1- metyl 2,3- dihydro1H imidazole 2- thione) are the antithyroid drugs used in the United States. Methimazole is used in most of Europe and Asia, and carbimazole -  methimazole analogue, is used in the United Kingdom and parts of the former British Commonwealth. Their primary effect is to inhibit thyroid hormone synthesis by interfering with thyroid peroxidase mediated iodination of tyrosine residues in thyroglobulin and is an important step in the synthesis of thyroxine and triiodothyronine. Propylthiouracil (but not methimazole or carbimazole), can block the conversion of thyroxine to triiodothyronine within the thyroid and in peripheral tissues. Antithyroid drugs may have clinically important immunosuppressive effects. Side effects of thionamides are usually mild, serious untoward effects are observed in < 5% of cases, more frequently during the initial phases of treatment, when the drug daily dose is higher.