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Antithyroid drug treatment for thyrotoxicosis 

Antithyroid drug treatment for thyrotoxicosis
Antithyroid drug treatment for thyrotoxicosis

Anthony Toft

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date: 27 January 2022

The most effective and commonly used antithyroid drugs are the thionamides, including carbimazole and its active metabolite methimazole (not available in the UK). These act by inhibiting the synthesis of thyroid hormones, principally by interfering with the iodination of tyrosine by serving as preferential substrates for the iodinating intermediate of thyroid peroxidase. Oxidized iodine is thus diverted from potential iodination sites in thyroglobulin. The iodinated antithyroid drugs are desulfurated and further oxidized to inactive metabolites. There is also some evidence for an immunosuppressive action which is of doubtful clinical significance as most patients relapse after drug withdrawal. Another thionamide, propylthiouracil, is, in addition, a potent inhibitor of type 1 outer ring deiodinase and acutely inhibits thyroxine (T4) to triiodothyronine (T3) conversion, but there is no good evidence to suggest that this effect is of any clinical relevance. Propylthiouracil tends to be reserved for those patients who have developed an adverse reaction to carbimazole or methimazole.

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