In the UK and Europe, the drug of first choice is carbimazole, which blocks the organification of iodine in the thyroid and reduces the formation of new thyroid hormone, while having no effect on the release of preformed thyroid hormone. Two alternative regimens are used for antithyroid therapy. In both, treatment is commenced with a large dose - for example carbimazole 15mg three times daily - and when the patient is clinically euthyroid, usually within six to eight weeks, the strategies differ. In the traditional procedure, the dose is rapidly reduced to be titrated against the clinical and biochemical response, aiming to achieve a maintenance dose of 10-15mg given once daily. In the blocking-replacement regimen, the high initial dose is maintained, and T4, 0.1mg or 0.15mg daily, is added.
