Antithyroid drugs (ATD) and thyrostatics are suppressive drugs meant to inhibit the production of thyroid hormones T4 and/or T3 in an effort to treat the symptoms of Graves’ disease. These medications include carbimazole, methimazole, and propylthiouracil (PTU). Carbimazole, its active metabolite methimazole, and propylthiouracil all act by inhibiting the enzyme thyroid peroxidase and in that way they block the synthesis (the production) of thyroid hormone.
Iodine-131 (Radioiodine) is given orally on a one-time basis to destroy the function of a hyperactive gland. The radioactive iodine is picked up by the active cells in the thyroid, which use iodine to produce T4, and destroys these cells. Radioablation is considered the definitive cure for hyperthyroidism by eliminating the target organ, but 80% of patients develop hypothyroidism soon after treatment and require permanent synthetic hormone replacement.
Theoretically the radioiodine could be dosed to only destroy part of the thyroid gland, but the dosage is extremely difficult to determine, and if thyroid tissue remains, the body still produces TSI which can continue to cause over production of thyroid hormone. In addition, for incompletely ablated women in their child bearing years the antibodies could be passed across the placenta during pregnancy, leading to the child developing Graves’ disease.
For patients who cannot tolerate medicines or who are allergic to or decline iodine-131, a surgical treatment option is available. Full or partial thyroidectomy is used uncommonly in the US and is not considered a primary option for Graves’ disease treatment, due to risks from surgery and anesthesia.