Thyroid and Antithyroid Drugs

Key points

• • In an underactive thyroid, the hormone thyroxine is replaced with levothyroxine, a synthetic form of the natural hormone.
• • In an overactive thyroid, thioamide drugs such as carbimazole and propylthiouracil block the enzyme that builds thyroid hormone.
• • Propylthiouracil also blocks the change of thyroxine (T4) into the more active T3 in the tissues.
• • Radioactive iodine is taken up by the thyroid and destroys the overactive tissue with its radiation, a common permanent way to treat an overactive gland.
• • Beta-blockers do not affect the gland but ease the racing pulse and tremor of an overactive thyroid until the other drugs take effect.
• • A serious but rare harm of the thioamides is a sharp fall in white cells (agranulocytosis), so a sore throat or fever must be checked.