Antithyroid Medications for Hyperthyroidism

Examples

propylthiouracil ( Propyl-Thyracil or PTU )

How It Works

Antithyroid medications reduce the overproduction of thyroid hormone by the thyroid gland.

Why It Is Used

Antithyroid medication is often the first treatment of choice because it does not cause permanent thyroid damage and takes effect more quickly than radioactive iodine therapy.1

Methimazole and propylthiouracil are both considered to be highly effective antithyroid medications.

In some cases, one medication works better than the other.

Methimazole is chosen most often because it can be given once a day, has fewer side effects, and is less expensive.
Propylthiouracil is the preferred medication for pregnant women because it is less likely to enter the bloodstream of the fetus. It also is commonly used to treat people who have severe hyperthyroidism, because it prohibits one type of thyroid hormone from converting into a more active form.
Antithyroid medications are also used for people who have Graves' ophthalmopathy and who must be treated with radioactive iodine therapy. Antithyroid medications decrease the risk of Graves' ophthalmopathy worsening when given before radioactive iodine therapy.

How Well It Works

Symptoms of hyperthyroidism can be expected to improve or go away within 1 to 8 weeks once treatment with antithyroid medications has started. However, it may take as long as 6 months for thyroid function to return to normal. Antithyroid medication treatment must be continued for at least 1 to 2 years to reduce the chance of the condition coming back.

Antithyroid medication is most effective for mild hyperthyroidism, for an initial episode of Graves' disease in people younger than 50 years of age, and for slight enlargement of the thyroid gland (small goiter).2

Antithyroid medication can be used again if hyperthyroidism returns after treatment has been stopped. However, your health professional may recommend radioactive iodine treatment because it can permanently and safely cure hyperthyroidism.

Side Effects

Reactions to antithyroid medication include:
br> Rash and itching. Switching from one antithyroid medication to another may stop the rash.
Joint aches (arthralgias).
Liver problems (hepatitis).
Severely low white blood cell count (agranulocytosis), which can interfere with your body's ability to fight off infection. This is a rare side effect and is more common in people over age 40. The white blood cell count will probably return to normal once the medication is stopped.
All of these side effects tend to go away when the medication is stopped.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What to Think About

Antithyroid medications are the most common form of treatment in European and Asian countries.

Tell your doctor about any sore throat, fever, or rash, which can indicate that your white blood cell count is low.

Antithyroid medications need to be taken at the same time every day.

Your doctor will check your thyroid hormone levels frequently and adjust your medications accordingly. Your doctor may prescribe low doses of thyroid medication along with antithyroid medication to keep thyroid hormone levels from falling too low.

During pregnancy, antithyroid medications should be given in the lowest dose possible to prevent hypothyroidism in the fetus. Medication dosages may be adjusted throughout the pregnancy. Antithyroid medications can pass through the placenta to the fetus and have also been found in a nursing mother's breast milk. However, these medications have not been found to cause serious harm to the fetus or newborn.

Children may be difficult to treat with antithyroid medication because their bodies are constantly changing.

See a list of questions to ask your doctor about medications. References

Citations

Felig P, Frohman LA (2001). The thyroid: Physiology, thyrotoxicosis, hypothyroidism, and the painful thyroid. Endocrinology and Metabolism, 4th ed. New York: McGraw-Hill.

Franklyn JA (1994). The management of hyperthyroidism. New England Journal of Medicine, 330(24): 1731–1738.

Felig P, Frohman LA (2001). The thyroid: Physiology, thyrotoxicosis, hypothyroidism, and the painful thyroid. Endocrinology and Metabolism, 4th ed. New York: McGraw-Hill.

Credits
Author Nancy Reid
Editor Terrance L. Smith, PhD, ELS
Associate Editor Lila Havens
Associate Editor Tracy Landauer
Primary Medical Reviewer Patrice Burgess, MD
- Family Medicine
Specialist Medical Reviewer Alan Dalkin, MD
- Endocrinology

From WebMD