THYROID HORMONES (Systemic)

Some commonly used brand names are:

In the U.S.—

  • Armour Thyroid 5
  • Cytomel 2
  • Levo-T 1
  • Levothroid 1
  • Levoxyl 1
  • Synthroid 1
  • Thyrar 5
  • Thyroid Strong 5
  • Thyrolar 3
  • Triostat 2
  • Westhroid 5

In Canada—

  • Cytomel 2
  • Eltroxin 1
  • PMS-Levothyroxine Sodium 1
  • Synthroid 1

Note:

For quick reference, the following thyroid hormones are numbered to match the corresponding brand names.

This information applies to the following medicines:
1. Levothyroxine (lee-voe-thye-ROX-een)
2. Liothyronine (lye-oh-THYE-roe-neen)
3. Liotrix (LYE-oh-trix)
4. Thyroglobulin (thye-roe-GLOB-yoo-lin)*
5. Thyroid (THYE-roid)§

Note:

This information does not apply to Thyrotropin.

* Not commercially available in the U.S.
† Not commercially available in Canada
‡ Generic name product may be available in the U.S.
§ Generic name product may be available in Canada

Category

  • Antineoplastic—Levothyroxine; Liothyronine; Liotrix; Thyroglobulin; Thyroid
  • Diagnostic aid, thyroid function—Levothyroxine; Liothyronine
  • Thyroid hormone—Levothyroxine; Liothyronine; Liotrix; Thyroglobulin; Thyroid

Description

Thyroid medicines belong to the general group of medicines called hormones. They are used when the thyroid gland does not produce enough hormone. They are also used to help decrease the size of enlarged thyroid glands (known as goiter) and to treat thyroid cancer.

These medicines are available only with your doctor's prescription, in the following dosage forms:

  • Oral
  • Levothyroxine
    • Tablets (U.S. and Canada)
  • Liothyronine
    • Tablets (U.S. and Canada)
  • Liotrix
    • Tablets (U.S.)
  • Thyroglobulin
    • Tablets
  • Thyroid
    • Tablets (U.S. and Canada)
  • Parenteral
  • Levothyroxine
    • Injection (U.S. and Canada)
  • Liothyronine
    • Injection (U.S.)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For thyroid hormones, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to thyroid hormones. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Use of proper amounts of thyroid hormone during pregnancy has not been shown to cause birth defects or other problems. However, your doctor may want you to change your dose while you are pregnant. This will make regular visits to your doctor important.

Breast-feeding—Use of proper amounts of thyroid hormones by mothers has not been shown to cause problems in nursing babies.

Children—Thyroid hormones have been tested in children and have not been shown to cause different side effects or problems in children than they do in adults.

Older adults—This medicine has been tested and has not been shown to cause different side effects or problems in older people than it does in younger adults. However, a different dose may be needed in the elderly. Therefore, it is important to take the medicine only as directed by the doctor.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking thyroid hormones, it is especially important that your health care professional know if you are taking any of the following:

  • Amphetamines
  • Anticoagulants (blood thinners)
  • Appetite suppressants (diet pills)
  • Cholestyramine (e.g., Questran)
  • Colestipol (e.g., Colestid)
  • Medicine for asthma or other breathing problems
  • Medicine for colds, sinus problems, or hay fever or other allergies (including nose drops or sprays)

Other medical problems—The presence of other medical problems may affect the use of thyroid hormones. Make sure you tell your doctor if you have any other medical problems especially:

  • Type 2 diabetes mellitus
  • Hardening of the arteries
  • Heart disease
  • High blood pressure
  • Overactive thyroid (history of)
  • Underactive adrenal gland
  • Underactive pituitary gland

Proper Use of This Medicine

Use this medicine only as directed by your doctor . Do not use more or less of it, and do not use it more often than your doctor ordered. Your doctor has prescribed the exact amount your body needs and if you take different amounts, you may experience symptoms of an overactive or underactive thyroid. Take it at the same time each day to make sure it always has the same effect.

If your condition is due to a lack of thyroid hormone, you may have to take this medicine for the rest of your life. It is very important that you do not stop taking this medicine without first checking with your doctor .

Dosing—The dose of these medicines will be different for different patients. Follow your doctor's orders or the directions on the label . The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets that you take depends on the strength of the medicine. The amount of thyroid hormone that you need to take every day depends on the results of your thyroid tests. However, treatment is usually started with lower doses that are increased a little at a time until you are taking the full amount. This helps prevent side effects.

  • For levothyroxine
  • For oral dosage form (tablets):
    • For replacing the thyroid hormone:
      • Adults and teenagers—At first, 0.0125 to 0.05 milligrams (mg) once a day. Then, your doctor may increase your dose a little at a time to 0.075 to 0.125 mg a day. The dose is usually no higher than 0.15 mg once a day.
      • Children less than 6 months of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.025 to 0.05 mg once a day.
      • Children 6 months to 12 months of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.05 to 0.075 mg once a day.
      • Children 1 to 5 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.075 to 0.1 mg once a day.
      • Children 6 to 10 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.1 to 0.15 mg once a day.
      • Children over 10 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.15 to 0.2 mg once a day.
  • For injection dosage form:
    • For replacing the thyroid hormone:
      • Adults and teenagers—50 to 100 micrograms (mcg) injected into a muscle or into a vein once a day. People with very serious conditions caused by too little thyroid hormone may need higher doses.
      • Children less than 6 months of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.019 to 0.038 mg once a day.
      • Children 6 months to 12 months of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.038 to 0.056 mg once a day.
      • Children 1 to 5 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.056 to 0.075 mg once a day.
      • Children 6 to 10 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.075 to 0.113 mg once a day.
      • Children over 10 years of age—The dose is based on body weight and must be determined by your doctor. The usual dose is 0.113 to 0.15 mg once a day.
  • For liothyronine sodium
  • For oral dosage form (tablets):
    • For replacing the thyroid hormone:
      • Adults and teenagers—At first, 25 micrograms (mcg) a day. Some patients with very serious conditions caused by too little thyroid hormone may need to take only 2.5 to 5 mcg a day at first. Also, some patients with heart disease or the elderly may need lower doses at first. Then, your doctor may increase your dose a little at a time to up to 50 mcg a day if needed. Your doctor may want you to divide your dose into smaller amounts that are taken two or more times a day.
    • For treating a large thyroid gland (goiter):
      • Adults—At first, 5 mcg a day. Some patients with heart disease or the elderly may need lower doses at first. Then, your doctor may increase your dose a little at a time to 50 to 100 mcg a day.
  • For injection dosage form:
    • For replacing the thyroid hormone in very serious conditions (myxedema coma):
      • Adults—At first, 10 to 50 mcg injected into a vein every four to twelve hours. Then, your doctor may want to adjust your dose depending on your condition.
      • Children—Use and dose must be determined by your doctor.
  • For liotrix (levothyroxine and liothyronine combination)
  • For oral dosage form (tablets):
    • For replacing the thyroid hormone:
      • Adults, teenagers, and children—At first, 50 micrograms (mcg) of levothyroxine and 12.5 mcg of liothyronine once a day. Some people with very serious conditions caused by too little thyroid hormone may need only 12.5 mcg of levothyroxine and 3.1 mcg of liothyronine once a day. Also, some elderly patients may need lower doses at first. Then, your doctor may want to increase your dose a little at a time to up to 100 mcg of levothyroxine and 25 mcg of liothyronine.
  • For thyroglobulin
  • For oral dosage form (tablets):
    • For replacing the thyroid hormone:
      • Adults, teenagers, and children—At first, 32 milligrams (mg) a day. Some people with very serious conditions caused by too little thyroid hormone may need to take only 16 to 32 mg a day at first. Then, the doctor may want you to increase your dose a little at a time to 65 to 160 mg a day.
  • For thyroid
  • For oral dosage form (tablets):
    • For replacing thyroid hormone:
      • Adults, teenagers, and children—60 milligrams (mg) a day. Some people with very serious conditions caused by too little thyroid hormone may need to take only 15 mg a day at first. Also, some elderly patients may need lower doses at first. Then, your doctor may want you to increase your dose a little at a time to 60 to 120 mg a day.

Missed dose—If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses. If you miss 2 or more doses in a row or if you have any questions about this, check with your doctor.

Storage—To store this medicine:

  • Keep out of the reach of children.
  • Store away from heat and direct light.
  • Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
  • Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

It is very important that your doctor check your progress at regular visits , to make sure that this medicine is working properly.

If you have certain kinds of heart disease, this medicine may cause chest pain or shortness of breath when you exert yourself. If these occur, do not overdo exercise or physical work. If you have any questions about this, check with your doctor.

Before having any kind of surgery (including dental surgery) or emergency treatment, tell the medical doctor or dentist in charge that you are taking this medicine .

Do not take any other medicine unless prescribed by your doctor. Some medicines may increase or decrease the effects of thyroid on your body and cause problems in controlling your condition. Also, thyroid hormones may change the effects of other medicines.

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur since they may indicate an overdose or an allergic reaction:

Less common or rare

Headache (severe) in children; skin rash or hives

Signs and symptoms of overdose

Chest pain; confusion; fast or irregular heartbeat; mood swings; muscle weakness; psychosis; restlessness (extreme); yellow eyes or skin; shortness of breath

For patients taking this medicine for underactive thyroid:

  • This medicine usually takes several weeks to have a noticeable effect on your condition. Until it begins to work, you may experience no change in your symptoms. Check with your doctor if the following symptoms continue:

Clumsiness; coldness; constipation; dry, puffy skin; listlessness; muscle aches; sleepiness; tiredness; weakness; weight gain

Other effects may occur if the dose of the medicine is not exactly right. These side effects will go away when the dose is corrected. Check with your doctor if any of the following symptoms occur:

Changes in appetite; changes in menstrual periods; diarrhea; fever; hand tremors; headache; increased sensitivity to heat; irritability; leg cramps; nervousness; sweating; trouble in sleeping; vomiting; weight loss

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

Revised: 06/21/2000

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