Cytomel

Cytomel is the brand name of the prescription drug liothyronine, which is used to treat hypothyroidism, a condition in which the thyroid gland doesn't produce enough thyroid hormone.

The medicine is also used to treat an enlarged thyroid gland, as a diagnostic test for hyperthyroidism (a condition where the thyroid gland produces too much thyroid hormone), or to treat thyroid cancer.

It's sometimes given to help treat certain types of depression.

Cytomel is a man-made hormone that replaces the body's natural thyroid hormone.

The Food and Drug Administration (FDA) approved the medicine in 1956. It's manufactured by Pfizer, Inc.

Cytomel Warnings

Cytomel contains a black-box warning because it shouldn't be used for weight loss or to treat obesity in people without a thyroid disorder.

The medicine may cause serious or life-threatening effects in individuals with normal thyroid function, especially if it's used with other medicines that control appetite.

Before taking Cytomel, tell your doctor if you have or have ever had:

• A heart attack or heart disease
• Chest pain
• An irregular heartbeat
• High blood pressure
• Hepatitis
• Myxedema (a skin or tissue disorder caused by severe hypothyroidism)
• An overactive thyroid
• Diabetes
• Adrenal gland problems
• An underactive pituitary gland
• Low testosterone levels
• Allergies to medications

Be sure to tell your physician you're taking Cytomel before having any type of surgery, including a dental procedure.

If you have diabetes, you should know that Cytomel may affect your blood sugar. Monitor your levels carefully and talk to your doctor before changing any of the doses of your diabetes medications.

Cytomel should be used with caution in elderly people, who may be more sensitive to the drug's side effects.

Children might experience hair loss during the first few months of using Cytomel. This symptom is usually temporary.

Continue to take Cytomel even if you feel well. Don't stop using the medicine without first talking to your doctor.

Your healthcare provider will likely perform frequent lab tests while you're taking Cytomel. Keep all appointments with your physician and laboratory.

Pregnancy and Cytomel

Cytomel isn't expected to harm an unborn baby, but tell your doctor if you become pregnant while taking this medicine.

The drug can pass into breast milk, so talk to your healthcare provider before breastfeeding a baby while using Cytomel.

Since thyroid hormone occurs naturally in the body, almost anyone can take liothyronine. However, you may not be able to use this medication if you have a thyroid disorder called thyrotoxicosis, or an adrenal gland problem that is not controlled by treatment.

Before taking liothyronine, tell your doctor if you have heart disease, angina (chest pain), coronary artery disease, congestive heart failure, diabetes, or problems with your pituitary or adrenal glands.

Tell your doctor if you are pregnant or breast-feeding.

To be sure this medication is helping your condition, your blood may need to be tested often. Visit your doctor regularly.

Keep using this medicine as directed, even if you feel well. You may need to take thyroid medication for the rest of your life.

Call your doctor if you notice any signs of thyroid toxicity, such as chest pain, fast or pounding heartbeats, feeling hot or nervous, or sweating more than usual.

Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label.

Liothyronine is usually taken once daily. Follow your doctor's instructions.

Your doctor may occasionally change your dose to make sure you get the best results.

If you are switching to liothyronine from any other thyroid medication, stop using the other medication before you start taking liothyronine.

To be sure this medication is helping your condition, your blood may need to be tested often. Visit your doctor regularly.

Keep using this medicine as directed, even if you feel well. You may need to take thyroid medication for the rest of your life.

Call your doctor if you notice any signs of thyroid toxicity, such as chest pain, fast or pounding heartbeats, feeling hot or nervous, or sweating more than usual.

If you need surgery, tell the surgeon ahead of time that you are using liothyronine. You may need to stop using the medicine for a short time.

Store at room temperature away from moisture and heat.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Less serious side effects may include temporary hair loss (especially in children).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In the U.S.

• Cytomel

Available Dosage Forms:

• Tablet

Therapeutic Class: Thyroid Supplement

• It is used to add thyroid hormone to the body.
• It is used to treat or prevent an enlarged thyroid gland.
• It is used to test for thyroid problems.

• If you have an allergy to liothyronine or any other part of Cytomel.
• If you are allergic to any drugs like this one, any other drugs, foods, or other substances. Tell your doctor about the allergy and what signs you had, like rash; hives; itching; shortness of breath; wheezing; cough; swelling of face, lips, tongue, or throat; or any other signs.
• If you have any of these health problems: Overactive thyroid gland or weak adrenal gland.

This is not a list of all drugs or health problems that interact with this medicine.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take Cytomel with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

• Store at room temperature.
• Store in a dry place. Do not store in a bathroom.
• Protect from light.
• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Check with your pharmacist about how to throw out unused drugs.

Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency, untreated thyrotoxicosis and apparent hypersensitivity to any of their active or extraneous constituents. There is no well-documented evidence from the literature, however, of true allergic or idiosyncratic reactions to thyroid hormone.

Animal studies have not been reported. Thyroid hormones do not readily cross the placenta. Clinical experience to date does not indicate any adverse effects on the fetus when thyroid hormones are administered to pregnant women. There are no controlled data in human pregnancy. AU TGA pregnancy category A: Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed. US FDA pregnancy category A: Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).

Use is considered acceptable. AU TGA pregnancy category: A US FDA pregnancy category: A Comments: -While clinical experience to date does not provide any evidence of fetal harm, some authorities recommend weighing the possible risk of fetal congenital abnormalities against the risk of untreated maternal hypothyroidism.

Summary of Use during Lactation

Liothyronine (T3) is a normal component of human milk. If replacement doses of liothyronine are required by the mother, it is not necessarily a reason to discontinue breastfeeding. However, because no information is available on the use of exogenous liothyronine during breastfeeding, an alternate drug may be preferred. The American Thyroid Association recommends that subclinical and overt hypothyroidism should be treated with levothyroxine in lactating women seeking to breastfeed.[1] Liothyronine dosage requirement may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.[2]

Drug Levels

Milk levels of liothyronine have not been measured after exogenous administration of T3 in humans. Liothyronine is a normal component of human milk. Although somewhat controversial, liothyronine, unlike levothyroxine (T4), might pass into milk in amounts that affect infant thyroid status.[3][4][5][6][7]

Maternal Levels. In a study of 56 mothers with thyroid disorders, 50 had hypothyroidism and were being treated with levothyroxine; 5 mothers had controlled hyperthyroidism with no medications and 1 had hyperthyroidism treated with a medication. Milk levels of thyroid hormones were free T4 4.5 ng/L, total T4 29.6 mcg/L, free T3 2.3 ng/L and total T3 0.35 mcg/L. The average milk to serum level ratios over the period were free T4 0.32, total T4 0.3, free T3 0.78 and total T3 0.26. Levels of free and total T3 and total T4 in milk were positively correlated with their respective plasma levels.[8]

Infant Levels. Relevant published information was not found as of the revision date.

Effects in Breastfed Infants

Relevant published information was not found as of the revision date. However, the thyroid hormone content of human milk from the mothers of very preterm infants appears not to be sufficient to affect the infants thyroid status.[9]

Effects on Lactation and Breastmilk

Adequate thyroid hormone serum levels are required for normal lactation. Replacing deficient thyroid levels should improve milk production caused by hypothyroidism. Supraphysiologic doses of liothyronine would not be expected to further improve lactation.

Alternate Drugs to Consider

Levothyroxine

References

1. Alexander EK, Pearce EN, Brent GA et al. 2016 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum. Thyroid. 2017;27:315-89. PMID: 28056690

2. Galofre JC, Haber RS, Mitchell AA et al. Increased postpartum thyroxine replacement in Hashimoto's thyroiditis. Thyroid. 2010;20:901-8. PMID: 20615129

3. Sato T, Suzuki Y. Presence of triiodothyronine, no detectable thyroxine and reverse triiodothyronine in human milk. Endocrinol Jpn. 1979;26:507-13. PMID: 499092

4. Varma SK, Collins M, Row A et al. Thyroxine, tri-iodothyronine, and reverse tri-iodothyronine concentrations in human milk. J Pediatr. 1978;93:803-6. PMID: 712487

5. Mallol J, Obregon MJ, Morreale de Escobar GM. Analytical artifacts in radioimmunoassay of L-thyroxin in human milk. Clin Chem. 1982;28:1277-82. PMID: 7074933

6. Oberkotter LV, Tenore A. Separation and radioimmunoassay of T3 and T4 in human breast milk. Horm Res. 1983;17:11-8. PMID: 6551313

7. Koldovsky O. Hormones in milk. Vitam Horm. 1995;50:77-149. PMID: 7709605

8. Zhang Q, Lian XL, Chai XF et al. [Relationship between maternal milk and serum thyroid hormones in patients with thyroid related diseases.]. Zhongguo Yi Xue Ke Xue Yuan Xue Bao. 2013;35:427-31. PMID: 23987491

9. van Wassenaer AG, Stulp MR, Valianpour F et al. The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infant. Clin Endocrinol. 2002;56:621-7. PMID: 12030913