Liothyronine Uses

Thyroid hormone occurs naturally in the body. The action thyroid hormones exert on the body includes effects on growth and development, cardiovascular function, gastrointestinal function, reproductive function, cognitive function, mental health, bone metabolism, glucose metabolism, and lipid metabolism. Both low and high thyroid hormone levels can cause problems. Cytomel (liothyronine) is used to treat an underactive thyroid gland (hypothyroidism). It supplies thyroid hormone in people whose body does not naturally produce the hormone. This medicine is used for primary hypothyroidism (thyroid-based) as well as secondary (pituitary) or tertiary hypothyroidism (hypothalamus-based).

Liothyronine is also used to suppress thyroid function in people with goiter (an enlarged thyroid gland) and for pituitary thyroid stimulating hormone (TSH) suppression in people with well-differentiated thyroid cancer. This medicine is also used during a thyroid suppression test for hyperthyroidism. 

There may be other uses of liothyronine—your health care professional or pharmacist can give you further drug information.

Liothyronine Mechanism of Action

Liothyronine is a synthetic form of the natural thyroid hormone triiodothyronine or T3. It is used as thyroid hormone replacement therapy in people who do not make enough of the hormone naturally.

Liothyronine Doses

Liothyronine is available as tablets in doses of 5 mcg, 25 mcg, and 50 mcg. 

The dose of liothyronine depends on various factors such as your age, body weight, cardiovascular status, other medical conditions, including pregnancy, other medications, diet, and the condition being treated. Therefore, the dose of Cytomel (liothyronine) is individualized, and periodic dose adjustments are made based on your clinical response and laboratory results. The typical doses of liothyronine are as follows:

Adults with hypothyroidism: Healthcare providers usually initiate Cytomel therapy at 25 mcg orally once per day. This dose can be increased by 25 mcg daily every 1-2 weeks, if needed. The usual maintenance dose is 25 mcg to 75 mcg once daily. Doctors typically start with a lower dose of 5 mcg in elderly patients and patients with cardiac disease.

Pediatric patients: The usual dosage is 5 mcg once daily for initiating Cytomel therapy in infants. This can be increased by 5 mcg daily every 3-4 days, if needed. The usual maintenance dose for infants is 20 mcg once daily. The dose for 1-year-old children is 50 mcg once daily. Children above 3 years of age usually require the full adult dosage. Newborns who are at risk of cardiac failure and pediatric patients who are at risk of hyperactivity may be started on a lower dose. 

Pregnant women: Pregnancy can affect thyroid hormone pharmacokinetics. An increase in the dose of this medicine is required for pregnant women with pre-existing hypothyroidism. The thyroid hormone dose is reduced to pre-pregnancy levels immediately after delivery. 

For pituitary TSH suppression in well-differentiated thyroid cancer: The dose of suppressive Cytomel therapy is adjusted to achieve normal serum TSH levels (a target TSH level within a therapeutic range). 

For thyroid suppression test: The recommended dose is one week of treatment with 75 mcg to 100 mcg daily. The uptake of radioactive iodine is measured before and after the 7 days of Cytomel (liothyronine) treatment. In people with normal thyroid function, radioiodine uptake falls significantly after treatment. A 50% or more drop in uptake indicates a normal thyroid-pituitary axis.

Switching from levothyroxine to liothyronine: Your doctor will tell you how to discontinue levothyroxine therapy and start liothyronine. The effects of levothyroxine can persist for several weeks, so they will start you on a low dose of liothyronine and gradually increase the dose based on your thyroid status. Your provider will monitor serum TSH periodically to evaluate your clinical and biochemical response to the medicine.