Liothyronine is a manufactured form of the thyroid hormone triiodothyronine (T3). It is most commonly used to treat hypothyroidism and myxedema coma. It is generally less preferred than levothyroxine. It can be taken by mouth or by injection into a vein.
Side effects may occur from excessive doses. This may include weight loss, fever, headache, anxiety, trouble sleeping, arrythmias, and heart failure. Use in pregnancy and breastfeeding is generally safe. Regular blood tests are recommended to verify the appropriateness of the dose being taken.
Liothyronine was approved for medical use in 1956. It is available as a generic medication. A month supply in the United Kingdom costs the NHS about 247 £ as of 2019. In the United States the wholesale cost of this amount is about US$22.40. In 2016 it was the 257th most prescribed medication in the United States with more than a million prescriptions.Liothyronine is a generally less preferred option to levothyroxine (T4) for people with hypothyroidism. It may be used when there is an impaired conversion of T4 to T3 in peripheral tissues. ABout 25 ug of liothyronine is equivalent to 100 ug of levothyroxine.
In thyroid cancer or Graves' disease, ablation therapy with radioactive iodine (131I) can be used to remove trace thyroid tissue that may remain after thyroidectomy (surgical excision of the gland). For 131I therapy to be effective, the trace thyroid tissue must be avid to iodine, which is achieved by elevating the person's TSH levels. For patients taking levothyroxine, TSH may be boosted by discontinuing levothyroxine for 3–6 weeks. This long period of hormone withdrawal is required because of levothyroxine's relatively long biological half-life, and may result in symptoms of hypothyroidism in the patient. The shorter half-life of liothyronine permits a withdrawal period of two weeks, which may minimize hypothyroidism symptoms. One protocol is to discontinue levothyroxine, then prescribe liothyronine while the T4 levels are falling, and finally stop the liothyronine two weeks before the radioactive iodine treatment.
Liothyronine may also be used for myxedema coma because of its quicker onset of action when compared to levothyroxine. Use for the treatment of obesity is not recommended.Liothyronine is the most potent form of thyroid hormone. As a salt of triiodothyronine (T3), it is chemically similar and pharmacologically equivalent to T3. As such, it acts on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline) by permissiveness. As monotherapy or in combination therapy with SSRIs, liothyronine may also enhance generation of new neurons in the central nervous system. The thyroid hormones are essential to proper development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds.
In comparison to levothyroxine (T4), liothyronine has a faster onset of action as well as a shorter biological half-life, which may be due to less plasma protein binding to thyroxine-binding globulin and transthyretin.