Liothyronine is a manufactured form of the

thyroid hormone File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus rect 66 216 386 25 ...

triiodothyronine Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. Production of T3 and its prohormone thyroxine ( ...

(T₃). It is most commonly used to treat

hypothyroidism Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as po ...

and

myxedema coma Myxedema coma is an extreme or decompensated form of hypothyroidism and while uncommon, is potentially lethal. A person may have laboratory values identical to a "normal" hypothyroid state, but a stressful event (such as an infection, myocardial ...

. It can be taken by mouth or by

injection into a vein Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...

. Side effects may occur from excessive doses. This may include weight loss, fever, headache, anxiety, trouble sleeping,

arrythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

s, and

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

. Use in

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

and

breastfeeding Breastfeeding, or nursing, is the process by which human breast milk is fed to a child. Breast milk may be from the breast, or may be expressed by hand or pumped and fed to the infant. The World Health Organization (WHO) recommends that br ...

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 generic drug is a pharmaceutical drug that contains the same chemical substance as a drug that was originally protected by chemical patents. Generic drugs are allowed for sale after the patents on the original drugs expire. Because the active ch ...

. In 2020, it was the 218th most commonly prescribed medication in the United States, with more than 2million prescriptions.

Medical uses

Liothyronine may be used when there is an impaired conversion of T₄ to T₃ in peripheral tissues. The dose of liothyronine for hypothyroidism is a lower amount than

levothyroxine Levothyroxine, also known as -thyroxine, is a manufactured form of the thyroid hormone thyroxine (T4). It is used to treat hypothyroidism, thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. It may also ...

due it being a higher concentrated synthetic medication. About 25 μg of liothyronine is equivalent to 100 μg of levothyroxine. In thyroid cancer or

Graves' disease Graves' disease (german: Morbus Basedow), also known as toxic diffuse goiter, is an autoimmune disease that affects the thyroid. It frequently results in and is the most common cause of hyperthyroidism. It also often results in an enlarged thyr ...

, ablation therapy with radioactive iodine ( ¹³¹I) can be used to remove trace thyroid tissue that may remain after

thyroidectomy A thyroidectomy is an operation that involves the surgical removal of all or part of the thyroid gland. In general surgery, endocrine or head and neck surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other conditi ...

(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 Biological half-life (also known as elimination half-life, pharmacologic half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration ( Cmax) to half of Cmax in the bl ...

, 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

because of its quicker onset of action when compared to levothyroxine. Use for the treatment of

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...

is not recommended.

Depression

Adding liothyronine to

tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants, which is important for the management of depression. They are second-line drugs next to SSRIs. TCAs were discovered in the early 1950s and wer ...

appears useful, especially in women. An algorithm developed from the STAR*D trial recommends liothyronine as an option when people have failed two antidepressant medications.

Pregnancy

Per the U.S. FDA, liothyronine is categorized as Pregnancy Category A.Cytomel (Liothyronine Sodium) Drug Information: Warnings and Precautions - Prescribing Information at RxList
retrieved on 29-October-2014 Thyroid hormone is minimally transferred to the fetus or placenta, however as of October 2014, studies have not shown any adverse effects to the fetus. Hypothyroid mothers should continue to take thyroid hormone replacement therapy throughout pregnancy to avoid adverse events."Liothyronine (Lexi-Drugs)". LexiComp. Retrieved 29 October 2014.

Nursing

Breastmilk contains a low amount of thyroid hormone, so it is important to exercise caution when breastfeeding while taking liothyronine.

Elderly

Older people should be started on lower doses of liothyronine. Plasma T₃ concentrations in this population are decreased by 25% to 40%. TSH must be routinely monitored since there is a risk of

coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...

hyperthyroidism Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism ...

and excessive bone loss from inadequate or abnormal thyroid replacement.

Contraindications

Any person with a hypersensitivity to liothyronine sodium or any active ingredient of the formulation should not be on this medication. If there is uncorrected

adrenal insufficiency Adrenal insufficiency is a condition in which the adrenal glands do not produce adequate amounts of steroid hormones. The adrenal gland normally secretes glucocorticoids (primarily cortisol), mineralocorticoids (primarily aldosterone), and androge ...

thyrotoxicosis Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism. ...

, a different approach to therapy must be considered.

Side effects

Liothyronine may cause a number of side effects, mostly similar to symptoms of

, which include: * weight loss * tremor * headache * upset stomach * vomiting * diarrhea * stomach cramps * nervousness * irritability * insomnia * excessive sweating * increased appetite * fever * changes in menstrual cycle * sensitivity to heat

Boxed warning

The package insert contains the following

boxed warning In the United States, a boxed warning (sometimes "black box warning", colloquially) is a type of warning that appears on the package insert for certain prescription drugs, so called because the U.S. Food and Drug Administration specifies that it ...

, as do all thyroid hormones:

Drugs with thyroid hormone activity, alone or together with other therapeutic agents, have been used for the treatment of obesity. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with
sympathomimetic amine Sympathomimetic drugs (also known as adrenergic drugs and adrenergic amines) are stimulant compounds which mimic the effects of endogenous agonists of the sympathetic nervous system. Examples of sympathomimetic effects include increases in heart ...
s such as those used for their anorectic effects.

Pharmacology

Liothyronine is the most potent form of thyroid hormone. As a

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

(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

SSRI Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions. SSRIs increase the extracellul ...

s, liothyronine may also enhance generation of new neurons in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

. 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

(T₄), liothyronine has a faster onset of action as well as a shorter

, which may be due to less

plasma protein binding Plasma protein binding refers to the degree to which medications attach to proteins within the blood. A drug's efficiency may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse or diffuse th ...

thyroxine-binding globulin Thyroxine-binding globulin (TBG) is a globulin protein that in humans is encoded by the ''SERPINA7'' gene. TBG binds thyroid hormones in circulation. It is one of three transport proteins (along with transthyretin and serum albumin) responsibl ...

and

transthyretin Transthyretin (TTR or TBPA) is a transport protein in the plasma and cerebrospinal fluid that transports the thyroid hormone thyroxine (T4) and retinol to the liver. This is how transthyretin gained its name: ''transports thyroxine and retinol'' ...

Pricing

The British

Competition and Markets Authority The Competition and Markets Authority (CMA) is the competition regulator in United Kingdom. It is a non-ministerial government department in the United Kingdom, responsible for strengthening business competition and preventing and reducing anti-com ...

launched an investigation into the alleged "excessive and unfair pricing" of liothyronine tablets in 2017. It alleged that Advanz Pharma overcharged the NHS from before 2007 to July 2017. The price of a pack increased by almost 1,600% from £4.46 before it was debranded in 2007 to £258.19 by July 2017.

References

External links

* {{Portal bar , Medicine Wikipedia medicine articles ready to translate Hormones of the thyroid gland Iodinated tyrosine derivatives Thyroid Pfizer brands Thyroid hormone receptor agonists Halogen-containing natural products Diphenyl ethers