|Systematic (IUPAC) name|
|Pregnancy cat.||A (US)|
|Legal status||℞-only (US)|
|Mol. mass||672.96 g/mol|
|(what is this?)|
Liothyronine is a form of thyroid hormone used to treat hypothyroidism and myxedema coma. It is marketed as the sodium salt under the brand name Cytomel (or Tertroxin in Australia).(The figure on the right shows the R isomer instead of the S)
Liothyronine is the most potent form of thyroid hormone. Chemically, it is nearly identical to triiodothyronine (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. 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.
Physicians can use this instead of or in addition to levothyroxine (T4) for patients undergoing thyroid withdrawal. When a patient has thyroid cancer or Graves' disease, ablation therapy with radioactive iodine (131I) can be used to remove any trace thyroid tissue. For 131I therapy to be effective, the trace thyroid tissue must be avid to iodine. The best method is to starve the tissue of iodine but this can lead to hypothyroid symptoms for the patient. Withdrawal from levothyroxine can be done but it takes six weeks of withdrawal for the remaining thyroid tissue to be completely starved. Six weeks is needed owing to levothyroxine's long half life. Six weeks can be inconvenient for the patient and delay treatment. Liothyronine instead can be taken and withdrawn from for two weeks to starve the thyroid tissue. This is much safer and more convenient than levothyroxine. Also, due to its quicker onset of action when compared to levothyroxine, it sometimes is a better option in patients with myxedema coma or in patients preparing for 133I therapy for thyroid cancer.
- weight loss
- upset stomach
- stomach cramps
- excessive sweating
- increased appetite
- changes in menstrual cycle
- sensitivity to heat
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 hormonalrequirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.
- MedlinePlus. "Liothyronine." Last accessed July 14, 2007.
- United States Food & Drug Administration. "Cytomel."[dead link] Last accessed July 14, 2007.