Liothyronine sodium

Overview
Liothyronine sodium is the L-isomer of triiodothyronine (T3), a form of thyroid hormone used to treat hypothyroidism and myxedema coma. It is marketed under the brand name Cytomel (or Tertroxin in Australia).

Pharmacology
Liothyronine is the most potent form of thyroid hormone. 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.

Side effects
Liothyronine may cause a number of side effects, 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
 * temporary hair loss, particularly in children during the first month of therapy

Black box warning
The package insert for Cytomel contains the following black box warning:

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 amines such as those used for their anorectic effects.