Liothyronine

Products

Liothyronine (T3) is commercially available in many countries in tablet form in combination with levothyroxine (T4) (Novothyral). In other countries, monopreparations without levothyroxine are also available.

Structure and properties

Liothyronine (C₁₅H₁₂I₃NO₄, M_r = 650.977 g/mol) is present in drugs as liothyronine sodium, a white to pale colored, hygroscopic powder that is practically insoluble in water. Liothyronine, unlike levothyroxine, is only triply iodinated.

Effects

Liothyronine (ATC H03AA02) is identical to endogenous thyroid hormone and is used for replacement therapy. The hormone is formed primarily in peripheral tissues by deiodination from levothyroxine and has numerous effects on metabolism, for example, energy metabolism, temperature regulation, and protein, carbohydrate, lipid, and nucleic acid metabolism. Liothyronine has a more rapid onset of action than levothyroxine and different pharmacokinetic properties. For example, the half-life is shorter compared with T4 and is approximately 1 to 1.5 days. Liothyronine is the main active hormone. Levothyroxine is therefore also referred to as a prehormone.

Indications

For the treatment of hypothyroidism, especially when there is insufficient conversion of T4 to T3.
For goiter and for diagnostic tests.

Dosage

According to the professional information. The dose is adjusted individually. Taking with food reduces bioavailability. Therefore, administration at least 30 minutes before eating is recommended.

Abuse

Thyroid hormones are misused by individuals without hypothyroidism for the treatment of obesity. They are not suitable for this purpose, according to the U.S. drug label. Misuse is strongly discouraged.

Contraindications

Hypersensitivity
Untreated hyperthyroidism
Untreated adrenal insufficiency
Untreated pituitary insufficiency
Acute myocardial infarction
Acute myocarditis
Acute pancarditis
Patients who have already had a myocardial infarction or who have concomitant angina, heart failure or tachycardic arrhythmias.
Pregnancy, when taken concomitantly with a thyrostatic agent.

Full precautions can be found in the drug label.

Interactions

Liothyronine has a high potential for drug-drug interactions.

Adverse effects

The most common potential adverse effects include palpitations, rapid heartbeat, insomnia, headache, and nervousness.