ATC Class:H03AA02
VA Class:HS851
Liotrix, a synthetic combination preparation containing levothyroxine sodium and liothyronine sodium, is a thyroid agent.
Combination thyroid preparations such as liotrix initially were developed because it was assumed that circulating triiodothyronine resulted from direct thyroidal secretion and that both hormones should be included in replacement preparations; however, it is now known that about 80% of triiodothyronine is derived from deiodination of thyroxine in peripheral tissues and that patients receiving levothyroxine replacement alone have normal serum triiodothyronine and thyroxine concentrations. Therefore, liotrix, which is a synthetic combination of levothyroxine sodium and liothyronine sodium, generally offers no therapeutic advantage over levothyroxine sodium, and while normalizing serum thyroxine concentrations, may result in excessive serum triiodothyronine concentrations.
Liotrix is used for supplementation replacement or of diminished or absent thyroid function resulting from primary causes including functional deficiency, primary atrophy, partial or complete absence of the gland, or the effects of surgery, radiation, or antithyroid agents. Liotrix may also be used for replacement or supplemental therapy in patients with secondary (pituitary) or tertiary (hypothalamic) hypothyroidism. Therapy must be maintained continuously to control the symptoms of hypothyroidism. Although levothyroxine sodium is considered the drug of choice for the treatment of congenital hypothyroidism (cretinism), liotrix has been used in the treatment of this condition. For a discussion of the treatment of congenital hypothyroidism, see Cautions: Pediatric Precautions, in the Thyroid Agents General Statement 68:36.04.
Liotrix may be used to suppress the secretion of thyrotropin (TSH) in the management of simple (nontoxic) goiter, in subacute or chronic lymphocytic thyroiditis, multinodular goiter, and in the management of thyroid cancer. Liotrix therapy may cause a reduction in goiter size.
Liotrix may be used with antithyroid agents in the treatment of thyrotoxicosis to prevent goitrogenesis and hypothyroidism.
Liotrix also may be used diagnostically in suppression tests to differentiate suspected mild hyperthyroidism or thyroid gland autonomy.
Liotrix is administered orally, usually as a single daily dose before breakfast.
Dosage of liotrix must be carefully adjusted according to individual requirements and response. The age and general physical condition of the patient and the severity and duration of hypothyroid symptoms determine the initial dosage and the rate at which dosage may be increased to the eventual maintenance dosage. Dosage should be initiated at a lower level in geriatric patients; in patients with long-standing disease, other endocrinopathies, or functional or ECG evidence of cardiovascular disease; and in patients with severe hypothyroidism. Adjustment of thyroid replacement therapy should be determined mainly by the patient's clinical response and confirmed by appropriate laboratory tests.
For the management of long-standing hypothyroidism (myxedema) in adults, the initial dosage is one tablet of Thyrolar®-1/2, and increased by one tablet of Thyrolar®-1/4 daily. The usual maintenance dosage is one tablet of Thyrolar®-1 to one tablet of Thyrolar®-2 daily. Lack of response to one Thyrolar®-3 tablet daily may suggest non-compliance or malabsorption. Serum thyrotropin (thyroid-stimulating hormone, TSH) and thyroxine (T4) concentrations usually return to normal after 2-3 weeks of therapy; adjustment of dosage should be made within the first 4 weeks of therapy based on suitable laboratory assessment.
For the treatment of congenital hypothyroidism in infants and children, the manufacturer recommends the following dosage ranges:
Liotrix shares the toxic potentials of other thyroid agents, and the usual precautions of thyroid agent therapy should be observed. (See Toxicity and Cautions in the Thyroid Agents General Statement 68:36.04.) Adverse reactions to liotrix result from overdosage and are manifested principally as signs and symptoms of hyperthyroidism.
The principal pharmacologic effect of exogenous thyroid hormones is to increase the metabolic rate of body tissues. Thyroid hormones are also involved in the regulation of cell growth and differentiation. Although the precise mechanism of action by which thyroid hormones affect metabolism and cellular growth and differentiation is not clearly established, it is known that these physiologic effects are mediated at the cellular level, principally via triiodothyronine; a major portion of triiodothyronine is derived from thyroxine by deiodination in peripheral tissues. Thyroxine is the major component of normal secretions of the thyroid gland and is therefore the principal determinant of normal thyroid function.
Liotrix is a synthetic combination preparation containing levothyroxine sodium and liothyronine sodium.
Current USP standards define liotrix as containing levothyroxine sodium and liothyronine sodium in a ratio of 4:1 by weight. Thus, Thyrolar®-1 contains 50 mcg of levothyroxine sodium and 12.5 mcg of liothyronine sodium, which is approximately equivalent to 60 mg of thyroid.
Commercially available liotrix tablets should be stored in tight, light-resistant containers at a cold temperature of 2-8°C.
Additional Information
For further information on chemistry, pharmacology, pharmacokinetics, uses, toxicity, cautions, acute toxicity, drug interactions, laboratory test interferences, and dosage and administration of liotrix, see the Thyroid Agents General Statement 68:36.04 and the individual monographs on Levothyroxine Sodium 68:36.04 and Liothyronine Sodium 68:36.04.
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
U.S. Pharmacopeia, an official public standards-setting authority for all prescription and over-the-counter medicines and other health care products manufactured or sold in the United States, has mandated new specifications for a component used in the manufacturing of Thyrolar. As a result, all strengths of Thyrolar are currently on long-term back order while Forest makes the modifications necessary to meet these new specifications. Forest is working diligently to complete these modifications. In the meantime, patients should speak with their physician regarding appropriate treatment for their condition, and check for future updates on the availability of Thyrolar through the Forest product availability toll-free hotline at (866) 927-3260.
Update: Actavis (formerly Forest) discontinued all Thyrolar presentations in September 2018.
Routes | Dosage Forms | Strengths | Brand Names | Manufacturer |
|---|---|---|---|---|
Oral | Tablets | Levothyroxine Sodium 12.5 mcg and Liothyronine Sodium 3.1 mcg | Thyrolar®-¼ | Forest |
Levothyroxine Sodium 25 mcg and Liothyronine Sodium 6.25 mcg | Thyrolar®-½ | Forest | ||
Levothyroxine Sodium 50 mcg and Liothyronine Sodium 12.5 mcg | Thyrolar®-1 | Forest | ||
Levothyroxine Sodium 100 mcg and Liothyronine Sodium 25 mcg | Thyrolar®-2 | Forest | ||
Levothyroxine Sodium 150 mcg and Liothyronine Sodium 37.5 mcg | Thyrolar®-3 | Forest |