Cytomel Information
Cytomel () Description
Thyroid hormone drugs are natural or synthetic preparations containing tetraiodothyronine (T, levothyroxine) sodium or triiodothyronine (T, liothyronine) sodium or both. T and T are produced in the human thyroid gland by the iodination and coupling of the amino acid tyrosine. T contains four iodine atoms and is formed by the coupling of two molecules of diiodotyrosine (DIT). T contains three atoms of iodine and is formed by the coupling of one molecule of DIT with one molecule of monoiodotyrosine (MIT). Both hormones are stored in the thyroid colloid as thyroglobulin.
Thyroid hormone preparations belong to two categories: (1) natural hormonal preparations derived from animal thyroid, and (2) synthetic preparations. Natural preparations include desiccated thyroid and thyroglobulin. Desiccated thyroid is derived from domesticated animals that are used for food by man (either beef or hog thyroid), and thyroglobulin is derived from thyroid glands of the hog. The United States Pharmacopeia (USP) has standardized the total iodine content of natural preparations. Thyroid USP contains not less than (NLT) 0.17 percent and not more than (NMT) 0.23 percent iodine, and thyroglobulin contains not less than (NLT) 0.7 percent of organically bound iodine. Iodine content is only an indirect indicator of true hormonal biologic activity.
Cytomel () (liothyronine sodium) Tablets contain liothyronine (L-triiodothyronine or LT), a synthetic form of a natural thyroid hormone, and is available as the sodium salt.
The structural and empirical formulas and molecular weight of liothyronine sodium are given below.
Liothyronine Sodium
L-Tyrosine, -(4-hydroxy-3-iodophenyl)-3,5-diiodo-, monosodium salt
Twenty-five mcg of liothyronine is equivalent to approximately 1 grain of desiccated thyroid or thyroglobulin and 0.1 mg of L-thyroxine.
Each round, white to off-white Cytomel () (liothyronine sodium) tablet contains liothyronine sodium equivalent to liothyronine as follows: 5 mcg debossed KPI and 115; 25 mcg scored and debossed KPI and 116; 50 mcg scored and debossed KPI and 117. Inactive ingredients consist of calcium sulfate, gelatin, starch, stearic acid, sucrose and talc.
Cytomel () Clinical Pharmacology
The mechanisms by which thyroid hormones exert their physiologic action are not well understood. These hormones enhance oxygen consumption by most tissues of the body, increase the basal metabolic rate and the metabolism of carbohydrates, lipids and proteins. Thus, they exert a profound influence on every organ system in the body and are of particular importance in the development of the central nervous system.
Cytomel () Indications And Usage
Thyroid hormone drugs are indicated:
Cytomel () (liothyronine sodium) Tablets can be used in patients allergic to desiccated thyroid or thyroid extract derived from pork or beef.
Cytomel () Contraindications
Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency, untreated thyrotoxicosis and apparent hypersensitivity to any of their active or extraneous constituents. There is no well-documented evidence from the literature, however, of true allergic or idiosyncratic reactions to thyroid hormone.
Cytomel () Warnings
The use of thyroid hormones in the therapy of obesity, alone or combined with other drugs, is unjustified and has been shown to be ineffective. Neither is their use justified for the treatment of male or female infertility unless this condition is accompanied by hypothyroidism.
Thyroid hormones should be used with great caution in a number of circumstances where the integrity of the cardiovascular system, particularly the coronary arteries, is suspected. These include patients with angina pectoris or the elderly, in whom there is a greater likelihood of occult cardiac disease. In these patients, liothyronine sodium therapy should be initiated with low doses, with due consideration for its relatively rapid onset of action. Starting dosage of Cytomel () (liothyronine sodium) Tablets is 5 mcg daily, and should be increased by no more than 5 mcg increments at 2-week intervals. When, in such patients, a euthyroid state can only be reached at the expense of an aggravation of the cardiovascular disease, thyroid hormone dosage should be reduced.
Morphologic hypogonadism and nephrosis should be ruled out before the drug is administered. If hypopituitarism is present, the adrenal deficiency must be corrected prior to starting the drug. Myxedematous patients are very sensitive to thyroid; dosage should be started at a very low level and increased gradually.
Severe and prolonged hypothyroidism can lead to a decreased level of adrenocortical activity commensurate with the lowered metabolic state. When thyroid-replacement therapy is administered, the metabolism increases at a greater rate than adrenocortical activity. This can precipitate adrenocortical insufficiency. Therefore, in severe and prolonged hypothyroidism, supplemental adrenocortical steroids may be necessary. In rare instances the administration of thyroid hormone may precipitate a hyperthyroid state or may aggravate existing hyperthyroidism.
Cytomel () Precautions
Thyroid hormone therapy in patients with concomitant diabetes mellitus or insipidus or adrenal cortical insufficiency aggravates the intensity of their symptoms. Appropriate adjustments of the various therapeutic measures directed at these concomitant endocrine diseases are required.
The therapy of myxedema coma requires simultaneous administration of glucocorticoids.
Hypothyroidism decreases and hyperthyroidism increases the sensitivity to oral anticoagulants. Prothrombin time should be closely monitored in thyroid-treated patients on oral anticoagulants and dosage of the latter agents adjusted on the basis of frequent prothrombin time determinations. In infants, excessive doses of thyroid hormone preparations may produce craniosynostosis.
Pregnant mothers provide little or no thyroid hormone to the fetus. The incidence of congenital hypothyroidism is relatively high (1:4000) and the hypothyroid fetus would not derive any benefit from the small amounts of hormone crossing the placental barrier. Routine determinations of serum T and/or TSH is strongly advised in neonates in view of the deleterious effects of thyroid deficiency on growth and development.
Treatment should be initiated immediately upon diagnosis and maintained for life, unless transient hypothyroidism is suspected, in which case, therapy may be interrupted for 2 to 8 weeks after the age of 3 years to reassess the condition. Cessation of therapy is justified in patients who have maintained a normal TSH during those 2 to 8 weeks.
Cytomel () Adverse Reactions
Adverse reactions, other than those indicative of hyperthyroidism because of therapeutic overdosage, either initially or during the maintenance period are rare (see ).
In rare instances, allergic skin reactions have been reported with Cytomel () (liothyronine sodium) Tablets.
Cytomel () Overdosage
Dosage should be reduced or therapy temporarily discontinued if signs and symptoms of overdosage appear. Treatment may be reinstituted at a lower dosage. In normal individuals, normal hypothalamic-pituitary-thyroidaxis function is restored in 6 to 8 weeks after thyroid suppression.
Treatment of acute massive thyroid hormone overdosage is aimed at reducing gastrointestinal absorption of the drugs and counteracting central and peripheral effects, mainly those of increased sympathetic activity. Vomiting may be induced initially if further gastrointestinal absorption can reasonably be prevented and barring contraindications such as coma, convulsions, or loss of the gagging reflex. Treatment is symptomatic and supportive. Oxygen may be administered and ventilation maintained. Cardiac glycosides may be indicated if congestive heart failure develops. Measures to control fever, hypoglycemia, or fluid loss should be instituted if needed. Antiadrenergic agents, particularly propranolol, have been used advantageously in the treatment of increased sympathetic activity. Propranolol may be administered intravenously at a dosage of 1 to 3 mg over a 10-minute period or orally, 80 to 160 mg/day, especially when no contraindications exist for its use.
Cytomel () Dosage And Administration
The dosage of thyroid hormones is determined by the indication and must in every case be individualized according to patient response and laboratory findings.
Cytomel () (liothyronine sodium) Tablets are intended for oral administration; once-a-day dosage is recommended. Although liothyronine sodium has a rapid cutoff, its metabolic effects persist for a few days following discontinuance.
Cytomel () How Supplied
Cytomel () (liothyronine sodium) Tablets: 5 mcg in bottles of 100; 25 mcg in bottles of 100; and 50 mcg in bottles of 100.
5 mcg 100’s: NDC 60793-115-01
25 mcg 100’s: NDC 60793-116-01
50 mcg 100’s: NDC 60793-117-01
Store between 15° and 30°C (59° and 86°F).
Prescribing Information as of March 2004.
Manufactured by: King Pharmaceuticals, Inc., Bristol, TN 37620
Cytomel () Labelgraphic
Cytomel () Labelgraphic
Cytomel () Labelgraphic
Cytomel () Labelgraphic
