WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS. Thyroid hormones, including Cytomel, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.
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 see, and.Indications and Usage for Cytomel. Hypothyroidism Cytomel is indicated as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Pituitary Thyroid-Stimulating Hormone(TSH) Suppression Cytomel is indicated as an adjunct to surgery and radioiodine therapy in the management of well-differentiated thyroid cancer. Table 1: Drugs That May Decrease T3 Absorption (Hypothyroidism) Potential impact: Concurrent use may reduce the efficacy of Cytomel by binding and delaying or preventing absorption, potentially resulting in hypothyroidism.Drug or Drug ClassEffectBile Acid Sequestrants-Colesevelam-Cholestyramine-ColestipolIon Exchange Resins-Kayexalate-SevelamerBile acid sequestrants and ion exchange resins are known to decrease thyroid hormones absorption. Administer Cytomel at least 4 hours prior to these drugs or monitor TSH levels. Table 2: Drugs That May Alter Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug ClassEffectClofibrateEstrogen-containing oral contraceptivesEstrogens (oral)Heroin / Methadone5-FluorouracilMitotaneTamoxifenThese drugs may increase serum thyroxine-binding globulin (TBG) concentration.Androgens / Anabolic SteroidsAsparaginaseGlucocorticoidsSlow-Release Nicotinic AcidThese drugs may decrease serum TBG concentration.Salicylates (2 g/day)Salicylates inhibit binding of T4 and T3 to TBG and transthyretin.
An initial increase in serum FT4 is followed by return of FT4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T4 levels may decrease by as much as 30%.Other drugs:CarbamazepineFurosemide (80 mg IV)HeparinHydantoins Non-Steroidal Anti-inflammatory Drugs- FenamatesThese drugs may cause protein binding site displacement. Furosemide has been shown to inhibit the protein binding of T4 to TBG and albumin, causing an increased free-T4 fraction in serum.
Furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower the total T4 level. Phenytoin and carbamazepine reduce serum protein binding of thyroid hormones, and total and FT4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid. Closely monitor thyroid hormone parameters. Table 3: Drugs That May Alter Hepatic Metabolism of Thyroid hormones Potential impact: Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of thyroid hormones, resulting in increased Cytomel requirements.Drug or Drug ClassEffectPhenobarbitalRifampinPhenobarbital has been shown to reduce the response to thyroxine. Phenobarbital increases L-thyroxine metabolism by inducing uridine 5'-diphospho-glucuronosyltransferase (UGT) and leads to a lower T4 serum levels. Changes in thyroid status may occur if barbiturates are added or withdrawn from patients being treated for hypothyroidism.
Rifampin has been shown to accelerate the metabolism of thyroid hormones. Table 4: Drugs That May Decrease Conversion of T4 to T3 Potential impact: Administration of these enzyme inhibitors decreases the peripheral conversion of T4 to T3, leading to decreased T3 levels. However, serum T4 levels are usually normal but may occasionally be slightly increased.Drug or Drug ClassEffectBeta-adrenergic antagonists (e.g., Propranolol 160 mg/day)In patients treated with large doses of propranolol (160 mg/day), T3 and T4 levels change, TSH levels remain normal, and patients are clinically euthyroid. Actions of particular beta-adrenergic antagonists may be impaired when a hypothyroid patient is converted to the euthyroid state.Glucocorticoids (e.g., Dexamethasone ≥4 mg/day)Short-term administration of large doses of glucocorticoids may decrease serum T3 concentrations by 30% with minimal change in serum T4 levels. However, long-term glucocorticoid therapy may result in slightly decreased T3 and T4 levels due to decreased TBG production (see above).Other drugs:AmiodaroneAmiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients.Antidiabetic TherapyAddition of Cytomel therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control, especially when Cytomel is started, changed, or discontinued see.
Oral AnticoagulantsCytomel increases the response to oral anticoagulant therapy. Therefore, a decrease in the dose of anticoagulant may be warranted with correction of the hypothyroid state or when the Cytomel dose is increased. Closely monitor coagulation tests to permit appropriate and timely dosage adjustments. Digitalis GlycosidesCytomel may reduce the therapeutic effects of digitalis glycosides. Serum digitalis glycoside levels may be decreased when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides. Antidepressant TherapyConcurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline) antidepressants and Cytomel may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines. Toxic effects may include increased risk of cardiac arrhythmias and central nervous system stimulation.
Cytomel may accelerate the onset of action of tricyclics. Administration of sertraline in patients stabilized on Cytomel may result in increased Cytomel requirements. KetamineConcurrent use of ketamine and Cytomel may produce marked hypertension and tachycardia. Closely monitor blood pressure and heart rate in these patients. SympathomimeticsConcurrent use of sympathomimetics and Cytomel may increase the effects of sympathomimetics or thyroid hormone.
Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease. Tyrosine-Kinase InhibitorsConcurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism. Closely monitor TSH levels in such patients.
Drug-Laboratory Test InteractionsConsider changes in TBG concentration when interpreting T4 and T3 values. Measure and evaluate unbound (free) hormone in this circumstance. Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentrations.
Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens and corticosteroids decrease TBG concentration. Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000. USE IN SPECIFIC POPULATIONS PregnancyRisk SummaryExperience with liothyronine use in pregnant women, including data from post-marketing studies, have not reported increased rates of major birth defects or miscarriages (see ). There are risks to the mother and fetus associated with untreated hypothyroidism in pregnancy. Since TSH levels may increase during pregnancy, TSH should be monitored and Cytomel dosage adjusted during pregnancy (see ). There are no animal studies conducted with liothyronine during pregnancy. Cytomel should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated.The estimated background risk of major birth defects and miscarriage for the indicated population is unknown.
General population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.Clinical ConsiderationsDisease-associated maternal and/or embryo/fetal riskMaternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery. Untreated maternal hypothyroidism may have an adverse effect on fetal neurocognitive development.Dose adjustments during pregnancy and the postpartum periodPregnancy may increase Cytomel requirements. Serum TSH levels should be monitored and the Cytomel dosage adjusted during pregnancy. Since postpartum TSH levels are similar to preconception values, the Cytomel dosage should return to the pre-pregnancy dose immediately after delivery see.DataHuman DataLiothyronine is approved for use as a replacement therapy for hypothyroidism. Data from post-marketing studies have not reported increased rates of fetal malformations, miscarriages, or other adverse maternal or fetal outcomes associated with liothyronine use in pregnant women.
LactationRisk SummaryLimited published studies report that liothyronine is present in human milk. However, there is insufficient information to determine the effects of liothyronine on the breastfed infant and no available information on the effects of liothyronine on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for Cytomel and any potential adverse effects on the breastfed infant from Cytomel or from the underlying maternal condition. Pediatric UseThe initial dose of Cytomel varies with age and body weight. Dosing adjustments are based on an assessment of the individual patient's clinical and laboratory parameters see,.In pediatric patients in whom a diagnosis of permanent hypothyroidism has not been established, discontinue thyroid hormone for a trial period, but only after the child is at least 3 years of age. Obtain serum TSH, T4, and T3 levels at the end of the trial period, and use laboratory test results and clinical assessments to guide diagnosis and treatment, if warranted see.Congenital Hypothyroidism see, Rapid restoration of normal serum T4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on intellectual development as well as on overall physical growth and maturation.
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Therefore, initiate thyroid hormone immediately upon diagnosis. Thyroid hormone is generally continued for life in these patients.Closely monitor infants during the first 2 weeks of thyroid hormone therapy for cardiac overload, arrhythmias, and aspiration from avid suckling.Closely monitor patients to avoid undertreatment or overtreatment. Undertreatment may have deleterious effects on intellectual development and linear growth.
Overtreatment is associated with craniosynostosis in infants, may adversely affect the tempo of brain maturation, and may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature see and.Acquired Hypothyroidism in Pediatric PatientsClosely monitor patients to avoid undertreatment and overtreatment. Undertreatment may result in poor school performance due to impaired concentration and slowed mentation and in reduced adult height. Overtreatment may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature.Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height. In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height see. Geriatric UseBecause of the increased prevalence of cardiovascular disease among the elderly, initiate Cytomel at less than the full replacement dose see and. Atrial arrhythmias can occur in elderly patients.
Atrial fibrillation is the most common of the arrhythmias observed with thyroid hormone overtreatment in the elderly. OverdosageThe signs and symptoms of overdosage are those of hyperthyroidism see and. In addition, confusion and disorientation may occur. Cerebral embolism, seizure, shock, coma, and death have been reported. Symptoms may not necessarily be evident or may not appear until several days after ingestion.Reduce the Cytomel dose or temporarily discontinued if signs or symptoms of overdosage occur. Initiate appropriate supportive treatment as dictated by the patient's medical status.For current information on the management of poisoning or overdosage, contact the National Poison Control Center at 1-800-222-1222 or www.poison.org. Cytomel DescriptionCytomel tablets contain the active ingredient, liothyronine (L-triiodothyronine or LT 3), a synthetic form of a thyroid hormone liothyronine in sodium salt form.
It is chemically designated as L-Tyrosine, O-(4-hydroxy-3-iodophenyl)-3,5-diiodo-, monosodium salt. The molecular formula, molecular weight and structural formula of liothyronine sodium are given below.Cytomel tablets contain liothyronine sodium equivalent to liothyronine in 5 mcg, 25 mcg, and 50 mcg.
Inactive ingredients consist of calcium sulfate, corn starch, gelatin, stearic acid, sucrose and talc. Cytomel - Clinical Pharmacology Mechanism of ActionThyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis.
Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins.The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues. PharmacodynamicsThe onset of activity of liothyronine sodium occurs within a few hours.
Maximum pharmacologic response occurs within 2 or 3 days. PharmacokineticsAbsorptionT3 is almost totally absorbed, 95 percent in 4 hours.
The hormones contained in the natural preparations are absorbed in a manner similar to the synthetic hormones.DistributionLiothyronine sodium (T3) is not firmly bound to serum protein. The higher affinity of levothyroxine (T4) for both thyroid-binding globulin and thyroid-binding prealbumin as compared to triiodothyronine (T3) partially explains the higher serum levels and longer half-life of the former hormone.
Both protein-bound hormones exist in reverse equilibrium with minute amounts of free hormone, the latter accounting for the metabolic activity.EliminationMetabolismThe major pathway of thyroid hormone metabolism is through sequential deiodination. Approximately 80% of circulating T3 is derived from peripheral T4 by monodeiodination. The liver is the major site of degradation for both T4 and T3.
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T3 is further deiodinated to diiodothyronine. Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation.ExcretionThyroid hormones are primarily eliminated by the kidneys. A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces. The biological half-life is about 2–1/2 days. Nonclinical Toxicology Carcinogenesis, Mutagenesis, Impairment of FertilityAnimal studies have not been performed to evaluate the carcinogenic potential, mutagenic potential or effects on fertility of liothyronine sodium. How Supplied/Storage and HandlingCytomel tablets (round, white to off-white) are supplied as follows. StrengthTablet MarkingsNDC – bottles of 1005 mcgDebossed with KPI on one side and 115 on the other side60793-115-0125 mcgScored on one side and debossed with KPI and 116 on the other side60793-116-0150 mcgScored on one side and debossed with KPI and 117 on the other side60793-117-01Store between 15°C and 30°C (59°F and 86°F).
Patient Counseling InformationDosing and Administration. Instruct patients that Cytomel should only be taken as directed by their healthcare provider. Instruct patients to notify their healthcare provider should they become pregnant or breastfeeding or are thinking of becoming pregnant, while taking Cytomel.Important Information. Inform patients that the liothyronine in Cytomel is intended to replace a hormone that is normally produced by the thyroid gland.