Check Orange Book at for more current information on preparations designated therapeutically equivalent by the FDA. Due to narrow therapeutic index, American Thyroid Association (ATA) and American Association of Clinical Endocrinologists (AACE ) recommend not to use levothyroxine sodium preparations interchangeably.Antidepressants - Tricyclics (e.g., Amitriptyline) - Tetracyclics (e.g., Maprotiline) - Selective Serotonin Reuptake Inhibitors (SSRI s; e.g., Sertraline) Concurrent use of tri/tetracyclic antidepressants and levothyroxine may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines.
Cardiac Glycosides Serum digitalis glycoside levels may be reduced in hyperthyroidism or when the hypothyroid patient is converted to the euthyroid state. Therapeutic effect of digitalis glycosides may be reduced. Cytokines - Interferon- - Interleukin-2 Therapy with interferon- has been associated with the development of antithyroid microsomal antibodies in 20 of patients and some have.Concomitant use of these agents impairs the compensatory increases in clotting factor synthesis. Prothrombin time should be carefully monitored in patients taking levothyroxine and oral anticoagulants and the dose of anticoagulant therapy adjusted accordingly.
Antacids - Aluminum Magnesium Hydroxides - Simethicone Bile Acid Sequestrants - Cholestyramine - Colestipol. Calcium Carbonate Cation Exchange Resins - Kayexalate Ferrous Sulfate Orlistat. Sucralfate Concurrent use may reduce the efficacy of levothyroxine by binding and delaying or preventing absorption, potentially resulting in hypothyroidism.Hyperthyroidism may develop over several weeks and may persist for several months after therapy discontinuation. Amiodarone may induce hyperthyroidism by causing thyroiditis. Drugs that may decrease T 4 absorption, which may result in hypothyroidism.
162 163 Initially, monitor response to therapy about every 68 weeks. Once normalization of thyroid function and serum TSH concentrations has been achieved, patients may be evaluated less frequently (i.e., every 612 months).Drugs that may alter T 4 and T 3 serum transport - but FT 4 concentration remains normal; and therefore, the patient remains euthyroid. Drugs that may increase serum TBG concentration Drugs that may decrease serum TBG concentration Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen Androgens / Anabolic Steroids Asparaginase.
Oral cholecystographic agents and amiodarone are slowly excreted, producing more prolonged hypothyroidism than parenterally administered iodinated contrast agents. Long-term aminoglutethimide therapy may minimally decrease T 4 and T 3 levels and increase TSH, although all values remain within normal limits in most patients.Specific indications include subclinical hypothyroidism and primary (thyroidal secondary (pituitary and tertiary (hypothalamic) hypothyroidism. Slideshow: Synthroid: The Hardest Working Drug Around? Considered drug of choice for the treatment of congenital hypothyroidism (cretinism).
However, serum T 4 levels are usually normal but may occasionally be slightly increased. In patients treated with large doses of propranolol ( 160 mg/day T 3 and T 4 levels change slightly, TSH levels remain normal, and patients are clinically euthyroid.A Oral Administration Administer orally on an empty stomach, preferably one-half to one hour before breakfast or the first food of the day. Administer Levoxyl tablets with a full glass of water to avoid choking, gagging, or difficulty in swallowing the tablet.
Phenytoin and carbamazepine reduce serum protein binding of levothyroxine, and total- and free- T 4 may be reduced by 20 to 40, but most patients have normal serum TSH levels and are clinically euthyroid.161 Dosage Available as levothyroxine sodium; dosage is expressed in terms of the salt. Adjust dosage carefully according to clinical and laboratory response to treatment. Avoid undertreatment or overtreatment. (See Therapy Monitoring under Cautions.) Initiate dosage at a lower level in geriatric patients, in patients with functional or ECG evidence of cardiovascular disease, and in.
Foods that decrease absorption of levothyroxine (e.g., soybean infant formula, soybean flour, cotton seed meal) should not be used for administering levothyroxine. IV Administration For solution compatibility information, see Compatibility under Stability.A Used IV for treatment of myxedema coma or other conditions when rapid thyroid replacement is required. Pituitary TSH Suppression Treatment or prevention of various types of euthyroid goiters, including thyroid nodules, subacute or chronic lymphocytic thyroiditis (Hashimotos thyroiditis and multinodular goiter.
The fetus, neonate, elderly and euthyroid patients with underlying thyroid disease (e.g., Hashimoto's thyroiditis or with Grave's disease previously treated with radioiodine or surgery) are among those individuals who are particularly susceptible to iodine-induced hypothyroidism.Growth Hormones - Somatrem - Somatropin Excessive use of thyroid hormones with growth hormones may accelerate epiphyseal closure. However, untreated hypothyroidism may interfere with growth response to growth hormone. Ketamine Concurrent use may produce marked hypertension and tachycardia; cautious administration to patients receiving thyroid hormone therapy is recommended.
An initial increase in serum FT 4 is followed by return of FT 4 to normal levels with sustained therapeutic serum salicylate concentrations, although total-T 4 levels may decrease by as much as 30.Drugs that may alter T 4 and T 3 metabolism Drugs that may increase hepatic metabolism, which may result in hypothyroidism Carbamazepine Hydantoins Phenobarbital Rifampin Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of levothyroxine, resulting in increased levothyroxine requirements.
144 The following are considered to be therapeutically equivalent to at least 1 reference listed drug: Levoxyl, Synthroid, Unithroid, and nonproprietary (generic) levothyroxine sodium preparations manufactured by Mylan, Sandoz, or Lannett.Calcium carbonate may form an insoluble chelate with levothyroxine, and ferrous sulfate likely forms a ferric-thyroxine complex. Administer levothyroxine at least 4 hours apart from these agents. Patients treated concomitantly with orlistat and levothyroxine should be monitored for changes in thyroid function.
Sympathomimetics Concurrent use 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.Continued administration results in a decrease in serum T 4 and normal FT 4 and TSH concentrations and, therefore, patients are clinically euthyroid. Salicylates inhibit binding of T 4 and T 3 to TBG and transthyretin.
Patients who have antithyroid antibodies before treatment are at higher risk for thyroid dysfunction during treatment. Interleukin-2 has been associated with transient painless thyroiditis in 20 of patients. Interferon- and - have not been reported to cause thyroid dysfunction.It should be noted that actions of particular beta-adrenergic antagonists may be impaired when the hypothyroid patient is converted to the euthyroid state. Short-term administration of large doses of glucocorticoids may decrease serum T 3 concentrations by 30 with minimal change in serum T 4 levels.
Drugs that alter thyroid hormone secretion. Drugs that may decrease thyroid hormone secretion, which may result in hypothyroidism. Aminoglutethimide Amiodarone Iodide (including iodine-containing radiographic contrast agents) Lithium Methimazole Propylthiouracil (PTU) Sulfonamides Tolbutamide Long-term lithium therapy can result in goiter in up to 50 of patients, and either subclinical or overt hypothyroidism, each in up to.Methylxanthine Bronchodilators - (e.g., Theophylline) Decreased theophylline clearance may occur in hypothyroid patients; clearance returns to normal when the euthyroid state is achieved. Radiographic Agents Thyroid hormones may reduce the uptake of 123 I, 131 I, and 99m Tc.
Toxic effects may include increased risk of cardiac arrhythmias and CNS stimulation; onset of action of tricyclics may be accelerated. Administration of sertraline in patients stabilized on levothyroxine may result in increased levothyroxine requirements.The following dosages have been recommended: Dosage for Management of Hypothyroidism in Pediatric Patients a160 Age Daily Dose mcg/kg mcg or 810 mcg/kg 6 mcg or 68 mcg/kg