Levothyroxine thyroid

See also Endocrine System Levothyroxine Thyroid Extract. 

Weitzman, S. P. Ginsburg, K. C. et al. (2009). "Colesevelam hydrochloride and lanthanum carbonate interfere with the absorption of levothyroxine." Thyroid, 19(1), 77-9. 

Sodium Levothyroxine. As one of the active principles of the thyroid gland, sodium levothyroxine [55-03-8] (levothyroxine sodium) can be obtained either from the thyroid glands of domesticated animals (10) or synthetically. It should contain 61.6—65.5% iodine, corresponding to 100 3% of the pure salt calculated on an anhydrous basis. Its chiral purity must also be ascertained because partial racemi2ation may occur during synthesis and because dl-T is available commercially. Sodium levothyroxine melts with decomposition at ca 235°C. It is prepared as pentahydrate [6106-07-6] from... 

Promoting an Optimai Response to Therapy Thyroid hormones are administered once a day, early in the morning and preferably before breakfast. An empty stomach increases the absorption of the oral preparation. Levothyroxine (Synthroid) also can be given intravenously and is prepared for administration immediately before use ... 

Lithium is concentrated in the thyroid gland and can impair thyroid hormone synthesis. Although goiter is uncommon, as many as 30% of patients develop at least transiently elevated thyroid-stimulating hormone values. Lithium-induced hypothyroidism is not usually an indication to discontinue the drug. Patients can be supplemented with levothyroxine if continuation of lithium is desired.30... 

Despite the availability of a wide array of thyroid hormone products, it is clear that synthetic levothyroxine (LT4) is the treatment of choice for almost all patients with hypothyroidism. LT4 mimics the normal physiology of the thyroid gland, which secretes mostly T4 as a prohormone. As needed, based on metabolic demands, peripheral tissues convert thyroxine (T4)... 

Levothyroxine (L-thyroxine, T4) is the drug of choice for thyroid hormone replacement and suppressive therapy because it is chemically stable, relatively inexpensive, free of antigenicity, and has uniform potency however, any of the commercially available thyroid preparations can be used. Once a particular product is selected, therapeutic interchange is discouraged. 

Because T3 (and not T4) is the biologically active form, levothyroxine administration results in a pool of thyroid hormone that is readily and consistently converted to T3. 

Up to 30% of patients on maintenance lithium therapy develop transiently elevated serum concentrations of thyroid-stimulating hormone, and 5% to 35% of patients develop a goiter and/or hypothyroidism, which is dose-related and more likely to occur in women. This is managed by adding levothyroxine to the regimen. 

Q76 Levothyroxine sodium is the synthetically prepared sodium salt of the natural isomer of thyroid hormone. Levothyroxine sodium tablets are unstable and require administration on an empty stomach. 

Levothyroxine is used to treat hypothyroidism (an underactive thyroid gland). Thyroid hormone can be made from beef and pork thyroid, but this lacks standardization and it is difficult to control dosage. The synthetic drug is more desirable. Levothyroxine is one of two important thyroid hormones. It is converted into the second important hormone, liothyronine, in the body. The key step in the synthesis of structures such as levothyroxine is the substitution of an iodonium salt by an iodinated phenol. Siql-like reactions on an aromatic ring are not common, but an iodonium salt provides a good leaving group. 

Hypothyroidism (myxedema) results when there is a breakdown of thyroid hormone production in the thyroid gland. Treatment consists of replacing this hormone with aforementioned drugs. Treatment with levothyroxine, 3,5,3, 5 -tetraiodothyronine, is preferred. Lyothyronin, L-3,5,5 -triiodothyronine, is also used, as is lotrix, a mixture of levothyroxine and levothyronine in a 4 1 ratio. Of the drugs of animal origin, thyroidin and thy-roglobulin (proloid) are used. 

Levothyronine has properties of levothyroxine however, it acts faster and binds less with blood proteins. Indications for using levothyronine are the same as with levothyroxine -hypothyroidism, euthyroid goiters, thyroiditis however, its use is considered more appropriate in the first stage of treatment. Synonyms of this drug are tibon, cinomel, tertroxin, and others. 

TSH suppression in well-differentiated thyroid cancer and thyroid nodules -The target level for TSH suppression in these conditions has not been established in controlled studies. In addition, the efficacy of TSH suppression for benign nodular disease is controversial. Therefore, individualize the dose of levothyroxine used for TSH suppression based on the specific disease and the patient being treated. 

In the treatment of well-differentiated (papillary and follicular) thyroid cancer, levothyroxine is used as an adjunct to surgery and radioiodine therapy. Generally, TSH is suppressed to less than 0.1 milliunits/L, and this usually requires a levothyroxine dose of greater than 2 mcg/kg/day. However, in patients with high-risk tumors, the target level for TSH suppression may be less than 0.01 milliunits/L. 

Exchange therapy - Nhen switching a patient to liothyronine from thyroid levothyroxine or thyroglobulin, discontinue the other medication, initiate liothyronine at a low dosage, and increase gradually according to the patient s response. Liothyronine has a rapid onset of action and that residual effects of the other thyroid preparation may persist for the first several weeks of therapy. 

Autoimmune polyglandular syndrome-Chron c autoimmune thyroiditis may occur in association with other autoimmune disorders. Treat patients with concomitant adrenal insufficiency with replacement glucocorticoids prior to initiation of treatment. Failure to do so may precipitate an acute adrenal crisis when thyroid hormone therapy is initiated. Patients with diabetes mellitus may require upward adjustments of their antidiabetic therapeutic regimens. Nontoxic diffuse goiter or nodular thyroid disease Use caution when administering levothyroxine to patients with nontoxic diffuse goiter or nodular thyroid disease in order to prevent precipitation of thyrotoxicosis. If the serum TSH is already suppressed, do not administer levothyroxine. 

Levothyroxine sodium (Levothwid, Synthroid, Levoxine) is the sodium salt of the naturally occurring levorota-tory isomer of T4. It is the preparation of choice for maintenance of plasma T4 and T3 concentrations for thyroid hormone replacement therapy in hypothyroid patients. It is absorbed intact from the gastrointestinal tract, and its long half-life allows for convenient once-daily administration. Since much of the T4 is deiodi-nated to T3, it is usually unnecessary to use more expensive preparations containing bothX4 and Tj.The aim is to establish euthyroidism with measured serum concentrations of T4, T3, and TSH within the normal range. 

Liotrix (Euthroid, Thywlar) is a 4 1 mixture of levothyroxine sodium and liothyronine sodium. Like levothyroxine, liotrix is used for thyroid hormone replacement therapy in hypothyroid patients. Although the idea of combining T4 and T3 in replacement therapy so as to mimic the normal ratio secreted by the thyroid gland is not new, it does not appear that liotrix offers any therapeutic advantage over levothyroxine alone. 

Levothyroxine (also marketed as Levoxyl, Levothroid, Synthroid, or L-thyroxine sodium) is the only thyroid system prescription that has recently featured prominently among the top 200 medications in the United States. Thus, 75.1 million, 80.7 million, and 79.4 million levothyroxine prescriptions were dispensed in 2003, 2004, and 2005, respectively. At these rates, levothyroxine by itself comprised 3.5, 2.9, and 3.4% of the total prescriptions in the top 200 most popular drugs in the United States in 2003, 2004, and 2005, respectively, making it the most prescribed drug. Levothyroxine is a synthetic version of the natural hormone thyroxine, which is released by the thyroid gland. The natural hormone is important in the development of fetuses and newborns, playing a role in cmcial processes such as the development... 

Levothyroxine is taken orally or intravenously and is normally prescribed to treat hypothyroidism or to suppress the release of thyroid hormone so as to manage cancerous thyroid nodules (i.e., thyroid cancer) and growth of goiters. Other less frequently prescribed thyroid and parathyroid drugs include methimazole (Tapazole), various iodides, lithioronine (Triostat), and liotrix (Thyrolar). 

Endoaine levothyroxine/amino acid Eltroxin/ thyroid gland of rm... 

Thyroid hormones levothyroxine sodium liothyronine sodium thyroid... 

Lithium Plus Thyroid Supplementation. Treatment-resistant and rapid-cycling bipolar patients may have an increased frequency of thyroid dysfunction. Further, some patients suffer from subclinical hypothyroidism and improve with the addition of thyroid supplementation. In this context, several case reports involving this population found that high doses of the thyroid hormone levothyroxine sodium (T ) were clinically beneficial (122,123 and 124). Kusalic (1.25) found that 6 of 10 rapid cyclers had hypothyroidism, based on their thyrotropin-releasing hormone stimulation tests. Further, the average number of mood episodes per year decreased by more than 75% (i.e., from 9.7 to 2.2) after thyroxine was added to the treatment regimen. 

The only effective treatment is replacement therapy with thyroid hormones. Levothyroxine, a synthetic levoisomer of thyroxine (T4), is the drug of choice since it is stable, relatively inexpensive, free of antigenicity, and of uniform potency. It results in a pool of thyroid hormone that is rapidly converted into the more potent T3. Levothyroxine can be administered orally or... 

See the Preparations Available section at the end of this chapter for a list of available preparations. These preparations may be synthetic (levothyroxine, liothyronine, liotrix) or of animal origin (desiccated thyroid). 

Synthetic levothyroxine is the preparation of choice for thyroid replacement and suppression therapy because of its stability, content uniformity, low cost, lack of allergenic foreign protein, easy laboratory measurement of serum levels, and long half-life (7 days), which permits once-daily administration. In addition, T4 is converted to T3 intracellularly thus, administration of... 

Levothyroxine (T4 ) Activation of nuclear receptors results in gene expression with RNA formation and protein synthesis Hypothyroidism See Table 38-1 maximum effect seen after 6-8 weeks of therapy Toxicity See Table 38-4 for symptoms of thyroid excess... 

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