L-Thyroxine

Thevier (Glaxo Wellcome) L-Thyroxin "Henning" (Henning Berlin) numerous combination preparations... 

Levothyrox (Lipha Sant6) L-thyroxine Roche (Roche) GB Eltroxin (Goldshield)... 

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. 

Amino Acid Systems Glutamine binding sites, 46, 414 labeling of the active site of r-aspartate /3-decarboxylase with yS-chloro-r-ala-nine, 46, 427 active site of r-asparaginase reaction with diazo-4-oxonorvaline, 46, 432 labeling of serum prealbumin with N-bro-moacetyl-L-thyroxine, 46, 435 a pyridoxamine phosphate derivative, 46, 441. 

Thioamides are reducing agents. They inhibit thyroid hormone synthesis by inhibiting the peroxidase enzymatic system, which catalyzes oxidation of iodide ions and iodine that are consumed in food, which is necessary for iodination of tyrosine derivatives. Thus they reduce the concentration of free iodine necessary to react with tyrosine derivatives, and they can also block oxidative addition reactions of mono- and diiodtyrosines, which form L-thyroxine and L-triiodothyronin. 

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaT ). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak 8-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion. 

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... 

Thyroxine is absorbed best in the duodenum and ileum absorption is modified by intraluminal factors such as food, drugs, gastric acidity, and intestinal flora. Oral bioavailability of current preparations of L-thyroxine averages 80% (Table 38-1). In contrast, T3 is almost completely absorbed (95%). T4 and T3 absorption appears not to be affected by mild hypothyroidism but may be impaired in severe myxedema with ileus. These factors are important in switching from oral to parenteral therapy. For parenteral use, the intravenous route is preferred for both hormones. 

Paul TL, Kerrigan J, Kelly AM, Braverman LE, Baran DT. Long-term L-thyroxine therapy is associated with decreased hip bone density in premenopausal women. JAMA 1988 259(21) 3137-41. 

Hiasa Y, Ishida T, Aihara T, Bando M, Nakai Y, Kataoka Y, Mori H. Acute myocardial infarction due to coronary spasm associated with L-thyroxine therapy. Clin Cardiol 1989 12(3) 161-3. 

Kologlu S, Baskal N, Kologlu LB, Laleli Y, Tuccar E. Hirsutism due to the treatment with L-thyroxine in patients with thyroid pathology. Endocrinologie 1988 26(3) 179-85. 

Exley A, O Malley BP. Depression in primary hypothyroidism masquerading as inadequate or excessive L-thyroxine consumption. Q J Med 1989 72(269) 867-70. 

Medeiros-Neto GA. Osteopenia e tratamento com L-tirox-ina. [Osteopenia and treatment with L-thyroxine.] Rev Assoc Med Bras 1995 41(l) 34-6. 

Stall GM, Harris S, Sokoll LJ, Dawson-Hughes B. Accelerated bone loss in hypothyroid patients overtreated with L-thyroxine. Ann Intern Med 1990 113(4) 265-9. 

Faber J, Galloe AM. Changes in bone mass during prolonged subclinical hyperthyroidism due to L-thyroxine treatment a meta-analysis. Eur J Endocrinol 1994 130(4) 350-6. 

Appetecchia M. Effects on bone mineral density by treatment of benign nodular goiter with mildly suppressive doses of L-thyroxine in a cohort women study. Horm Res 2005 64(6) 293-8. 

Heijckmann AC, Huijberts MS, Geusens P, de Vries J, Menheere PP, Wolffenbuttel BH. Hip bone mineral density, bone turnover and risk of fracture in patients on long-term suppressive L-thyroxine therapy for differentiated thyroid carcinoma. Eur J Endocrinol 2005 153(l) 23-9. 

Galvan G. Hyperthyreosis factitia durch L-Thyroxinabusus ein Fallbericht. [Factitious hyperthyroidism caused by L-thyroxin abuse. Case report.] Acta Med Austriaca 1983 10(2-3) 79-81. 

Hack JB, Leviss JA, Nelson LS, Hoffman RS. Severe symptoms following a massive intentional L-thyroxine ingestion. Vet Hum Toxicol 1999 41(5) 323-6. 

Heyma P, Larkins RG, Higginbotham L, Ng KW. D-pro-pranolol and DL-propranolol both decrease conversion of L-thyroxine to L-triiodothyronine. BMJ 1980 281(6232) ... 

When TSH contacts its receptor-sites located throughout the thyroid gland a series of enzymic reactions occur using tyrosine and iodine as substrates or raw materials to produce and/or release L-Thyroxine (T-4). This is then released into the vascular system so it can circulate. It should be noted that T-4 is an active form of thyroid hormone. 

Cytomel is the synthetic form of T-3/L-triiodothyronine and was a commonly known trade or brand name among athletes. T-3/L-triiodothyronine is used as a form of thyroid hormone therapy mostly in Europe. Most bodybuilders favored this drug over synthetic forms of T-4/L-thyroxine due to its vastly superior activity level. 

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