Chemical structure of thyroxine
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Liothyronine Sodium

The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. An important component in the synthesis is iodine. The major form of thyroid hormone in the blood is thyroxine (T4). This is converted to the active T3 within cells by deiodinases. These are further processed by decarboxylation and deiodination to produce iodothyronamine (T1a) and thyronamine (T0a). more...

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Circulation

Most of the thyroid hormone circulating in the blood is bound to transport proteins :

  • Thyroxine-binding globulin (TBG)
  • Thyroid-binding prealbumin (TBPA) - this protein is also responsible for the transport of retinol, and so now has the preferred name of transthyretin (TTR)
  • albumin.

Only a very small fraction of the circulating hormone is free (unbound) - T4 0.03% and T3 0.3%. This free fraction is biologically active, hence measuring concentrations of free thyroid hormones is of great diagnostic value. These values are referred to as fT4 and fT3. Another critical diagnostic tool is the amount of thyroid-stimulating hormone that is present. When thyroid hormone is bound, it is not active, so the amount of free T3/T4 is what is important. For this reason, measuring total thyroxine in the blood can be misleading.

Function

The thyronines act on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline).The thyroid hormones are essential to proper development and differentiation of all cells of the human body. To various extents, they regulate protein, fat and carbohydrate metabolism. But they have their most pronounced effects on how human cells use energetic compounds. Numerous physiological and pathological stimuli influence thyroid hormone synthesis.

The thyronamines function via some unknown mechanism to inhbit neuronal activity; this plays an important role in the hibernation cycles of mammals. One effect of administering the thyronamines is a severe drop in body temperature.

Related diseases

Both excess and deficiency of thyroxine can cause disorders.

  • Thyrotoxicosis or hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine, free triiodothyronine, or both. It is a common disorder that affects approximately 2% of women and 0.2% of men.
  • Hypothyroidism is the case where there is a deficiency of thyroxine.

Medical use of thyroid hormones

Both T3 and T4 are used to treat thyroid hormone deficiency (hypothyroidism). They are both absorbed well by the gut, so can be given orally. Levothyroxine, the most commonly used form, is a stereoisomer of physiological thyroxine, which is metabolised more slowly and hence usually only needs once-daily administration.

Thyronamines have no medical usages yet, though their use has been proposed for controlled induction of hypothermia which causes the brain to enter a protective cycle, useful in preventing damage during ischemic shock.

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Jones Medical acquires two endocrine products from SmithKline Beecham Corp.; acquisition is fifth in past 22 months
From Business Wire, 6/30/97

ST. LOUIS--(BUSINESS WIRE)--June 30, 1997--Jones Medical Industries Inc. (NASDAQ:JMED) today announced the $22.8 million acquisition of Cytomel(R) (liothyronine sodium tablets) and Triostat(R) (liothyronine sodium injection) from SmithKline Beecham Corp. (SKB).

Cytomel(R) is a T3 thyroid replacement hormone used to treat various chronic thyroid disorders. Triostat(R) is an injectable form of T3 used to treat more acute hypothyroid disorders. Both products are marketed under approved New Drug Applications (NDA).

Cytomel(R) has not been actively promoted in over 15 years and Triostat(R) is a relatively new drug, having received its NDA in 1991. These products will be promoted by JMED's sales organization.

Dennis M. Jones, chairman and CEO, said, "The addition of two strategic sole source products to our growing endocrine sales focus is very exciting. As we continue to grow our leading thyroid products, Levoxyl(R) (T-4) and Tapazole(R), (Methimazole, USP) the two new products will help to further develop JMED's endocrine franchise."

Jones Medical Industries Inc. is an emerging specialty pharmaceutical manufacturer with 1996 sales of $100.2 million and a five-year compounded growth rate of 28 percent. The company's strategy is to continue building a portfolio of growing products through the acquisition of under-promoted, pre-approved products from other firms. This strategy has allowed JMED to avoid the risks associated with new drug development and the lengthy and costly Food and Drug Administration approval process. The acquisition of the two SKB products is JMED's 16th acquisition to date and the fifth in the past 22 months.

For more information contact Investor Relations at 314/576-6100.

CONTACT: Jones Medical Industries Inc.

Investor Relations, 314/576-6100

COPYRIGHT 1997 Business Wire
COPYRIGHT 2004 Gale Group

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