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Levothyroxine (Molecule of the Month for November 2003)


There are several forms of Thyroid Disease - Hyperthyroidism, Hypothyroidism, Toxic Nodular Goiter, and Toxic Multi-nodular Goiter. The auto-immune disorders, Graves' Disease and Hashimoto's Disease can cause Thyroid Disease, but are more factually dysfunctions of the immune system that play havoc with the endocrine system. Each form of Thyroid Disease has one list of symptoms, which are all very similar, and one list of individual symptoms supposedly unique to that form. But in reality, the symptoms are as variant as the sufferers, although all fall within the list of the symptoms of thyroid disorders.

The thyroid is the prime controller of all metabolic processes. The hormones it produces can manage or mismanage your entire person. Thyroid Disease is not an uncommon condition. 8,000,000 people in America have it and don't know it. It can mask itself as many alternative conditions, and can be a devastating experience. Thyroxine (T4) is only produced by the thyroid gland in the body. The thyroid gland also produces triiodothyronine (T3), which is a biologically active hormone. Through the action of a selenium protein thyroxine is also transformed to triiodothyronine in the liver and the kidneys. This hormone is also produced locally in the pituitary gland and in the cerebral cortex. In therapy one uses the synthetically produced L-isomer (levothyroxine).

Levothyroxine is the drug of choice for the treatment of primary hypothyroidism. All forms of this disease (congenital, "spontaneous", end stage of an autoimmune thyroid disease [Hashimoto], after a thyroidectomy or a radio iodine therapy, etc.) respond to levothyroxine. The aim of the treatment is to normalize increased thyrotrophin levels (TSH). The periodical monitoring of these values makes an individual dosage possible. Specialists sometimes administer intravenous levothyroxine or triiodothyronine for myxoedema, the end stage of decompensated hypothyroidism. Levothyroxine is also effective for secondary hypothyroidism due to pituitary or hypothalamic disease; in this case monitoring of the free T4 index has to be performed.

The principal effect of thyroid hormones is to increase the metabolic rate of body tissues. The thyroid hormones are also concerned with growth and development of tissues in the young. The major thyroid hormones are L-thyroxine (T4) and L-triiodothyronine (T3). The amounts of T4 and T3 released from the normally functioning thyroid gland are regulated by the amount of thyrotropin (TSH) secreted from the anterior pituitary gland. T4 is the major component of normal thyroid gland secretions and is therefore the primary determinant of normal thyroid functions. T4 acts as a substrate for physiologic deiodination to T3 in the peripheral tissues. The physiologic effects of thyroid hormones are mediated at the cellular level primarily by T3. LEVOXYL (L-thyroxine) tablets taken orally provide T4 which upon absorption cannot be distinguished from T4 that is secreted endogenously.

Formal Chemical Name (IUPAC)

Picture of Levothyroxine

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Picture of Levothyroxine

C15 H11 I4 N O4

Update by Karl Harrison
(Molecule of the Month for November 2003 )