Medicine

Levothyroxine, also L-thyroxine, synthetic T4, or 3,5,3',5'-tetraiodo-L-thyronine, is a synthetic form of thyroxine (thyroid hormone). The natural hormone is chemically in the L-form, as is the pharmaceutical agent. Dextrothyroxine (D-thyroxine) briefly saw research as an anticholesterol agent but was pulled due to cardiac side-effects. The EU has recently standardized the use of the International Nonproprietary Name "levothyroxine" for the drug. Common brand names include Thyrax, Euthyrox, Levaxin, L-thyroxine and Eltroxin in Europe; Thyrox in South Asia; Eutirox, Levoxyl and Synthroid in North America. There are also numerous generic versions.

The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine (T4), which has a longer half life than T3. The ratio of T4 to T3 released in the blood is roughly 20 to 1. Thyroxine is converted to the active T3 (three to four times more potent than T4) within cells by deiodinases (5'-iodinase). These are further processed by decarboxylation and deiodination to produce iodothyronamine (T1a) and thyronamine (T0a).

Both excess and deficiency of thyroxine can cause disorders. Hyperthyroidism (an example is Graves Disease) 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. Thyrotoxicosis is often used interchangeably with hyperthyroidism, but there are subtle differences. Although thyrotoxicosis also refers to an increase in circulating thyroid hormones, it can be caused by the intake of thyroxine tablets or by an over-active thyroid, whereas hyperthyroidism refers solely to an over-active thyroid. Hypothyroidism (an example is Hashimoto's thyroiditis) is the case where

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 synthetic thyroxine form, is a stereoisomer of physiological thyroxine, which is metabolised more slowly and hence usually only needs once-daily administration. Natural desiccated thyroid hormones, also under the commercial name Armour Thyroid, is derived from pig thyroid glands, it is a "natural" hypothyroid treatment containing 20% T3 and traces of T2, T1 and calcitonin. Also available are synthetic combinations of T3/T4 in different ratios (such as Thyrolar) and pure-T3 medications

Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and are regulated by TSH made by the thyrotrophs of the anterior pituitary gland. Because the effects of T4 in vivo are mediated via T3 (T4 is converted to T3 in target tissues; T3 is 3- to 5- fold more active than T4). Thyroxine (3,5,3',5'-tetraiodothyronine) is produced by follicular cells of the thyroid gland. It is produced as the precursor thyroglobulin (this is not the same as TBG), which is cleaved by enzymes to produce active T4. Thyroxine is produced by attaching iodine atoms to the ring

Tricyanoaminopropene (TRIAP, TCAP, Malononitrile Dimer, 1,1,3-tricyano-2-amino-1-propene) is a nootropic drug which mimics the function of nerve growth factor and increases the growth of nerves and tissue regeneration both in isolated tissues[1] and in vivo. It stimulates the action of the enzyme choline acetyltransferase, resulting in increased acetylcholine production.[2] This then results in increased synthsis of RNA in many different tissues in the body. [3] However it also suppresses the production of thyroxine, causing temporary hypothyroidism which returns to normal once the drug is discontinued.[4] Tricyanoaminopropene reduces the amnesia produced by electroconvulsive shock,[5] and animal tests suggested nootropic activity,[6][7][8] but no beneficial

Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. Thyroid-stimulating hormone (TSH) activates the production of thyroxine (T4) and T3. This process is under regulation. In the thyroid, T4 is converted to T3. TSH is inhibited mainly by T3. The thyroid gland releases greater amounts of T4 than T3, so plasma concentrations of T4 are 40-fold higher than those of T3. Most of the circulating T3 is formed peripherally by deiodination of T4 (85%), a process that involves the removal of iodine from carbon 5 on the outer ring of T4. Thus, T4 acts as prohormone for T3. This thyroid hormone

Carbimazole is used to treat hyperthyroidism. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole. Methimazole prevents the peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin, hence reducing the production of the thyroid hormones T3 and T4 (thyroxine).

Due to the iodine content of the agent (37.3% by weight), abnormalities in thyroid function are common. Amiodarone is structurally similar to thyroxine (a thyroid hormone), which contributes to the effects of amiodarone on thyroid function. Both under- and overactivity of the thyroid may occur on amiodarone treatment. Measurement of free thyroxine (FT4) alone may be unreliable in detecting these problems and thyroid-stimulating hormone (TSH) should therefore also be checked every 6 months.[12] Hypothyroidism (slowing of the thyroid, called the Wolff-Chaikoff effect) occurs frequently; in the SAFE trial, which compared amiodarone with other medications for the treatment of atrial fibrillation, biochemical

Increases cardiac output Increases heart rate Increases ventilation rate Increases basal metabolic rate Potentiates the effects of catecholamines (i.e increases sympathetic activity) Potentiates brain development Thickens endometrium in females

Leave a Reply

Name (required)

Mail (will not be published) (required)

Website