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Encyclopedia > Levothyroxine
Systematic (IUPAC) name
CAS number 51-48-9
ATC code H03AA01
PubChem 853
DrugBank APRD00235
Chemical data
Formula C15H10I4NNaO4 
Mol. mass 798.86 (anhydrous)
Pharmacokinetic data
Bioavailability ~100%
Metabolism Mainly in liver, kidneys, brain and muscles
Half life ca. 7 days (in hyperthyroidism 3-4 days, in hypothyroidism 9-10 days)
Excretion Through feces and urine
Therapeutic considerations
Pregnancy cat.

A (FDA) Image File history File links Size of this preview: 442 × 600 pixelsFull resolution (811 × 1100 pixel, file size: 34 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... The Anatomical Therapeutic Chemical Classification System is used for the classification of drugs. ... A section of the Anatomical Therapeutic Chemical Classification System. ... PubChem is a database of chemical molecules. ... The DrugBank database available at the University of Alberta is a unique bioinformatics and cheminformatics resource that combines detailed drug (i. ... A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... For other uses, see Carbon (disambiguation). ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... For the record label, see Iodine Recordings. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... For sodium in the diet, see Edible salt. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... The molecular mass (abbreviated Mr) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... In pharmacology, bioavailability is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. ... Drug metabolism is the metabolism of drugs, their biochemical modification or degradation, usually through specialized enzymatic systems. ... It has been suggested that Effective half-life be merged into this article or section. ... The kidneys are important excretory organs in vertebrates. ... The pregnancy category of a pharmaceutical agent is an assessment of the risk of fetal injury due to the pharmaceutical, if it is used as directed by the mother during pregnancy. ...

Legal status

Prescription only The regulation of therapeutic goods, that is drugs and therapeutic devices, varies by jurisdiction. ...

Routes Oral, Intravenous

Levothyroxine, also known as 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. In pharmacology and toxicology, a route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ...

The EU has recently standardized the use of the name "levothyroxine" for the drug. Common brand names include ""Thyrax"", "Euthyrox", "Levaxin" and "Eltroxin" in Europe, and "Levoxyl" and "Synthroid" in the U.S. There are also numerous generic versions approved by the Food and Drug Administration. This article is about brands in marketing. ... A generic drug (pl. ... “FDA” redirects here. ...



This medicine is a hormone replacement usually given to patients with thyroid problems, specifically, hypothyroidism. It is also given to people who have Goitre or an enlarged thyroid gland. This article or section does not cite its references or sources. ... A goitre (BrE), or goiter (AmE) (Latin struma), also called a bronchocele, is a swelling in the neck (just below Adams apple or larynx) due to an enlarged thyroid gland. ...


It is recommended that levothyroxine be taken half an hour to an hour before meals to maximize its absorption. It is also recommended that the patient take the tablet with one glass of water to ease swallowing as well as to help the tablet dissolve for absorption.

Precautions and side effects

There are also foods and other substances that can interfere with absorption of thyroxine replacement. Avoid taking calcium and iron supplements within 4 hours of the medication and avoid taking soy products within 3 hours of the medication as these can reduce absorption of the medication.

Synthetic levothyroxine may have adverse side effects like: palpitations, nervousness, headache, difficulty sleeping, insomnia, swelling of the legs and ankles, weight loss and/or increased appetite. Some may be allergic to the medicine. If the patient develops a severe reaction to this drug like difficulty breathing, shortness of breath or swelling of the face and tongue it is imperative that the patient immediately seek medical attention.

Marketing and approvals

Levothyroxine 25mcg tablets
Levothyroxine 25mcg tablets

Synthroid is the most prescribed brand of T4 in United States. Synthroid was marketed in 1955,[1] but was not FDA approved at that time as it was considered "generally regarded safe". In the 1990s, in response to debate as to whether Synthroid was more effective than other levothyroxine preparations, (which ended up concluding that there was little difference between Synthroid and generic brands[2] all levothyroxine preparations were required to undergo the formal FDA approval process. Synthroid was approved by the FDA on 2002-07-24.[3] Image File history File links Metadata Size of this preview: 800 × 557 pixelsFull resolution (2182 × 1518 pixel, file size: 923 KB, MIME type: image/jpeg) These tablets were prescribed on the National Health Service for my use as a treatment for Hypothyroidism. ... Image File history File links Metadata Size of this preview: 800 × 557 pixelsFull resolution (2182 × 1518 pixel, file size: 923 KB, MIME type: image/jpeg) These tablets were prescribed on the National Health Service for my use as a treatment for Hypothyroidism. ... “FDA” redirects here. ...


  1. ^ Company Report on Abbott
  2. ^ WorstPills.org
  3. ^ FDA approval

External links

  • Detailed Euthyrox (Levothroid/Levothyroxine) Consumer Information: Uses, Precautions, Side Effects
  • Leaflet



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