Levothyroxine

This article is about levothyroxine as a pharmaceutical drug. For its role as a hormone, see Thyroid hormone.

Levothyroxine
Clinical data
Trade namesSynthroid, Levoxyl, Thyrax, Eltroxin, others
Other names3,5,3′,5′-Tetraiodo-L-thyronine
AHFS/Drugs.comMonograph
MedlinePlusa682461
License data
Pregnancy
category
Routes of
administration		Oral, intravenous
ATC code
Legal status
Legal status
Pharmacokinetic data
Bioavailability40-80%[5]
MetabolismMainly in liver, kidneys, brain and muscles
Elimination half-lifeca. 7 days (in hyperthyroidism 3–4 days, in hypothyroidism 9–10 days)
ExcretionFeces and urine
Identifiers
  • (S)-2-Amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoic acid
CAS Number
PubChem CID
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.000.093 Edit this at Wikidata
Chemical and physical data
FormulaC15H11I4NO4
Molar mass776.874 g·mol−1
3D model (JSmol)
Melting point231 to 233 °C (448 to 451 °F) [6]
Solubility in waterSlightly soluble (0.105 mg·mL−1 at 25 °C)[7] mg/mL (20 °C)
  • NC(Cc1cc(I)c(Oc2cc(I)c(O)c(I)c2)c(I)c1)C(O)=O
  • InChI=1S/C15H11I4NO4/c16-8-4-7(5-9(17)13(8)21)24-14-10(18)1-6(2-11(14)19)3-12(20)15(22)23/h1-2,4-5,12,21H, 3,20H2, (H, 22,23)/t12-/m0/s1 checkY
  • Key:XUIIKFGFIJCVMT-LBPRGKRZSA-N

Levothyroxine, also known as L-thyroxine, is a synthetic form of the thyroid hormone thyroxine (T4).[5][8] It is used to treat thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma.[5] It may also be used to treat and prevent certain types of thyroid tumors.[5] It is not indicated for weight loss.[5] Levothyroxine is taken orally (by mouth) or given by intravenous injection.[5] Levothyroxine has a half-life of 7.5 days when taken daily, so about six weeks is required for it to reach a steady level in the blood.[5]

Side effects from excessive doses include weight loss, trouble tolerating heat, sweating, anxiety, trouble sleeping, tremor, and fast heart rate.[5] Use is not recommended in people who have had a recent heart attack.[5] Use during pregnancy has been found to be safe.[5] Dosing should be based on regular measurements of thyroid-stimulating hormone (TSH) and T4 levels in the blood.[5] Much of the effect of levothyroxine is following its conversion to triiodothyronine (T3).[5]

Levothyroxine was first made in 1927.[8] It is on the World Health Organization's List of Essential Medicines.[9] Levothyroxine is available as a generic medication.[5] In 2021, it was the third most commonly prescribed medication in the United States, with more than 89 million prescriptions.[10][11]

  1. ^ "Levothyroxine Use During Pregnancy". Drugs.com. 31 July 2019. Retrieved 22 February 2020.
  2. ^ "FDA-sourced list of all drugs with black box warnings (Use Download Full Results and View Query links.)". nctr-crs.fda.gov. FDA. Retrieved 22 October 2023.
  3. ^ "THOXINE (Accord Healthcare Pty Ltd)". Therapeutic Goods Administration.
  4. ^ "Regulatory Decision Summary - Tirosint". Health Canada. 23 October 2014. Retrieved 7 June 2022.
  5. ^ a b c d e f g h i j k l m "Levothyroxine Sodium". The American Society of Health-System Pharmacists. Archived from the original on 21 December 2016. Retrieved 8 December 2016.
  6. ^ Harington CR (1926). "Chemistry of Thyroxine: Constitution and Synthesis of Desiodo-Thyroxine". The Biochemical Journal. 20 (2): 300–313. doi:10.1042/bj0200300. PMC 1251714. PMID 16743659.
  7. ^ DrugBank DB00451
  8. ^ a b King TL, Brucker MC (2010). Pharmacology for Women's Health. Jones & Bartlett Publishers. p. 544. ISBN 978-1-4496-5800-7. Archived from the original on 10 September 2017.
  9. ^ World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
  10. ^ "The Top 300 of 2021". ClinCalc. Archived from the original on 15 January 2024. Retrieved 14 January 2024.
  11. ^ "Levothyroxine - Drug Usage Statistics". ClinCalc. Retrieved 14 January 2024.