Levothyroxine sodium |
![]() Last updated: 16/09/2025 |
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(Also known as: L-thyroxine sodium) |
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A synthetic thyroid hormone replacement compound used in veterinary medicine | |
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Used to treat hypothyroidism (low thyroid hormone) and to prevent growth of goiters | |
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Dogs; Cats |
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Approved - usually supplied as a prescription only medicine to be authorised by a veterinarian (POM-V) | |
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Approved |
Chemical structure |
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Levothyroxine sodium exhibits chiral isomerism, due to the presence of a single asymmetric carbon atom bonded to the amino group in its molecular structure. This stereocentre allows for the existence of two forms: the L-isomer (levothyroxine) and the D-isomer (dextrothyroxine). Only the L-form occurs naturally (as thyroxine) and is biologically active. | |
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C₁₅H₁₂I₄NNaO₅ | |
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C1=C(C=C(C(=C1I)OC2=CC(=C(C(=C2)I)O)I)I)CC(C(=O)[O-])N.O.[Na+] | |
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C1=C(C=C(C(=C1I)OC2=CC(=C(C(=C2)I)O)I)I)C[C@@H](C(=O)[O-])N.O.[Na+] | |
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ANMYAHDLKVNJJO-LTCKWSDVSA-M | |
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InChI=1S/C15H11I4NO4.Na.H2O/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);;1H2/q;+1;/p-1/t12-;;/m0../s1 | |
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Yes |
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Common Name | Relationship | Link |
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levothyroxine sodium monohydrate | Hydrate | ![]() |
General status |
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Medicinal drug: synthetic thyroxime | |
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Synthetic hormone | |
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Synthetic | |
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Acts as endogenous thyroxine, stimulating metabolism, growth, development and differentiation of tissues | |
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[Thyroid hormone receptor alpha, Agonist], [Thyroid hormone receptor beta, Agonist] | |
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25416-65-3 | |
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55-03-8 | |
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200-221-4 | |
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23667619 | |
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Synthetic thyroid hormones: Thyroid hormones | |
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QH03AA01 | |
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No | |
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816.87 | |
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sodium;(2S)-2-amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoate;hydrate | |
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Commercial |
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Current | |||
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1949, first synthesised; 2000s, off-label animal use | |||
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Usually formulated as tablets for oral administration | |||
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The commercial production of levothyroxine sodium involves a highly controlled synthetic process designed to yield the biologically active L-isomer of thyroxine. The synthesis typically starts with iodinated precursors that undergo selective coupling and oxidation reactions to form the tetraiodinated diphenyl ether structure characteristic of thyroxine. Precision in stereochemistry is critical, as only the L-form mimics endogenous thyroid hormone activity. Once synthesised, the compound is converted into its sodium salt to enhance solubility, stability, and bioavailability. | |||
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Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used. |
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As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below. | ||||||||||
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Known metabolites |
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Terrestrial ecotoxicology |
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> 20 | F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment ) Rat4 = Verified data |
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General |
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> 20 | F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment ) Rat4 = Verified data |
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Metabolised mainly in liver & kidneys, eliminated via the faeces and urine | V3 V = ChemID Online Databases; Chemspider; PubChem. (ChemID ) 3 = Unverified data of known source |
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Health issues |
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Blood toxicant High doses may induce thyrotoxicosis which may cause weight loss, increased appetite, palpitations, nervousness, diarrhoea, abdominal cramps as well as other symptoms |
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Will emit toxic fumes when heated to decomposition | |||
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Not listed (Not listed) | |||
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None allocated | |||
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levothyroxine sodium | ||
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Record last updated: | 16/09/2025 |
Contact: | aeru@herts.ac.uk |
Please cite as: | Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242 |