- Molecular NameLevothyroxine
- Synonym(-)-Thyroxine; 3,3',5,5'-Tetraiodo-L-thyronine; L-Thryoxin; L-Thyroxine; Laevothyroxinum; Levo-t; Levothyroxin; Levothyroxine Sodium; O-(4-Hydroxy-3,5-diidophenyl)-3,5-diiodo-L-tyrosine; T4 levothyroxine; Tetraiodothyronine; THX; Thyroxine iodine
- Weight776.872
- Drugbank_IDDB00451
- ACS_NO51-48-9
- Show 3D model
- LogP (experiment)N/A
- LogP (predicted, AB/LogP v2.0)2.54
- pka2.2, 6.7, 10.1
- LogD (pH=7, predicted)1.97
- Solubility (experiment)N/A
- LogS (predicted, ACD/Labs)(ph=7)-4.71
- LogSw (predicted, AB/LogsW2.0)0.0
- Sw (mg/ml) (predicted, ACD/Labs)0.01
- No.of HBond Donors4
- No.of HBond Acceptors5
- No.of Rotatable Bonds5
- TPSA92.78
- StatusFDA approved
- AdministrationOral, Intravenous
- PharmacologyA synthetic form of thyroxine (thyroid hormone).
- Absorption_valueN/A
- Absorption (description)Incompletely and variably absorbed after oral administration. 48 to 80% of an administered dose may be absorbed.
- Caco_2N/A
- BioavailabilityN/A
- Protein bindingN/A
- Volume of distribution (VD)N/A
- Blood/Plasma Partitioning ratio (D_blood)N/A
- MetabollsmIt is metabolised, in the liver and kidney, by de-iodination to liothyronine (tri-iodothyronine) which is the principal active form of levothyroxine; further de-iodination to thyroacetic acid (4-p-hydroxyphenoxy-phenylacetic acid), and conjugation with glucuronic acid and sulfate also occur. Deamination and decarboxylation of levothyroxine to the tetrone is a further metabolic pathway. Elimination from the body is slow.
- Half life6~7 days which may be increased in pregnancy or myxoedema and decreased in hyperthyroidism.
- ExcretionAbout 30 to 55% of a dose is excreted in the urine and 20 to 40% is eliminated in the faeces; of the urinary material about 40% is thyroacetic acid and 20% is liothyronine. Endogenous serum-levothyroxine concentrations range from 50 to 120 μg/L in normal subjects. A minimum amount of the drug crosses the placenta and can be detected in breast milk.
- Urinary ExcretionN/A
- CleranceN/A
- ToxicityA 34-year-old male ingested approx. 900 tablets (a total of 720 mg) levothyroxine. He became lethargic 2 to 3 days after administration, had vomiting and insomnia on day 4; was agitated, aggressive, and incoherent on day 5 and was confused when he returned to hospital on day 6. While in hospital for 6 days, he was tachycardic. Free levothyroxine concentrations were >130 μg/L on day 6 and 12 μg/L on day 12. By day 15 he had lost 20 kg in weight. [J. B. Hack et al.,Vet. Hum. Toxicol.,1999, 41(5), 323–326.]
- LD50 (rat)N/A
- LD50 (mouse)N/A