T4 Levothyroxine Sodium
Levothyroxine is a synthetic form of thyroxine T4, an endogenous hormone secreted by the thyroid gland, which is converted to its active metabolite, L-triiodothyronine (T3). T4 and T3 bind to thyroid receptor proteins in the cell nucleus and cause metabolic effects through the control of DNA transcription and protein synthesis. Like its naturally secreted counterpart, levothyroxine is a chiral compound in the L-form. Absorption of orally administered levothyroxine from the gastrointestinal tract ranges from 40 to 80%, with the majority absorbed from the jejunum and upper ileum. Levothyroxine absorption is increased by fasting and decreased in certain malabsorption syndromes, by certain foods, and with age. The bioavailability of the drug is decreased by dietary fiber. Greater than 99% of circulating thyroid hormones are bound to plasma proteins including thyroxine-binding globulin, thyroxine-binding prealbumin, and albumin. Only free hormone is metabolically active. The primary pathway of thyroid hormone metabolism is through sequential deiodination. The liver is the main site of T4 deiodination, and along with the kidneys are responsible for about 80% of circulating T3. In addition to deiodination, thyroid hormones are also excreted through the kidneys and metabolized through conjugation and glucuronidation and excreted directly into the bile and the gut where they undergo enterohepatic recirculation.
For more information on T4:
400mcg per mL in a 30mL bottle
|Chemical Names||3,5, 3′, 5′-Tetraiodo-L-thyronine|
|Molecular Weight||776.87 g/mol|