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, transthyretin (previously called 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.Half-life elimination is 6–7 days for people with normal lab results; 9–10 days for people with hypothyroidism; 3–4 days for people with hyperthyroidism. Thyroid hormones are primarily eliminated by the kidneys (about 80%), with urinary excretion decreasing with age. The remaining 20% of T4 is eliminated in the stool. History
Thyroxine was first isolated in pure form in 1914, at the Mayo Clinic by Edward Calvin Kendall from extracts of hog thyroid glands. The hormone was synthesized in 1927 by British chemists Charles Robert Harington and George Barger. Society and culture
Economics
As of 2011, levothyroxine was the second-most commonly prescribed medication in the U.S., with 23.8 million prescriptions filled each year.In 2016, it became the most commonly prescribed medication in the U.S., with more than 114 million prescriptions. Available forms
Levothyroxine for systemic administration is available as an oral tablet, an intramuscular injection, and as a solution for intravenous infusion.
These regulations replaced the earlier sex verification rules.Following a series of legal challenges, regulations called the Eligibility Regulations for the Female Classification (Athletes with Differences of Sexual Development) were released on 1 May 2019. These regulations apply only to athletes who have a DSD, high testosterone and virilization, and no longer include hyperandrogenism from non-DSD-related causes such as PCOS. Such DSDs, often seen in people who have a Y chromosome and testes, include 5α‐reductase deficiency, partial androgen insensitivity, and congenital adrenal hyperplasia. Social definition
Cultural variation can define hyperandrogenism socially—apart from clinical and chemical definitions—to make some hair growth unacceptable even if it is considered clinically normal based on metrics like the Ferriman-Gallwey score. For example, only pubic and axillary hair may be tolerated in North American women, while other androgen-dependent hair such as growth on the upper lip, over the linea alba, on the thighs, and around the areola is not. Organizations
Professional organizations such as the Androgen Excess and PCOS Society exist to promote the research, treatment, diagnosis, and prevention of such disorders and to educate the public and scientific community about them. See also
Hypoandrogenism
Hypergonadism
Hypergonadotropic hypergonadism
Hypogonadism
Hyperestrogenism
Hypoestrogenism
Androgen-dependent condition

References


== External links ==