Latest research on Levothyroxine

The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form triiodothyronine which exerts a broad spectrum of stimulatory effects on cell metabolism. [PubChem]

Latest findings

After exclusion of women on thyroid-related medications (Levothyroxine n=18, Propylthiouracil n=3) and women with overt biochemical hypothyroidism (n=10) or hyperthyroidism (n=1) on the blood samples, data from 956 women were included in this study. [source, 2016]
The Thyroid is absent, the hormone levels are low, the physician prescribes a dose of Levothyroxine to replace what the body would otherwise manufacture, and that resolves the problem. [source, 2016]
Synthetic levothyroxine (L-T4) has been available since the 1960s, and despite its availability for 60 years physicians can be divided in their treatment of these patients. [source, 2016]
Standard of care is to titrate the L-T4 to suppress the serum thyroid-stimulating hormone (TSH) level, which is otherwise trophic for growth of normal as well as malignant thyroid cells. [source, 2016]
In the absence of a Thyroid gland, exogenous L-T4 is efficiently converted to T3. [source, 2016]
Serum T3 levels remain stable after L-T4 administration but vary widely after oral administration of liothyronine (L-T3). [source, 2016]
Moreover, L-T4 is a better regulator of TSH secretion as it is more likely than T3 to pass the blood–brain barrier. [source, 2016]
This is why L-T4 has been the drug of choice for long-term treatment of athyreotic individuals.14 [source, 2016]
There are many factors that can interfere with L-T4 bioavailability and efficacy that need to be taken into consideration when prescribing THR therapy. [source, 2016]
The adequacy of L-T4 replacement dose depends, among other things, on the patient’s age, sex, menopausal status, and body weight. [source, 2016]