levothyroxine products by the FDA greatly interests the members of the ATA. When L-T4 is used to treat thyroid disease, the patient must receive an accurate and predictable amount of hormone and obtain a reproducible biological effect with each dose. In the clinical setting, the dose is determined by a combination of the presence or absence of thyroid-related symptoms as well as results from thyroid blood tests, especially TSH. Multiple factors affect the final dose, including body mass, drug absorption and metabolism, the amount of residual functioning thyroid tissue, interference with absorption or metabolism by other medications or food, and patient compliance.
Hormones controlled by a biofeedback mechanism provide a unique situation in which the body provides an indication of whether or not the dosage is appropriate. Close monitoring of TSH concentrations enables practitioners to provide patients with an appropriate amount of medication to ensure that thyroid hormone levels fall within a narrow optimal physiological window.
We understand that bioequivalence for levothyroxine products is currently based on the design