conferring bioequivalence, unless the active parent cannot be measured in vivo.
Finally TSH. TSH is a biomarker and it's an indirect measure. It's downstream from what is being administered and it's considerably more variable than thyroxine. It's also very easily influenced by other environmental factors, such as time of day and ambient temperature.
To kind of give you an idea of where each of these measures fits into this negative feedback system, let's start with the lower left-hand corner, with the L-T4 or T4 inputs. Once you have conversion to T3, the T3 has an inhibitory effect on the hypothalamus which ultimately results in a reduction in the amount of TSH secretion from the anterior pituitary, but this is not a mutually exclusive event. As mentioned before, other factors influence the TSH values.
According to the Code of Federal Regulations, in descending order of accuracy, sensitivity and reproducibility for determining bioavailability and bioequivalence of a drug product, the best choice for evaluating bioequivalence is the concentration of the