thyroxine with a baseline correction.
Now, let me discuss some of the rationale behind the study design. First of all, the use of healthy subjects allows us to do a single-dose study and a single-dose crossover study is the most sensitive method for evaluating the true formulation differences between products and that's really what we're looking at. A single-dose study cannot be conducted in patients. A 600 microgram dose in healthy subjects provides concentrations that are significantly higher than the individual subject's baseline T4 values, and the farther away from the baseline that you actually get, the more accurate the evaluation of the products. The issue of nonlinearity is really not an issue since the subject is receiving the same amount of drug in each treatment period.
Regarding the bioequivalence measures that have been discussed this morning, total thyroxine is the preferred measure for demonstrating bioequivalence. It can be accurately measured in vivo and is the drug that is being administered to the subject. T3, on the other hand, is merely an active metabolite, and the Food and Drug Administration does not use active metabolites for