particularly with oral T4, we have an instance where one can actually measure biological equivalence; that is, the effect on a tissue of the body, which is what bioequivalence should truly mean. Measurement of serum TSH should be done following an appropriate length of time, four to six weeks, to account for the long half-life of L‑T4. This would allow the medication's true biological equivalence to be assessed under clinically relevant conditions.
The ATA recognizes the complex nature of the issues being discussed today. Our main interest is to ensure that all L-T4 preparations are reliable sources of thyroxine replacement and that any determination of bioequivalence for such preparations be based both on pharmacologic and therapeutic bioequivalence. Therefore, we feel it imperative that the biological effect of L-T4 as measured by TSH be part of any method the FDA considers for evaluating equivalency of such preparations.
DR. KIBBE: Thank you, Dr. Robbins.
Our next speaker on the schedule is James Hennessey.