FDA Warning Deletion Response

August 3, 2005

Steven Galson, M.D.
Director, Center for Drug Evaluation and Research
Food and Drug Administration
5600 Fishers Lane, HFD-240
Rockville, MD 20857

Dear Dr. Galson:
We are writing on behalf of the American Thyroid Association, The Endocrine Society, and the American Association of Clinical Endocrinologists to express our deep concern and dismay that FDA has recently instructed some—and perhaps all thyroxine manufacturers—to delete the warning that patients have retitration of their thyroxine dose when they are switched between brands.

At our recent joint workshop, FDA itself acknowledged that not all thyroxine brands have been determined to be interchangeable. FDA further pledged to cooperate in heightening public awareness of this fact. As you are aware, our societies—representing this country’s clinical experts in thyroid disease management—also still have serious concerns about the lax bioequivalence standard that has been employed to approve certain thyroxine products as therapeutically equivalent.

In light of these facts, we find FDA’s action to remove the warning regarding dose retitration after switching brands to be inconsistent and irresponsible. It appears to neglect the welfare of 13 million Americans who depend on precise dosing of their thyroxine, which is widely recognized to be a narrow therapeutic index drug.

Consequently, we ask that you defer this action until there has been an opportunity to explain the agency’s reasoning and consider our serious concerns. We will be calling you soon to set up a meeting to discuss this important issue, and to explore the other items that we discussed pursuing at our joint workshop.

Yours truly,

Paul W. Ladenson, MD President American Thyroid Association	Leonard Wartofsky, MD President-Elect The Endocrine Society	Carlos R. Hamilton, Jr., MD, FACE Immediate Past President American Assn. of Clinical Endocrinologists

cc: Lester M. Crawford, DVM, PhD, Commissioner