FDA Re-Opens Its Public Comment Period on Levothyroxine Sodium Therapeutic Equivalence (Brand Switching)

Letter from ThyCa: Thyroid Cancer Survivors’ Association, Inc. 
September 2005

Dear Friends,

I invite you to read this message and to write to the FDA (using the FDA’s online comment form, as explained below) prior to September 23, 2005, on an issue of critical importance to thyroid cancer patients.

The issue is Levothyroxine Sodium Therapeutic Equivalence. The informal term for this issue is “brand switching.”

This is a chance for all of us to make our voices heard.

The FDA has re-opened its public comment period on this issue. We now have the opportunity to try to get the FDA to reverse a decision it made more than a year ago regarding Levothyroxine Sodium Therapeutic Equivalence (brand switching).

To summarize:

In 2004, the FDA ruled that some different brands of levothyroxine sodium are bioequivalent. Because of this ruling, pharmacies are allowed to switch brands when they refill a prescription, without informing the physician or the patient.

ThyCa does not support one levothyroxine brand over another. We advocate the importance of sticking with the brand of levothyroxine you took when you had your blood measured. This issue is important, because the FDA ruling means that our levothyroxine can be changed and no one will request (or pay for) a blood test on our behalf.

The FDA did not consult the endocrinology leadership before deciding. The American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE), and The Endocrine Society (TES) all oppose this decision. Immediately after the FDA ruling, they urged the FDA to reverse its decision. ThyCa: Thyroid Cancer Survivors’ Association, Inc., has supported their efforts, both in ThyCa’s public comments and in written messages.

On May 23, 2005, the FDA and the ATA, AACE, and TES held a day-long joint public meeting.

Speakers on behalf of the professional thyroid and endocrinology associations included two of ThyCa’s medical advisors, Paul Ladenson, M.D. of Johns Hopkins, who also is President of the ATA, and Steven Sherman, M.D. of M.D. Anderson Cancer Center.

Additional speakers from ATA, AACE, and TES included James Hennessey, M.D. of Brown University; E. Chester Ridgway, M.D., University of Colorado Health Sciences Center and 2003-2004 President of The Endocrine Society; and Leonard Wartofsky, M.D. M.P.H. of the Washington Hospital Center, the Uniformed Services University of the Health Sciences, and Georgetown University Medical School (who is also the President-Elect of The Endocrine Society).

ThyCa: Thyroid Cancer Survivors’ Association presented a statement during the public comment period, and followed with a written statement during the FDA’s open docket period.

This web page has the full transcript of the May 23 meeting:
ThyCa’s comments start on page 128 of the transcript. ThyCa’s web site has background information and ThyCa’s statement.

The FDA has now re-opened its docket for public comments on this topic. The docket will remain open until September 23, 2005. You may send your comments online, via this web site page:

All comments must be received by the FDA by September 23, 2005.

The docket number and title are Docket Number 2005N-0137, Levothyroxine Sodium Therapeutic Equivalence; Public Meeting. (There are many other dockets on this FDA page. Please check to see that your comments use the Levothyroxine Sodium comment form.)

This is our chance to influence a decision that is crucial to the health of thyroid cancer patients.

Please help. Please write to the FDA as soon as possible, because the deadline is approaching. Read the further details and key points below, and write to the FDA, using the online form, by September 23, 2005.

If you have any questions, please write to thyca@thyca.org.

Wishing you all good health.

Gary Bloom
Board Chair
ThyCa: Thyroid Cancer Survivors’ Association, Inc.


  • ATA, AACE, and TES pointed out that the FDA did not consult with the thyroidology/endocrinology associations and endocrinology leadership before it made its decision.
  • ATA, AACE, and TES explained that endocrinology research and clinical experience demonstrate clearly that different brands of levothyroxine are not bioequivalent.
  • They also noted that brand switching is particularly risky to the health of vulnerable populations, including thyroid cancer patients. This issue is also important to other thyroid patients.
  • Thyroid cancer specialist physicians agree that thyroid cancer patients with papillary or follicular thyroid cancer or one of their variants should stay on the same brand, because different brands produce different TSH levels at the same dose.
  • Thyroid cancer patients need to maintain an appropriate TSH level to prevent growth or recurrence of our thyroid cancer. Switching brands makes it impossible to maintain the TSH suppression that most of us need. Switching brands requires re-testing for TSH level after 6 weeks. Any decision to switch should be made by the patient and the physician, not the pharmacy.
  • The current FDA ruling means that a pharmacy can switch brands when it refills a prescription.
  • ThyCa agrees with ATA, AACE, TES that we do not support or oppose any particular brand of levothyroxine sodium. What is crucial is that the patient stay on the same brand and NOT switch, because switching requires the expense and life disruption of having an additional blood test for TSH level.
  • Further details and background are on the American Thyroid Association web site at www.thyroid.org, linked in several places in the center section of ATA’s home page.
  • A patient information sheet titled “Know Your Pills” is on the web site of ThyCa: Thyroid Cancer Survivors’ Association, Inc.