Dr. Cobbs Clarifies His Position on Thyroid Hormone Replacement

Dr. Cobbs responds to questions from Tony Kingkade, regarding the use of branded t4 (Synthroid), in the treatment of hypothyroidism. Dr. Cobbs, Chief of Endocrinology at North General Medical Center, writes:

Mr Kingkade has a very interesting opinion. I prefer to deal with the facts. First, the AACE position was posted after not before the FDA approved other brands of levothyroxine. Second, the FDA has stated that they do not use TSH to assess equivalence of levothyroxine preparations. They use area under the curve concentration which is not as accurate. Endocrinologists use a sensitive TSH assay which is more precise.

There is no myth if you read the literature. Since so many people misunderstand the facts, a joint position paper was published on the internet.
AACE, The Endocrine Society and the American Thyroid Association published the joint statement. The statement was published after the FDA refused to listen to the opinions of all three groups of endocrinologists. The joint statement is the one that states that branded levothyroxine should be used instead of generics. And it was issued in 2004

Also for the record, the FDA allows for significant variance from the stated dosage. Some generics are more “bioavailable” and others are less available resulting in differing thyroid function test results despite all claiming to be the exact same strength using FDA standards. Differing manufacturing techniques account for the differences.

As for the Boots paper, Boots was wrong in withholding their paper however a careful review of the other published literature reveals many other papers that demonstate differences in blood levels of different brands even when the dosage claims to be the same.

For the record, I am not a paid speaker for any pharmaceutical company. I have taught and continue to teach endocrinology to residents, attending physicians and medical students for more than 20 years. I prefer to deal with facts as represented in the published literature. A drug company paid speaker gives a promotional lecture. Don’t expect facts from them.

The facts stand for themselves. The recommendation to use branded levothyroxine is that of AACE, The Endocrine Society and the American Thyroid Association. I stand by the recommendation of all three associations of endocrinologists. The facts speak for themselves.

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