Are All Levothyroxine Products the Same?
According to a study published in the April, 1997 issue of the Journal of the American Medical
4&dopt=Abstract]See PubMed Reference), Synthroid was found to be "bioequivalent" to Levoxyl
and two other generic levothyroxine products. (Bioequivalent means that a drug has the same biological
effects of that to which a medicine was compared.) The research was conducted by Synthroid's former
manufacturers, Boots Pharmaceuticals and Knoll Pharmaceuticals, but results were not published for
seven years. The company claimed it had concerns about the methodology of the research itself had
commissioned, however critics claimed that the research was a disappointment to the company, which
had been intended to show that Synthroid was superior in quality and therefore reason to justify prices
two to three times higher than competitive levothyroxine products. The research was published despite
the manufacturer's protest. (The
publication of the research also led to a class action lawsuit filed against Synthroid's manufacturer
in 1997, claiming that patients were overcharged during the period the research was not published, paying
more for a produt that was allegedly superior, when the research disproved this. This class action lawsuit
has ostensibly been settled in late
, however payments to patients have yet to be disbursed.)
At present, it could be argued that the levothyroxine products are not "the same" because only two of
the four brand name products are FDA-approved. As the FDA wrote in its August 2000 approval notice
for Unithroid, the first levothyroxine approved: ""Although oral levothyroxine drugs products have been
marketed in the United States since the 1950's, the approval of Unithroid represents the first time that
a single ingredient oral levothryoxine product has been approved by the FDA. The unapproved thyroid
hormone replacement products that have been on the market have been associated with stability and
potency problems. These problems have resulted in product recalls and have the potential to cause serious
health consequences to the public. With the approval of the NDA for Unithroid, patients and physicians
now have available to them an oral levothryroxine sodium drug product that has been determined to be
safe and effective by the FDA and that also meets FDA standards for manufacturing processes, purity,
potency, and stability."
The approval of Levoxyl, which took place in May of 2001, also added a second approved levothyroxine
to the list of FDA-approved drugs.
Since Levothroid has filed but is still awaiting approval, and Synthroid has yet to file for approval, they
are still considered unapproved thyroid hormone replacement products, and have yet to receive official
FDA approved status, which determines them to be safe and effective and that also meets FDA standards
for manufacturing processes, purity, potency, and stability.
Is It Hard to Switch Thyroid Medicines? Should You Switch?
People react differently to different thyroid medications. For example, some people are allergic to the
fillers and dyes in one brand or dosage size of a levothyroxine product, but not to another. In other cases,
if you have been taking a product that has had fluctuating potency, you may have had to switch dosages
numerous times in response to fluctuating TSH levels and symptoms. And even in getting a refill of the
same brand, or in switching from one brand to another, you may encounter batches of levothyroxine that
have differing potencies, despite being the same stated "dosage."
Thyroid patients who require levothyroxine for the treatment of their thyroid condition may find that it
is in their best interest to be taking a product that has been shown, through the rigorous government FDA
approval process, to be a stable, consistent, potent levothyroxine drug that has minimal variations in
potency, and assured stability, and will be consistently available without any risk -- however remote --
of interruption or regulatory difficulties.
Ultimately, your doctor is the best person to advise you regarding any potential changes in your thyroid