increased cardiovascular risk. This opinion then can demonstrate that any study of bioequivalence must include serum TSH measured at steady state.
We have provided a review to the committee which I believe further outlines the basis for this conclusion. If, however, the existing guidelines are not amended to reflect the principles which I've discussed, the resulting effect may be that substitution of non-therapeutically equivalent L-thyroxine preparations will produce unwanted effects among the over 10 million patients currently treated for hypothyroidism in the United States.
Switching a patient from one formulation of L‑thyroxine sodium to another approved under the current guidelines would require that the physician perform repeat TSH testing and dosage adjustments to assure that these patients remain euthyroid. Otherwise, it could well be expected that as many as 20 percent of these substituted patients would experience a fall in TSH. For the over 60-year-old segment of the population, that change would place 10,000 patients each year at risk for iatrogenic atrial fibrillation.