between 1987 and 1994, nearly half had occurred when patients had received a refill of a product on which they had been stable for years.
So in 1997, in an effort to standardize levothyroxine sodium tablets and to reduce the instances of therapeutic failures, the FDA declared levothyroxine sodium tablets a new drug and sponsors wishing to continue to market their particular product needed to submit either an NDA or file a citizen's petition describing why an NDA was not necessary for their product.
At about this same time, essentially in concert with the Federal Register Notice, the FDA recognized, in part due to the large number of manufacturers of this product, that we needed to come up with a consistent set of guidelines for this product and so a guidance for industry was put together. This guidance was intended to address issues of bioavailability, as Dr. Conner pointed out earlier, and was never intended to be used on its own for the purposes of bioequivalence.
I've chosen three topics here, I've highlighted them in red, to discuss a little bit further