Data for a once-weekly version of Byetta did not adequately show that batches of commercially manufactured Byetta were comparable with batches manufactured earlier for use in clinical trials.
That's what the U.S. Food and Drug Administration told one of Lilly's partners on Byetta, San Diego-based Amylin Pharmaceuticals Inc., according to an announcement released today by a third partner on the drug, Cambridge, Mass.-based Alkermes Inc.
Amylin manufactured commercial versions of Byetta at its plant in Ohio, according to Alkermes' statement. Alkermes made batches of Byetta used in clinical trials.
Alkermes' statement said that if the FDA requires a new clinical study on once-weekly Byetta, it could delay the date by which the companies submit their request for approval of the once-weekly version.
That submission is currently scheduled to happen before July 2009.
Lilly began selling a once-a-day version of Byetta in 2005, splitting revenue with Amylin. Byetta generated $637 million in U.S. sales last year. Analysts estimated that the once-weekly version would push U.S. sales above $1 billion in 2010 and zoom to nearly $1.7 billion by 2014.
Lilly receives only half of Byetta's U.S. sales but all of its international sales.
But analyst excitement about Byetta has waned somewhat since late August, when the FDA as well as Lilly and Amylin reported several cases - some fatal - of patients developing pancreatitis while taking the drug. However, no causal link has been established between Byetta and pancreatitis.
Citigroup analyst John Boris said Byetta could receive more warnings on its label, which might discourage doctors from prescribing it as much.
"We see downside risk to our (once-weekly Byetta) estimates given safety concerns, flattening prescription trends and rising competition," Boris wrote in an Aug. 26 research note.