Amylin Staunchly Defends Byetta

Amylin conducted a two-year cancer study of long-acting Byetta in rats and mice and found a statistically significant increase in tumors only in female rates treated with doses of long-acting Byetta four-fold higher than what would be given to humans.

By comparison, says Wilhelm, Novo Nordisk's liraglutide was found to cause tumors in male and female rats, sometimes at human-equivalent doses.

Nine cases of "spontaneous" thyroid cancer have been reported in the approximate 1 million diabetes patients taking Byetta, according to FDA records, but none of these tumors were fatal nor of the type under FDA scrutiny with liraglutide.

"The FDA asked us for this information last year. At the time we weren't sure why, but looking back now, it makes sense," says Wilhelm, adding that the FDA has not asked for any follow-up data regarding Byetta and tumor risk.

Amylin may have cleaner animal safety data, but it remains to be seen whether the FDA will, regardless, consider thyroid tumor risk to be a class effect of the GLP-1 agonist drugs. And even if the FDA gives long-acting Byetta a clean bill of health, the agency could still place restrictions on the drug that would hurt its commercial prospects.

Byetta not only faces competition from Novo Nordisk's liraglutide, but from other classes of diabetes drugs like Merck's(MRK) Januvia and saxagliptin from Bristol-Myer Squibb(BMY) and AstraZeneca(AZN).

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