Amylin and Eli Lilly, plus partner Alkermes have suffered a major setback with the news that regulators in the USA have turned down Bydureon, the firm's long-acting, once-weekly version of the diabetes blockbuster Byetta.

The US Food and Drug Administration has issued a complete response letter regarding the New Drug Application for Bydureon (extended-release exenatide) and wants quite a bit more information on the treatment. Specifically, the agency has requested "a thorough QT study" to look at the potential arrhythmia liability with exposures of exenatide "higher than typical therapeutic levels".

The FDA also wants to see the results of the ongoing DURATION-5 study to evaluate the efficacy, and the labeling of the safety and effectiveness, of Bydureon. Amylin and Lilly noted that the FDA did not cite any concerns about manufacturing processes it mentioned in an earlier  CRL issued in March, adding that discussions with the agency regarding a risk evaluation and mitigation strategy and product labelling "will continue following submission of the additional data".

All of this is going to take a while and the companies' goal is to submit their reply to the CRL by the end of 2011.  The package will then probably require a six-month review so the chances of an approval from the FDA are minimal before the middle of 2012.

Amylin is putting a brave face on the news and chief medical officer Orville Kolterman said "we remain confident in Bydureon based on the extensive exenatide database, including more than seven years of clinical experience with Byetta". Whether investors will share his confidence is debatable and when the markets open in the USA, shares of Lilly and especially those of Amylin are likely to suffer.

The FDA's rejection is good news for Novo Nordisk's Victoza (liraglutide) which like Byetta is a glucagon-like peptide-1 (GLP-1) receptor agonist but is injected once a day, not twice like the Amylin/Lilly drug.

Meantime, Amylin announced that unaudited  product sales for the third quarter of $154.0 million, down 20.1% on the like, year-earlier period. Byetta brought in $132.4 million, a fall of 22.6%.