Amylin, Eli Lilly and Alkermes will have to wait a bit longer before they can start selling a once-weekly version of its diabetes blockbuster Byetta as regulators in the USA want clarification on the labelling.

The US Food and Drug Administration has issued a complete response letter regarding the New Drug Application for the injectable treatment which will be called Bydureon (extended-release exenatide). The three partners say that the requests raised in the letter primarily relate to the finalisation of the product labeling “with accompanying risk evaluation and mitigation strategy and clarification of existing manufacturing processes”.

However Lilly and Amylin point out that no new trials are needed, nor is there any mention in the letter containing requests related to a December 2009 pre-approval inspection by the FDA at Amylin’s manufacturing facility in Ohio. The agency had listed 10 observations, one of which was that procedures “designed to prevent microbiological contamination of drug products purporting to be sterile are not established and followed."However, all of those observations have been addressed,” the firms stress.

Orville Kolterman, senior vice president of R&D at Amylin, was surprisingly upbeat this morning, saying that the letter “is a significant step forward in our ability to bring this important therapy to patients”. He added that “we have a clear path forward and are working diligently to submit our response to the FDA in the next few weeks”.

Despite Dr Kolterman’s enthusiasm, the letter is a blow given that it comes at a time when the twice-daily injectable Byetta (exenatide) is facing up to competition from the newest glucagon-like peptide-1 (GLP-1) receptor agonist to hit the market, Novo Nordisk’s Victoza (liraglutide). The latter is injected once a day.