Is Eli Lilly and Co. about to have another Effient experience?

Lilly and its development partner are trying to get approval for a once-weekly version of the anti-diabetes drug Byetta. The new drug will be called Bydureon.

But the U.S. Food and Drug Administration last week pushed its self-declared deadline for rendering a decision on the drug to Oct. 22. The previous deadline was in March.

Bydureon is key for keeping Lilly competitive in the diabetes game. Earlier this year, the FDA approved a Byetta competitor called Victoza, which is manufactured by Lilly’s diabetes nemesis, Denmark-based Novo Nordisk N/S.

Victoza is a once-daily injectible medicine, compared with the twice-daily injections required with Byetta.

Analysts expect Byetta sales to peak this year at more than $800 million (although Lilly shares that revenue with San Diego-based Amylin Pharmaceuticals Inc.) and then start falling off. But they expect Bydureon sales to reach $800 million to $1 billion by 2015.

Lilly needs to ramp up any new drug as soon as possible so it can build up revenue before Lilly’s bestselling anti-psychotic Zyprexa faces generic competition in October 2011.

Lilly had hoped that the blood thinner Effient would help offset the loss of Zyprexa sales. But the FDA took a year longer than promised to render a decision on the drug. And, because of a severe warning about bleeding causes by the drug, sales so far have been paltry.