Bydureon, Amylin Pharmaceuticals (Nasdaq: AMLN) and Eli Lilly's (NYSE: LLY) once-weekly version of their twice-daily Byetta, has been beating up other diabetes drugs in a series of head-to-head clinical trials called Duration.

In Duration-2 the drug topped Merck's (NYSE: MRK) Januvia and Takeda's Actos. In Duration-3 Bydureon proved better than sanofi-aventis' (NYSE: SNY) Lantus. Bydureon also beat its older brother, Byetta, in Duration-1 and Duration-5.

But all those trials were in diabetics who couldn't control their glucose levels with other drugs. The final frontier for Bydureon is new patients who haven't started on treatment. The companies announced those results yesterday from the out-of-sequence Duration-4 study.

Unfortunately it was a mixed bag for Bydureon. When measuring A1C levels, a long-term measure of glucose levels, the drug clearly beat Januvia, but seemed to work only as well as Actos and a generic called metformin. Patients on Bydureon lost weight like they had in previous trials -- more than those on Januvia and Actos -- but metformin produced a similar decrease in weight.

Merely tying a generic in the two most important measures for a diabetes drug isn't exactly great for marketing, but I'm not sure how much of a blow this is for Amylin, Lilly, and their partner Alkermes (Nasdaq: ALKS), which contributed the extended-release technology to make Bydureon. Going after the monotherapy market was going to be tough for Bydureon.

Byetta is approved as a monotherapy, but it doesn't seem to have helped much in its battle against Novo Nordisk's (NYSE: NVO) Victoza; sales were down 8% quarter over quarter in the first quarter.

The convenience of Bydureon's once-weekly cycle -- as opposed to Byetta's twice-daily regimen -- might be enough to help Bydureon compete against an oral drug that has to be taken daily. But I'd say that Bydureon probably needed to trounce metformin by a wide margin to justify the cost difference between copays for a brand-name and a generic drug.

Given the progressive nature of diabetes, Amylin and Lilly will be able to pick up the patients soon enough after metformin is no longer able to control the glucose levels. That is, assuming there are no more surprises and Bydureon gets past the Food and Drug Administration in October.

Todd Wenning thinks the deals are getting good again.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.