Sometimes you roll the dice. And sometimes you end up with snake eyes.

Today Amylin Pharmaceuticals (Nasdaq: AMLN) and partners Eli Lilly (NYSE: LLY) and Alkermes (Nasdaq: ALKS) announced results of their head-to-head clinical trial comparing Bydureon with Novo Nordisk's (NYSE: NVO) diabetes drug Victoza. "Craps" isn't quite an extreme enough description.

The companies only needed Bydureon to be as good as Victoza for the trial to be a success. Bydureon is only injected once a week compared with Victoza's daily needle pricks. Unfortunately, the drug couldn't even manage that; Bydureon lowered patients A1C level, an indicator of average blood sugar, by 1.3 percentage points, compared with a reduction of 1.5 percentage points for Victoza.

The full data set isn't out yet, and it's possible that some of the other measurements -- weight loss, for instance -- could end up in favor of Bydureon, but this is still a major blow as A1C level is the gold standard for diabetes clinical trials.

The results won't keep Bydureon off the market; a 1.3 percentage point reduction is still impressive, and Amylin expects to submit an application for a third time in the second half of the year.

But once it makes it to market, the data is going to make it harder for Amylin and Eli Lilly to push the drug. The fewer injections that Bydureon provides are a great benefit, but it may not be enough to overcome the seemingly inferior efficacy.

The companies were setting up Bydureon as the go-to drug between oral medications and daily injections. With the increase in oral medications -- Bristol-Myers Squibb (NYSE: BMY) and AstraZeneca (NYSE: AZN) have one in the works, for instance -- and today's data, Bydureon might get passed up with many patients going straight from oral medications to Victoza.

Craps, indeed.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool has a disclosure policy.