Year-over-year decreases in sales are never a good thing, but Amylin Pharmaceuticals' (NASDAQ:AMLN) investors need to keep the slight drop in sales of its diabetes drug Byetta in context. That comparison to the second quarter of 2008 came before reports of pancreatitis started hurting sales.

Frankly, recent sales look pretty good, considering how the last few quarters went after those reports came out:

Metric

Q2 2008

Q3 2008

Q4 2008

Q1 2009

Q2 2009

Byetta sales (in millions)

$177.5

$179.9

$162.7

$157.7

$175.1

Sequential quarterly increase (decrease)

12%

1.4%

(9.6%)

(3.1%)

11%

Source: Company press releases.

That's a pretty solid rebound, folks. Amylin and Eli Lilly (NYSE:LLY) jiggered their sales force around, which hopefully will keep the momentum going. The only potential hiccup could come if Novo Nordisk (NYSE:NVO) gets its competing once-daily diabetes drug, Victoza, approved in the U.S.

The longer the Food and Drug Administration holds out on Novo Nordisk, the better for Amylin and Eli Lilly. The two are expecting to hear in the first quarter of next year about their marketing application for once-weekly Byetta, developed using Alkermes' (NASDAQ:ALKS) extended-release technology.

The potential for once-weekly Byetta towers over the twice-daily version. In addition to converting current patients, Amylin and Eli Lilly are going after the complete spectrum of type 2 diabetics. In head to head trials, they've shown that once-weekly Byetta works better than oral medications -- Merck's (NYSE:MRK) Januvia and Takeda's Actos -- that are used early in a patient's progression, and against sanofi-aventis' (NYSE:SNY) Lantus, which is an insulin product used when oral drugs are insufficient to keep blood sugar levels in check.

Even though it's had two drugs approved for four years, Amylin is still very much a development-stage drugmaker. It could have a blockbuster in once-weekly Byetta, but investors will have to be patient. Are you listening, Carl?

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