Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Amylin Pharmaceuticals (Nasdaq: AMLN) plummeted more than 20% Thursday after its type 2 diabetes drug Bydureon failed to meet primary endpoints in a 26-week study.

So what: The once-weekly Bydureon injection, which Amylin is co-developing with Alkermes (Nasdaq: ALKS) and Eli Lilly (NYSE: LLY), was shown to be less effective at reducing blood sugar levels than Novo Nordisk's (NYSE: NVO) daily treatment, Victoza. Amylin shares had been recovering steadily from the late October beating they took when the FDA requested more data on Bydureon's heart risks, but today's disappointing setback puts them right back near those 52-week lows.

Now what: Amylin remains far too speculative for most investors. While Bydureon could certainly still get approved, there now seems to be a lot of concern on Wall Street about how it could compete. Amylin has posted less-than-stellar sales over the past few years, and with Bydureon's prospects not shining as brightly as they once did, there's very little reason to get involved.

Interested in more info on Amylin? Add it to your watchlist.

Fool contributor Brian Pacampara owns no position in any of the companies mentioned. Try any of our Foolish newsletter services free for 30 days.

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's disclosure policy always gets a perfect score.