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: Biotech company Amylin Pharmaceuticals (Nasdaq: AMLN) and Alkermes (Nasdaq: ALKS) saw their shares plunge in dramatic fashion this morning, on news that U.S. regulators have declined to approve their long-acting diabetes drug Bydureon.

So what: Amylin's shares spiraled a staggering 50%, while Alkermes was down a nasty 30%. Ely Lilly (NYSE: LLY), which co-developed Bydureon, fell about 4%. On the positive side, shares of Danish drug giant Novo Nordisk (NYSE: NVO) popped 10% on the news, as Bydureon is viewed as a serious threat to Novo's diabetes drug franchise.

Now what: Today's decision marks the second Food and Drug Administration rejection of Bydureon, but this one comes on a nasty, Roy Halladay-like curveball. The FDA's request for more data on Bydureon's potential heart risks comes as a huge surprise and, as resident biotech Fool Brian Orelli noted, represents somewhat of a worst-case scenario for the drug. Bydureon will now be delayed as long as 20 months, and the competitive landscape is only expected to be more daunting by that time. While it's always tempting to jump on a jaw-dropping price plunge, this Fool's stomach just isn't strong enough to do it today.

Interested in more info on Alkermes and Amylin? Add them to your watchlist by clicking here and here, respectively.

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

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