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 drugmaker Elan (NYSE: ELN) dipped as much as 16% today after it and its drug development partners reported disappointing late-stage trial results for Alzheimer's treatment bapineuzumab.

So what: In 2009, Elan sold the rights to its Alzheimer's' immunotherapy program to Janssen Pharmaceuticals, a subsidiary of Johnson & Johnson (NYSE: JNJ), but retained financial interests in bapineuzumab. Last night, Pfizer (NYSE: PFE) and marketing partner J&J noted that bapineuzumab wasn't effective versus the placebo in one of its four ongoing late-stage trials to treat mild-to-moderate forms of Alzheimer's. Specifically, this trial targeted the APoE4 gene. All companies involved plan to continue with the three remaining trials.

Now what: Bad news all around today, because there aren't many options available to treat Alzheimer's. Eli Lilly (NYSE: LLY) is also developing a competing Alzheimer's drug, solanezumab, with data expected sometime over the next few months, but even it is down in sympathy with Elan.

Speaking specifically of Elan, which is best known for multiple sclerosis drug Tysabri, which it markets in partnership with Biogen Idec (Nasdaq: BIIB), I wouldn't consider today's move lower a buying opportunity. For the most part, Tysabri sales have matured, and after today's results there are few guarantees that its remaining trials will provide better results. All things considered, there are far better values and stronger pipelines out there than what Elan has to offer.

Craving more input? Start by adding Elan to your free and personalized Watchlist so you can keep up on the latest news with the company.