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: Regeneron Pharmaceuticals (Nasdaq: REGN) dropped 12% in intraday trading today after an analyst at RBC Capital downgraded the stock from outperform to sector perform.

So what: The last few days have been a wild ride for Regeneron shareholders. After soaring Wednesday on positive news related to the company's Zaltrap drug, the stock tanked yesterday on news that has negative implications for a macular degeneration treatment it is developing with Bayer.

Now what: The Food and Drug Administration is expected to decide whether to approve Regeneron's macular degeneration treatment by Aug. 20, giving the drug near-term profit potential. Lucentis, a competing treatment from Roche and Novartis (NYSE: NVS), is $2,000 per injection. This week, The New England Journal of Medicine published a study showing that Roche's cancer drug Avastin -- which costs a mere $50 per injection -- is also a very effective treatment for macular degeneration. That suggests the revenue and profit potential of Regeneron's treatment, if approved, could be only a small fraction of previous expectations.   

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Fool contributor Cindy Johnson does not own shares of any company named above. 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 Motley Fool has a disclosure policy.