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 drug developer Isis Pharmaceuticals (Nasdaq: ISIS) hardly looked like a model of fertility today as they fell 10.5% in heavy intraday trading.

So what: Third-quarter sales came in far short of analyst estimates, and the $0.27 net loss per share was surprisingly large.

Now what: Management kept a stiff upper lip and told analysts to focus on the approval process for potential blockbuster drug Kynamro, a collaboration with genetics giant Genzyme. The company does indeed have an impressive drug pipeline in place considering the small scale of its operations. Just remember that Isis is a heap of potential with very little real-world success or fully FDA-approved drugs to fall back on, and things could get ugly if the government doesn't cooperate. Take a look at the chart for Elan (NYSE: ELN) in 2005 or 2008, and you'll see why nerves of steel are required for bets on this type of wonder-drug.

Interested in more info about Isis Pharmaceuticals? Click here to add it to My Watchlist.