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 biotech Theravance (Nasdaq: THRX) have tanked today by as much as 10% after a negative analyst rating came early this morning.

So what: Morgan Stanley has started coverage of Theravance shares with an underweight rating, complete with a $12 price target in tow. That figure would represent a loss of 38% relative to yesterday's closing price of $19.37.

Now what: This is just one analyst's rating, and Theravance is set to report its fourth-quarter and full-year 2011 results on Feb. 9, which should shed some more light on its fundamentals. That $12 estimate is notably even lower than when shares got crushed earlier this month over safety concerns related to its Relovair experimental lung drug. With that plunge still fresh in shareholders' collective memory, a bit of bearishness goes a long way down.

Interested in more info on Theravance? Add it to your watchlist by clicking here.

Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. 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 Motley Fool has a disclosure policy.