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 Durata Therapeutics (NASDAQ:DRTX), a prior to Friday clinical-stage biopharmaceutical company developing unique therapies to treat infectious diseases and acute illnesses, fell as much as 15% after the Food and Drug Administration approved Dalvance (previously dalbavancin) for the treatment of acute bacterial skin and skin structure infections, or ABSSSI.

So what: Following the closing bell Friday, Durata issued a press release informing investors that the FDA had approved its lead injectable therapy. Dalvance is given as a two-dose regimen: first 1000 mg over 30 minutes, followed a week later by 500 mg over 30 minutes. This therapy could mark a big improvement in patient quality of care as it likely beats the prospect of twice daily infusion for patients taking the current standard of treatment. According to Durata, the time needed to build up its salesforce, as well as dot it's "I's" and cross it's "t's" when it comes to final qualification activities puts it on pace to ship Dalvance in the third quarter.

Now what: "So why are shares lower?" you're probably wondering. This looks like a common case of buy the rumor, but sell the news. Durata shares have soared heading into this approval from less than $7 a year ago to nearly $17 per share as of last week. However, we've also witnessed plenty of therapies that should have succeeded, or were expected to succeed, limp out of the gate due to poor marketing efforts or incorrect pricing. Durata has chosen to market Dalvance without a partner so there is some degree of launch execution risk here, although the convenience of its two-dose IV regimen does give it the feel of an instant winner. With annual peak sales estimates of around $400 million and Durata, following today's drop, only valued around $400 million, even a lukewarm start for Dalvance could spell an undervaluation for Durata shares. Now don't get me wrong; I'm not expecting shares to soar or anything. However, with most biotech stocks trading at a multiple of greater than one for their lead drug I can easily see Durata tacking on gains over the coming years.

Durata shares have soared over the past year, but even it could struggle to keep pace with this top stock over the long run
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Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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