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 Sagent Pharmaceuticals (Nasdaq: SGNT) plummeted 23% on Thursday after its full-year guidance disappointed Wall Street.

So what: Sagent's second-quarter results managed to top estimates -- EPS loss of $0.17 on revenue of $42.7 million -- but downbeat sales guidance for 2012 is forcing analysts to cut their valuation estimates considerably. Management cited increased competitive pressure, supply constraints at a major partner, and delayed product launches for the downbeat outlook, triggering serious concerns over its growth going forward.

Now what: Management now sees full-year revenue of $180 million-$200 million, down significantly from its prior view of $200 million-$250 million and well below the analyst consensus of $221 million. "Despite having to revise our near-term expectations, we continue to be focused on the long term development of the business and remain committed to achieving our strategic initiatives and growth trajectory," Chairman and CEO Jeffrey Yordon reassured investors. Of course, when you add the new revenue uncertainty to Sagent's already-speculative nature, I'd be cautious about buying into that turnaround talk.    

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Fool contributor Brian Pacampara owns no position in any of the companies mentioned. Try any of our Foolish newsletter services free for 30 days.

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