Merck (MRK) withdrew its long-term financial guidance, issued a gloomy outlook for 2011 and revealed a big fourth-quarter loss on Thursday, driving the drug giant’s stock sharply lower.

Whitehouse Station, NJ-based Merck said it lost $500 million, or 17 cents a share, last quarter, compared with a profit of $6.5 billion, or $2.35 a share. That loss was triggered by a $1.7 billion charge due to a setback for its experimental blood clot preventer vorapaxar.

Excluding one-time items, the pharmaceutical giant said it earned 88 cents a share, exceeding the Street’s view of 83 cents.

Boosted by its $41 billion acquisition of Schering-Plough, fourth-quarter sales jumped 20% to $12.1 billion, surpassing the $11.53 billion analysts had called for.

“These results clearly demonstrate the benefits of the post-merger Merck with our broader product portfolio, robust late-stage pipeline and expanded global footprint,” CEO Kenneth Frazier said in a statement.

Due to the potential for bleeding, vorapaxar has been ruled inappropriate for stroke patients. Merck had been hoping vorapaxar, which was in the Schering-Plough pipeline, would generate annual sales of $3 billion or more.

Merck also issued a tepid guidance, saying it sees 2011 non-GAAP EPS of $3.64 to $3.76. Even the high end of that new range would trail consensus calls for $3.82. Merck sees its 2011 revenue growing in the low to mid-single digit percent range from 2010’s $46 billion.

Citing setbacks in its vorapax clinical program and “industry pressures” like greater austerity measures in the European Union and the “additional impact” of the U.S. health-care overhaul, Merck yanked its long-term forecast. The drug maker had targeted high single-digit growth of its non-GAAP EPS from 2009 to 2013.

"Looking ahead, our focus will be on delivering sustainable, profitable top-line growth," Frazier said. "To do that, Merck will continue to innovate, make disciplined investments in our business and continue to drive out inefficiencies in our operations.”

Hurt by the gloomy guidance, Merck’s stock slumped 3.16% to $32.75 in Thursday’s premarkets.. The stock had already been down 6% on the year as of Wednesday’s close.

The results and market reaction contrast sharply with that of rival Pfizer (PFE), which earlier this week soared 5.5% after beating the Street and announcing plans to buy back another $5 billion of its stock.

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