Merck (MRK) revealed on Thursday it swung to a stronger-than-expected fourth-quarter profit as the big drug maker benefited from fewer charges and a 2% rise in sales.

The blue-chip company said it earned $1.51 billion, or 49 cents a share, compared with a loss of $531 million, or 17 cents a share, a year earlier. The year-earlier loss was caused in part by a $1.7 billion writedown tied to its anti-clotting treatment Vorapaxar.

Excluding one-time items, Merck earned 97 cents a share, topping the Street’s view of 95 cents.

Whitehouse Station, N.J.-based Merck said revenue increased 2% to $12.29 billion, missing consensus calls for $12.5 billion.

Like most big drug makers, Merck is grappling with the expiration of U.S. exclusivity deals on key revenue-driving drugs like Singulair.

“We closed out 2011 with a high-quality fourth quarter by growing the top and bottom lines. Our overall performance for the year confirms our ability to achieve strong operating results while investing for the longer term,” CEO Kenneth Frazier said in a statement.

Looking ahead, Merck projected full-year non-GAAP earnings of $3.75 to $3.85 a share, compared with a profit of $3.77 a share in 2011 and estimates from analysts for $3.83. Revenue is expected to be nearly flat at last year’s $48 billion, while Wall Street had expected $47.6 billion.

“As we begin 2012 and look ahead, we are optimistic about our underlying business, our current momentum and the early success of our strategy,” Frazier said.

Sales of Merck’s blockbuster Singulair asthma drug jumped 8% last quarter to $1.46 billion, while diabetes treatment Januvia saw a 42% surge in revenue to $960 million.

Merck warned it expects to see a “significant decline in sales” following the August expiration of the U.S. patent for Singulair.

Merck said Vytorin, which is used to treat high cholesterol, suffered a 16% decline in revenue to $475 million, while sales of arthritis treatment Remicade slumped 28% to $511 million.

Shares of Merck, which have rallied 14% over the past year, climbed 1.48% to $38.63 ahead of Thursday’s open.

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