Merck & Co Inc reported better-than-expected third-quarter profit, as a favorable tax rate and lower merger costs helped offset plunging sales of asthma drug Singulair, its former flagship product that began facing cheaper generics in August.

Merck, the No. 2 U.S. drugmaker, said on Friday it earned $1.73 billion, or 56 cents per share, compared with $1.69 billion, or 55 cents per share, a year earlier.

Excluding special items, Merck earned 95 cents per share. Analysts, on average, expected 92 cents.

Revenue fell 4 percent to $11.49 billion, below Wall Street expectations of $11.57 billion.

Merck tightened its full-year profit forecast to between $3.78 and $3.82 per share, from its earlier view of $3.75 to $3.85 per share.

Sales of Singulair tumbled 55 percent to $602 million in the quarter. But many of its newer products - including treatments for diabetes, hepatitis C and HIV - posted double-digit sales gains that helped cushion Singulair's free fall.

(Reporting by Ransdell Pierson; Editing by Lisa Von Ahn and Jeffrey Benkoe)