Bristol-Myers Squibb Co's first-quarter results beat expectations, bolstered by the weaker dollar and demand for its drugs to treat cancer, rheumatoid arthritis and hepatitis B.

The company said on Thursday it earned $1.37 billion, or 57 cents per share. That compared with $1.1 billion, or 43 cents per share, in the year-earlier period.

Excluding special items, Bristol-Myers earned 58 cents per share. Analysts on average expected 53 cents, according to Thomson Reuters I/B/E/S.

Revenue rose 4 percent to $5.01 billion, topping a Wall Street forecast of $4.95 billion.

Sales of the company's biggest product, blood-clot preventer Plavix, rose 6 percent to $1.76 billion. Demand for the pill, sold in partnership with Sanofi-Aventis , is expected to plunge a year from now, when cheaper generics become available in the United States.

Bristol-Myers, whose shares rose 0.7 pct in premarket trading, is counting on a number of highly promising new drugs to cushion that blow.

U.S. regulators in March approved Yervoy (ipilimumab), which prolonged lives of patients with melanoma in clinical trials and is expected to garner blockbuster sales.

The company's experimental blood thinner Eliquis (apixaban) and Nulojix (belatacept) drug to prevent rejection of transplanted kidneys, have won backing from European drug regulators.

Bristol-Myers, whose first-quarter results were also helped by lower taxes, reaffirmed it expects earnings this year, excluding special items, of $2.10 to $2.20 per share -- little changed from 2010.

Sales of Orencia, used to treat rheumatoid arthritis, rose 18 percent to $199 million, while sales of leukemia treatment Sprycel jumped 31 percent to $172 million. Baraclude, for hepatitis B, grew 27 percent to $275 million.

But some older drugs held down results, including blood pressure treatment Avapro, whose sales fell 8 percent to $290 million, and colon cancer drug Erbitux, whose sales slipped 1 percent to $165 million.

Sales of schizophrenia treatment Abilify, once one of Bristol-Myers' fastest-growing products, rose just 1 percent to $624 million. The company now keeps a lower percentage of Abilify sales under a restructured agreement with its longtime partner Otsuka Pharmaceutical Co.

(Reporting by Ransdell Pierson; Editing by Derek Caney and John Wallace)