Amgen Inc. on Thursday reported higher first-quarter profit on strong sales of its drugs to treat anemia, arthritis and infection in chemotherapy patients, and it raised its 2005 earnings forecast.

The Thousand Oaks-based biotechnology firm reported net income of $854 million (67 cents per diluted share) for the first quarter ended March 31, compared with $690 million (52 cents) for the like period a year earlier. Revenue rose to $2.8 billion from $2.3 billion in the year-ago period.

Amgen said its first-quarter earnings would have been $924 million (72 cents per share), compared with $752 million (57 cents) for the like period a year earlier if it had not incurred special charges related to its major acquisitions of Immunex Corp. and Tularik Inc. Revenue was not affected.

Without the acquisition costs, Amgen’s adjusted net income of 72 cents a share beat analysts’ forecasts of 68 cents a share on revenue of $2.87 billion.

The company’s rise in revenue was spurred by a surge in product sales, which increased 24 percent to $2.7 billion from $2.2 billion in the first quarter of 2004.

Worldwide sales of Aranesp, its drug for anemia in cancer and kidney dialysis patients, rose 33 percent to $723 million for the quarter, while Epogen, an earlier version of the drug, had sales of $583 million, a 1 percent decline. Sales of Enbrel for arthritis and psoriasis jumped 49 percent to $592 million. Combined sales of Neupogen and Neulasta, which are used to reduce chemotherapy-related infections, were $795 million, up 20 percent from a year ago.

The company also increased its full-year guidance for total revenue growth to a range of low double-digits to mid-teens from a previous range of high single-digits to low teens. And it raised its adjusted earnings per share guidance to a range of $2.80 to $2.90 from the previous range of $2.70 to $2.85.

Including the expenses related to the acquisitions, Amgen expected earnings per share to be in the range of $2.62 to $2.72 for the full year.