Amgen Inc. said on Thursday its fourth-quarter earnings rose 20 percent on sales of its rheumatoid arthritis and anemia drugs, but results missed estimates by a penny, sending its stock falling nearly 5 percent.

Shares of Amgen fell 4.7 percent to settle at $71.90 on Thursday. Also contributing to the drop was the company’s announcement that it was still enrolling patients in an ongoing clinical trial of its highly anticipated colon cancer drug panitumumab, and was not ready to release interim results.

The Thousand Oaks-based biotechnology company reported fourth-quarter net income of $824 million (66 cents per share), compared with $689 million (53 cents) for the like period a year earlier. Revenue rose 12 percent to $3.3 billion.

Excluding certain expenses related to the acquisitions of Immunex Corp., Tularik Inc. and other items, the company reported adjusted net income of $928 million (75 cents per share), compared to $749 million (58 cents) in the year-prior period.

Analysts expected earnings of 76 cents per share on revenue of $3.33 billion.

Fourth-quarter sales for its anti-anemia drug Aranesp rose 24 percent to $873, driven by increased demand. U.S. Aranesp sales were $579 million versus $449 million in the prior year. Sales of Amgen’s older anemia-fighter, Epogen, fell 10 percent to $626 million, as doctors switched to prescribing Aranesp, a move that is expected to stabilize by mid-2006.

Combined sales of Neulasta and Neupogen, drugs that boost white blood cells to fight infection in chemotherapy patients, rose 19 percent to $928 million, fueled by increased demand for Neulasta. Sales of Enbrel rose 19 percent to $674 million.

Total fourth-quarter product sales increased 14 percent to $3.2 billion from $2.8 billion in the fourth quarter of 2004.

The company expects full-year adjusted earnings of $3.55 to $3.70 per share on revenue of $13.9 billion to $14.4 billion.

Amgen also announced that it and South San Francisco-based Genentech Inc. have settled a long-running dispute over access to the cornerstone patents for manufacture and use of antibodies, by granting licenses for each other’s patents. Genentech was the world’s first biotech company, and the companies are the two largest biotechs by market capitalization.