CAMBRIDGE, Mass. (AP) — Biogen Idec Inc. said Tuesday its profit jumped 34 percent in the third quarter due to lower amortization costs and increased sales of its multiple sclerosis drug Tysabri. The Cambridge, Mass., drugmaker said its profit rose to $277.6 million, or 95 cents per share, from $206.8 million, or 70 cents per share. Excluding one-time costs, Biogen said it earned $1.12 per share, well ahead of Wall Street estimates. Revenue rose 3 percent, to $1.12 billion from $1.09 billion. According to Thomson Reuters, analysts expected a profit of $1.04 per share and revenue of $1.11 billion. Sales of Tysabri grew 21 percent to $207 million, Biogen said. At the end of the quarter, 46,200 patients were using Tysabri, up from 43,300 at the end of the second quarter. Tysabri is used for multiple sclerosis and Crohn's disease, and in the U.S., Biogen sells Tysabri through a partnership with Elan Corp. PLC. Sales of the company's top seller, Avonex for multiple sclerosis, grew 1 percent to $580 million. Biogen reported lower amortization costs on the expectation of greater sales of Avonex because of an extension of the drug's patent protection. In September, Biogen received a patent that covers Avonex until 2026. The patents supporting the drug had been scheduled to expire in 2013. Biogen reported $284 million in revenue from the cancer and rheumatoid arthritis drug Rituxan, down from $299 million a year ago. It markets the drug through a partnership with Roche AG's Genentech unit. Total U.S. sales of Rituxan rose 2 percent, to $670 million from $655 million. For the full year, Biogen said it still expects to earn at least $2.97 per share, or more than $3.85 per share excluding one-time costs. On average, analysts expect $3.92 per share. The company expects revenue growth in the mid to high single digits. Earlier it called for an increase in the high single digits. The company said it approved a $1 billion stock repurchase in October, and can buy back another 6 million shares under a previous repurchase plan. Biogen had 289 million shares on the market at the end of September. In premarket trading, Biogen stock slipped 94 cents to $48.45.