Updated from 8:15 a.m. EDT

Biogen Idec ( BIIB) reported a second-quarter loss, but driven by double-digit sales increases for Avonex and Rituxan it blew past analysts' revenue and adjusted profit forecasts.

The Cambridge, Mass., biotech reported a loss of 50 cents a share on the bottom line, reflecting costs related to its acquisition of cancer drug developer Conforma Therapeutics and privately held Swiss pharma Fumapharm, and stock options expenses.

Excluding items, the company earned 57 cents a share, up 33% from a year ago. Analysts surveyed by Thomson First Call were expecting 49 cents a share.

Biogen reported sales of $660 million for the quarter, up from $606 million a year ago and above the $636.4 million expected by analysts. The beat reflected sales of multiple sclerosis drug Avonex and blood cancer drug Rituxan. Avonex sales were up 12% to $429 million, while Rituxan sales rose 17% to $526 million in the quarter.

Rituxan sales had been reported by Biogen's marketing partner Genentech ( DNA). Biogen's share of the drug's pretax co-promotion profits was up 11% to $206 million.

Biogen was trading down 2.8% to $40.40 at midmorning Wednesday.

During the quarter, another MS drug Biogen sells, Tysabri, was reapproved by regulators in the U.S. and Europe. The drug, which is marketed with Ireland's Elan ( ELN), was pulled last year when it was linked to a rare and potentially deadly brain disease. However, regulators determined that the drug's benefits significantly outweighed the risks in patients with recurring or worsening MS who had tried numerous other treatments, including Avonex, to no avail.

Earlier this week, Biogen said it had made the drug available to U.S. patients again, but it's still currently training health care providers on its risk-management plan. That could delay some patients' access to the drug by another five to 10 weeks.

Still, the thoroughness of the risk-management plan makes it more likely that insurers will cover the drug, possibly without the need for precertification, the company said during a conference call.

"We expect Tysabri will enhance our neurology business and begin to accelerate top-line growth over the coming quarters," said Biogen CEO James Mullen in a prepared statement.

The company reiterated its full-year earnings guidance of between $1.95 and $2.10 a share.