BIIB Biogen Inc

Biogen Idec Inc. (BIIB) disclosed five more cases of a rare brain infection in multiple sclerosis patients on Tysabri, which it sells with Elan Corp. (ELN), bringing the total number of cases to 75 as of Nov. 2.

The Weston, Mass., biotech company also reported an additional death among patients that have developed the infection--known as progressive multifocal leukoencephalopathy, or PML--a number that is now 15.

The number of PML cases is important because if the infection rate climbs too high, the drug's sales growth may drop. Regulators have said that they watch the cases, but have concluded that the benefits of the medicine to MS patients outweigh the risks.

The overall global PML rate is about 0.96 per 1,000 patients, a company spokeswoman said, which still falls within the 1-in-1,000 rate previously seen in clinical trials and implied on the drug's label. But the rate has been rising, and multiple Wall Street analysts raised concern about the trend on Wednesday as the MS market is becoming increasingly competitive.

"Given this PML rate increase, we expect it to cross the 1/1000 incidence threshold sometime during the next two months," Barclays Capital analyst Jim Birchenough said in a note to clients.

Food and Drug Administration officials weren't immediately available for comment.

Sales of Tysabri are important to the future growth of Biogen and Elan. There is hope that the development of a blood test may better determine the chances of patients contracting PML. Although the overall risk of the infection is small, the test may make patients and physicians more comfortable with using the drug.

Tysabri is considered to be a highly effective therapy for multiple sclerosis, but its growth has been stunted by concerns about PML. The drug was temporary withdrawn from the market beginning in 2005 and relaunched in 2006 with a strict access plan that monitors every patient using the drug.

Meanwhile, the MS treatment market is getting increasingly competitive, something that Wall Street believes could put some pressure on Tysabri and Biogen as a whole. Biogen get most of its revenue from MS treatments Avonex and Tysabri, and hasn't launched a new drug since the approval of Tysabri in 2004.

Novartis AG's (NVS) Gilenya, the first oral therapy for the disease, was recently approved, and numerous other therapies are in development.

Earlier this month, Biogen unveiled a sweeping restructuring plan that cuts costs--including facility closings and layoffs--and focuses the company on developing neurology treatments and defending its current franchise of MS drugs.

The moves came after a business review by new Chief Executive George Scangos, who joined the company in July.

As of Sept. 30, 55,100 patients were using the drug around the world. In total, about 75,500 patients have used the drug since its launch.

Of the total PML cases, 33 were in the U.S., 38 were in the European Union and four were in other areas.

The risk of the infection increases with the number of monthly infusions that a patient receives, but that rate appears to drop after 30 months of use. Biogen views the drop as inconclusive, because there aren't enough patients at the longer duration to have enough confidence in that finding.

The most recent data update translates to a rate of 1.49 cases per 1,000 for patients on the drug for a year or longer, but rises to 1.97 per 1,000 for those on the drug for two years or longer.

Looked at another way, the rate is about 1.49 cases per 1,000 patients on the drug for between two and three years. The incidence is about 0.37 case per 1,000 patients in those using it for one to two years, and it is essentially nonexistent in patients using it for less than a year.

-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com

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