Biogen (BIIB), Elan's (ELN) Facing Massive Challenges

The number of cases of progressive multifocal leukoencephalopathy, or PML, in patients taking Biogen Idec (Nasdaq:BIIB) and Elan's (NYSE:ELN) Tysabri increased by nearly 12% in less than a month. Annualize that out, and it isn't a pretty picture.

The latest monthly update listed 10 new cases of PML, bringing the total count to 95. The brain infection has killed 20 of the 95 patients that have been stricken while taking the multiple sclerosis drug.

As the number of patients taking Tysabri increases, we're bound to see the PML cases increase, but the update for January was considerably higher than the last two updates; November had four new cases and December had six.

Of course, one month doesn't make a trend, and Biogen points out the overall rate is still fairly low at 1.16 per 1,000 patients.

The question is where does it cross the line from being an acceptable risk to being an unacceptable one. Tysabri is the best multiple sclerosis drug out there, but there's a point at which doctors and patients won't think the benefits outweigh the risk, and they'll head to other treatments such as Teva Pharmaceutical's (Nasdaq:TEVA) Copaxone, Novartis' (NYSE:NVS) Gilenya, and Rebif, which is sold by Merck KGaA and Pfizer (NYSE:PFE).




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