All the worry about slowing adoption of Biogen Idec (NASDAQ:BIIB) and Elan's (NYSE:ELN) multiple sclerosis drug Tysabri seems to have been for naught. Despite increasing numbers of patients on Tysabri coming down with progressive multifocal leukoencephalopathy (PML) -- a life-threatening brain infection -- sales looked pretty good last quarter.

Not only were worldwide sales of Tysabri up 27% to $254 million, but patients are moving onto the drug at a quickening pace. In the first quarter of the year, the companies added about 170 patients per week, while in the second quarter that number increased to more than 260 per week.

There's some concern Biogen and Elan might lose revenue if patients start taking drug holidays to remove the Tysabri from their bodies. (Tysabri inhibits the immune system, which is believed to allow the brain infection.) Fortunately, there doesn't seem to be much of that going on, with revenue per patient holding relatively steady.


Q1 2008

Q2 2008

Q3 2008

Q4 2008

Q1 2009

Q2 2009

U.S. Tysabri Sales (in millions)







Approximate Number of Commercial U.S. Patients on Tysabri







Revenue per Patient







Source: Company press releases.

The good news for Biogen didn't stop with Tysabri. Sales of its other multiple sclerosis drug, Avonex, grew 12%, thanks in part to price increases. Pfizer (NYSE:PFE) and Teva Pharmaceutical (NASDAQ:TEVA) have also raised the price of their multiple sclerosis drugs, but investors shouldn't count on price increases for continued growth, especially as leaders in Washington try to get health-care costs under control.

Contrary to Carl Icahn's view, I think Biogen is in a pretty good position right now. It recently licensed the rights to an Acorda Therapeutics' (NASDAQ:ACOR) drug to help multiple sclerosis patients walk, and its pipeline is progressing -- albeit at a slower pace than most investors would hope for. As long as Biogen can keep Tysabri sales growing at a decent pace, investors should be rewarded while they wait.

Don't wait! Read this Foolishness now:

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