The financial press can finally drop the "potential" in front of blockbuster when describing Biogen Idec (NASDAQ:BIIB) and Elan's (NYSE:ELN) multiple sclerosis drug, Tyasbri. As part of the J.P. Morgan Healthcare Conference, Biogen announced that sales of Tysabri had passed the $1 billion mark in 2009, making it an official blockbuster.

Whoopty do.

Whether sales were $1.01 billion or $999 million last year doesn't really matter. The $1 billion in annual sales is an arbitrary figure that we've assigned the delineate "blockbusters" to make them sound important.

What really matters is how many patients are going onto Tysabri. While the drug works better than other multiple sclerosis drugs like Biogen's Avonex, Teva Pharmaceutical's (NASDAQ:TEVA) Copaxone, Novartis' (NYSE:NVS) Extavia, and Rebif from Pfizer (NYSE:PFE) and EMD Serono, it also increases the risk of a potentially deadly brain infection called progressive multifocal leukoencephalopathy (PML). Biogen and Elan have to find a way to convince patients and their doctors that the benefit is worth the risk.

At the end of the year, it doesn't look like the companies are getting it done.


Q1 2009

Q2 2009

Q3 2009

Q4 2009

Number of patients on Tysabri





Quarter-over-quarter increase





Source: Company press releases.

These are quarterly growth figures, so there's some seasonality to the numbers. Biogen blamed the slower growth in the third quarter on summer vacations. I expect it'll blame the fourth quarter on December holidays.

Don't expect "Tysabri: The Comeback Story" to become a big-screen blockbuster just yet. Unfortunately, until the companies come out with a treatment for PML or a test to determine the susceptibility of getting PML, sales growth may be stuck.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Pfizer is an Inside Value recommendation. Novartis is a Global Gains pick. Try any of our Foolish newsletters today, free for 30 days. The Fool has a disclosure policy.