Saturday, June 25

Tysabri Update: Possible Fourth and Fifth Cases of PML; Hope for Return to the Marketplace; Risks Continue

MSAA News: LINKSeveral articles on the topic of Tysabri® (natalizumab) and the possible development of progressive multifocal leukoencephalopathy (PML) were posted on the New England Journal of Medicine's website on June 9th . While these case studies and editorials were originally to be published in July, news of a suspected fourth case of PML in a Tysabri-treated patient prompted the journal to post the articles in advance online. More recently (on June 13 th ), The Wall Street Journal announced a possible fifth case of PML, involving a woman who has been hospitalized.

To review, Tysabri was given early approval in November 2004 by the Food and Drug Administration (FDA) for the treatment of MS. The drug had shown initial success in clinical trails and was expected to be a strong candidate for the long-term treatment of MS. The drug was suspended, however, in February 2005 after PML (a brain virus that is often fatal) was confirmed in two patients taking both Tysabri and Avonex® (interferon beta-1a).

The first patient died and the second patient appears to be improving. A third case was discovered upon the re-examination of a patient who took Tysabri in the treatment of Crohn's Disease and died in 2003. An investigation is now underway regarding the possible fourth and fifth cases of PML.

A letter from three doctors at Biogen Idec (makers of Tysabri) may also be viewed on the New England Journal of Medicine's website at . The correspondence notes that while little is known about PML and JC virus, studies suggest that PML is not uniformly fatal, and cases of PML may be preceded by the JC virus. Additionally, a test may be able to determine the presence of the JC virus in a patient's plasma. The doctors speculate that through early diagnosis, Tysabri treatment could be discontinued in time to allow patients to recover, providing hope for some that Tysabri may return to the marketplace.

According to The Wall Street Journal's press release dated June 9, 2005, Dr. Joseph Berger from the University of Kentucky Medical Center has some concerns. He warns that while the idea of early diagnosis and recovery is a possibility, it does carry associated risks. For instance, the studies being reviewed only have a few years of data available, and the risk of developing PML could potentially increase after several years of treatment. Additionally, Tysabri remains in the body for three months after treatment is stopped, which could increase the risk of developing PML even if the treatment is discontinued following the discovery of the JC Virus.

Biogen Idec is conducting a large analysis of thousands of patients who took Tysabri. Results of this evaluation are expected to be available by the end of the summer.

Information for this writing was obtained from the New England Journal of Medicine ( ), Reuters, and The Wall Street Journal.