Voluntary Suspension of Tysabri® (Natalizumab) Marketing

March 3, 2005

On February 28, 2005, Biogen Idec and Elan Pharmaceuticals announced a voluntary suspension in the marketing of Tysabri®. Commercialization is suspended and physicians are asked to suspend dosing of Tysabri immediately.

Tysabri is the latest drug approved for the treatment of MS, which was released in November 2004. Tysabri is a humanized monoclonal antibody designed to block activated leukocytes from crossing the blood-brain barrier (BBB) and to prevent the inflammatory phase of multiple sclerosis. For more information on Tysabri, please see "FDA Approves Tysabri®(formerly Antegren) For The Treatment
of Multiple Sclerosis".

The voluntary suspension of Tysabri is based on reports of dramatic events occurring in two patients treated with both Tysabri and Avonex at the same time during clinical trials. One patient was confirmed as having fatal Progressive Multifocal Leukoencephalopathy (PML), and a second patient is suspected of having developed the disorder. PML is a viral disease occurring in immuno-depressed patients. To learn more about Progressive Multifocal Leukoencephalopathy (PML), please refer to the following section.

Both patients were enrolled in a long-term clinical trial, receiving Tysabri in combination with Avonex for more than two years (37 and 28 months exactly). So far, no case of PML has been reported in patients treated with Tysabri alone or Avonex alone.

As of today, no causal association has been made between the use of Tysabri, in conjunction with Avonex, and PML. The mechanism leading to the development of PML for these two reported patients is unknown. Additional investigations are in progress by Biogen Idec to determine the association of Tysabri in PML. While waiting for the results of these investigations and as a safety procedure, Biogen Idec and Elan Pharmaceuticals have decided to voluntarily suspend the marketing of Tysabri.

The FDA is reporting this suspension at www.fda.gov/cder/drug/advisory/natalizumab.htm , but is not making any final decision regarding Tysabri at this time. To keep patients and families up-to-date with this suspension of Tysabri, further information will be posted on MSAA's web site as soon as it becomes available.

Christian CD Poncet, PhD
Multiple Sclerosis Association of America
706 Haddonfield Road, Cherry Hill, New Jersey 08002
(800) 532-7667