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U.S. Department of Health and Human Services

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Questions and Answers on Tysabri (natalizumab) Regarding Lifting of the Clinical Hold

[2/15/2006]

1) Why is FDA lifting the clinical hold? 

We received detailed information on the extensive re-examination that Biogen and Elan undertook on all patients who had received natalizumab in clinical studies under an IND. No additional cases of PML were identified. The better understanding of the actual occurrence of PML in these patients permitted better estimation of the potential risk of PML occurring in the future. In addition, Biogen has proposed a resumption of natalizumab administration under an IND study with very specific plans for close monitoring of patients.


2) Will Tysabri be available to all patients? 

Biogen has proposed to FDA only to resume administration of natalizumab to patients who had previously been receiving the drug within an IND study at the time of the suspension of use in February 2005. Those patients would need to discuss with their Study physician the potential risks and potential benefits of resuming treatment with natalizumab, and will be able to make a decision after that discussion. Biogen has not proposed to administer the drug to anyone who had not previously been receiving it under an IND study. Biogen has submitted an application to FDA to resume marketing the drug for more widespread use. That application has a due date for a decision by FDA in late March 2006.

3) What happens to the other holds on similar products and what is our process for lifting these holds? 

The lifting of the clinical hold on natalizumab may lead to requests from other product sponsors to begin or resume clinical studies for molecules that act in a similar manner. FDA will consider each of those proposals as they are received. An important aspect to consider is whether the potential risk of a specific product is reasonable in the setting of a specific disease, type of patient, and other currently available therapies for that type of patient.


4) Is there still a significant safety concern with the product, and if so, why did we lift this hold?

FDA remains very concerned about the potential for PML associated with natalizumab use. However, the currently available information are not adequate to clearly define the level of risk or the exact circumstances when this risk occurs. Furthermore, the existing efficacy data with natalizumab indicate this is a very effective product and multiple sclerosis is a devastating neurologic disease. Therefore, if a study is done in a manner that provides as much safety monitoring as feasible, it is reasonable to resume studying this product under IND to obtain more safety-related information that may permit us to begin to better understand how large or small the true risks associated with natalizumab are.