The patients, who are in stable condition, are the first confirmed cases of PML in Tysabri users since the drug was reintroduced in the U.S. and approved in Europe two years ago, according to Biogen Idec and Elan, the companies that co-market Tysabri.
As of July 31, one of the patients is at home and walking; the other patient is hospitalized, according to Biogen Idec's report to the U.S. Securities and Exchange Commission (SEC).
Biogen Idec learned of the first case on July 30 and the second case a day later, and filed the SEC report yesterday; Biogen Idec has also reported the cases to the FDA and regulators in Europe. The FDA is reviewing the data and is in discussions with Biogen Idec.
Tysabri already carries a "black box" warning -- the FDA's sternest warning -- about PML risk. PML risk-management programs have been in place for two years for U.S. and European Tysabri users. Education and awareness about PML risk "was critical" in identifying and managing the two new PML cases, says Naomi Aoki, Biogen Idec's director of public affairs.
Given the known risk of PML, new cases aren't unexpected, notes Aoki. But she says Tysabri is "an important therapeutic option for patients, especially for patients who have very aggressive MS or whose MS has continued to progress despite treatment with other therapies -- and the risk-benefit ratio of the drug remains favorable."
Tysabri and PML
Tysabri is a monoclonal antibody given by a health care professional. In the U.S., it's approved to treat patients with relapsing forms of MS in order to reduce the frequency of flare-ups, and to treat Crohn's disease.
The FDA first approved Tysabri in 2004. PML cases led Tysabri's makers to voluntarily take the drug off the U.S. market in February 2005. The FDA allowed Tysabri to return to the U.S. market in June 2006, after an FDA advisory panel recommended doing so.
Biogen Idec and Elan reintroduced Tysabri in the U.S. in July 2006; at the same time, the drug was approved in the European Union. The FDA approved Tysabri for the treatment of Crohn's disease in January 2008.