The case of the Crohn's patient, Dr. Tyler noted, is significant because it indicates “that neither concurrent use of Avonex [interferon β-1a] or underlying neurologic disease like MS is necessary” for the development of PML in patients taking Tysabri.
All agree that while the new reports clarify the association between treatment with natalizumab and the occurrence of PML, questions about the magnitude of risk need to be answered before the drug can be brought back to the market.
“There's a big interest in bringing [Tysabri] back, but the viability of the drug will depend on our ability to predict risk of PML and know how great a risk PML is for MS patients,” said Michael Kaufman, M.D., director of the MS Center at Carolinas Health Care in Charlotte, N.C., and an investigator in one of the Tysabri trials.
“Two cases out of hundreds with MS … could be the tip of the iceberg, or it could be the only two who were susceptible to it,” he said.
Despite her patient's partial recovery, Dr. Langer-Gould told this newspaper she fears that if the drug were prescribed for longer periods of time, “it would be highly likely we would see many more cases of PML resulting in death or significant life-long disability as well as other toxicities.”
According to a short “correspondence” written by leaders at the Cambridge, Mass.-based Biogen Idec Inc., a panel established by the company is currently reviewing all suspicious and ambiguous findings to evaluate them for PML (NEJM [Epub ahead of print], June 9, 2005. Article DOI:10.1056/NEJMc055235. Available from www.nejm.com
A spokesman for Biogen Idec and Elan Corp. told CLINICAL NEUROLOGY NEWS that once they have a better understanding of the risks of PML—perhaps later this summer—the companies will share their findings with the FDA and European regulatory agencies, and “together, the compan[ies] and agencies will make a decision about how to proceed with the drug.”
In the NEJM reports, Dr. Langer-Gould, Dr. Berger, and Dr. Koralnik each report having received consulting and/or lecture fees from Biogen Idec.