Tysabri, the MS Drug Haunted by Deadly Side Effect, Doesn’t Look So Deadly Anymore
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that might offer doctors clues as to which individual patients have an elevated risk of getting PML from the start, and which ones are less likely to become infected. The key to determining this could lie in a relatively common lab technology, known as Elisa, that can detect whether a patient has antibodies in the blood made to fight the JC virus that can awaken from a dormant state to cause PML in Tysabri patients. About half of adults are estimated to have these antibodies, which suggest that JC virus is lurking in the body with the potential to become an opportunistic infection in at least some Tysabri patients. The remaining patients are thought to have no JC virus in their systems, and therefore would be considered less likely to get PML, Sandrock says.
Biogen also has a lot of other strategies for minimizing the risk of PML. It is forming a consortium with the makers of other drugs that have been linked to the side effect, such as rituximab (Rituxan), efalizumab (Raptiva), alemtuzumab (Campath), and mycophenolate (Cellcept), Sandrock says. The idea is that accumulating more data in a global database will help each company deal with the issue, Sandrock says.
There are other ideas in the works as well, such as a vaccine to protect against PML—”we’re very excited about that,” Sandrock says—and a potential anti-PML treatment called mephaquin, which is commonly used to treat malaria. A Biogen collaboration with Cambridge, MA-based Alnylam Pharmaceuticals to develop an RNA interference-based treatment for PML has stopped, Sandrock says.
Pressure to show progress with innovative new treatments, vaccines, or drug holidays will surely intensify if the incidence of PML keeps climbing past that 1-in-1,000 benchmark rate as patients stay on the treatment for years. The pressure to figure out how to best manage PML will come from investors, regulators, and from the patients themselves, who want to make sure that they can still get the drug.
“Not a week goes by around here that we don’t hear a story from a patient who has had their life transformed by this treatment,” Sandrock says. “The benefit has been confirmed, by real life stories. And we’ve made a lot of progress at mitigating the risk.”