The Food and Drug Administration on Monday said it was expanding its label warning of potentially deadly brain infections for patients taking
multiple sclerosis treatment Tysabri.
Tysabri was previously removed from the market after being linked to progressive multifocal leukoencephalopathy (PML), but was relaunched with a warning on its label. News of the drug's connection to
of PML since its approval in the European Union and the re-entry into the U.S. market two years ago in July hit shares of companies. Biogen fell 26% and Elan plummeted 45% after the cases were disclosed.
On Monday, the FDA said the label will now include the risk of progressive PML with Tysabri when it's used alone. PML is a known risk of Tysabri, but previous cases in patients with MS were seen in combination with other therapies that affect the immune system. Regulators said they still believe Tysabri monotherapy may have a lower risk of PML than when the drug is used with other immunomodulatory medications.
"We view the label change as relatively minor and believe it reflects the FDA's support for continued Tysabri use," wrote Thomas Weisel Partners' analyst Ian Somaiya in a note Monday. The analyst expects sales could continue to beat estimates, but maintained a market weight rating "given our concern for further downside risk if and when PML cases are confirmed in the U.S."
The two recent cases occurred after 17 and 14 months of treatment, respectively, both in Europe. Biogen said Tuesday that as of Aug. 25, both were clinically stable.
Roughly 39,000 patients have been treated with Tysabri worldwide, with approximately 12,000 patients receiving treatment for a least one year. No new cases have been seen in the U.S., where about 7,500 patients have received the drug for more than a year and roughly 3,300 patients have had it for at least eighteen months.
There are reports of
of PML in Tysabri patients on the FDA's Adverse Event Reporting System (AERS) database. However, it is not public how many suspected cases of PML currently exist, or the rate at which they turn out to be false alarms.
Biogen said Tuesday that they haven't received any reports of additional confirmed cases of PML in patients treated with Tysabri since the two discussed in late July.
"The physician response has been largely supportive -- they've been pleased to see these cases have been detected early and have been managed," said Biogen Idec spokeswoman Naomi Aoki on Tuesday. Aoki noted that PML with Tysabri use is one of the most communicated drug risks, and thus the emergence of cases was not a surprise.
Biogen shares recently were down 1.9%, at $52.48, while Elan shares were off fractionally to $14.23.