Biogen, Elan Drug Gets New FDA Warning

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 suspected casesof 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.