BOSTON (Reuters) - Biogen Idec Inc said on Friday that a multiple sclerosis patient who had been diagnosed with a rare brain infection while taking its drug Tysabri has died, sending the company’s shares down nearly 3 percent.
Biogen and its partner Elan Corp Plc disclosed the case in October. Naomi Aoki, a spokeswoman for Biogen, said the company learned of the patient’s death earlier this week.
Tysabri is seen as crucial to the growth of both companies. The drug was temporarily withdrawn from the market in 2005 after it was linked with a rare brain infection known as progressive multifocal leukoencephalopathy, or PML.
The drug was reintroduced in July 2006 with stricter safety warnings.
So far, there have been four new cases of PML, an infection rate that is still less than the one in 1,000 warned of in the drug’s label. Nearly 18,000 patients have received at least a year of Tysabri. But investors are watching to see if the rate increases, and they are also looking at how successfully patients can recover.
“While we continue to believe the benefit/risk profile of Tysabri as favorable, we believe this death could lead the FDA and physicians to alter how future PML cases are managed,” said Christopher James, an analyst at Rodman & Renshaw.
The patient who died was a United States patient who had received 14 monthly infusions of Tysabri as a stand-alone treatment. Previously she had received other therapies.
After developing the brain infection, the patient was treated with a procedure known as plasmapheresis, in which blood is removed, cleared of the drug, and replaced.
While the U.S. patient died, two patients who developed PML in Europe, and whose cases were announced in July, appear to be recovering following treatment, even though one had not been expected to survive. Earlier this month, Biogen announced that a fourth patient had developed PML. This patient, in Europe, is still alive.
The European patient that had not been expected to survive had developed a condition known as immune reconstitution inflammatory syndrome, or IRIS. This occurs when the immune system, in eliminating an infection, produces an excessive inflammatory response that can worsen symptoms.
The patient was treated with corticosteroids.
Geoff Meacham, an analyst at J.P. Morgan, said it seems likely the U.S. patient, having gone through plasmapheresis, died of IRIS, and that since the European patient recovered, it might be possible to manage IRIS using steroids and close monitoring. Biogen declined to confirm this theory, citing patient privacy.
“In our view, the rate of PML is now critical to assessing the launch trajectory, and the regulatory outlook, should it stay in the 1/1000 range,” Meacham said in a research note.