Biogen Inc. shares sank after doctors in a top medical journal said more instances of brain infections may occur in people taking a type of medication that includes the drugmaker’s top-selling multiple sclerosis treatment.
The shares fell 5.6 percent to $316.60 at the close in New York following the publication of the letter in the New England Journal of Medicine, in which doctors in the Netherlands called for “further studies concerning safety monitoring and new methods for identification of patients at risk” for people taking dimethyl fumarate.
More cases may arise as more people use dimethyl fumarate, the doctors said. Biogen makes a formulation of dimethyl fumarate marketed as Tecfidera.
Biogen reported in October that a patient had developed a rare brain infection and died while on Tecfidera. The company modified the drug’s label to reflect the case. A second, non-fatal brain infection of a Tecfidera patient was reported last month, and a Dutch psoriasis patient died of the same type of infection while on a high dose of another delayed-release dimethyl fumarate made by a compounding pharmacy.
“If the reported findings develop into a pattern of opportunistic infections, then we should expect increasing headline risk and potential headwinds to Tecfidera usage,” said Matthew Roden, an analyst at UBS AG, in a research note. Biogen may have to update Tecfidera’s label again in the U.S. and Europe to reflect the risks, he said.
“We believe that Tecfidera is an excellent treatment choice because it continues to offer people living with MS a combination of strong efficacy and safety,” Biogen said in a statement. About 155,000 patients have been treated with Tecfidera worldwide.
Biogen’s competitors have also dealt with cases of brain infection. Earlier this week, the U.S. Food and Drug Administration released a safety warning about Gilenya, manufactured by Novartis AG. The drug, also used to treat multiple sclerosis, has been linked to as many as two cases of brain infection, U.S. regulators said. Gilenya isn’t a dimethyl fumarate like Tecfidera.
The brain infection observed in the patients on Tecfidera and Gilenya, called progressive multifocal leukoenceophalopathy, is caused by a virus and affects the brain’s white matter. PML symptoms include loss of language ability and memory and vision problems, according to the U.S. National Institutes of Health.
Tecfidera sales will reach $3.6 billion this year and $5.2 billion by 2020, according to analysts’ estimates compiled by Bloomberg.
Shares of Cambridge, Massachusetts-based Biogen had lost 1.2 percent this year through Wednesday’s close.