US regulators on Friday approved a new multiple sclerosis drug co-developed by Biogen Inc. for patients whose relapses aren’t sufficiently controlled by existing therapies.

The once-a-month drug, called Zinbryta, can be injected under the skin by patients. It was developed by Cambridge-based Biogen in partnership with AbbVie Inc., a North Chicago, Ill., drug maker that opened a Cambridge lab earlier this month to focus on neurological diseases.

Zinbryta is Biogen’s sixth MS drug approved by the Food and Drug Administration.

Its sales could be limited because, unlike Biogen’s best-selling MS treatments Avonex, Tysabri, and Tecfidera, the new drug won’t be available for newly diagnosed patients. FDA regulators approved it as a third-line therapy for patients who have an inadequate response to two or more MS drugs. It will be sold under a restricted distribution program.


Zinbryta’s drug label carries a “boxed warning,” common in MS medicines, of serious safety risks. Among the risks are severe and potentially life-threatening liver injuries and immune conditions that include inflammation of the colon, skin reactions, and enlargement of the lymph nodes. The warning also cited increased risks of infections and depression.

Biogen is the global leader in MS, marketing about half the drugs approved to treat the often disabling disease of the central nervous system. MS affects 2.5 million people worldwide.

Biogen senior vice president Ralph Kern said Zinbryta, which works in a different way than existing MS medicines, will bring another option to patients experiencing relapses.

“MS effects each person differently,” he said. “Zinbryta is an important new option for relapsing MS patients.’’

Because it was approved as a follow-on treatment, Zinbryta’s sales will come at the expense of other drugs marketed by Biogen and its competitors.

Robert Weisman can be reached at robert.weisman@globe.com.