(Reuters) - Biogen Inc will stop testing established drug Tysabri for the treatment of acute ischemic stroke after it failed a mid-stage study, the U.S. drugmaker said on Wednesday.

Tysabri, which made nearly $2 billion in 2017 sales, belongs to Biogen’s franchise of multiple sclerosis (MS) drugs that has driven much of the Cambridge, Massachusetts-based company’s explosive growth in recent years.

Tysabri’s stroke trial comes as Biogen’s MS portfolio, which is led by top-selling drug Tecfidera, faces mounting competition from Roche AG’s Ocrevus and Sanofi SA’s Aubagio.

Analysts, who have viewed Biogen’s plans to develop Tysabri for stroke as risky, were unsurprised by the trial’s failure.

“Tysabri’s failure in stroke this morning is likely to have limited impact, as our sense had been that expectations were quite low,” said RBC Capital Markets analyst Brian Abrahams.

Ischemic strokes require immediate medical attention and occur when blood supply is cut off to part of the brain.

In the mid-stage trial, Biogen’s treatment failed to improve patients’ self-dependence and their ability to perform daily activities when compared with a placebo.

Biogen also has other drugs in mid-stage trials including treatments for Alzheimer’s disease and stroke.

Its closely watched Alzheimer’s drug candidate aducanumab is in late-stage testing, while another Alzheimer’s treatment failed a mid-stage study in December.

“We continue to believe Biogen’s mid-stage neuro pipeline is scientifically sound and should generate more interest as programs reach later stages,” RBC’s Abrahams said.

Biogen’s shares were slightly lower on Wednesday morning.