UPDATE 1-Biogen stops testing Tysabri to treat stroke after study fails

(Adds background on stroke, analyst comment)

Feb 7 (Reuters) - Biogen Inc said on Wednesday it would stop developing its multiple sclerosis drug Tysabri to treat patients with acute ischemic stroke after it failed a mid-stage study.

The treatment did not improve patients' self-dependence and their ability to perform daily activities when compared with a placebo, the drugmaker said.

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

Analysts have called Biogen's move to develop Tysabri for ischemic strokes as "high risk."

"Stroke is very challenging and even if it works, (Wall Street) may be hesitant to ascribe too much value as Biogen would need to run a larger trial and the commercial opportunity is still far off," Jefferies analyst Michael Yee said last month.

Tysabri had sales of $1.97 billion in 2017. (Reporting by Manas Mishra in Bengaluru; Editing by Savio D'Souza and Sai Sachin Ravikumar)