Acorda Therapeutics(ACOR) - Get Report shares are trading lower Monday after the company's latest failed attempt to expand the use of its top-selling drug Ampyra.

A mid-stage study of Ampyra in patients with walking difficulties following a stroke "did not show sufficient efficacy" to support further clinical development, Acorda said Monday.

The company's stock fell 9% to $19.30 per share in early Monday trading on the disappointing Ampyra news.

Ampyra is approved to improve the walking ability of multiple sclerosis patients. Ampyra sales of $437 million in 2015 made up 89% of Acorda's total revenue. The drug is expected to generate $489 million in sales this year, according to FactSet estimates.

Future Ampyra revenue is at risk due to an ongoing inter partes review of the drug's patents. A decision on the patent challenge is expected next year.

With expansion of Ampyra into additional indications on hold, Acorda says it will now focus research and development resources on a late-stage Parkinson's disease drugs CVT-301 and tozadenant, along with earlier assets CVT-427 in migraine, SYN120 in Parkinson's and rHIgM22 in MS.

At Friday's close, Acorda's market value was less than two times 2017 revenue, a sign investors were already uneasy about the company's future growth prospects, including the Ampyra stroke trial.

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