UPDATE 2-Acorda shares fall over FDA concerns for MS drug

* Secondary review indicated "very limited effect"

* FDA advisers to weigh drug on Wednesday

* Shares fall more than 18 percent
(Adds share price, company comment, background on drug)

By Susan Heavey

WASHINGTON, Oct 9 (Reuters) - Acorda Therapeutics Inc's
(ACOR.O) proposed drug to help multiple sclerosis patients walk
better appears to have a "very limited effect" even though the
drug met its main clinical trial goals, U.S. regulatory staff
said in documents released on Friday.

Shares of the drugmaker fell more than 18 percent after the
Food and Drug Administration released the staff scientists'
review.

While Acorda's drug, called Amaya, does not aim to treat
the degenerative disease, the company is seeking FDA approval
as a treatment to help improve patients' ability to walk. On
Wednesday of next week, a group of outside experts will meet to
discuss the drug and offer the FDA advice about whether to
allow its use.

Multiple sclerosis is a degenerative disease that affects
the central nervous system and can cause vision problems,
muscle weakness, difficulty balancing and even paralysis in
some more serious cases.

"Walking impairment is one of the most common MS-related
functional impairments and can lead to profound disability and
reduced quality of life," Acorda said in separate documents
released on Friday.

The company said its two studies showed that Amaya
"provides rapid, significant, and clinically relevant
improvements in walking ability" and that patients reported
positive experiences with its use.

One study of nearly 300 patients found that 35 percent of
the 224 Amaya-treated subjects improved their walking speed
compared with 8 percent of the 72 patients given a placebo.

Looking at percentages, there was a statistically
significant difference in patients' walking ability, but the
actual time it took patients on average to walk 25 feet was not
different for those given the drug versus a placebo, the FDA
staff said.

Additionally, secondary analyses of the data "gave
inconsistent results, and indicated a very limited effect on
walking speed," they added.

"For these reasons, it appears that the clinical meaning of
the differences seen ... is in question," FDA staff said in
their review.

Amaya contains fampridine, which is widely known to cause
seizures -- a factor that also must be weighed, the FDA staff
said. The risk for seizures is linked to the dose, and the FDA
said it also planned to ask its advisers if Acorda should study
a dose smaller than the proposed 10 milligram version before
being approved.

Despite the FDA staff's concerns, some analysts said they
expected the drug ultimately to receive the agency's backing.

J.P. Morgan analyst Geoff Meacham and his colleagues said
some of the FDA's concerns came as "a modest negative
surprise," but that the agency's advisory panel was likely to
support the drug.

Acorda's stock was off 17.6 percent at $18.35 in midday
trade on the Nasdaq.
(Reporting by Susan Heavey, editing by Dave Zimmerman and
Matthew Lewis)