Shares in Acorda Therapeutics have taken a bashing after documents released ahead of a US panel meeting on Wednesday claimed that the firm’s multiple sclerosis treatment Amaya “has a very limited effect”.

Documents have been released on the website of the US Food and Drug Administration ahead of a meeting of its Peripheral and Central Nervous System Drugs Advisory Committee on October 14, which will evaluate Amaya (fampridine) for the improvement of walking ability in people with MS. The drug is a novel, oral sustained-release compound.

Acorda has conducted two trials tracking the ability of MS patients to complete a 25-foot walk. One of them, involving nearly 300 patients found that 35% of the 224 Amaya-treated subjects improved their walking speed compared with 8% of 72 patients on placebo.

Both studies showed a statistical improvement in walking ability compared with those on placebo but the FDA staffers note that the actual time to complete the exercise did not improve. "For these reasons”, the review claims, “it appears the clinical meaning of the differences seen on the primary outcomes is in question".

The staffers also noted an increased risk of seizures with Amaya and a link with urinary tract infections. Acorda’s own briefing documents state that no evidence of seizures has been shown when the drug is given at the recommended 10mg dose.

Despite the concerns expressed by the staffers, most analysts remain fairly confident that the FDA will look kindly on the drug. Deutsche Bank’s Mark Schoenbaum wrote a research note saying that most MS specialists "do not seem phased" by Amaya’s seizure risk and expects the panel to recommend approval but with a black box warning about the latter.

However, Phil Nadeau, an analyst at Cowen & Co, issued a research note saying that “fampridine’s panel on Wednesday is going to be somewhat more contentious than we had anticipated”. He added that “it would seem from the documents that the FDA may be moving the goal posts on Acorda”.

In July, Biogen Idec signed a deal to acquire the rights to the drug outside the USA.