Acorda Therapeutics ( ACOR) disclosed Tuesday that U.S. regulators have refused to review the company's multiple sclerosis drug for approval. The Food and Drug Administration sent Acorda a "refuse to file" letter regarding its new drug application for fampridine, a drug designed to improve the walking ability of patients with multiple sclerosis. Acorda submitted fampridine to the agency on Feb. 2. Regulators cited "format issues" with the electronic application of fampridine as reason for the letter. The FDA has asked Acorda to reformat some of the fampridine data in the submission and requested more "supporting information," the company said. Acorda didn't provide any details about the type of additional information that was requested but did state that the FDA hasn't asked for additional clinical trials to be performed. "We are surprised by this development," said Acorda CEO Ron Cohen, in a statement. "We plan to address the issues raised in this letter with FDA expeditiously as we believe Fampridine-SR is potentially an important, first in class treatment option for people suffering with MS." Acorda shares closed Monday at $24.90.