The primary objective is to assess the activity of nerispirdine in improving the ability to walk, in patients with multiple sclerosis (MS).

Secondary objectives:

• To assess other measures of walking ability, tiredness, and lower limb muscular strength, spasticity, clinical assessment by subject and clinical assessment of change by the Study Investigator
• To assess the safety and tolerance of nerispirdine
• To evaluate the pharmacokinetics (PK) parameters of nerispirdine

Total duration per patient is approximately 19 weeks in total, comprising a 3-week screening period inclusive of a 2-week placebo run-in period, a 14-week treatment period, and a 2-week placebo run-out (follow-up) period

Inclusion Criteria:

• Clinically definite MS (according to McDonald criteria),

Exclusion Criteria:

• Multiple sclerosis exacerbation or clinical relapse within 6-month prior to the screening visit.
• Subject who is not able to complete two trials of a timed 25 foot walk, with or without an assisted device,
• Patients without valid V1, V2, and V4 T25-FW measurements are not eligible for randomization.
• Female patients who are either pregnant or breastfeeding.

Other protocol-defined inclusion/exclusion criteria may apply.