Efficacy and Safety of 4-aminopyridine on Cognitive Performance and Motor Function of Patients With Multiple Sclerosis

Each patient will take two capsules every 8 hours after meals, for a total of 6 capsules/day. The 4-aminopyridine dosage will increase 10 mg/4 weeks by substitution of placebo instead of 4-aminopyridine capsules; such that patients will receive from 40 to 60 mg. distribute in 6capsules/day throughout the study.

The placebo arm will include Microcrystalline Cellulose placebo