Dose comparison trial of sustained-release fampridine in multiple sclerosis

To examine the efficacy and safety of three different doses of sustained-release fampridine in people with multiple sclerosis (MS). This multicenter, randomized, double-blind, placebo-controlled, parallel-group study recruited 206 participants at 24 centers in the United States and Canada. After a single-blind, 2-week placebo run-in, participants were randomly assigned to receive fampridine (10, 15, or 20 mg twice daily) or placebo for 15 weeks. The primary efficacy variable was percent change in walking speed based on the timed 25-foot walk. Trends for increased walking speed were consistent across dose groups vs placebo, but not significant, on the prospective analysis. An increase from baseline in lower extremity strength during the 12-week stable-dose period was seen in the groups receiving 10- and 15-mg doses, compared with placebo (p = 0.018 and 0.003). There were no significant changes in other secondary assessments. Post hoc analysis revealed subsets of participants in each dose group with walking speeds during the treatment period that were consistently faster than during the nontreatment period. There were significantly more "consistent responders" in the drug-treated groups than in the placebo group (36.7% compared with 8.5%). Consistent responders showed significantly greater improvement in self-assessed ambulation on the 12-Item MS Walking Scale than did nonresponders. Fampridine was generally well tolerated. Severe and serious adverse events were more frequent at the highest dose. This phase 2 study suggests that a subgroup of patients, when treated with fampridine, experiences a clinically relevant improvement in walking ability, which is sustained for at least 14 weeks.