Dalfampridine is a lipid-soluble small molecule that more readily crosses the blood-rain barrier and, therefore, its effects on the central nervous system (CNS) have been the subject of greater focus. The initial Phase 2 study determined the safety of escalating doses of dalfampridine in subjects with multiple sclerosis (MS), to explore a number of outcome measures, and examine dose related efficacy. A battery of assessments was performed weekly, including the MS Functional Composite (MSFC), fatigue questionnaires, lower extremity manual muscle testing, and spasticity assessment using the Ashworth scale. The results supported the idea that quantitative functional outcome measures (such as walking speed derived from timed gait and lower extremity muscle testing) were sufficiently sensitive to demonstrate efficacy. Based on evaluation, the US food and drug administration (FDA) approved the extended release (ER) formulation of dalfampridine (daily oral dose of 10 mg BID) for use in MS to improve walking.