• Timed Walk Responders (Patients Who Showed Consistent Improvement on the Timed-25 Foot Walk) [ Time Frame: Days 14, 42, 70 and 98 of treatment, corresponding to the four on-drug visits during double-blind treatment period. ] [ Designated as safety issue: No ]
  Patients who showed a faster walking speed for at least three of the four on-drug visits during the double-blind treatment period as compared to the maximum speed for any of the five off-drug visits.
  
  

• Lower Extremity Manual Muscle Test; Ashworth Score for Spasticity [ Time Frame: Days 14, 42, 70, 98 ] [ Designated as safety issue: No ]
  

Multiple sclerosis (MS) is a disorder of the body's immune system that affects the central nervous system (CNS). Normally, nerve fibers carry electrical impulses through the spinal cord, providing communication between the brain and the arms and legs. In people with MS, the fatty sheath that surrounds and insulates the nerve fibers (called "myelin") deteriorates, causing nerve impulses to be slowed or stopped. As a result, patients with MS may experience periods of muscle weakness and other symptoms such as numbness, loss of vision, loss of coordination, paralysis, spasticity, mental and physical fatigue and a decrease in the ability to think and/or remember. These periods of illness may come (exacerbations) and go (remissions). Fampridine-SR is an experimental drug that has been reported to possibly improve muscle strength and walking ability for some people with MS. This study will evaluate the effects and possible risks of taking Fampridine-SR in subjects with MS.