To assess the safety and efficacy of 10 milligram (mg) twice a day (b.i.d.) Fampridine-SR in patients diagnosed with multiple sclerosis (MS), in a double-blind, placebo-controlled, parallel group study.

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.

Inclusion Criteria:

• Have a confirmed diagnosis of multiple sclerosis
• Are able to walk with or without an assistive device

Exclusion Criteria:

• Pregnancy, breastfeeding or females of childbearing potential not using adequate birth control
• Participating in other investigational drug trials
• A medical history or clinical findings that preclude entry into the study
• A medication history that precludes entry into the study
• Previously treated with 4-aminopyridine (4-AP)