2 Your Health:New drug may improve MS mobility

Multiple sclerosis (MS) is a condition characterized by the destruction of areas of myelin, the fatty covering that surrounds the nerve fibers in the spinal cord. The spinal cord is like an electrical line that carries nerve signals to/from the brain and body. When an area of myelin is damaged, the nerve signals can “short-circuit” (like a break in an electrical cord) and communication is disrupted. Myelin destruction occurs when the body’s immune system mistakenly attacks its own tissue. However, the exact trigger for this process is unknown. 

Andrew Goodman, M.D., Neurologist with the University of Rochester Medical Center, says one of the most common impairments associated with MS is trouble walking, caused by weakness, fatigue and troubles with coordination and balance. Researchers are testing a medication that may greatly improve walking ability in patients with MS. The drug is called Fampridine-SR (also known as 4-aminopyridine).

When myelin is damaged, electrically charged particles, called potassium ions, leak out through channels in the axon (the nerve extension). The leaking ions causes the nerve’s electrical current to dissipate, short circuiting the signals and disrupting nerve communication. According to the manufacturer (Acorda® Therapeutics), Fampridine-SR closes off the exposed potassium channels. This keeps the potassium ions from leaking out and allows the nerve signals to travel uninterrupted through damaged areas of myelin.

Fampridine is an oral medication that’s taken two times a day. In a phase III study, researchers randomly assigned more than 300 patients to receive either Fampridine or a placebo for 14 weeks. The investigators found 35 percent of those taking Fampridine had a significant improvement in their walking ability versus 8 percent of those taking a placebo. The results were published in the February 28, 2009 issue of The Lancet.

Goodman says Fampridine is designed to be used after the myelin has already been damaged. There is no proof the drug will prevent future damage. If the medication is stopped, the symptoms will return.

Acorda® Therapeutics has filed a new drug application with the FDA and has received a Priority Review status. The FDA is expected to make an approval decision for the drug by early next year.