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A new symptomatic treatment for MS

Ampyra (dalfampridine) is a new medicine to improve MS symptoms that was approved by the FDA in January 2010.  
Ampyra is a continuous release formulation of 4-aminopyridine (4AP).  4AP has been around and used in MS for a long time, but well designed studies demonstrating a measurable benefit in MS were only completed in the last few years. 
One of the things that happens with demyelination in MS is that nerve signals can't get through demyelinated areas.  Depending on what that nerve does, this can cause weakness, numbness, vision problems, and the other symptoms that occur in MS.  Without getting into the details, fampridine is supposed to improve the transmission of nerve signals through areas of damaged myelin, and improve symptoms.  It is a symptomatic treatment, i.e. it treats the symptoms of MS, but it does not modify the course of MS by reducing number of relapses or accumulation of disability.  Although symptomatic treatments don't alter the course of disease, they can make a big difference in quality of life.   
In my experience with Ampyra and 4AP, the benefit in any person is hard to predict.  Some people feel it makes a big difference in their daily activities while other people don't notice any difference.  This probably reflects the severity, type, and location of the damage that MS has caused in the brain and spinal cord.  4AP would be expected to improve conduction across moderately damaged areas, but not in areas with severe damage.  In the clinical studies, about 30 to 40% of the subjects were considered responders. 
The FDA approved Ampyra because it had a measurable effect on walking speed.  It probably should also have benefits on other symptoms which are harder to measure, including sensory symptoms and fatigue. 
The most concerning side effect of Ampyra is seizures.  The risk of seizures increases with higher doses of the drug, and is reduced by a carefully controlled dose and the continuous release formulation.  But some seizures occurred in patients who were taking the drug as recommended. 

J. William Lindsey, MD
University of Texas Multiple Sclerosis Research Group
Houston, Texas

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