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Can 4-aminopyridine Improve Visual Function in MS Patients?

Summary and Comment |
July 1, 2013

Can 4-aminopyridine Improve Visual Function in MS Patients?

  1. Ellen M. Mowry, MD, MCR

Preliminary data showing a benefit in some patients with multiple sclerosis should prompt further investigations of this medication.

  1. Ellen M. Mowry, MD, MCR

The purpose of this study was to assess if 4-aminopyridine (4-AP), a potassium-channel blocker that improves nerve conduction along demyelinated axons, improves visual acuity or other measures of visual function in multiple sclerosis (MS) patients with optic neuropathy. (An extended-release formulation is FDA-approved to improve walking in MS.) Enrolled patients had retinal nerve fiber layer thickness (RNFL) of ≤80 µm in one or both eyes or had a >10-µm difference between their eyes. They underwent baseline high-contrast and low-contrast (2.5% and 1.25%) visual acuity testing, optical coherence tomography, and visual evoked potentials (measuring P100 latency). Twenty two patients were randomized to compounded 4-AP (titrated over 5 weeks to a final dose of 10 mg three times daily) or placebo. Participants crossed over to the opposite treatment for weeks 6 to 10. Visual-function testing was performed at weeks 5 and 10.

Only 14 participants were included in the final analysis (2 withdrew, and 6 were excluded for relapse or nonadherence). The primary outcome (≥5-letter improvement on the 2.5% low-contrast chart) did not differ significantly between treatments. When all 28 eyes were assessed, the P100 latency improved by –1.20 milliseconds on 4-AP and increased by 1.57 milliseconds on placebo, a significant difference; the differences were more pronounced in eyes with RNFL thickness of 60 to 70 µm (–1.88 vs. +2.57 msec).

Comment

Standard multiple sclerosis therapies reduce the risk for new disease activity, but interventions that improve quality of life through reduction of symptoms are needed. Treatment with 4-aminopyridine appears to improve some physiologic measures of vision. Whether the results were clinically meaningful is unclear, and the lack of an intent-to-treat analysis may bias the results. Still, larger studies of 4-AP's utility in MS are warranted.

Dr. Mowry is Assistant Professor of Neurology, the Johns Hopkins University, Baltimore, MD.

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