Multiple sclerosis (MS) is an anti-inflammatory. demyelinating disorder of the central nervous system. Acute optic neuritis is a common feature of MS, which can damage vision through neurodegeneration of the optic nerve. As phenytoin has been found to be neuroprotective in preclinical models, this study was designed to determine whether this medication can be neuroprotective for patients with acute optic neuritis.

This randomized, double-blind, placebo-ontrolled trial included patients 18-60 years of age with MS and acute demyelinating optic neuritis. Participants were randomized to receive either phenytoin to achieve serum concentrations appropriate for epilepsy, or placebo. the patients were assessed by the treating physician at one and three months from baseline. The primary outcome measure was the change in retinal nerve fiber layer thickness (RNFL) in the affected eye at six months compared to the unaffected eye.

Of the 81 patients available for follow-up, the mean RNFL thickness remsined stsble in the unaffected eye. In the modified intention-to-treat population, the adiusted mean difference in six-month RNFL in the affected eye (phenytoin group minus placebo group) was 7.15 um (P＝0.021). This represents a 30% reduction in the extent of RNFL loss with phenytoin as compared with placebo.

This study of patients with multiple sclerosis and acute demyelinating optic neuritis, found that phenytoin can be neuroprotective, reducing the loss of RNFL thickness.