Patients with acute demyelinating optic neuritis who received the anticonvulsant drug phenytoin lost 30% less of their retinal nerve fiber layer than did placebo-treated patients in a randomized, phase II study.
“The results of this clinical trial support the concept of neuroprotection using phenytoin to inhibit voltage-gated sodium channels in patients with acute optic neuritis,” wrote Dr. Rhian Raftopoulos of the National Hospital for Neurology and Neurosurgery, London, and coauthors (Lancet Neurol. 2016 Jan 25. doi: 10.1016/S1474-4422(16)00004-1).
Courtesy National Eye Institute
The study in 86 individuals with acute optic neuritis randomized 29 participants to receive 4 mg/kg per day of oral phenytoin, 13 to 6 mg/kg per day of oral phenytoin, and 44 to placebo for 3 months; all were randomized within 14 days of vision loss. One-third of the patients had previously been diagnosed with multiple sclerosis or were diagnosed at presentation, and 74% had at least one brain lesion on MRI.
Treatment with phenytoin resulted in a decline of mean retinal nerve fiber layer thickness in the affected eye from 130.62 mcm at baseline to 81.46 mcm at 6 months, compared with a decline from 125.20 mcm to 74.29 mcm in the placebo group, representing an adjusted mean difference of 7.15 mcm that reached statistical significance.
The researchers also noted a significant 34% reduction in macular volume loss in the treatment arm, compared with placebo, representing an adjusted mean difference of 0.20 mm3. However, the treatment had no significant effect on low-contrast visual acuity and visual evoked potentials.
The most common adverse event in the treatment arm was maculopapular rash, which was judged as severe in one patient treated with phenytoin.
The study was supported by the U.S. National Multiple Sclerosis Society, the Multiple Sclerosis Society of Great Britain and Northern Ireland, Novartis, the U.K. National Institute for Health Research, and the NIHR UCLH/UCL Biomedical Research Centre. Several authors declared personal fees, trial funding, grants, and consultancies for pharmaceutical companies, including Novartis.