Epilepsy drug increases visual field defects, study confirms

LIVERPOOL, England — An anti-epilepsy drug awaiting regulatory approval in the United States appeared to cause visual field defects in more than 40% of patients, a long-term study here found. Patients with epilepsy who were prescribed vigabatrin had a high incidence of asymptomatic visual field defects, according to the study.

Published in the August issue of Journal of Neurology, Neurosurgery and Psychiatry, the study confirms earlier published findings of ocular side effects from the drug. Previous studies indicated vigabatrin causes visual field constriction in about 30% of patients; this study put the figure at 43%. The defects are in most cases peripheral and therefore asymptomatic.

Andrew Nicolson, MD, and colleagues here at The Walton Center for Neurology and Neurosurgery retrospectively reviewed the charts of 98 patients with epilepsy who were given vigabatrin any time from 1989 to 2001. Of these patients, 42 had abnormal visual fields with no alternative cause other than the anti-seizure drug, the authors said.

Previous reports have indicated that vigabatrin, indicated as a monotherapy for the treatment of infantile spasms, increases the concentration of gamma-amino butyric acid in the brain and retina and is associated with a number of ocular side effects. The drug has been approved in more than 60 countries for the adjunctive management of partial epilepsy.

The authors of the new report noted that in 75 patients who had stopped using vigabatrin because of visual field abnormalities, seizure control was no different or had improved on other medication in 66 patients (88%) and had deteriorated in only seven (9%).

“Many patients taking vigabatrin have not been counseled about the risks,” the authors write. “In clinical practice, an individual risk to benefit ratio needs to be taken into consideration.”