Interim report on the incidence of visual field defects in patients on long term vigabatrin therapy

The incidence was determined of visual field defects in patients in the Pre scription-Event Monitoring (PEM) study, treated for greater than or equal t o 6 months with the antiepileptic drug vigabatrin. Questionnaires were sent to the general practitioners of the 7228 patients in the PEM study, treate d with vigabatrin for greater than or equal to 6 months, to ascertain wheth er any serious adverse events, including changes in vision, had occurred. O phthalmologists were asked to give the results of the perimetry tests and t heir opinion of the cause of the visual field defect for those patients ref erred to them. 6793 (94%) of the 7228 questionnaires were returned. 5090 (7 5%) contained clinical data. 328 patients were deceased. Seventy seven case s identified from the 4762 surviving patients, are being followed up with o phthalmologists, To date, 2 weeks after posting, 12 cases of visual field d efect have been confirmed by formal perimetry tests. Ten of these 12 were c onsidered to be probably or possibly related to vigabatrin use, giving an i ncidence of 2.0 per 1000 patients compared with 0.4 per 1000 patients in th e original PEM cohort. These interim results show a substantial increase in the incidence of visual field defects associated with long term use of vig abatrin and demonstrate that PEM can be used to assess long latency adverse events. Copyright (C) 1999 John Wiley & Sons, Ltd.