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 Prescription-Event Monitoring (PEM) study, treated for > or =6 months with the antiepileptic drug vigabatrin. Questionnaires were sent to the general practitioners of the 7228 patients in the PEM study, treated with vigabatrin for > or =6 months, to ascertain whether any serious adverse events, including changes in vision, had occurred. Ophthalmologists were asked to give the results of the perimetry tests and their opinion of the cause of the visual field defect for those patients referred to them. 6793 (94%) of the 7228 questionnaires were returned. 5090 (75%) contained clinical data. 328 patients were deceased. Seventy seven cases identified from the 4762 surviving patients, are being followed up with ophthalmologists. To date, 2 weeks after posting, 12 cases of visual field defect have been confirmed by formal perimetry tests. Ten of these 12 were considered to be probably or possibly related to vigabatrin use, giving an incidence of 2.0 per 1000 patients compared with 0.4 per 1000 patients in the original PEM cohort. These interim results show a substantial increase in the incidence of visual field defects associated with long term use of vigabatrin and demonstrate that PEM can be used to assess long latency adverse events.