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The legacy of vigabatrin in a regional epilepsy clinic

Objectives: To review all patients who had received vigabatrin at the Walton Centre to determine the incidence of visual field defect, seizure outcome if vigabatrin had been stopped, and adherence to guidelines on the use of vigabatrin in clinical practice. Methods: Retrospective review of 583 patients prescribed vigabatrin at any time between 1989 and 2001 from a regional and satellite epilepsy clinic. Data were collected on dose and duration of treatment, results of quantitative perimetry, and reasons for, and outcome of, discontinuation. Results: The visual fields were abnormal with no alternative cause in 42 of the 98 tested (43%). There was no clear relation between the cumulative dose of vigabatrin received and the occurrence of a visual field abnormality. Fifty patients continued taking vigabatrin, and a further 84 were lost to follow up while taking vigabatrin. In 75 patients who had stopped vigabatrin due to a visual field abnormality or concern over this potential adverse effect, the seizure control was no different or had improved in 66 (88%), while it had deteriorated in only 7 (9%). Conclusions: This study confirms the previously reported high incidence of asymptomatic visual field defects associated with vigabatrin. Many patients taking vigabatrin may not have been counselled about the risks, and there are significant cost implications in tracing and assessing those patients lost to follow up. Switching over to another antiepileptic drug usually does not result in deterioration in seizure control, but in clinical practice an individual risk to benefit ratio needs to be taken into consideration.