Modelling the risk of visual field loss arising from long-term exposure to the antiepileptic drug vigabatrin: a cross-sectional approach

Wild, John Millington ORCID: https://orcid.org/0000-0003-3019-3889, Fone, David Lawrence ORCID: https://orcid.org/0000-0002-6476-4881, Aljarudi, Saleh Hassan, Lawthom, Charlotte, Smith, Philip E. M. ORCID: https://orcid.org/0000-0003-4250-2562, Newcombe, Robert Gordon ORCID: https://orcid.org/0000-0003-4400-8867 and Lewis, Gareth D. 2013. Modelling the risk of visual field loss arising from long-term exposure to the antiepileptic drug vigabatrin: a cross-sectional approach. CNS Drugs 27 (10) , pp. 841-849. 10.1007/s40263-013-0100-z

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Abstract

Background: The antiepileptic drug vigabatrin has been used widely since 1989, but has only been approved for use in the US since 2009. The risk:benefit of vigabatrin is generally predicated upon an assumed frequency of associated visual field loss (VAVFL) of approximately 31 %. This estimate is based upon relatively short-term usage (up to 4–5 years) and it is essential to determine whether the frequency of VAVFL increases with longer-term usage. Objective: The aim of this study was to model, from cross-sectional evidence, over greater ranges of treatment duration and cumulative dose than previously evaluated, the risk (frequency) of VAVFL with increasing exposure to vigabatrin. Study Design and Setting This was a retrospective cohort study undertaken in a regional hospital epilepsy clinic. Patients: The cohort comprised 147 consecutive patients treated with vigabatrin for refractory complex partial (focal) seizures, who had all undergone ophthalmological examination and who had undertaken perimetry, reliably, according to a standard and robust protocol. The visual field plots were evaluated masked to treatment duration and dose. Main Outcome Measure: The risk (frequency) of VAVFL with increasing exposure to vigabatrin was modelled, from the cross-sectional evidence, by standard and plateau logistic regression. Results: The cohort comprised 80 females and 67 males (mean age 40.3 years, standard deviation 13.7). The median duration of vigabatrin exposure was 7.9 years (interquartile range 3.6–11.0, range 0.2–16.1 years); 46 patients (31 %) had received vigabatrin for over 10 years. Eighty-seven patients (59 %) exhibited VAVFL; the proportion with VAVFL was higher in males (66 %) than females (54 %). The plateau model for duration and for cumulative dose exhibited a better fit than the standard model (both p < 0.001). The modelled frequency of VAVFL increased with increasing exposure up to approximately 6 years duration and 5 kg cumulative dose, and plateaued at approximately 76 % (95 % CI 67–85) and 79 % (95 % CI 70–87), respectively. Severity of VAVFL, classified in terms of the visual field index Mean Deviation, was not significantly associated with either duration or cumulative dose of therapy. Conclusion: Clinicians and patients, in enabling informed choice, should be alert to the possible substantial increased risk:benefit for VAVFL with increasing long-term exposure to vigabatrin and the ensuing increased cost:benefit resulting from the necessary additional visual assessments.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Medicine Optometry and Vision Sciences Neuroscience and Mental Health Research Institute (NMHRI)
Subjects:	R Medicine > RE Ophthalmology R Medicine > RM Therapeutics. Pharmacology
Publisher:	Springer
ISSN:	1172-7047
Last Modified:	11 Dec 2022 09:29
URI:	https://orca.cardiff.ac.uk/id/eprint/51653

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