Retention of Antiseizure Medications for Epilepsy in Multiple Sclerosis: A Retrospective Observational Study.

Purpose: Epilepsy in multiple sclerosis (MS) is rare, and longitudinal clinical studies evaluating treatment with antiseizure medications (ASMs) are difficult to conduct. We instead designed a nationwide register study to estimate retention rates of ASMs prescribed as initial monotherapy for epilepsy in MS and inves-tigated factors influencing their retention. Methods: multiple sclerosis patients with a first prescription of ASM for epilepsy were identified by cross-referencing the Swedish MS register with comprehensive national registers. One and five-year retention rates of ASMs were estimated using Kaplan-Meier analysis. Cox proportional regression was employed to estimate hazard ratios (HR) of discontinuation for different ASMs as well as for baseline predictors. Results: One hundred and twenty-nine MS patients were included. The most commonly prescribed ASMs were: carbamazepine (n = 38, 29.5%), lamotrigine (n = 33, 25.6%) and levetiracetam (n = 19, 14.7%). One-year retention rates (95% CI) were: lamotrigine 87.5% [76, 98.9], carbamazepine 60.5% [45, 76], levetiracetam 60.2% [37.2, 83.2], valproate 51.3% [23, 79.6] and phenytoin 44.4% [11.8, 77]. Fiveyear retention rates (95% CI) were: lamotrigine 74.4% [57.3, 91.5], carbamazepine 52.2% [34.9, 69.4], valproate 51.3% [23.1, 79.5] and phenytoin 14.8% [0, 40.9]. With carbamazepine as reference, lam-otrigine was the only ASM that displayed a lower hazard of discontinuation, HR 0.41 [0.17, 0.99]. We could not identify any baseline factors that influenced the risk of discontinuation. Conclusion: Lamotrigine displayed the lowest risk of discontinuation when prescribed as initial monotherapy for epilepsy in MS. Newer ASMs generally compared well to older ones, at least suggesting non-inferiority. (c) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).