Efficacy of levetiracetam in epilepsy and effect of concomitant drugs on the incidence of somnolence as an adverse effect

Purpose: Somnolence is a major adverse effect associated with levetiracetam (LEV) administration in epilepsy treatment, and it can prompt patients to discontinue the drug. This study aimed to assess the efficacy of LEV and evaluate the incidence and risk factors of somnolence caused by LEV administration.Methods: Medical records of patients with epilepsy treated with LEV between October 2010 and June 2018 were retrospectively analyzed to evaluate drug efficacy. We also analyzed the corresponding incidence of somnolence and its associated factors.Results: Ninety-five patients were included in the study. Of these, 55 (58.9%) showed more than 50% seizure reduction. There was no significant difference in efficacy between the monotherapy (n=38) and adjunctive therapy (n=57) groups. Twenty-nine patients (30.5%) experienced somnolence, and nine patients (9.5%) discontinued LEV. In total, nine patients (23.7%) treated with LEV as monotherapy and 20 patients (35.1%) treated with LEV as adjunctive therapy experienced somnolence, with no significant difference between the two groups. Regarding concomitant antiepileptic drug use, only valproic acid (VPA) significantly induced somnolence. Multiple logistic regression analysis showed that LEV as adjunctive therapy to VPA was a risk factor for somnolence (odds ratio, 3.95; 95% confidence interval, 1.43-11.36; p=0.0079).Discussion: Our data showed that the efficacy of LEV and the incidence of somnolence due to LEV therapy were comparable to those reported previously. Incidence of somnolence increased when patients were treated with LEV as adjunctive therapy to VPA. Discontinuation of LEV due to somnolence might be decreased by avoiding adjunctive treatment with VPA.