Long-Term Effects of Safinamide on Dyskinesia in Mid- to Late-Stage Parkinson's Disease: A Post-Hoc Analysis

Background: Safinamide is a novel alpha-aminoamide with dopaminergic and non-dopaminergic properties developed as adjunctive therapy for patients with PD. Results from a 24-month double-blind controlled study suggested that as add-on to levodopa (and other PD medications) the benefits of safinamide on dyskinesia may be related to severity of dyskinesia at baseline. Objective: This post-hoc analysis further characterized the effects of safinamide on dyskinesia in mid-to late-stage PD patients. Methods: Patients were stratified by the presence or absence of dyskinesia at baseline, and by whether or not the dose of levodopa had been changed during the 24-month treatment period. Differences between safinamide and placebo were evaluated using the Wilcoxon rank-sum test. Results: For the overall treated population (with or without baseline dyskinesia), safinamide 100 mg/day significantly improved the dyskinesia rating scale score, compared with placebo, in the subgroup of patients with no change in levodopa dose (p = 0.0488). For patients with baseline dyskinesia, improvements over placebo were also significant (p = 0.0153) in patients with or without changes in levodopa dose, and nearly significant (p = 0.0546) in patients with no change in levodopa dose, suggesting that these improvements were not due to levodopa dose reductions. Conclusions: While no statistically significant difference in mean DRS scores was seen between safinamide and placebo in the original study population, the present post-hoc analysis helps to provide a meaningful interpretation of the long-term effects of safinamide on dyskinesia. These results may be related to safinamide state-and use-dependent inhibition of sodium channels and stimulated glutamate release, and are unlikely due to reduced dopaminergic stimulation.