Objective: Investigate the efficacy of immediate-release (IR) amantadine in reducing the risk of peak-dose dyskinesia in early Parkinson's disease (PD) as add-on to levodopa.
Background: While the use of amantadine to manage dyskinesia in PD is well supported by controlled clinical trials, data on its efficacy in patients without motor complications remain limited.
Methods: This 22-month, multicenter, randomized, placebo-controlled trial (NCT01538329) enrolled early PD patients on stable levodopa (≥150 mg/day for ≤1 year) without motor complications. The study included three double-blind phases: an 18-month treatment phase with adjunct amantadine-IR (200 mg/day) or placebo (Period 1), a 3-month delayed-start phase where all participants received amantadine-IR (Period 2), and a 1-month washout with placebo (Period 3). The primary outcome was dyskinesia incidence at month 18; secondary outcomes included dyskinesia rates at the end of Periods 2 and 3 to assess potential long-lasting mechanisms of the drug. Exploratory outcomes investigated the potential effects of amantadine-IR on motor and non-motor symptoms and quality of life.
Results: A total of 207 patients were randomized to amantadine-IR (N = 99) or placebo (N = 108). Significantly fewer patients in the amantadine-IR group developed dyskinesia versus placebo during Period 1 (11% vs. 22%, P = 0.025), while the mean daily dose of levodopa (95% CI) increased by 70 (21-119) mg less (P = 0.005). The proportion of patients with dyskinesia was less in the amantadine-IR group versus placebo at the end of Periods 2 and 3, but the difference was not statistically significant (12% vs. 20%, P = 0.13 and 16% vs. 22%, P = 0.23, respectively). Mild but significant positive effects on freezing of gait, fatigue, and quality of life were observed during Period 1. The safety profile of amantadine-IR was in line with previous reports.
Conclusions: Adjunctive amantadine-IR in early PD halved dyskinesia incidence over 18 months. Long-lasting mechanisms could not be demonstrated and merit further investigation. Exploratory positive findings on the potential benefit of amantadine-IR on symptoms like freezing of gait and fatigue also call for further investigation. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.
Keywords: Parkinson's disease; amantadine; dyskinesia; levodopa.
© 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.