Background: In a recent acute study, amantadine was found to have antidyskinetic effect against levodopa-induced motor complications in patients with Parkinson disease. The longevity of this effect was not addressed but is of interest in light of the controversy in the literature regarding the duration of amantadine's well-established antiparkinsonian action.
Objective: To determine the duration of the antidyskinetic effect of amantadine in advanced Parkinson disease.
Design: One year after completion of an acute, double-blind, placebo-controlled, crossover study, patients returned for re-evaluation of motor symptoms and dyskinesias using a nonrandomized, double-blind, placebo-controlled follow-up paradigm.
Setting: National Institutes of Health Clinical Center.
Patients: Seventeen of the original 18 patients with advanced Parkinson disease complicated by dyskinesias and motor fluctuations participated in this study; 1 was lost to follow-up. Thirteen of the 17 individuals had remained on amantadine therapy for the entire year.
Interventions: Ten days prior to the follow-up assessment, amantadine was replaced with identical capsules containing either amantadine or placebo.
Main outcome measures: Parkinsonian symptoms and dyskinesia severity were scored using standard rating scales, while subjects received steady-state intravenous levodopa infusions at the same rate as 1 year earlier.
Results: One year after initiation of amantadine cotherapy, its antidyskinetic effect was similar in magnitude (56% reduction in dyskinesia compared with 60% 1 year earlier). Motor complications occurring with the patients' regular oral levodopa regimen also remained improved according to the Unified Parkinson's Disease Rating Scale (UPDRS-IV).
Conclusion: The beneficial effects of amantadine on motor response complications are maintained for at least 1 year after treatment initiation.