To establish the efficacy of a 20 mg/d dose of istradefylline for reducing the percentage of OFF time in patients with advanced Parkinson's disease (PD) treated with levodopa. Patients who meet entry criteria will be randomized in a 1 to 1 ratio to either istradefylline or matching placebo. Patients will be treated for 12 weeks and will have interim visits and end of treatment visit to assess the efficacy and safety of istradefylline as compared to placebo.
To establish the efficacy of a 20 mg/day dose of istradefylline for reducing the percentage of OFF time in patients with advanced Parkinson's disease (PD) treated with levodopa.