To establish the efficacy of 10, 20 and 40 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 10, 20 or 40 mg or matching placebo. Patients will be treated for 12 weeks and will have interim visits and end of treatment visit to assess efficacy and safety.
To establish the efficacy of 10, 20 and 40 mg/d dose of istradefylline for reducing the percentage of OFF time in patients with advanced Parkinson's disease (PD) treated with levodopa.