Safety and Tolerability of Tozadenant as Adjunctive Therapy in Levodopa-Treated Patients With Parkinson's Disease.

Each patient will participate for up to 52 weeks, which includes a Screening Period, followed by a Baseline Visit and open-label treatment for 1 year with a safety Follow-up 4 weeks after the last treatment. * Screening Period: up to 6 weeks. * Open-Label Treatment Period: 52 weeks (1 year) * Post-Treatment Safety Follow Up: 4 weeks.