A 12-week Study of Pramipexole Extended Release (ER) in Patients With Parkinson's Disease (PD), Followed by a 52-week Long-term Treatment Period

The objective of this trial is to investigate the safety, tolerability, trough plasma concentration, and efficacy of pramipexole ER in comparison with those of pramipexole IR administrated orally for 12 weeks in patients with PD on levodopa (L-DOPA) therapy (the double-blind period). The double-blind period will be followed by the open-label 52 week administration of pramipexole ER to evaluate the long term safety and efficacy (the open-label period).