Influence of Piribedil (Clarium®) on Vigilance and Cognitive Function in Patients With Parkinson's Disease Compared to Other Non-Ergot Dopamine Agonists

Inclusion Criteria: * Male or female Caucasian patients aged 35 to 80 years; * Patients with idiopathic Parkinson's disease; * Hoehn \& Yahr stages 1 to 4; * Stable medication with anti-parkinsonian medication, including stable treatment with pramipexole or ropinirole, for at least 4 weeks prior to Screening; * Significant daytime sleepiness: Epworth Sleepiness Scale score equals or is higher than 11 under previous therapy with pramipexole or ropinirole; * Patients who have read and understood the patient information sheet and have provided a signed written informed consent form; * Patients are considered to be compliant to the study regimen. Exclusion Criteria: * Treatment of Parkinson's disease with any dopamine agonist other than pramipexole or ropinirole within 4 weeks prior to Screening; * Known hypersensitivity to Clarium® or its excipients; * Patients with daytime sleepiness caused by other factor's than Parkinson's disease, i.e., idiopathic narcolepsy, shift work, severe alcohol abuse, obstructive diseases, sleep apnea syndrome, or Periodic limb movement disorder; * Secondary and atypical Parkinson syndrome; * Depression (Beck Depression Inventory score higher than 16); * Dementia (Mini-Mental State Examination score equals or is lower than 24); * Severe disability in extremities which could influence clinical assessments; * Clinically significant disease concerning the lung, liver or kidney; * Any acute or chronic infection that may influence the outcome of the study; * Cardiovascular shock; * Acute myocardial infarction; * Congestive heart failure NYHA class III or IV; * Uncontrolled arterial hypertension (diastolic blood pressure equals or is higher than 105 mmHg) or clinically relevant hypotension; * Evidence of clinically active cancer; * Color vision defect that may have impact on assessment of FWIT; * History of substance abuse; * Intake of benzodiazepines (or derivates) if not at stable dose for at least 4 weeks prior to Screening; intake of antiallergic agents (H1 receptor antagonists, except selective, non-sedating H1-antihistamines, e.g. loratadine and others), substances with psychostimulant properties (e.g., amphetamine, modafinil), or antidepressants if not at stable dose for at least 2 months prior to Screening; * Current treatment with neuroleptic agents (except for clozapine); * Female patients who are pregnant or lactating; * Female patients of childbearing potential who do not use a highly effective method of birth control (failure rate less than 1% per year when used consistently and correctly), e.g., implants, injectables, combined oral contraceptives in combination with a barrier method, some intrauterine contraceptive devices, sexual abstinence, or a vasectomized partner; * Mental condition rendering the patient unable to understand the nature, scope and possible risks of the study; * Patient has a history of or is suspicious of unreliability, poor co-operation or non-compliance with medical treatment; * Patients are currently or previously (within the last 28 days) participating in another study of an investigational drug; * Patients who were previously enrolled in this study; * Patients with known Hepatitis B or C or HIV infection; * Patients who are employees of the sponsor or patients who are employees or relatives of the investigator.