A Placebo- and Active Controlled Study of Preladenant in Subjects With Moderate to Severe Parkinson's Disease (P04938)

Inclusion Criteria: * Must have a diagnosis of moderate to severe idiopathic Parkinson's disease. * Must have received prior therapy with L dopa for approximately 1 or more years immediately before Screening and must continue to have a beneficial clinical response to L dopa * Must have been on a stable dopaminergic treatment regimen for at least the 5 weeks immediately before Randomization. Participants receiving other adjunctive treatments (eg, dopamine agonists, anticholinergics, entacapone) or taking only L dopa are permitted, provided the treatment regimen has been taken for at least 5 weeks prior to randomization * Must be experiencing motor fluctuations with or without dyskinesias within the 4 weeks immediately before Screening, must be experiencing a minimum of 2 hours/day of "off" time, and have a Hoehn \& Yahr stage between 2.5 and 4 when in the "on" state * Must be capable of maintaining an accurate and complete symptom diary and to adhere to dose and visit schedules with or without the help of a caregiver * Must have results of a physical examination and screening clinical laboratory tests clinically acceptable to the investigator * If sexually active or plan to be sexually active agree to use a highly effective method of birth control while in the study and for 2 weeks after the last dose of study drug. Males must also not donate sperm during the trial within 2 weeks after the last dose of study drug Exclusion Criteria: * Must not have a form of drug induced or atypical parkinsonism, a cognitive impairment, bipolar disorder, untreated major depressive disorder, schizophrenia, or other psychotic disorder; history of exposure to a known neurotoxin, or any neurological features not consistent with the diagnosis of PD as assessed by the investigator * Must not have a history of repeated strokes or head injuries, or a stroke within 6 months of Screening * Must not have poorly-controlled diabetes or abnormal renal function * Must not have had surgery for their PD * Must not be at imminent risk of self-harm or harm to others * Must not have sleep attacks or compulsive behavior that would interfere with the integrity of the trial or would pose a risk to the subject in participating in the trial * Must not have a systolic blood pressure (BP) ≥150 mm Hg OR diastolic BP ≥95 mm Hg at Screening * Must not have had any clinically significant cardiovascular event or procedure for 6 months prior to study start, including, but not limited to, myocardial infarction, angioplasty, unstable angina, or heart failure; and must not have heart failure staged New York Heart Association Class III or IV * Must not have an alanine aminotransferase (ALT) or aspartate amino transferase (AST) ≥3 x the upper limit of normal (ULN) or total bilirubin (T-BIL) ≥1.5 x ULN * Must not have a history of serologically confirmed hepatic dysfunction (defined as viral infection \[Hepatitis B or C; Epstein Barr virus (EBV); cytomegalovirus (CMV)\]) or a history of diagnosis of drug or alcohol induced hepatic toxicity or frank hepatitis * Must not have a history within the past 5 years of a primary or recurrent malignant disease with the exception of adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or in situ prostate cancer with a normal prostate-specific antigen (PSA) post resection * Must not have received certain prespecified medications or ingested high tyramine-containing aged cheeses (eg, Stilton) for a prespecified time window before the trial, during the trial, and for 2 weeks after the trial * Must not have an average daily consumption of more than three 4 ounce glasses (118 mL) of wine or the equivalent * Must not have a severe or ongoing unstable medical condition (eg, any form of clinically significant cardiac disease, symptomatic orthostatic hypotension, seizures, or alcohol/drug dependence) * Must not have allergy/sensitivity to investigational product(s) or its/their excipients * A female subject must not be breast-feeding, considering breast-feeding, pregnant, or intending to become pregnant * Must not have used preladenant ever, or any investigational drugs within 90 days immediately before Screening