Dyskinesia in Parkinson's Disease (Study P04501)

The purpose of the study is to assess the efficacy and safety of a range of doses of SCH 420814 (preladenant) when used together with a stable dose of L-dopa/dopa decarboxylase inhibitor to treat Parkinson's disease. In this study, we will be comparing 3 doses (1 mg, 2 mg, and 5 mg taken twice a day) of preladenant with placebo (sugar pill). Following an Interim Analysis (temporary hold for new enrollment-ongoing subjects will continue on treatment) to review drug safety, a new dose group of 10 mg (taken twice a day) may be added.

Approximately 160 participants will be randomized in this study in approximately 22 study centers worldwide for the first part of this study. Following the Interim Analysis, 40 new participants may be added, for a total of 200 participants. The study is double blind, which means neither you nor your study doctor will know whether you are receiving the study medication or placebo.


Eligibility Criteria:
Inclusion Criteria:

* Participants must be 30 years of age, of either sex and of any race, with a diagnosis of moderate to severe idiopathic Parkinson's disease for at least 5 years.
* Women of childbearing potential must have a negative serum pregnancy test at Visit 2 (Week -1). If participant is postmenopausal (not surgically induced), she must be postmenopausal by history for at least 2 years before study entry. If not, proper birth control must be used.

Note: Acceptable methods of birth control include oral or injectable hormonal contraceptive, medically prescribed intrauterine device (IUD), and double-barrier method (eg, condom in combination with spermicide). Bilateral tubal ligation is an acceptable method of birth control for this study.

* Participants' clinical laboratory tests (complete blood count \[CBC\], blood chemistries, and urinalysis) must be within normal limits or clinically acceptable to the investigator/sponsor.

Exclusion Criteria:

* Participants with any form of drug-induced or atypical parkinsonism, cognitive impairment (Mini-Mental State Examination \[MMSE\] score \<=23), a history of Diagnostic and Statistical Manual of Mental Disorders IV (DSM IV) diagnosed major depression, unstable mild depression or psychosis, or participants taking tolcapone will be excluded. (Participants with mild depression who are well controlled on a stable dose of an antidepressant medication for at least 4 weeks before screening will be eligible.)
* All participants with a severe or ongoing unstable medical condition will be excluded including those with a history of poorly controlled diabetes, obesity associated with metabolic syndrome, uncontrolled hypertension, cerebrovascular disease, or any form of clinically significant cardiac disease, symptomatic orthostatic hypotension, renal failure, history of abnormal renal function, seizures, alcohol/drug dependence, or previous surgery for Parkinson's disease.
* Average daily consumption of more than two 4-oz (120 mL) glasses of wine or their equivalent.
* Because it is not known whether preladenant passes into breast milk and because the effects, if any, of preladenant on the developing human are unknown, women who are breastfeeding or who are considering breastfeeding are excluded from this trial.
* Participants with allergy/sensitivity to study drug or its excipients.
* Participants with any clinically significant condition or situation, other than the condition being studied that, in the opinion of the investigator, would interfere with the study evaluations or optimal participation in the study.
* Participants who have used any other investigational drugs within 30 days of Screening.
* Participants who are participating in any other clinical study.