(the FDA did not grant permission for use of this drug--was it based upon Phase II safety trials??? I cannot recall the specifics, though this abstract just appeared in one of the alerts to which I subscribe. Granted it is but a 12 week placebo controlled study)
Paula, the first author is the PD doc who is the speaker from that fabulous web link you gave on a previous post http://neurotalk.psychcentral.com/thread47277.html

http://www.ncbi.nlm.nih.gov/pubmed/18519872

Neurology. 2008 Jun 3;70(23):2233-40. Links
A 12-week, placebo-controlled study (6002-US-006) of istradefylline in Parkinson disease.Stacy M, Silver D, Mendis T, Sutton J, Mori A, Chaikin P, Sussman NM.
Division of Neurology, Duke University Medical Center, Durham, NC 27705, USA. mark.stacy@duke.edu

BACKGROUND: The safety and efficacy of istradefylline, a selective adenosine A(2A) receptor antagonist, was evaluated in a 12-week, double-blind study in levodopa-treated Parkinson disease (PD) subjects with motor complications. METHODS: Levodopa-treated PD subjects (n = 395) received istradefylline 20 mg/day (n = 163), istradefylline 60 mg/day (n = 155), or placebo (n = 77) at 40 sites. The primary efficacy variable was the change in the percentage of time per day spent in the OFF state. Secondary measurements assessed change in ON time, Unified Parkinson's Disease Rating Scale, and Clinical Global Impression. Safety monitoring included clinical laboratory, electrocardiograms, vital signs, physical/neurologic examinations, and adverse events (AEs). RESULTS: Changes from baseline to endpoint in the percentage OFF time in the active groups compared with placebo were -4.35% (95% CI -8.16 to -0.54; p = 0.026) for istradefylline 20 mg/day and -4.49% (95% CI -8.35 to -0.62; p = 0.024) for 60 mg/day; these changes were significant (analysis of covariance). For total hours, istradefylline demonstrated mean differences from placebo of -0.64 hours (95% CI -1.30 to 0.01) for 20 mg/day and -0.77 hours (95% CI -1.44 to -0.11) for 60 mg/day (p = 0.065; overall treatment effect). Clinical response occurred by the second week and was maintained throughout the study. Istradefylline was well tolerated. The common AEs were dyskinesia, nausea, dizziness, and hallucinations. CONCLUSIONS: Istradefylline demonstrated a significant reduction in the percentage of awake time per day spent in the OFF state, which resulted in a clinically meaningful reduction in OFF time, without an increase in ON time with troublesome dyskinesia, and was well tolerated as adjunctive treatment to levodopa in Parkinson disease.

PMID: 18519872 [PubMed - in process]