BACKGROUND: We evaluated the efficacy and safety of istradefylline, a selective 
adenosine A2A receptor antagonist administered as adjunctive treatment to 
levodopa for 12 weeks in a double-blind manner in Parkinson's disease patients 
with motor complications in Japan.
METHODS: A total of 373 subjects were randomized to receive placebo (n=126), 
istradefylline 20 mg/day (n=123), or istradefylline 40 mg/day (n=124). The 
primary efficacy variable was the change in daily OFF time. Other secondary 
variables were also evaluated.
RESULTS: The change in daily OFF time was significantly reduced in the 
istradefylline 20 mg/day (-0.99 hours, P=.003) and istradefylline 40 mg/day 
(-0.96 hours, P=.003) groups compared with the placebo group (-0.23 hours). The 
most common adverse event was dyskinesia (placebo, 4.0%; istradefylline 20 
mg/day, 13.0%; istradefylline 40 mg/day, 12.1%).
CONCLUSIONS: Istradefylline reduced daily OFF time and was well tolerated in 
Japanese PD patients with motor complications on levodopa treatment.