BACKGROUND: Istradefylline, a selective adenosine A2A receptor antagonist, has 
been reported to improve daily "off time" and motor symptoms in patients with 
Parkinson's disease (PD). However, the effect of istradefylline on sleep 
problems has not been thoroughly investigated.
METHODS: We evaluated the effect of istradefylline on daytime sleepiness, sleep 
disturbances, and motor symptoms in 22 PD patients who were affected by the 
wearing off phenomenon in an open-label, 3-month study. Participants received 
20-40mg/day istradefylline once daily (morning) over a 3-month period. The 
Epworth Sleepiness Scale (ESS), PD sleep scale (PDSS)-2 and PD Questionnaire 
(PDQ-8) were administered at baseline, 2weeks, 1month, 2months and 3months. At 
baseline and 3months, patients were evaluated on the Movement Disorder Society 
Revision of the Unified PD Rating Scale (MDS-UPDRS) parts III and IV.
RESULTS: Twenty-one patients (95.5%) completed the study. At 3months, MDS-UPDRS 
part III (-5.3, p=0.0002) and part IV (-2.5, p=0.001) scores improved and off 
time decreased significantly (-50.1min, p=0.0004). PDQ-8 scores were unchanged 
at 3months. ESS scores decreased significantly at 2months and 3months (-2.4 and 
-3.3, respectively, p<0.0001), but the total PDSS-2 scores did not change.
CONCLUSION: Istradefylline improved daytime sleepiness in PD patients, possibly 
through its effect on enhancing alertness. In addition, the lack of significant 
changes in the total PDSS-2 scores over the study period suggests istradefylline 
had no negative impact on sleep.