ADORA2A and Parkinson disease: Istradefylline (KW-6002, (E)-8-(3,4-Dimethoxystyryl)-1,3-diethyl-7-methyl-3,7-dihydro-1H-purine-2,6-dione, Nourianz®) is the first novel A2AR antagonist approved by the US FDA as an adjunctive therapy with levodopa and carbidopa for the treatment of PD patients experiencing “OFF” symptoms and did not exacerbate dyskinesia caused by levodopa [40,41,42].