<qa>  What is the starting dosage of istradefylline?This is a Phase III open-label study, in which patients with Parkinsons disease PD who have completed a qualifying istradefylline study will be treated with istradefylline for a period of up to one additional year. Starting dosage of istradefylline will be 40 mgd and maintenance dosage will be at the discretion of the Investigator. The available doses for istradefylline are 20 and 40 mgd. Open-label istradefylline treatment will be initiated after a patient has satisfied all criteria for participation. 