Dopamine replacement therapy effectively treats the early motor symptoms of 
Parkinson's disease (PD). However, its association with the development of motor 
complications limits its usefulness in late stages of the disease. Adenosine 
A(2A) receptors are localised to the indirect striatal output function and 
control motor behaviour. They are active in predictive experimental models of PD 
and appear to be promising as the first major non-dopaminergic therapy for PD. 
Istradefylline is a novel adenosine A(2A) receptor antagonist currently in Phase 
III clinical trials for efficacy in patients with PD; results from Phase II 
clinical trials demonstrated that it provides a clinically meaningful reduction 
in 'off' time and an increased 'on' time with non-troublesome dyskinesia in 
levodopa-treated patients with established motor complications, and is safe and 
well tolerated.