<qa>  What was the name of the study that consisted of 4 treatment periods?This was a multicentre, randomised, double-blind, placebo- and active-controlled, four-way crossover study. The study consisted of 4 treatment periods in at least 16 patients with PD treated with standard release levodopacarbidopa Sinemet. Patients were randomly assigned to treatment with placebo, nebicapone 75 mg, nebicapone 150 mg or entacapone 200 mg Comtan in 4 different sequences. 