Onset and duration of effect of extended-release carbidopa-levodopa in advanced Parkinson's disease.

Background: In patients with Parkinson's disease (PD), oral dosing of extended-release carbidopa-levodopa (Rytary, IPX066 [ER CD-LD]) achieves peak levodopa plasma concentrations within 1 hour and maintains them for 4-6 hours.

Aims: To compare the onset and duration of ER CD-LD benefit with those of immediate-release carbidopa-levodopa (IR CD-LD) in PD patients with motor fluctuations, using crossover data, and to evaluate which threshold values of improvement in finger-tapping and Unified Parkinson's Disease Rating Scale (UPDRS) motor scores yield results most similar to those for trained raters' "on"/"off" assessments.

Methods: Patients underwent serial "on"/"off" rating and provided serial finger-tapping and UPDRS motor scores after receiving, in an "off" state, their usual morning IR dose or an ER dose designed to produce a similar levodopa peak concentration. Predefined improvement thresholds for analysis were 10%, 15%, and 20% increases in finger-tapping score and 2.5, 5, 7, and 11-point decreases in UPDRS motor score. Serial plasma samples were assayed for levodopa.

Results: Among 27 patients, mean time to onset of an "on" state was similar for ER compared with IR CD-LD (0.83 vs 0.81 hour), but mean duration was significantly longer for ER CD-LD than for IR CD-LD (5.56 vs 2.69 hours; P <0.0001). Duration was best matched by a $20% improvement in finger-tapping, a $11-point improvement in UPDRS motor score, and a levodopa plasma concentration $1,000 ng/mL.

Conclusion: For ER CD-LD, observer assessments of "on" state were corroborated by sustained treatment effects. Correlations among "on"-state duration, finger-tapping score, and UPDRS motor score may suggest clinically relevant thresholds for acute assessment of treatment benefit.