Impact of Adjunctive Istradefylline on Dyskinesia Onset in Patients with Parkinson's Disease Exhibiting Wearing-Off:...

Motor complications become major treatment challenges in patients with Parkinson's disease (PD). Istradefylline (IST) is used as an adjunct to levodopa in patients with PD exhibiting wearing-off (WO), but its impact on the onset of dyskinesia remains unclear. The objective of this study was to investigate the effect of IST on dyskinesia onset in patients with PD exhibiting WO.

In this 3-year, multicenter, randomized, open-label, parallel-group, controlled study, 214 patients with levodopa-treated PD exhibiting WO without pre-existing dyskinesia were randomized (1:1) to either adjunctive IST (IST group) or to adding another or increasing the dose of other anti-PD drugs (non-IST group). The primary endpoint was the time to onset of dyskinesia.

Over 3 years, the incidence of dyskinesia was 37.9% and 41.1% in the IST and non-IST groups, respectively. The time to onset of dyskinesia was not significantly different between the IST versus non-IST groups (median: 1100.00 vs. 1082.00 days). When dividing patients by age, the rate of time to onset of dyskinesia was lower in the IST group in patients aged ≥ 68 years (median) and in the non-IST group for patients aged < 68 years and patients aged < 60 years at PD onset. The levodopa-equivalent daily dose (LEDD) was significantly lower throughout the study period, by 57 mg on average, in the IST group than in the non-IST group. Efficacy and safety indexes were not significantly different between the two groups.

Adjunctive IST showed no difference in the onset of dyskinesia compared with adding another or increasing the dose of other anti-PD drugs, and displayed equivalent efficacy and tolerability, while maintaining a lower LEDD in this long-term study of patients with PD exhibiting WO. These findings support the use of adjunctive IST as a viable treatment option for patients with PD exhibiting WO.

University hospital Medical Information Network clinical trials registry (UMIN000024536) and Japan Registry of Clinical Trials (jRCTs071180014).