Background: In patients with dementia with Lewy bodies (DLB), it is unknown whether adjunct zonisamide is as effective and safe as increasing levodopa dose when levodopa has inadequate efficacy on parkinsonism.
Objective: To compare adjunct zonisamide 25 mg/day versus an increased levodopa dose (increased by 100 mg/day) in patients with DLB treated with levodopa ≤300 mg/day for parkinsonism.
Methods: The DUEL study was a multicenter, randomized, controlled, open-label, parallel-group, interventional, non-inferiority trial. During the observation period, levodopa was administered at ≤300 mg/day for 4 weeks. Subsequently, patients were randomized to receive adjunct zonisamide 25 mg/day or levodopa increased by 100 mg/day.
Results: Respective adjusted mean changes in MDS-UPDRS Part III total score at 16 and 24 weeks (primary endpoint) were -6.3 and -4.4 in the zonisamide add-on and -0.8 and 2.0 in the levodopa increase groups. The adjusted mean difference at 24 weeks was -6.4 (95% confidence interval [CI] -13.5, 0.7); the upper limit of the 95% CI (0.7) was lower than the non-inferiority margin (3.0). No significant between-group differences were observed in total scores of the MDS-UPDRS Part II, Eating Questionnaire, EuroQol-5 dimension-5 level, Zarit Caregiver Burden Interview, or other secondary endpoints. No notable between-group differences were observed in adverse event incidences.
Conclusion: Adjunct zonisamide 25 mg/day may yield moderate improvement in motor symptoms in patients with DLB when the levodopa effect is insufficient, but it could not be verified that the zonisamide 25 mg/day was as effective as levodopa 100 mg/day because levodopa showed no sufficient efficacy as assumed.
Keywords: Alzheimer’s disease; Lewy body disease; dementia with Lewy bodies; levodopa; parkinsonism; randomized controlled trial; zonisamide.