A responder analysis of memantine treatment in patients with Alzheimer disease maintained on donepezil

Objective: The objective of this study was to examine the clinical utility of memantine for moderate-to-severe Alzheimer disease (AD) using responder analyses. Method: Data from a previously published 24-week, randomized, double-blind, placebo-controlled trial of 10 mg memantine twice a day in patients with moderate-to-severe AD (N = 404) on stable donepezil therapy were evaluated using three sets of responder criteria. Response rates were calculated and analyzed for the intention-to-treat population using a generalized estimating equations model. The following outcomes were examined separately and in combination: the Alzheimer's Disease Cooperative Study-Activities of Daily Living 19-Item Inventory (ADCS-ADL19), Severe Impairment Battery (SIB), Clinician's Interview-Based Impression of Change Plus Caregiver Input (CIBIC-Plus), and Neuropsychiatric Inventory (NPI). Results: When treatment response required cognitive improvement relative to baseline, memantine yielded higher response rates than placebo. When treatment response was defined as stabilization of individual outcomes, memantine resulted in significantly higher response rates than placebo for all outcomes, with number needed to treat (NNT) ranging from 8-10. More conservative definitions of response that required simultaneous stabilization on multiple outcome measures again favored memantine treatment for six of 10 combinatorial definitions. Conclusions: These responder analyses may assist clinicians in evaluating the impact of memantine in a relevant clinical scenario, i.e., in patients with AD previously stabilized on a cholinesterase inhibitor. The current results indicate that in this setting, memantine produces both improvement and stabilization of symptoms, across multiple outcomes, and thus provides a clinically important treatment benefit for patients with moderate-to-severe AD.