Efficacy of memantine in people with moderate to severe Alzheimer's disease with and without background donepezil therapy: Pooled analysis of four randomized trials

Abstract

Memantine is an NMDA receptor antagonist approved for the treatment of moderate to severe Alzheimer's disease (AD); donepezil is a cholinesterase inhibitor (ChEI), approved for mild to severe AD in the US. Treatment of AD typically involves initiation of donepezil therapy in early stages, with memantine added as the disease progresses to moderate and severe stages. Two large 24-week randomized trials and several observational studies suggest that this combined treatment is superior to monotherapy with either drug; while results of one small 52-week randomized trial generated debate. To further investigate the effects of combination therapy vs monotherapy, we pooled four similarly designed randomized, placebo-controlled trials of memantine in patients with moderate to severe AD and compared Baseline-to-Endpoint changes in measures of cognition (SIB), function (ADCS-ADL 19), behavior (NPI), and global clinical status (CIBIC-Plus), stratified by treatment/concurrent therapy regimen (placebo, memantine, placebo/donepezil, or memantine/donepezil). All patients from two memantine monotherapy trials (MRZ-9001–9605 and MEM-MD-01; N=567) and donepezil-treated patients from two memantine add-on trials (MEM-MD-02 and MEM-MD-50; N=841) were pooled and Endpoint changes from Baseline for the SIB, ADCS-ADL 19, NPI, and CIBIC-Plus were assessed using a mixed-effects model with repeated measures (observed cases). Due to the exploratory nature of this analysis, no corrections for multiple comparisons were performed. At study Endpoint, the memantine/donepezil treatment group was significantly superior to placebo (P<0.001) and both memantine and placebo/donepezil monotherapy groups (P<0.05) on all four efficacy measures. There were no statistically significant differences between memantine and placebo/donepezil monotherapy groups on the CIBIC-plus, ADCS-ADL 19, and NPI; however, the placebo/donepezil group performed significantly better than the memantine group on the SIB (P<0.001). Both memantine and placebo/donepezil treatment groups were significantly better than placebo on the SIB, ADCS-ADL 19, and CIBIC-plus (P<0.01), but no significant treatment differences were observed among these three treatment groups on the NPI. This pooled analysis is in agreement with evidence suggesting that adding memantine to stable donepezil treatment in patients with moderate to severe AD is associated with improvements across several clinical domains, compared with monotherapy using either drug. Appropriately powered, long-term, prospective studies of add-on therapy in AD are warranted.