Study of the strength of the evidence and the redundancy of the research on pharmacological treatment for Alzheimer's disease: a cumulative meta-analysis and trial sequential analysis

Purpose To study the strength of the evidence on efficacy, safety and acceptability of cholinesterase inhibitors (ChEI) and memantine for Alzheimer's disease (AD); and to determine the number of redundant post-authorisation trials. Methods A cumulative meta-analysis with a trial sequential analysis (TSA) was performed. Primary outcomes were cognitive function assessed with ADAS-cog or SIB scales, discontinuation due to adverse events (AE) and discontinuation for any reason. The redundancy of post-authorisation clinical trials was studied by determining the novel aspects of each study on patient, intervention, comparator and trial outcome characteristics. Two criteria of futile trial (lenient and strict) were used. Results A total of 63 randomised clinical trials (RCTs) (16,576 patients) were included. It was conclusive that neither ChEI nor memantine achieved clinically significant improvement in cognitive function. In relation to safety, there was sufficient evidence to conclude that donepezil caused a clinically relevant increase on dropouts due to AE whereas the evidence was inconclusive for the remaining interventions. Regarding acceptability, it was conclusive that no ChEI improved treatment discontinuation while it was uncertain for memantine. The proportion of redundant trials was 5.6% with the lenient criteria and 42.6% with the strict one. Conclusions The evidence is conclusive that ChEI and memantine do not achieve clinically significant symptomatic improvement in AD while the acceptability of ChEI is unsatisfactory. Although evidence on the safety of pharmacological interventions for AD and acceptability of memantine is inconclusive, no further RCTs are needed as their efficacy is not clinically relevant. Redundant trials were identified but their number depends on the criteria of futility used.