Joanne M. Ho, Marco Ghassemi, Carmen H. Ng, Erik Blondal, Paul A. Khan, Areti Angeliki Veroniki, Jemila S. Hamid, Laure Perrier, Sumit R. Majumdar, John D. Ivory, Huda M. Ashoor, Andrea C. Tricco, Patricia Rios, Charlene Soobiah, Brenda Hemmelgarn, Sharon E. Straus, Fatemeh Yazdi
Background/Objectives
To examine the comparative effectiveness and safety of cognitive enhancers for Alzheimer's disease (AD).
Design
Systematic review and Bayesian network metaanalysis (NMA).
Setting
MEDLINE, EMBASE, Cochrane Library, CINAHL, Ageline (inception–March 2016).
Participants
Individuals with AD in randomized controlled trials (RCTs), quasi-RCTs, and nonrandomized studies.
Intervention
Any combination of donepezil, rivastigmine, galantamine, or memantine.
Measurements
Two reviewers independently screened titles, abstracts, and full-texts; abstracted data; and appraised risk of bias.
Results
Twenty thousand three hundred forty-three citations were screened, and 142 studies were included (110 RCTs, 21 non-RCTs, 11 cohort studies). NMA found that donepezil (Mini-Mental State Examination: mean difference (MD) = 1.39, 95% credible interval (CrI) = 0.53–2.24), donepezil+memantine (2.59, 95% CrI = 0.12–4.98), and transdermal rivastigmine (2.02, 95% CrI = 0.02–4.08) improved cognition more than placebo. NMA found that donepezil (Alzheimer's Disease Assessment Scale–cognitive: MD = −3.29, 95% CrI = −4.57 to −1.99) and galantamine (MD = −2.13, 95% CrI = −3.91 to −0.27) improved cognition more than placebo. NMA found that donepezil+memantine (MD = −5.23, 95% CrI = −8.72 to −1.56) improved behavior more than placebo. NMA found that donepezil (MD = −0.32, 95% CrI = −0.46 to −0.19), donepezil+memantine (MD = −0.57, 95% CrI = −0.95 to −0.21), oral rivastigmine (MD = −0.38, 95% CrI = −0.56 to −0.17), and galantamine (MD = −3.79, 95% CrI = −6.98 to −0.59) improved global status more than placebo. NMA found that galantamine decreased the odds of mortality (odds ratio = 0.56, 95% CrI = 0.36–0.87). No agent increased risk of serious adverse events, falls, or bradycardia. Some increased risk of headache (oral rivastigmine), diarrhea (oral rivastigmine, donepezil), nausea (oral rivastigmine, donepezil, galantamine), and vomiting (oral rivastigmine, donepezil, galantamine).
Conclusion
An exhaustive review of the literature involving 142 studies demonstrated that cognitive enhancers in general have minimal effects on cognition according to minimal clinically important difference and global ratings. The drugs appear safe, but this must be interpreted cautiously because trial participants may have less comorbidity and fewer adverse effects than those treated with these drugs in clinical practice.
