Impact of study design and patient population on outcomes from cholinesterase inhibitor trials

The authors conducted a comparative review of study designs and patient populations used in pivotal trials investigating various cholinesterase inhibitors (tacrine, donepezil, rivastigmine, galantamine, controlled-release physostigmine, and metrifionate) and their impact on outcomes reported. Study design parameters that were investigated of adverse dropouts and serious adverse gated included patient selection, definitions of adverse dropouts and serious adverse events, effective doses used, dosing flexibility (fixed versus flexible), forced titration, and titration rate. Population characteristics included medical comorbidity and disease severity. Data suggest that differences in study designs and patient populations affect outcomes. Therefore, caution should be taken before making decisions on relative efficacy, safety, and tolerability, because clinical studies are not always directly comparable.