The primary purpose of this study is to evaluate proof of mechanism (POM) and long-term safety and tolerability of E2511 in participants with Early AD. The study consists of 2 parts. In Part A, participants will be randomly assigned to receive either E2511 or donepezil. In Part B, participants will receive E2511 only. Once Part A and Part B participants complete the Core Trial (which includes Pretreatment and Treatment phases) they will have the option to enter the Extension Phase where they will receive E2511 for 18 months.
Meet the National Institute on Aging and the Alzheimer's Association (NIA-AA) core clinical criteria for MCI due to AD-intermediate likelihood.
Have a global Clinical Dementia Rating Scale (CDR) score of 0.5 and a CDR Memory Box score of greater than or equal to (>=) 0.5 at Screening and Baseline.
Meet the NIA-AA core clinical criteria for probable AD dementia.
Have a global CDR score of 0.5 to 1.0 and a CDR Memory Box score of >=0.5 at Screening and Baseline.
Females who are breastfeeding or pregnant at Screening or Baseline (as documented by a positive beta-human chorionic gonadotropin [β-hCG] or human chorionic gonadotropin [hCG] test with a minimum sensitivity of 25 International Units per Liter [IU/L] or equivalent units of β-hCG [or hCG]). A separate baseline assessment is required if a negative screening pregnancy test was obtained more than 72 hours before the first dose of trial drug.
total abstinence (if it is their preferred and usual lifestyle)
an intrauterine device or intrauterine hormone-releasing system (IUS)
a contraceptive implant