Safety and Efficacy of Suvorexant (MK-4305) for the Treatment of Insomnia in Participants With Alzheimer's Disease (MK-4305-061)

Inclusion Criteria

• Diagnosis of probable Alzheimer's disease based on either a) the National Institute on Aging - Alzheimer's Association (NIA-AA) criteria or b) the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, (DSM-5) criteria for AD.
• Have sleep complaints that meet DSM-5 criteria for a diagnosis of insomnia (e.g., difficulty initiating or maintaining sleep, and/or early morning awakenings with inability to return to sleep for at least 3 nights per week for ≥ the past 3 months prior to study start, despite adequate opportunity for sleep) based on the investigator's judgment and by the participant's sleep history, as assessed by the sleep items on the Insomnia Diagnostic Interview and Sleep History assessments.
• Be willing to stay overnight in a sleep laboratory and must be willing to stay in bed for at least 8 hours for PSG testing
• Regular bedtime is between 8 pm and 1 am and is willing to maintain it for the duration of the trial
• Be able and willing to wear an activity/sleep watch on the wrist throughout the day and night
• Based on the investigator's judgment the participant should: a) be able to speak, read, and understand the language of the trial staff and the informed consent form; b) possess the ability to respond verbally to questions, follow instructions, and complete study assessments; c) be able to adhere to dose and visit schedules.
• Have a reliable and competent trial partner (e.g., spouse, family member, or other caregiver) who:
• a) Signs their own informed consent, after the trial has been explained to them, and before Screening assessments;
• b) Is not diagnosed with dementia;
• c) Resides with the participant overnight and has a close relationship with the participant (defined as daily face-to-face contact, at least 15 waking hours a week for at least 3 months prior to Visit 1);
• d) Accompanies the participant to and from trial visits and stays overnight at the sleep laboratory for the 3 PSG visits;
• e) Assumes responsibility for trial medication procedures (e.g., witnessing and/or helping to administer trial medication, assessing compliance), for completion of the sleep e-diary each morning, and oversight of the activity/sleep watch worn throughout the trial;
• f) Answers questions regarding the trial partner's sleep quality and trial partner's distress related to the subject's behaviors.
• If female, not of childbearing potential as indicated by one of the following: has reached natural menopause, defined as:
• a) ≥45 years of age with either: ≥12 months of spontaneous amenorrhea OR ≥6 months of spontaneous amenorrhea with serum follicle stimulating hormone (FSH) levels > 40 IU/L as determined by the central laboratory
• b) has had a hysterectomy;
• c) has had bilateral tubal ligation; or
• d) has had a bilateral oophorectomy (with or without a hysterectomy) and greater than 6 weeks have passed since the surgery
• Be willing to provide a blood sample for Apolipoprotein E (APOE) genotyping

Exclusion Criteria

• Apnea Hypopnea Index (AHI) score > 30 or Periodic Leg Movements with Arousal per hour of Sleep (PLMA) > 30.
• Resides in a nursing home (or similar institutional facility); assisted-living facilities are not excluded if full-time nursing care is not required.
• Has a Modified Hachinski Ischemia Scale (MHIS) Score > 4 at Screening (i.e., evidence of vascular dementia)
• Has a known history of recent (or past) stroke that in the investigator's opinion confounds the diagnosis of either AD or insomnia
• Has evidence of a clinically relevant neurological disorder other than the disease being studied (i.e., probable AD) at Screening, including but not limited to: vascular dementia, parkinsonism, frontotemporal dementia, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, progressive supranuclear palsy, neurosyphilis, dementia with Lewy bodies, other types of dementia, mental retardation, hypoxic cerebral damage, cognitive impairment due to other d