Inclusion Criteria:

• Present with mild AD dementia based on the National Institute on Aging (NIA) and the Alzheimer's Association (AA) disease diagnostic criteria as determined by a qualified clinician approved by the Sponsor or designee.
• Mini-Mental State Examination score of 20 to 26 inclusive at screening visit.
• Has a florbetapir PET scan consistent with the presence of amyloid pathology at screening.

Exclusion Criteria:

• Significant neurological disease affecting the central nervous system (CNS), other than AD, that may affect cognition or ability to complete the study, including but not limited to, other dementias, serious infection of the brain, Parkinson's disease, multiple concussions, or epilepsy or recurrent seizures (except febrile childhood seizures).
• Ocular pathology that significantly limits ability to reliably evaluate vision or the retina.
• Use of strong inducers of cytochrome P450 3A (CYP3A) within 30 days before baseline.
• Sensitivity to florbetapir or ¹⁸F-AV-1451.
• Contraindication to MRI or PET or poor venous access for blood draws.

Inclusion Criteria:

• 55-79 years old;
• ≥ 8 years of education;
• Study partner is available who has frequent contact with the participant (e.g. an average of 10 hours per week or more), and can accompany the participant to all clinic visits for the duration of the protocol;

• Evidence of early AD, as defined by all of the following:

  1. Memory complaint by subject or study partner that is verified by a study partner;

  2. Objective memory impairment for age, documented by scoring below the education adjusted cutoff of the Logical Memory II subscale (Delayed Paragraph Recall) from the Wechsler Memory Scale Third Edition (the maximum score is 25):

     • ≤ 8 for 16 or more years of education, or
     • ≤ 4 for 8-15 years of education;
     • Essentially preserved general cognitive function;
     • Largely intact functional activities;
     • Not demented;
• Cerebrospinal fluid (CSF) biomarker results consistent with early AD, including CSF Aβ-42 levels ≥ 180 pg/mL and ≤ 690 pg/mL;
• Clinical Dementia Rating (Global) = 0.5; Memory Box score must be at least 0.5;
• Must be fluent in the language of the cognitive testing material being administered;
• Stability of permitted medications for 4 weeks prior to study start; subjects receiving acetylcholinesterase inhibitors and/or memantine should be on stable dose of those medications for at least 12 weeks prior to study start with every effort to maintain stable dose for the duration of the study;
• Visual and auditory acuity adequate for neuropsychological testing;
• Good general health with no diseases expected to interfere with the study;
• Must provide written informed consent for APOe4 genotype testing;
• Must provide written informed consent for CSF sampling.

Exclusion Criteria:

• Any significant neurological disease other than suspected incipient AD, such as Parkinson's disease, multi-infarct dementia, Huntington's disease, normal pressure hydrocephalus, brain tumor, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma followed by persistent neurologic defaults or known structural brain abnormalities;
• Major depressive episode, as described in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) within the past 6 months, which could lead to difficulty complying with the protocol;
• History of schizophrenia or bipolar disorder (DSM-IV criteria);
• History of alcohol or substance abuse or dependence within the past 3 years (DSM-IV criteria);
• Currently taking medications that could lead to difficulty complying with the protocol; subjects must be on a stable dose of current medications for 4 weeks prior to study entry, with the exception of acetylcholinesterase inhibitors and/or memantine, which must be on a stable dose for at least 12 weeks prior to study entry;
• Investigational agents are prohibited one month prior to entry and for the duration of the trial;
• Currently taking medications known to be CYP2C9 inducers (i.e. carbamazepine and rifampicin);
• Currently taking cromolyn, or have taken cromolyn, within the past 12 months;
• Chronic daily use of high-dose NSAID for osteoarthritis, rheumatoid arthritis, or other chronic inflammatory diseases ("chronic" defined as 3200 mg/day for >2 weeks);
• Chronic daily use of aspirin exceeding standard of care guidelines for low dose aspirin therapy for prevention of stroke and/or other recommended uses;
• Allergy to cromolyn (also known as Intal®, Nasalcrom®, Opticrom®, Gastrocrom®, etc.);
• Allergies to ibuprofen (Advil®, Motrin®, Nuprin®, etc.) or aspirin;
• Clinically significant respiratory disorders with impaired respiratory effort or difficulty taking inhaled drugs;
• Uncontrolled chronic asthma;
• Abnormal pulmonary function test, defined for this protocol as: FEV1/FVC < predicted value for subject AND FEV1 < 70% of predicted value, indicating moderate or severe respiratory obstruction;
• Taking inhaled protein products on a chronic basis;
• Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the protocol;
• Pregnancy or lactation for female subjects of child-bearing potential (i.e., < two years post-menopausal or not surgically sterile);
• For sexually active male subjects, unwillingness or incapability of using appropriate contraception methods;
• Severe renal or hepatic impairment.

Inclusion criteria:

• Patients with early signs of dementia of Alzheimer Type
• Male and female patients with an age of at least 55 years
• Previous use of AD medications (AChEIs, memantine) is allowed up 3 month prior to screening. Patients who are currently taking AChEIs are eligible as long as they have been using a stable dose for at least 3 months prior to screening and no change is foreseen for the duration of the study. This dose must be consistent with the product label in the concerned country. Patients currently taking memantine are excluded.
• Patients must have at least 6 years of formal education and fluency in the test language as verbally confirmed by the patient and documented by the study investigator.
• Patients must have a reliable study partner (per investigator judgement, for instance a family member, partner etc., guardian or, if applicable, a legal representative)

Exclusion criteria:

• Cognitive impairment or dementia with any etiology other than AD
• Substantial concomitant cerebrovascular disease (defined by a history of a stroke / intracranial haemorrhagia) temporally related to the onset of worsening of cognitive impairment per investigator judgement
• Medical history or diagnosis of any of symptomatic and unstable/uncontrolled conditions per investigator judgement
• Any other psychiatric disorders such as schizophrenia, or mental retardation
• Previous participation in investigational drug studies of mild cognitive impairment/DAT within three months prior to screening. Having received active treatment in any other study targeting disease modification of AD like Aß immunization and tau therapies. Previous participation in studies with non-prescription medications, vitamins or other nutritional formulations is allowed.
• Clinically significant uncompensated hearing loss in the judgment of the investigator. Use of hearing aids is allowed.

Inclusion criteria:

• Male and female patients with an age of at least 55 years
• Body weight not lower than 50 kgs
• Patients with a confirmed diagnosis of prodromal AD on neuropsychological testing defined as:

Mini-Mental State Examination (MMSE) score: greater or equal 24 and a global CDR-score of 0 or 0.5 and

Free and Cued Selective Recall Reminding Test (FCSRT) score:

free recall test: lower or equal 20 (out of 48) and total recall test: lower or equal 42 (out of 48)

Patients who do not reach the required score in FCSRT will additionally perform the Wechsler Memory Visual Paired Associates test. If the Wechsler Memory Visual Paired Associates test shows a cognitive deficit worse than 1 standard deviation to the mean (compared to the reference values of age and educational norms for inclusion), then the patients can be considered to be eligible for the study.

• Confirmation of abnormal markers of AD pathology either via a), or alternatively b) mentioned below:

  1. Presence in cerebrospinal fluid of (samples taken within past 4 months may be eligible,:

     low Aß1-42 concentrations (< 640 pg/mL) and increased total tau concentrations (> 375 pg/ml), or / and low Aß1-42 concentrations (< 640 pg/mL) and increased phospho-tau concentrations (> 52 pg/mL in cerebrospinal fluid), or

  2. Abnormal amyloid deposition in a cerebral PET scan. Scans performed in the past according to the recommendation in the protocol are acceptable
• Patients who have not received prescribed drugs for treatment of AD (including acetyl cholinesterase inhibitors (donepezil, galantamine, rivastigmine, tacrine, phenserine) and Memantine within three months prior to screening
• Patients must have at least 6 years of formal education and fluency in the test language as verbally confirmed by the patient and documented by the study investigator.
• Patients must have given written informed consent in accordance with Good Clinical Practice (GCP) and local legislation prior to any study procedures. All patients must be able to give informed consent personally and have capacity for such consent. An informed consent given by a legal representative will not be accepted.
• Patients must have a reliable study partner (per investigator judgement, for instance a family member, partner, guardian etc.)

Exclusion criteria:

• Mild cognitive impairment with any etiology other than prodromal AD (for example: neurosyphilis, craniocerebral trauma, small vessel disease) based on clinical data and/or current laboratory findings and/or a pre-existing MRI or CT of the brain (CCT). If previous cranial imaging is not available or older than 12 months prior to screening then a CCT or MRI needs to be performed at screening
• Substantial concomitant cerebrovascular disease (defined by a history of a stroke / intracranial haemorrhagia) temporally related to the onset of worsening of cognitive impairment per investigator judgement
• Medical history of cancer (except for basal cell carcinoma) and/or treatment for cancer within the last 5 years
• Medical history or diagnosis of any of symptomatic and unstable/uncontrolled conditions per investigator judgement
• Severe renal impairment defined with a glomerular filtration rate (GFR) < 30ml/min/1.73m2 in the screening central lab report
• Any other psychiatric disorders such as schizophrenia, or mental retardation
• Any suicidal actions in the past 2 years (per investigator judgement i.e. actual attempt, interrupted attempt, aborted attempt, or preparatory acts or behaviour)
• Any suicidal ideation of type 4 or 5 in the Columbia Suicide Severity Rating Scale (C-SSRS) in the past 3 months (i.e. active suicidal thought with intent but without specific plan, or active suicidal thought with plan and intent)
• Previous participation in investigational drug studies of mild cognitive impairment within three months prior to screening. Having received active treatment in any other study targeting disease modification like Aß immunization and tau therapies. Previous participation in studies with non-prescription medications, vitamins or other nutritional formulations is allowed.
• Significant history of drug dependence or abuse (including alcohol, as defined in Diagnostic and Statistical Manual of Mental Disorders [DSM-V] or in the opinion of the investigator) within the last two years, or a positive urine drug screen for cocaine, heroin, or marijuana.
• Known history of HIV infection
• Any planned surgeries requiring general anaesthesia, or hospitalisation for more than 1 day during the study period
• Pre-menopausal women (last menstruation <= 1 year prior to informed consent) who are nursing or pregnant or are of child-bearing potential and are not practicing an acceptable method of birth control
• For male patients: Men who are able to father a child, unwilling to be abstinent or to use an adequate form of effective contraception for the duration of study participation and for at least 28 days after treatment has ended.
• Use of any investigational drug or procedure for other indications within 3 months or 6 half-lives (whichever is longer) prior to randomization.

• Intake of the following medications within 3 months prior to randomization and intended to be initiated during the duration of the trial:

  1. tricyclic antidepressants,
  2. antidepressants that are monoamine oxidase inhibitors,
  3. neuroleptics with moderate or greater anticholinergic potency (e.g. chlorpromazine, fluphenazine, loxapine, perphenazine, thioridazine),
  4. anticholinergic medications

The following drugs may be given as needed if the total daily dose was stable 8 weeks prior to randomisation and is expected to be for the duration of the trial:

1. neuroleptics listed in the protocol

2. benzodiazepines and sedatives listed in the protocol

   • Clinically significant uncompensated hearing loss in the judgment of the investigator. Use of hearing aids is allowed.
   • Known hypersensitivity to the drug product excipients

Inclusion Criteria:

• Diagnosis of probable Alzheimer Disease (AD) with documented evidence of progression of disease
• Mini Mental State Examination (MMSE) score of 21-26, inclusive
• Clinical Dementia Rating global score of 0.5 or 1
• Rosen-Modified Hachinski Ischemia Score less than or equal to 4
• Brain magnetic resonance imaging (MRI) consistent with the diagnosis of probable AD
• Concurrent use of cholinesterase inhibitor or memantine with stable dose for at least 3 months prior to randomization
• Caregiver willing to participate and be able to attend clinic visits with patient
• Ability to ingest oral medications

Exclusion Criteria:

• Significant neurological or psychiatric disease other than Alzheimer's disease
• Participants with evidence or history of severe drug allergies (resulting in dyspnea or severe rash).
• Any contraindications to MRI (e.g., clinically significant claustrophobia, non-removable ferromagnetic implants). Patients with contraindications to MRI may undergo computed tomography (CT) on approval by sponsor.
• Any contraindications to the FDG-PET study (e.g. allergy to any component of the FDG dose) in the cohort undergoing a PET scan.
• Previous exposure to investigational or non-investigational therapies for Alzheimer's disease within 6 months of screening
• History of cancer within the last 5 years except adequately treated cervical carcinoma in-situ, cutaneous basal cell or squamous cell cancer, or non-progressive prostate cancer not requiring treatment
• Women of childbearing potential
• Uncontrolled blood pressure and/or blood pressure above 160/100
• Prescription medical food intended for dietary management of the metabolic processes associated with Alzheimer's disease.
• Diagnosis or history of cerebrovascular stroke, severe carotid stenosis, cerebral hemorrhage, intracranial tumor, subarachnoid hemorrhage.
• Patients with unstable, uncontrolled diabetes (HbA1c > 7.7%) and those requiring insulin.

Key Inclusion Criteria:

• Must meet all of the following clinical criteria for MCI due to AD or mild AD and must have:
• A Clinical Dementia Rating (CDR)-Global Score of 0.5.
• Objective evidence of cognitive impairment at screening
• An MMSE score between 24 and 30 (inclusive)
• Must have a positive amyloid Positron Emission Tomography (PET) scan
• Must consent to apolipoprotein E (ApoE) genotyping
• If using drugs to treat symptoms related to AD, doses must be stable for at least 8 weeks prior to screening visit 1
• Must have a reliable informant or caregiver

Key Exclusion Criteria:

• Any medical or neurological condition (other than Alzheimer's Disease) that might be a contributing cause of the subject's cognitive impairment
• Have had a stroke or Transient Ischemic Attack (TIA) or unexplained loss of consciousness in the past 1 year
• Clinically significant unstable psychiatric illness in past 6 months
• History of unstable angina, myocardial infarction, advanced chronic heart failure, or clinically significant conduction abnormalities within 1 year prior to Screening
• Indication of impaired renal or liver function
• Have human immunodeficiency virus (HIV) infection
• Have a significant systematic illness or infection in past 30 days
• Relevant brain hemorrhage, bleeding disorder and cerebrovascular abnormalities
• Any contraindications to brain magnetic resonance imaging (MRI) or PET scans
• Alcohol or substance abuse in past 1 year
• Taking blood thinners (except for aspirin at a prophylactic dose or less)

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply

Key Inclusion Criteria:

• Must meet all of the following clinical criteria for MCI due to AD or mild AD and must have:
• A Clinical Dementia Rating (CDR)-Global Score of 0.5.
• Objective evidence of cognitive impairment at screening
• An MMSE score between 24 and 30 (inclusive)
• Must have a positive amyloid Positron Emission Tomography (PET) scan
• Must consent to apolipoprotein E (ApoE) genotyping
• If using drugs to treat symptoms related to AD, doses must be stable for at least 8 weeks prior to screening visit 1
• Must have a reliable informant or caregiver

Key Exclusion Criteria:

• Any medical or neurological condition (other than Alzheimer's Disease) that might be a contributing cause of the subject's cognitive impairment
• Have had a stroke or Transient Ischemic Attack (TIA) or unexplained loss of consciousness in the past 1 year
• Clinically significant unstable psychiatric illness in past 6 months
• History of unstable angina, myocardial infarction, advanced chronic heart failure, or clinically significant conduction abnormalities within 1 year prior to Screening
• Indication of impaired renal or liver function
• Have human immunodeficiency virus (HIV) infection
• Have a significant systematic illness or infection in past 30 days
• Relevant brain hemorrhage, bleeding disorder and cerebrovascular abnormalities
• Any contraindications to brain magnetic resonance imaging (MRI) or PET scans
• Alcohol or substance abuse in past 1 year
• Taking blood thinners (except for aspirin at a prophylactic dose or less)

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply

Inclusion Criteria:

• Weight between 40 and 120 kilograms (Kg) inclusive
• Availability of a person (referred to as the "caregiver") who in the investigator's judgment:
• Has frequent and sufficient contact with the participant to be able to provide accurate information regarding the participant's cognitive and functional abilities, agrees to provide information at clinic visits (which require partner input for scale completion), signs the necessary consent form, and has sufficient cognitive capacity to accurately report upon the participant's behavior and cognitive and functional abilities
• Fluency in the language of the tests used at the study site
• Adequate visual and auditory acuity, in the investigator's judgment, sufficient to perform the neuropsychological testing (eye glasses and hearing aids are permitted)
• Evidence of the AD pathological process, by a positive amyloid assessment either on cerebrospinal fluid (CSF) amyloid beta 1-42 levels as measured on the Elecsys beta-amyloid(1-42) test system or amyloid PET scan by qualitative read by the core/central PET laboratory
• Demonstrated abnormal memory function at screening
• Screening mini mental state examination (MMSE) score of greater than or equal to (>=) 22 points and Clinical Dementia Rating-Global Score (CDR-GS) of 0.5 or 1.0
• Meets National Institute on Aging/Alzheimer's Association (NIAAA) core clinical criteria for probable AD dementia or prodromal AD (consistent with the NIAAA diagnostic criteria and guidelines for mild cognitive impairment (MCI)
• If receiving symptomatic AD medications, the dosing regimen must have been stable for 3 months prior to screening

Exclusion Criteria:

• Any evidence of a condition other than AD that may affect cognition such as other dementias, stroke, brain damage, autoimmune disorders (e.g. multiple sclerosis) or infections with neurological sequelae.
• History of major psychiatric illness such as schizophrenia or major depression (if not considered in remission)
• At risk of suicide in the opinion of the investigator
• Presence of significant cerebral vascular pathology as assessed by MRI central reader
• Unstable or clinically significant cardiovascular, kidney or liver disease (e.g., myocardial infarction)
• Uncontrolled hypertension
• Screening hemoglobin A1c (HbA1C) >8%
• Poor peripheral venous access
• History of cancer except:

If considered to be cured or If not being actively treated with anti-cancer therapy or radiotherapy

- Known history of severe allergic, anaphylactic, or other hypersensitivity reactions to chimeric, human, or humanized antibodies or fusion proteins

Key Inclusion Criteria for Mild Cognitive Impairment due to Alzheimer's Disease

- Intermediate likelihood:

1. Subjects who meet the National Institute of Aging - Alzheimer's Association (NIA-AA) core clinical criteria for mild cognitive impairment due to Alzheimer's disease - intermediate likelihood
2. Subjects who have a CDR score of 0.5 and a Memory Box score of 0.5 or greater at Screening and Baseline
3. Subjects who report a history of subjective memory decline with gradual onset and slow progression over the last one year before Screening; MUST be corroborated by an informant

Key Inclusion Criteria for Mild Alzheimer's Disease Dementia:

1. Subjects who meet the NIA-AA core clinical criteria for probable Alzheimer's disease dementia
2. Subjects who have a CDR score of 0.5-1.0 and a Memory Box score of 0.5 or greater at Screening and Baseline

Inclusion Criteria that must be met by all subjects:

1. Subjects with objective impairment in episodic memory as indicated by at least 1 standard deviation below age-adjusted mean in the Wechsler Memory Scale - IV Logical Memory II (WMS-IV LMII):

   1. Less than or equal to 15 for age 50 to 64 years
   2. Less than or equal to 12 for age 65 to 69 years
   3. Less than or equal to 11 for age 70 to 74 years
   4. Less than or equal to 9 for age 75 to 79 years
   5. Less than or equal to 7 for age 80 to 90 years
2. Positive amyloid load as indicated by PET or CSF assessment
3. Age between 50 and 90 years, inclusive
4. Mini Mental State Examination (MMSE) score equal to or greater than 22, and equal to or less than 30, at Screening and Baseline
5. Body Mass Index (BMI) greater than 17 and less than 35 at Screening
6. Females must not be pregnant or lactating, and specified contraceptive precautions must be followed
7. Subjects on acetylcholinesterase inhibitor or memantine therapy for Alzheimer's disease (AD) must be on a stable dose for at least 12 weeks prior to baseline
8. Subjects must have identified caregivers/informants
9. Subjects must provide written informed consent

Key Exclusion Criteria:

1. Any neurological condition that may be contributing to cognitive impairment above and beyond that caused by the subject's AD
2. History of transient ischemic attacks (TIA), stroke, or seizures within 12 months of Screening
3. Any psychiatric diagnosis or symptoms, (e.g., hallucinations, major depression, or delusions) that could interfere with study procedures in the subject
4. Contraindications to MRI scanning, including cardiac pacemaker/ defibrillator, ferromagnetic metal implants, e,g., in skull and cardiac devices other than those approved as safe for use in MR scanners
5. Evidence of other clinically significant lesions that could indicate a dementia diagnosis other than AD on brain MRI at Screening, or other significant pathological findings on brain MRI at Screening
6. A prolonged QT/QTc interval (QTc greater than 450 ms) as demonstrated by a repeated electrocardiogram (ECG)
7. Certain other specified medical conditions
8. Severe visual or hearing impairment that would prevent the subject from performing psychometric tests accurately

Inclusion Criteria:

• Clinical diagnosis of probable mild Alzheimer disease (AD) based on National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS/ADRDA) criteria or major NCD based whether or not receiving AD approved medication
• Cerebral spinal fluid (CSF) result consistent with the presence of amyloid pathology
• Availability of a person ('caregiver') who in the investigator's judgment has frequent and sufficient contact with the participant, and is able to provide accurate information regarding the participant's cognitive and functional abilities
• Fluency in the language of the tests used at the study site
• Willingness and ability to complete all aspects of the study
• Adequate visual and auditory acuity, in the investigator's judgment, sufficient to perform the neuropsychological testing (eye glasses and hearing aids are permitted)
• If currently receiving approved medications for AD, the dosing regimen must have been stable for 3 months prior to screening
• Agreement not to participate in other research studies for the duration of this trial and its associated substudies

PART 2 - All participants who have been randomized and are actively participating in the study are eligible for Part 2

Exclusion Criteria:

• Dementia or neurocognitive disorder (NCD) due to a condition other than AD, including, but not limited to, frontotemporal dementia, Parkinson disease, dementia with Lewy bodies, Huntington disease, or vascular dementia
• History or presence of clinically evident vascular disease potentially affecting the brain that in the opinion of the investigator has the potential to affect cognitive function
• History or presence of stroke within the past 2 years or documented history of transient ischemic attack within the last 12 months
• History or presence of systemic autoimmune disorders potentially causing progressive neurologic disease with associated cognitive deficits
• History of schizophrenia, schizoaffective disorder, or bipolar disorder
• Alcohol and/or substance use disorder (according to the DSM-5) within the past 2 years (nicotine use is allowed)
• History or presence of atrial fibrillation
• Within the last 2 years, unstable or clinically significant cardiovascular disease (e.g., myocardial infarction, angina pectoris, cardiac failure New York Heart Association Class II or higher)
• Uncontrolled hypertension
• Chronic kidney disease
• Impaired hepatic function

PET imaging substudy, in addition to above:

- Prior participation in other research study or clinical care within the last year such that the total radiation exposure would exceed the local or national annual limits

Part 2 Participants who have been discontinued from the study

Inclusion Criteria:

• Gradual and progressive change in the participant's memory function over more than 6 months, reported by participant and study partner
• Mini-Mental State Examination score of 20-30 inclusive at screening
• Objective impairment in memory as evaluated by memory test performed at screening
• For a diagnosis of mild Alzheimer's Disease (AD), participant meets the National Institute on Aging and the Alzheimer's Association (NIA-AA) criteria for probable AD
• For a diagnosis of MCI due to AD, participant meets NIA-AA criteria for MCI due to AD

Exclusion Criteria:

• Significant neurological disease affecting the central nervous system, other than AD, that may affect cognition or ability to complete the study, including but not limited to, other dementias, serious infection of the brain, Parkinson´s disease, or epilepsy or recurrent seizures
• History of clinically evident stroke, or multiple strokes based on history or imaging results
• History of clinically important carotid or vertebrobasilar stenosis or plaque
• History of multiple concussions with sustained cognitive complaints or objective change in neuropsychological function in the last 5 years
• Participants with a current Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition diagnosis of Major Depressive Disorder or any current primary psychiatric diagnosis other than AD if, in the judgment of the investigator, the psychiatric disorder or symptom is likely to confound interpretation of drug effect, affect cognitive assessments, or affect the participant´s ability to complete the study
• History of alcohol or drug abuse or dependence (except nicotine dependence) within 2 years before the screening
• Within 1 year before the screening or between screening and baseline, any of the following: myocardial infarction; moderate or severe congestive heart failure, New York Heart Association class III or IV; hospitalization for, or symptom of, unstable angina; syncope due to orthostatic hypotension or unexplained syncope; known significant structural heart disease (eg, significant valvular disease, hypertrophic cardiomyopathy), or hospitalization for arrhythmia
• Congenital QT prolongation
• History of cancer within the last 5 years, with the exception of non-metastatic basal and/or squamous cell carcinoma of the skin, in situ cervical cancer, non-progressive prostate cancer or other cancers with low-risk of recurrence or spread
• Current serious or unstable clinically important systemic illness that, in the judgment of the investigator, is likely to affect cognitive assessment, deteriorate, or affect the participant's safety or ability to complete the study, including hepatic, renal, gastroenterologic, respiratory, cardiovascular, endocrinologic, immunologic, or hematologic disorders

Inclusion Criteria:

• Participants previously enrolled in AMARANTH (NCT02245737) who meet eligibility criteria for delayed start I8D-MC-AZFD.

Exclusion Criteria:

• Participants who participate in AMARANTH (NCT02245737) who develop new conditions precluding them from enrolling into I8D-MC-AZFD.

Inclusion Criteria:

• Participant must meet the National Institute on Aging (NIA) and the Alzheimer's Association (AA) (NIA-AA) criteria for probable AD dementia.
• MMSE score of 20 to 26 inclusive at screening visit.
• For a diagnosis of mild AD dementia, participant must have a CDR global score of 0.5 or 1, with the memory box score ≥0.5 at screening.
• Evidence of amyloid pathology.
• The participant must have a reliable study partner with whom he/she cohabits or has regular contact.

Exclusion Criteria:

• Significant and/or current neurological disease affecting the central nervous system, other than AD, that may affect cognition or ability to complete the study, including but not limited to, other dementias, repetitive head trauma, serious infection of the brain, Parkinson's disease, epilepsy, or cervicocranial vascular disease.
• Participants with any current primary psychiatric diagnosis other than AD if, in the judgment of the investigator, the psychiatric disorder or symptom is likely to confound interpretation of drug effect, affect cognitive assessment, or affect the participant's ability to complete the study. Participants with history of schizophrenia or other chronic psychosis are excluded.
• Within 1 year before the screening visit or between screening and randomization, any of the following: myocardial infarction; moderate or severe congestive heart failure, New York Heart Association class III or IV; hospitalization for, or symptoms of, unstable angina; syncope due to orthostatic hypotension or unexplained syncope; known significant structural heart disease (such as, significant valvular disease, hypertrophic cardiomyopathy); or hospitalization for arrhythmia.
• Congenital QT prolongation.
• Intermittent second- or third-degree atrioventricular (AV) heart block or AV dissociation or history of ventricular tachycardia.
• A corrected QT (QTcF) interval measurement >470 milliseconds (men and women) at screening (as determined at the investigational site).
• History of malignant cancer within the last 5 years.
• History of vitiligo and/or current evidence of post-inflammatory hypopigmentation.
• Calculated creatinine clearance <30 milliliters per minute (Cockcroft-Gault formula; Cockcroft and Gault 1976) at screening.
• Currently enrolled in any other clinical trial involving an investigational product or any other type of medical research judged not to be scientifically or medically compatible with this study.