TerminatedPhase 3Results posted

A Study to Evaluate Safety and Tolerability of Aducanumab in Participants With Alzheimer's Disease Who Had Previously Participated in the Aducanumab Studies 221AD103, 221AD301, 221AD302 and 221AD205

Phase 3b Open-Label, Multicenter, Safety Study of BIIB037 (Aducanumab) in Subjects With Alzheimer's Disease Who Had Previously Participated in the Aducanumab Studies 221AD103, 221AD301, 221AD302 and 221AD205

Lead sponsor

Biogen

Asset

Aducanumab

Listed sites

297

Recruiting sites

Enrollment

1,696

actual

Study population

Alzheimer’s disease

Key I/E criteria

•Age 50-90•MRI contraindications excluded

Primary endpoint

•Core Treatment Period

Footprint

Where this trial recruits

Site locations as reported to ClinicalTrials.gov. Site count is not enrollment count; per-site enrollment is not available from source.

Identifiers

Registered as

Eudract number2019-004368-22

Org study ID221AD304

NCT IDNCT04241068

Timeline

Milestones

Study first posted2020-01-27actual

Study start2020-03-02actual

Primary completion2024-07-22actual

Study completion2024-07-22actual

Last update posted2025-02-21actual

Results first posted2025-02-21actual

Assets

Drug assets

Aducanumab

Study populations

Who this study enrolls

Alzheimer’s disease

Eligibility

Who can enroll

Minimum age50 Years

Maximum age90 Years

SexAll

Healthy volunteersNot accepted

Inclusion criteria

Key Inclusion Criteria:

Core Treatment Period:

•Participant was participating in an aducanumab clinical study at the time of the announcement of early termination (feeder studies).

•Has one care partner who, in the Investigator's opinion, has adequate contact with the participant as to be able to provide accurate information about the participant's cognitive and functional abilities.

LTE Treatment Period:

•Participant must have completed the Core study period (Week 102) and adequately tolerated 10 mg/kg of aducanumab during the Core study period in the opinion of the Investigator.

•Has one informant/care partner who, in the Investigator's opinion, has frequent and sufficient contact with the participant as to be able to provide accurate information about the participant's cognitive and functional abilities

Exclusion criteria

Core Treatment Period:

•Any medical or neurological condition (other than Alzheimer's Disease) that might be a contributing cause of the participant's cognitive impairment.

•Stroke or any unexplained loss of consciousness within 1 year prior to Screening.

•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.

•A seizure event that occurred after the last visit of the feeder study and before Screening for this study.

•Evidence of impaired liver function as shown by an abnormal liver function profile at Screening.

•History of or known seropositivity for HIV.

•Clinically significant systemic illness or serious infection within 30 days prior to or during Screening.

•Contraindications to having a brain magnetic resonance imaging (MRI).

LTE Treatment Period:

•Any medical or psychiatric contraindication or clinically significant abnormality that, in the opinion of the Investigator, will substantially increase the risk associated with the participant's enrollment in and completion of the study.

Note- Other protocol defined Inclusion/Exclusion criteria may apply.

Endpoints (10)

What's being measured

Protocol endpoints and posted registry outcome measures, grouped into outcome categories. Composite endpoints show their component event types. Standard codes (LOINC, SNOMED CT) are shown where available.

Coverage by outcome category

Amyloid biomarkers

Other (unclassified)

Safety / tolerability / PK

Amyloid biomarkers

4 endpoints

Primary/protocol endpoint

Core Treatment Period: Number of Participants With Amyloid-Related Imaging Abnormality-Edema (ARIA-E)

Time frame:Up to Week 118

event count, event

Primary/protocol endpoint

Core Treatment Period: Number of Participants With Amyloid-Related Imaging Abnormality- Hemorrhage or Superficial Siderosis (ARIA-H)

Time frame:Up to Week 118

event count, event

Primary/registry result

Core Treatment Period: Number of Participants With Amyloid-Related Imaging Abnormality-Edema (ARIA-E)

Time frame:Up to Week 118

event count, event

Posted result

Group	Value (count_of_participants), Participants	Reported bounds
Aducanumabn=1656 Participants	422	-

Primary/registry result

Core Treatment Period: Number of Participants With Amyloid-Related Imaging Abnormality- Hemorrhage or Superficial Siderosis (ARIA-H)

Time frame:Up to Week 118

event count, event

Posted result

Group	Value (count_of_participants), Participants	Reported bounds
Aducanumabn=1656 Participants	505	-

Safety / tolerability / PK

2 endpoints

Primary/protocol endpoint

Core Treatment Period: Number of Participants With Treatment-Emergent Adverse Events (TEAEs) and Serious TEAEs

Time frame:From the first dose of study drug to end of follow-up (up to Week 118)

event count, event

Primary/registry result

Core Treatment Period: Number of Participants With Treatment-Emergent Adverse Events (TEAEs) and Serious TEAEs

Time frame:From the first dose of study drug to end of follow-up (up to Week 118)

event count, event

Posted result

Group	Value (count_of_participants), Participants	Reported bounds
AducanumabTEAEsn=1696 Participants	1549	-
Serious TEAEsn=1696 Participants	318	-

Other (unclassified)

4 endpoints

Primary/protocol endpoint/low confidence

Core Treatment Period: Number of Participants With AEs Leading to Treatment Discontinuation (TD) and Study Withdrawal (SW)

Time frame:From the first dose of study drug to end of follow-up (up to Week 118)

event count, event

Primary/protocol endpoint/low confidence

Core Treatment Period: Number of Participants With Positive Antidrug Antibodies (ADAs) in Serum

Time frame:Up to Week 102

event count, event

Primary/registry result/low confidence

Core Treatment Period: Number of Participants With AEs Leading to Treatment Discontinuation (TD) and Study Withdrawal (SW)

Time frame:From the first dose of study drug to end of follow-up (up to Week 118)

event count, event

Posted result

Group	Value (count_of_participants), Participants	Reported bounds
AducanumabAEs leading to TDn=1696 Participants	168	-
AEs leading to SWn=1696 Participants	129	-

Primary/registry result/low confidence

Core Treatment Period: Number of Participants With Positive Antidrug Antibodies (ADAs) in Serum

Time frame:Up to Week 102

event count, event

Posted result

Group	Value (count_of_participants), Participants	Reported bounds
Aducanumabn=1595 Participants	19	-

Provenance

Sources

Trial identity, design, statusClinicalTrials.gov API v2

Snapshot dateJuly 21, 2026

Endpoint classificationDelfa ADRD endpoint taxonomy

Results tableClinicalTrials.gov results section

Trial facts come from public ClinicalTrials.gov records. Endpoint categories are Delfa's classification of those records, not a ClinicalTrials.gov field. All figures reflect the July 21, 2026 snapshot.