Results from the Phase III Clarity AD open-label extension (OLE) trial (NCT03887455) showed that weekly 360 mg subcutaneous autoinjector (SC-AI) dosing of Eisai and Biogen’s Leqembi (lecanemab-irmb) maintained comparable efficacy, pharmacokinetics, and biomarker outcomes to the standard biweekly 10 mg/kg intravenous (IV) regimen in patients with early Alzheimer disease (AD). According to Biogen, the findings also demonstrated a favorable safety profile and high user acceptability, underscoring the SC-AI’s potential to improve treatment adherence and reduce the care burden for patients and caregivers.¹

Can a Subcutaneous Option for Leqembi Maintain the Same Benefits as IV Infusion?

Clarity ADTrial Background and Design

• The placebo-controlled, double-blind, parallel-group, 18-month Clarity AD trial evaluated the efficacy of Leqembi in 1,906 patients with early-stage AD.
• In the OLE phase, the trial evaluated the long-term safety and tolerability of Leqembi and whether its long-term effects as measured by the Clinical Dementia Rating-Sum of Boxes (CDR-SB) at the end of the core study were maintained over time.
• The dual primary endpoints of the OLE were the number of patients reporting one or more treatment-related adverse events (AEs) and a change from core study baseline in CDR-SB.²

Key Findings on SC-AI Efficacy and Safety

• Results showed that the SC-AI form of Leqembi demonstrated a <1% rate of systemic injection or infusion reactions compared to 26% in the IV group.
• Clinical and biomarker responses—including measures such as CDR-SB, amyloid PET, and plasma biomarkers—were consistent between SC and IV dosing arms.
• Notably, no cases of amyloid-related imaging abnormalities-edema were observed among patients on the 360 mg weekly SC maintenance dose.

Usability Studies Support Home-Based Administration

To ensure the safe and effective use of the SC-AI, Eisai conducted additional usability and tolerability studies. A human factors study with 110 participants—including early AD patients, and healthcare professionals—found that 95% were able to successfully administer the SC-AI dose. In a separate acceptability study involving 126 participants, more than 95% reported the device was easy to use, convenient, and feasible for administration, even in a home setting. Participants expressed high satisfaction, with all patients indicating support for the SC-AI’s introduction.¹

Regulatory Progress and Global Reach

Leqembi was first granted accelerated approval by the FDA for IV use for the treatment of AD on January 6, 2023.3 From there, full approval was granted on July 7, 2023, marking the first approved treatment shown to reduce the rate of disease progression and to slow cognitive and functional decline in adults with AD.⁴

In January, the FDA approved Eisai and Biogen’s supplemental Biologics License Application for IV dosing of Leqembi once every four weeks based on results from the core part of the Clarity AD trial. Results show that Leqembi slowed disease progression by 24% at 18 months, while the treatment decline of activities of daily living was 37% at 18 months.5 Also in January, the FDA accepted a Biologics License Application for an SC maintenance dosing option of Leqembi, which was supported by the Clarity AD OLE.⁶

Alzheimer Disease Burden and Public Health Implications

According to the Alzheimer’s Association, approximately seven million people in the United States are currently living with AD, including 6.9 million over the age of 65 years, 73% of whom are over 75 years of age. Women account for more than two-thirds of AD cases, and older Black Americans are twice as likely as older white Americans to develop the disease. Without a breakthrough treatment, the total number of individuals affected is projected to rise to 12.7 million by 2050.⁶

International Approvals

Currently, Leqembi is approved in the United States, Japan, China, South Korea, Hong Kong, Israel, the United Arab Emirates, Great Britain, Mexico, and Macau.⁶

References

1. New Data Presented at AAIC Demonstrates Investigational LEQEMBI® (lecanemab-irmb) 360 mg Subcutaneous Maintenance Dosing Could Offer a New Option for Ongoing Treatment of Early Alzheimer’s Disease. Biogen. July 30, 2025. Accessed July 30, 2025. https://investors.biogen.com/news-releases/news-release-details/new-data-presented-aaic-demonstrates-investigational-leqembir
2. A Study to Confirm Safety and Efficacy of Lecanemab in Participants With Early Alzheimer's Disease (Clarity AD). Clinicaltrials.gov. Accessed July 30, 2025. https://clinicaltrials.gov/study/NCT03887455
3. FDA Approves Leqembi. Drugs.com. Accessed July 30, 2025. https://www.drugs.com/newdrugs/fda-approves-leqembi-lecanemab-irmb-under-accelerated-approval-pathway-alzheimer-s-5955.html
4. FDA Grants Traditional Approval for Leqembi (lecanemab-irmb) for the Treatment of Alzheimer’s Disease. Drugs.com. Accessed July 30, 2025. https://www.drugs.com/newdrugs/fda-grants-traditional-approval-leqembi-lecanemab-irmb-alzheimer-s-6056.html
5. FDA Approves Supplemental Biologics License Application for Intravenous Maintenance Dosing of Leqembi in Alzheimer Disease. PharmExec. January 27, 2025. Accessed July 30, 2025. https://www.pharmexec.com/view/fda-approves-supplemental-biologics-license-application-intravenous-maintenance-dosing-leqembi-alzheimer-disease
6. FDA Accepts Eisai, Biogen’s Biologics License Application for Subcutaneous Leqembi in Early Alzheimer Disease. PharmExec. January 14, 2025. Accessed July 30, 2025. https://www.pharmexec.com/view/fda-accepts-eisai-biogen-biologics-license-application-subcutaneous-leqembi-early-alzheimer-disease