FDA Approves Once-Weekly Dosing for Lecanemab-irmb to Treat Early Alzheimer Disease

The FDA has approved the biologics license application for lecanemab-irmb (Leqembi Iqlik; Eisai), the first and only anti-amyloid therapy to provide a once-weekly, at-home subcutaneous (SC) injection for patients with early Alzheimer disease (AD).¹ The weekly autoinjector allows patients and caregivers to continue treatment after completing 18 months of intravenous (IV) infusions.

Lecanemab-irmb will be available in the US starting October 6, 2025.

The FDA’s approval of lecanemab-irmb is supported by data from sub-studies of the phase 3 Clarity AD (NCT03887455) open-label extension trial, which evaluated SC dosing in individuals with early AD. Results showed that patients who transitioned to the weekly 360 mg lecanemab-irmb autoinjector after 18 months of IV treatment maintained clinical and biomarker benefits comparable to continued IV dosing.

The safety of SC administration was assessed in more than 600 patients across dose ranges, with 49 patients specifically receiving the weekly 360 mg maintenance dose. Importantly, the group had no local or systemic injection-related adverse events. Overall, the safety profile was consistent with IV therapy, though systemic reactions were far less common with subcutaneous dosing.

Approximately 11% of patients experienced mild to moderate local injection-site reactions, while fewer than 1% reported mild systemic symptoms such as headache or fatigue. Amyloid-related imaging abnormalities (ARIA) occurred at similar rates between subcutaneous and IV groups, aligning with background rates in untreated patients. ARIA is most often asymptomatic, though it can be serious or fatal, and typically arises within the first 6 months of IV initiation.

Lecanemab first received FDA accelerated approval in January 2023 for the treatment of AD, making it only the second anti-amyloid therapy cleared for clinical use.² The decision was based on the phase 2b Study 201 (NCT01767311), which showed the antibody reduced amyloid plaques, a hallmark of the disease, in patients with mild cognitive impairment or mild dementia due to AD. The approval came amid scrutiny following the controversial authorization of aducanumab, but subsequent phase 3 data from the Clarity AD trial strengthened the evidence base for lecanemab.

In July 2024, the FDA approved a supplemental biologics license application for IV maintenance dosing of lecanemab, offering patients with early-stage AD the option to transition from biweekly to a once-every-4-week dosing after completing 18 months of initiation therapy.³ Recent findings have demonstrated that a monthly maintenance dose preserves the clinical and biomarker benefits of lecanemab, continues to slow disease progression, and helps patients maintain cognitive and functional abilities.

The SC maintenance option with lecanemab-irmb offers meaningful advantages for both patients and the health care system, according to a press release by Biogen.¹ For patients and care partners, the ability to self-administer treatment at home reduces the burden of frequent visits to infusion centers, shortens treatment time, and supports long-term adherence.

“Health care providers reported that the device has the potential to provide a new option for patients who are responding well to Leqembi and should continue treatment,” according to the press release. “The SC formulation also has the potential to reduce health care resources associated with IV maintenance dosing, such as preparation for infusion and nurse monitoring, while increasing infusion capacity for new eligible patients to begin initiation treatment and streamlining the overall AD treatment pathway.”

References

1. FDA approves Leqembi Iqlik (lecanemab-irmb) subcutaneous injection for maintenance dosing for the treatment of early Alzheimer's disease. News release. Biogen. August 29, 2025. Accessed September 2, 2025. https://investors.biogen.com/news-releases/news-release-details/fda-approves-leqembir-iqliktm-lecanemab-irmb-subcutaneous

2. Joszt L. FDA approves lecanemab to treat early Alzheimer disease. AJMC^®. January 6, 2023. Accessed September 2, 2025. https://www.ajmc.com/view/fda-approves-lecanemab-to-treat-early-alzheimer-disease

3. McCormick B. FDA approves new maintenance dosing for lecanemab to treat early-stage Alzheimer disease. AJMC. January 27, 2025. Accessed September 2, 2025. https://www.ajmc.com/view/fda-approves-new-maintenance-dosing-for-lecanemab-to-treat-early-stage-alzheimer-disease