TOKYO & STOCKHOLM — November 28, 2025. Eisai, in partnership with BioArctic, has submitted a New Drug Application (NDA) to Japan’s Pharmaceuticals and Medical Devices Agency (PMDA) for a subcutaneous autoinjector formulation (SC-AI) of Leqembi® (lecanemab), marking a major step toward enabling at-home treatment initiation for patients with early Alzheimer’s disease. If approved, lecanemab would become Japan’s first anti-amyloid therapy offering a self-administered weekly subcutaneous injection from the start of treatment, potentially transforming patient access and easing pressure on healthcare systems.
Science Significance
The new subcutaneous formulation of lecanemab is supported by robust scientific data from multiple sub-studies within the Phase 3 Clarity AD open-label extension, which confirmed that once-weekly SC dosing of 500 mg achieves drug exposure equivalent to the approved IV regimen. The SC option demonstrated comparable biomarker improvements, similar clinical benefits and a favorable safety profile, with less than 2% incidence of systemic injection or infusion-related reactions. These findings highlight a significant scientific advancement in delivering an anti-amyloid protofibril monoclonal antibody—maintaining disease-modifying efficacy while enabling a simpler, faster and more accessible administration route.
Regulatory Significance
This NDA represents a pivotal regulatory milestone for one of the world’s most widely approved Alzheimer’s disease treatments, already authorized in 51 countries with ongoing review in nine additional regions. PMDA approval of the SC autoinjector would introduce a new administration route for initiation dosing, complementing Japan’s existing IV option and further aligning national regulatory practice with evolving global standards for Alzheimer’s therapy access. The application builds on a similar U.S. filing, reflecting an international regulatory movement toward more flexible dosing pathways for disease-modifying Alzheimer’s treatments.
Business Significance
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The SC formulation has the potential to significantly expand market uptake by removing dependence on infusion centers, optimizing resource allocation and enabling faster treatment initiation for eligible patients—an important business advantage as demand for Alzheimer’s treatments continues to rise. For Eisai and BioArctic, this represents a strategic enhancement to the Leqembi franchise, which already includes IV and SC maintenance dosing approvals in major markets. With BioArctic entitled to royalties and Nordic commercialization rights, the SC-AI pathway strengthens revenue potential across Asia, Europe and North America and reinforces the companies’ long-term global Alzheimer’s strategy.
Patients’ Significance
For individuals living with early Alzheimer’s disease and their caregivers, the ability to receive once-weekly injections at home could dramatically reduce treatment burden, eliminate the need for regular hospital visits and support greater long-term adherence—a critical factor in maintaining disease-modifying benefits. The SC autoinjector’s 15-second injection time, ease of use and reduced resource requirements align with the real-world needs of a population facing progressive cognitive decline. This formulation could help widen access at a moment when early intervention offers the strongest chance of preserving cognitive and functional capacity.
Policy Significance
Japan’s rapidly aging population and increasing Alzheimer’s prevalence make scalable, resource-efficient therapies a national priority. Approval of the SC formulation would support public-health goals by reducing hospital workload, enabling decentralized care models and improving the sustainability of dementia-management pathways. As national healthcare authorities emphasize early detection and timely initiation of disease-modifying therapies, an at-home treatment option could help align system capacity with patient need, reinforcing Japan’s leadership in adopting innovative Alzheimer’s interventions.
The submission of the NDA for subcutaneous Leqembi marks a significant evolution in the treatment landscape for early Alzheimer’s disease in Japan. By combining proven anti-amyloid efficacy with highly practical at-home administration, Eisai and BioArctic aim to help patients access therapy earlier, more consistently and with fewer barriers. If approved, the SC autoinjector would extend the impact of one of the world’s leading Alzheimer’s treatments and further solidify Japan’s commitment to advancing innovative, patient-centered neurodegenerative care.
Source: BioArctic press release
