Japan Approves LEQEMBI Pen, First At-Home Subcutaneous Alzheimer's Treatment
核心洞察
Eisai and Biogen announced Japan's approval of LEQEMBI Pen (搜索), a subcutaneous autoinjector formulation of lecanemab, as a new route of administration for early Alzheimer's disease (搜索).
The approval makes Japan the third country globally to clear the subcutaneous formulation, following the United States in July 2026 and China in September 2026.
Two pens totaling 500 mg are given once weekly, with each injection taking about 15 seconds and demonstrating exposure similar to biweekly intravenous dosing.
Eisai Co., Ltd. and Biogen Inc. announced on Sept. 16, 2026 that Japan has approved "LEQEMBI Pen (搜索)," the subcutaneous (SC) formulation of the anti-amyloid beta (搜索) (Aβ) protofibril antibody LEQEMBI (generic name: lecanemab), as a new route of administration for early Alzheimer's disease (搜索). Japan becomes the third country globally to approve the SC formulation, following the United States in July 2026 and China in September 2026, according to the companies.
The autoinjector formulation enables administration by a care partner or by patient self-administration, with two pens totaling 500 mg administered once weekly. With the approval, LEQEMBI treatment now offers once-weekly SC administration at home in addition to intravenous (IV) administration every two weeks in a hospital setting. Eisai and Biogen noted the pen is the first and only anti-amyloid treatment in Japan that enables at-home administration for Alzheimer's disease (搜索).
Dosing, Exposure and Safety Data
The usual dose of lecanemab (recombinant) under the new route is 500 mg injected subcutaneously once weekly. The companies state that LEQEMBI Pen (搜索) may reduce the time required for anti-amyloid therapy administration compared with IV infusions, with an approximate injection time of 15 seconds per injection.
The approval is based on integrated results of data and associated modeling and simulation from the 18-month core study of the Phase 3 Clarity AD study of LEQEMBI in patients with mild cognitive impairment (MCI) due to AD or mild AD dementia, collectively referred to as early AD, as well as multiple SC administration sub-studies in its subsequent long-term extension (LTE) study. Once-weekly administration of the 500 mg SC formulation demonstrated similar exposure to IV administration once every two weeks and supported the expectation that the SC formulation provides efficacy comparable to that of the IV formulation.
The overall safety profile of SC administration was generally similar to that of IV administration, while systemic injection/infusion-related reactions were observed less frequently with SC administration (1.4%) than with IV administration. That incidence figure refers to participants newly initiated on lecanemab treatment via SC administration, based on clinical data obtained from once-weekly subcutaneous administration of lecanemab 720 mg using vial formulations.
For amyloid-related imaging abnormalities (ARIA) monitoring, brain magnetic resonance imaging (MRI) is performed prior to initiating treatment and at specified time points after treatment initiation, as with IV administration.
Self-Administration Conditions in Japan
At-home self-administration using LEQEMBI Pen (搜索) will be possible after it is listed in the injectable drug list designated by the Minister of Health, Labour and Welfare that health insurance doctors can administer or prescribe, following deliberation and approval by the Central Social Insurance Medical Council, in principle within 60 days after approval.
The companies outlined conditions stipulated for self-administration. When initiating administration, treatment must be administered by a physician or under the direct supervision of a physician at a medical facility. The applicability of self-administration must be carefully considered, and implemented only after thorough education and training, confirmation that the patient or family member/caregiver understands the risks associated with administration and how to respond to them, and confirmation that they are able to reliably administer the drug themselves, under the management and guidance of a physician.
Rationale and Treatment Pathway Impact
According to the companies, at-home administration may reduce the burden of clinic visits for patients and their care partners and provide greater flexibility in treatment, allowing patients to make treatment choices that better fit their lifestyles, including fewer constraints on going out and traveling. The improved convenience and flexibility are expected to lower barriers to initiating and continuing treatment with LEQEMBI.
LEQEMBI Pen (搜索) also has the potential to reduce healthcare resources associated with IV dosing, such as nurse monitoring, as well as maintaining infusion capacity. These features are expected to contribute to further streamlining the overall Alzheimer's disease (搜索) treatment pathway.
The companies describe AD as a progressive, relentless disease with Aβ and tau (搜索) as hallmarks, caused by a continuous underlying neurotoxic process driven by protofibrils (搜索) that begins before amyloid plaque accumulation and continues after plaque removal. They state that only LEQEMBI fights AD in two ways, targeting both protofibrils and amyloid plaque. Protofibrils are thought to be the most toxic Aβ species contributing to brain damage in AD and are believed to play a major role in cognitive decline; reducing protofibrils may reduce neuronal damage and cognitive impairment, potentially preventing progression of AD.
Global Regulatory and Development Status
Lecanemab is the result of a strategic research alliance between Eisai and BioArctic. It is a humanized immunoglobulin gamma 1 (IgG1) monoclonal antibody directed against aggregated soluble (protofibril) and insoluble forms of amyloid-beta. It has been approved in 53 countries and regions including Japan, the U.S., China, Canada, Europe, South Korea, Taiwan, and Saudi Arabia, and is under regulatory review in 6 countries.
In September 2023, Eisai received approval in Japan for lecanemab for slowing progression of MCI and mild dementia due to AD. Following the initial phase with treatment every two weeks for 18 months, IV maintenance dosing every four weeks is approved in 9 countries and regions including the U.S., China and the UK, with applications filed in 11 countries and regions. The U.S. FDA approved Eisai's Biologics License Application for subcutaneous maintenance dosing (360 mg) with LEQEMBI IQLIK (搜索) in August 2025. For subcutaneous initiation treatment (500 mg), approval was obtained in the U.S. in July 2026 and China in September 2026, and applications are under review in 2 countries.
Eisai serves as the lead for lecanemab's development and regulatory submissions globally, with Eisai and Biogen co-commercializing and co-promoting the product and Eisai having final decision-making authority. BioArctic has the right to commercialize lecanemab in the Nordic region and is preparing for commercialization there together with Eisai, with no development costs for lecanemab in Alzheimer's disease (搜索) and entitlement to payments tied to sales milestones and royalties on global sales.
Ongoing Studies in Earlier and Inherited Disease
Since July 2020, the Phase 3 AHEAD 3-45 study of lecanemab in individuals with preclinical AD — clinically normal with intermediate or elevated brain amyloid — has been ongoing and was fully recruited in October 2024. The four-year study is conducted as a public-private partnership between Eisai, Biogen and the Alzheimer's Clinical Trial Consortium, funded by the National Institute on Aging, part of the National Institutes of Health.
Since January 2022, the Tau (搜索) NexGen clinical study for Dominantly Inherited Alzheimer's disease (搜索), conducted by the Dominantly Inherited Alzheimer Network Trials Unit and led by Washington University School of Medicine in St. Louis (搜索), has been ongoing and includes lecanemab as the backbone anti-amyloid therapy.