Eisai and Biogen Approve Subcutaneous LEQEMBI for Early Alzheimer’s in Japan

Eisai Co., Ltd. and Biogen Inc. have announced that their anti-amyloid beta (Aβ) protofibril antibody, LEQEMBI, is now approved in Japan for subcutaneous (SC) administration as a treatment for early Alzheimer’s disease (AD). This approval marks a significant advancement in the treatment of AD, offering patients a more convenient and flexible option for managing their condition.

LEQEMBI Pen, the new autoinjector formulation, enables administration by a care partner or the patient themselves. Each treatment consists of two pens, each containing 500 mg of lecanemab, to be administered once weekly. This new method of administration is expected to reduce the time required for therapy, with an approximate injection time of 15 seconds per injection. The at-home administration option is anticipated to alleviate the burden of frequent clinic visits, allowing patients to better manage their treatment schedules according to their lifestyles.

The approval of LEQEMBI Pen in Japan comes after the integrated results of data and associated modeling and simulation from the 18-month core study of the Phase 3 Clarity AD study, which evaluated the efficacy of lecanemab in patients with mild cognitive impairment (MCI) due to AD or mild AD dementia. The SC formulation demonstrated similar exposure to the IV administration once every two weeks, supporting the expectation that it provides comparable efficacy. The overall safety profile of SC administration was generally similar to that of IV administration, with systemic injection/infusion-related reactions observed less frequently (1.4%) in participants newly initiated on lecanemab treatment via SC administration.

Eisai serves as the lead for lecanemab’s development and regulatory submissions globally, with both companies co-commercializing and co-promoting the product. Eisai retains final decision-making authority. The approval of LEQEMBI Pen in Japan is part of a broader strategy to expand the availability of this treatment to more patients, with the potential to reduce healthcare resource utilization and streamline the overall AD treatment pathway.

The approval of LEQEMBI Pen in Japan is the third country globally to approve this SC formulation, following the U.S. and China. The product is expected to be listed in the injectable drug list designated by the Minister of Health, Labour and Welfare, allowing for at-home self-administration. However, certain conditions must be met, including initial administration by a physician or under their direct supervision, and thorough education and training for patients and their care partners.

Lecanemab, the generic name for LEQEMBI, is a humanized immunoglobulin gamma (IgG1) monoclonal antibody directed against aggregated soluble (protofibril) and insoluble forms of amyloid-beta (Aβ). Since its approval in Japan for slowing the progression of mild cognitive impairment and mild dementia due to AD, lecanemab has been approved in 53 countries and regions, including the U.S., China, Canada, Europe, South Korea, Taiwan, and Saudi Arabia. The U.S. FDA approved Eisai’s Biologics License Application (BLA) for subcutaneous maintenance dosing in August 2025, and the U.S. and China approved the subcutaneous initiation treatment in July and September 2026, respectively.

The approval of LEQEMBI Pen in Japan is part of a larger effort to provide more flexible and convenient treatment options for patients with AD. Eisai and Biogen have been collaborating on the development and commercialization of AD treatments since 2014, with a focus on reducing the burden of care and improving patient outcomes. The approval of LEQEMBI Pen is expected to contribute to the overall goal of providing innovative and effective treatments for AD, ultimately helping to address the growing global need for effective AD therapies.