TOKYO and CAMBRIDGE, Mass., Nov. 28, 2025 - (JCN Newswire) - Eisai Co., Ltd. (Headquarters: Tokyo, CEO: Haruo Naito, “Eisai”) and Biogen Inc. (Nasdaq: BIIB, Corporate headquarters: Cambridge, Massachusetts, CEO: Christopher A. Viehbacher, “Biogen”) announced today that Eisai has filed a new drug application for “LEQEMBI(R)” (brand name, generic name: lecanemab) seeking approval for a subcutaneous formulation (subcutaneous autoinjector: SC-AI) as a new route of administration to Japan’s Pharmaceuticals and Medical Devices Agency (PMDA).

The application is based on data from multiple subcutaneous (SC) administration sub-studies of lecanemab conducted as part of the Phase 3 Clarity AD open-label extension (OLE), following the 18-month core study in individuals with Mild Cognitive Impairment (MCI) due to Alzheimer‘s disease (AD) or mild stage of AD dementia (collectively referred to as early AD). It was confirmed that the once weekly administration of SC-AI 500mg resulted in equivalent exposure to once every two weeks intravenous (IV) administration and similar clinical and biomarker benefits. Subcutaneous administration demonstrated a safety profile similar to IV administration, with less than 2% incidence of systemic injection/infusion-related reactions.

If approved, the SC-AI of 500 mg (two 250 mg injections) could be used to administer a once-weekly dose at home from the initiation of treatment, as an alternative to the current IV administration every two weeks dose in the hospital setting. The potential approval of SC-AI would expand the option for patients and care partners to receive LEQEMBI treatment at home. The injection time for each autoinjector (250mg injection) is approximately 15 seconds. The SC formulation also has the potential to reduce healthcare resources associated with IV dosing, such as preparation for infusion and nurse monitoring, while streamlining the overall AD treatment care pathway.

AD is a progressive, relentless disease with amyloid beta (Aβ) and tau as hallmarks that is caused by a continuous underlying neurotoxic process driven by protofibrils* that begins before amyloid plaque accumulation and continues after plaque removal.1,2,3 Only LEQEMBI fights AD in two ways – targeting both protofibrils and amyloid plaque, which can impact tau downstream. 

LEQEMBI is currently approved in 51 countries and regions and is under regulatory review in 9 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.

* Protofibrils are believed to contribute to the brain injury that occurs with AD and are considered to bethe most toxic form of Aβ, having a primary role in the cognitive decline associated with this progressive, debilitating condition.1 Protofibrils cause injury to neurons in the brain, which in turn, can negatively impact cognitive function via multiple mechanisms, not only increasing the development of insoluble Aβ plaques but also increasing direct damage to brain cell membranes and the connections that transmit signals between nerve cells or nerve cells and other cells. It is believed the reduction of protofibrils may prevent the progression of AD by reducing damage to neurons in the brain and cognitive dysfunction.2 

For more details, please visit: https://www.eisai.com/news/2025/pdf/enews202582pdf.pdf

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