Eisai has submitted a new drug application seeking approval from Japan’s Pharmaceuticals and Medical Devices Agency (PMDA) for Leqembi’s (lecanemab) subcutaneous (SC) formulation (SC-AI) for early Alzheimer’s disease. 

The formulation will serve as a new administration route.

Eisai’s application is based on data from several SC administration sub-studies of lecanemab, conducted within the Phase III Clarity AD open-label extension, after the core study for 18 months in people with mild cognitive impairment due to mild stage Alzheimers' dementia.  

The studies confirmed that once-weekly SC autoinjector SC-AI 500mg administration resulted in equivalent exposure to intravenous dosing every two weeks, with similar biomarker and clinical outcomes. 

The SC route showed a safety profile comparable to intravenous administration, with under 2% of participants experiencing systemic injection or infusion-related reactions.  

If approved, patients could self-administer the SC-AI 500mg dose (two 250mg injections) at home once weekly from the start of treatment, as an alternative to the existing hospital-based intravenous dosing every two weeks. 

The potential approval of the SC-AI formulation would expand treatment options for care partners and patients, allowing Leqembi to be used at home.  

Each 250mg autoinjector has an injection time of 15 seconds. The subcutaneous formulation may also reduce healthcare resources needed for intravenous dosing, such as nurse monitoring and preparation, streamlining the Alzheimer's treatment care pathway. 

Leqembi has received approval in 51 countries and regions, with regulatory evaluation ongoing in a further nine. Eisai oversees global development and regulatory activities and collaborates with Biogen on commercialisation and promotion efforts.  

In November 2025, Eisai and Biogen announced the UK MHRA's approval for Leqembi for intravenous maintenance dosing once every four weeks to treat early Alzheimer's.