Bioequivalence of Subcutaneous Formulation Demonstrated

Eisai (4523) and Biogen (BIIB) have released the latest clinical data on the Leqembi (lecanemab) subcutaneous autoinjector (SC-AI) formulation at AAIC 2026. The clinical results show that the subcutaneous formulation, administered once weekly at a dose of 500mg, achieved a drug exposure ratio of 104% compared to the existing intravenous (IV) formulation, which is administered every two weeks at a dose of 10mg/kg (90% confidence interval: 99.1% to 109%), clearly demonstrating bioequivalence. The consistent pharmacokinetic (PK) profile observed across all weight quartiles provides clinical validity, indicating that a fixed dose can be administered regardless of individual patient characteristics. This will create an environment where patients can self-administer the drug at home without hospital visits, which will significantly improve long-term treatment adherence.

Equivalent Efficacy and Safety Based on Exposure

This clinical data clearly demonstrates that the cognitive function improvement efficacy and safety of Leqembi are determined by the drug exposure level in the body, rather than the route of administration. Both the amyloid positron emission tomography (Amyloid PET) results, which measured the rate of removal of soluble amyloid-beta (Aβ) protofibrils in the brain, and the Clinical Dementia Rating-Sum of Boxes (CDR-SB) scores were comparable to the IV formulation. The incidence of amyloid-related imaging abnormalities-edema (ARIA-E), a key indicator of adverse events, is also expected to be similar to the IV group. The low incidence of anti-drug antibodies (ADA), which induce an immune response, at 1.4%, and the absence of neutralizing antibodies further support the long-term safety of the drug.

Long-Term Treatment Benefits Confirmed by Real-World Evidence (RWE) in Clinical Practice

Real-world evidence (RWE) from two Alzheimer's treatment centers in the United States, presented at the conference, shows that the subcutaneous formulation maintains its efficacy in actual clinical practice. A 36-month follow-up study of 28 patients at the Alzheimer's Research Treatment Center showed that the subcutaneous treatment group had a significantly slower rate of cognitive decline compared to the natural history control group. At FirstChoice Neurology, 91% of patients (10 out of 11) in the maintenance therapy group showed improvement or stabilization of symptoms on the Mini-Mental State Examination (MMSE). A survey of patients and caregivers also showed a satisfaction rate of up to 97%, indicating that the improved convenience is directly linked to an improvement in patients' quality of life.

Global Regulatory Timelines and Competition for Market Leadership

Following the approval of the Leqembi subcutaneous formulation for maintenance therapy (SC maintenance) by the U.S. Food and Drug Administration (FDA) in August 2025, Eisai plans to expand the application of the autoinjector to the initiation phase. Eisai has already submitted an application for the subcutaneous formulation to the Pharmaceuticals and Medical Devices Agency (PMDA) in Japan in November 2025, and in January 2026, it completed the submission of an application to the National Medical Products Administration (NMPA) in China, accelerating its global expansion. In contrast to Eli Lilly (LLY), whose Kisunla (donanemab-azbt) is still primarily administered intravenously, the launch of the subcutaneous autoinjector will be a significant differentiator. It will bypass the bottleneck of intravenous infrastructure in hospitals, increase the number of prescriptions, and solidify Eisai's position as a leader in the Alzheimer's market.