Eisai Co., Ltd. and Biogen Inc. (Nasdaq: BIIB) presented clinical data at the Alzheimer's Association International Conference (AAIC) 2026 in London on July 12 showing that a subcutaneous autoinjector (SC-AI) formulation of Leqembi (lecanemab) achieved drug exposure comparable to the approved intravenous regimen in patients with early Alzheimer's disease.

The data showed that a once-weekly 500 mg SC-AI dose achieved bioequivalence to the IV initiation regimen of 10 mg/kg every two weeks, with an exposure ratio of 104% (90% confidence interval: 99.1%–109%). Exposure remained consistent across body weight quartiles.

Amyloid removal, clinical efficacy, and the incidence of a side effect called ARIA-E were driven by lecanemab exposure rather than route of administration, according to the data. The overall safety profile of the SC-AI was described as generally consistent with the IV formulation. Injection-related reactions were observed, most of which were localized. The incidence of anti-drug antibodies was 1.4% in the SC-AI group, with no neutralizing antibodies detected.

Real-world data from two U.S. Alzheimer's treatment centers were also presented. At the Alzheimer's Research and Treatment Center, 28 patients receiving SC administration showed slower cognitive decline over 36 months compared with a matched natural history cohort. At First Choice Neurology and Visionary Investigators Network, 10 of 11 evaluable patients showed improvement or remained stable on a cognitive measure after at least six months of SC maintenance therapy.

Patient and care partner surveys across the two sites showed satisfaction rates ranging from 75% to 97% and willingness to recommend treatment ranging from 92% to 100%.

The SC-AI formulation for initiation remains under FDA review. The FDA approved subcutaneous maintenance dosing under the name Leqembi IQLIK in August 2025. Applications for subcutaneous formulations are also under review in other markets. Eisai leads lecanemab development globally, with Eisai and Biogen co-commercializing the product.