Priority Review Granted for Weekly Subcutaneous Lecanemab Dosing in Early Alzheimer Disease

Eisai and Biogen announced that the FDA has accepted its supplemental biologics license application (sBLA) for the subcutaneous (SC) autoinjector formulation of lecanemab-irmb (Leqembi Iqlik) as a weekly starting dose for patients with early Alzheimer disease (AD), granting the application priority review with a PDUFA action date of May 24, 2026.¹ If this new 500-mg dosing regimen is approved, it would offer an alternative to the currently available biweekly intravenous 250-mg dosing used at treatment initiation.

“If the FDA approves a subcutaneous starting dose for Leqembi, it will mark a major step toward expanding access for patients and caregivers,” Laura Nisenbaum, PhD, executive director of drug development at the Alzheimer’s Drug Discovery Foundation, told NeurologyLive^®. “Start-to-finish subcutaneous delivery opens the door to at-home administration—similar to diabetes and GLP-1 therapies—representing a breakthrough that will ultimately make it easier to combine multiple treatments and target the full spectrum of Alzheimer’s pathobiology.”

For background, in August 2025, the FDA approved a new 360-mg, once-weekly SC maintenance dosing option for lecanemab that follows 18 months of biweekly intravenous therapy.² Administration of lecanemab-irmb using the autoinjector requires approximately 15 seconds per 250-mg injection. Compared with intravenous administration, the SC formulation may reduce health care resource utilization associated with infusion-based delivery, including infusion preparation and nurse monitoring.

Data supporting the sBLA included evaluations of SC lecanemab administered at various doses, including analyses from substudies in the open-label extension (OLE) of the phase 3 Clarity AD trial (NCT03887455) conducted after completion of the 18-month core study in patients with early AD. Findings from the OLE revealed that weekly administration of the 500-mg SC dose resulted in pharmacokinetic exposure comparable to that of biweekly intravenous dosing, all while showing similar clinical and biomarker effects. In addition, SC dosing demonstrated a safety profile comparable to intravenous administration, with systemic injection- or infusion-related reactions occurring in fewer than 2% of participants.

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Beyond dosing and administration considerations, additional analyses from the Clarity AD study have explored lecanemab’s pharmacodynamic effects. Previously, investigators developed a sensitive immunoassay using lecanemab to selectively quantify amyloid-β protofibrils in cerebrospinal fluid (CSF). Application of this assay in analyses of phase 3 Clarity AD data showed increases in CSF amyloid-β protofibril levels following lecanemab treatment, findings that were interpreted as evidence of target engagement.³

In the analysis, presented at the 18th Clinical Trials on Alzheimer’s Disease (CTAD) Conference, held December 1-4, 2025, in San Diego, California, a total of 410 participants (placebo, n = 207; lecanemab, n = 203) had CSF samples at baseline, and 253 participants (placebo, n = 127; lecanemab, n = 126) had both baseline and at least 1 post baseline sample over the 18-month core study period. At baseline, CSF Aβ-PF were positively correlated with neurogranin, a marker of synaptic dysfunction (r = 0.153, P = .0127), and negatively correlated with amyloid PET centiloid (r = -0.202, P = .0005).

In the lecanemab-treated group, findings showed that total CSF Aβ-PF levels, including both free and bound forms, increased relative to placebo at all post baseline assessments (P = .0126 at 12 months and numerically higher at 18 months). Among participants who achieved amyloid negativity (Centiloid less than 30) at 18 months, researchers observed that those receiving lecanemab had a greater percent change of CSF Aβ-PF from baseline compared with participants who remained amyloid positive (Centiloid less than 30).

In October 2025, Eisai and Biogen reported that lecanemab-irmb is now available in the United States as a SC maintenance treatment for patients with mild cognitive impairment or mild dementia because of AD.⁴ In a recent interview, NeurologyLive^® spoke with Robert Przybelski, MD, MS, a professor of geriatrics and gerontology at the University of Wisconsin, to gain personal and clinical insights on the decision. Throughout the conversation, he emphasized the advantages of the self-administered autoinjector, particularly for patients who live in rural areas or those who travel seasonally. Although the therapy is generally well-received and simplifies treatment administration, he noted that proper training may be essential because of the complexity of the injection process.

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REFERENCES
1. FDA Accepts LEQEMBI® IQLIK^TM (lecanemab-irmb) Supplemental Biologics License Application as a Subcutaneous Starting Dose for the Treatment of Early Alzheimer's Disease under Priority Review. News release. Eisai and Biogen. January 25, 2026. Accessed January 26, 2026. https://www.eisai.com/news/2026/pdf/enews202605pdf.pdf
2. FDA Approves LEQEMBI® IQLIK™ (lecanemab-irmb) Subcutaneous Injection for Maintenance Dosing for the Treatment of Early Alzheimer's Disease. News release. Eisai and Biogen. August 29, 2025. Accessed January 26, 2026. https://media-us.eisai.com/2025-08-29-FDA-Approves-LEQEMBI-R-IQLIK-TM-lecanemab-irmb-Subcutaneous-Injection-for-Maintenance-Dosing-for-the-Treatment-of-Early-Alzheimers-Disease
3. New Data Presented at CTAD 2025 Confirms Pharmacological Effect of LEQEMBI® (lecanemab-irmb) on Neurotoxic Aβ Protofibrils in CSF. News release. Eisai. December 2, 2025. Accessed January 26, 2026. https://www.eisai.com/news/2025/news202584.html
4. Eisai and Biogen Announce U.S. Availability of LEQEMBI® IQLIK™ (lecanemab-irmb) Subcutaneous Injection Maintenance Dose for Treatment of Early Alzheimer's Disease. News release. Eisai and Biogen. October 6, 2025. Accessed January 26, 2026. https://investors.biogen.com/news-releases/news-release-details/eisai-and-biogen-announce-us-availability-leqembir-iqliktm