Eisai has won Japanese regulatory approval for a subcutaneous version of its Alzheimer's drug Leqembi that patients or caregivers can inject at home once a week, the company said on September 16. The autoinjector, marketed as Leqembi SC 250 mg Pen, is dosed as two 250 mg pens delivering a combined 500 mg once weekly, with each injection taking about 15 seconds. That adds a home option alongside the drug's existing intravenous regimen, administered every two weeks at a hospital or clinic.
Eisai calls it the first and only anti-amyloid therapy in Japan approved for at-home administration, and the third country to clear the SC formulation after the United States in July 2026 and China in September 2026.
| Feature | IV infusion (existing) | SC pen (newly approved) |
|---|---|---|
| Frequency | Every two weeks | Once a week |
| Setting | Medical facility | Home, pending listing on the injectable drug list |
| Administered by | Medical staff | Self-administered after training, about 15 seconds per pen |
| Status in Japan | In use since 2023 approval | Approved September 16, 2026; home use pending Central Social Insurance Medical Council review |
Home use is not automatic. Before patients can self-inject, Japan's Central Social Insurance Medical Council must review and approve the product, a process expected within roughly 60 days of approval, and the drug must then be added to the health ministry's list of insurer-approved injectable medicines physicians can prescribe. Even after listing, Eisai says treatment must start at a medical facility under a doctor's direct supervision, and patients or caregivers must complete sufficient training and demonstrate they understand the risks and can administer the drug reliably before doing so under a doctor's ongoing guidance.
The approval rests on data from the drug's Clarity AD Phase 3 trial and its long-term extension, where sub-studies of subcutaneous dosing found that once-weekly 500 mg SC exposure matched biweekly IV dosing closely enough to expect similar efficacy. Safety looked broadly similar between the two routes, and injection-related systemic reactions were less frequent under SC dosing, at 1.4%, though that figure comes from a related weekly 720 mg subcutaneous vial study in newly treated patients rather than the approved 500 mg pen dose itself. Monitoring for ARIA (amyloid-related imaging abnormalities) still requires MRI scans at the same checkpoints used for IV treatment.
Eisai says the approval will have only a minor effect on its earnings forecast for the year ending March 2027, and its guidance issued on May 15, 2026 stands unchanged. Lecanemab, Leqembi's generic name, is now approved in 53 countries and regions and under review in six more, with biweekly IV maintenance dosing cleared in nine countries and filed in eleven others. Eisai leads global development and regulatory filings for the drug and retains final decision-making authority, while Biogen co-commercializes and co-promotes it under their long-running Alzheimer's alliance.
For patients now making fortnightly trips to an infusion chair, the pen promises fewer clinic visits and less strain on nursing and infusion capacity. Whether that promise reaches Japanese homes depends on how quickly the Central Social Insurance Medical Council moves and how the injectable-list process plays out over the coming weeks.