Key Takeaways
The U.S. Food and Drug Administration extended its review for a new formulation of Eisai Co., Ltd. and Biogen Inc.’s Alzheimer’s treatment, Leqembi, by three months after requesting additional information on the companies’ application. The new target action date for the subcutaneous, once-weekly injection is August 24, 2026.
"The FDA has not raised any concerns to date regarding the approvability of LEQEMBI IQLIK as a starting dose," the companies said in a joint statement, noting they believe the comprehensive data package strongly supports its use for initiation therapy.
The delay stems from the FDA’s determination that the requested information constitutes a "major amendment" to the supplemental Biologics License Application (sBLA), requiring more time for a full review. This application is for using the subcutaneous version as a starting dose. A maintenance-only version of the subcutaneous injection was previously approved on August 26, 2025.
The extension pushes back a much-anticipated, more convenient treatment option for patients with early Alzheimer's disease. While the intravenous version is already approved, a weekly subcutaneous injection offers greater flexibility and could broaden the drug's adoption. For Eisai and Biogen, a timely approval is key to maximizing revenue from their flagship neurology asset.
Leqembi is a monoclonal antibody directed against amyloid-beta plaques in the brain, a hallmark of Alzheimer's disease. Treatment should be initiated in patients with mild cognitive impairment or the mild dementia stage of the disease.
However, the treatment carries a significant boxed warning for Amyloid-Related Imaging Abnormalities (ARIA), which can manifest as brain edema (ARIA-E) or brain hemorrhage (ARIA-H). These side effects are usually asymptomatic but can be serious and, in rare cases, fatal. In clinical trials, ARIA was observed in 21% of Leqembi patients compared to 9% of those on placebo.
The risk of developing ARIA is notably higher for patients who are Apolipoprotein E e4 (ApoE e4) homozygotes, representing about 15% of the Alzheimer's patient population. In trials, 45% of ApoE e4 homozygotes on Leqembi experienced ARIA, compared to just 13% of noncarriers. The FDA recommends testing for ApoE e4 status before starting treatment to inform risk.
The most common adverse reactions include infusion-related reactions (26% vs. 7% for placebo), ARIA-H (14% vs. 8%), and ARIA-E (13% vs. 2%).
The delay for the subcutaneous starting dose formulation adds another chapter to the drug's regulatory journey. Investors and patients will now watch for the new PDUFA date on August 24, 2026, as the next major catalyst for the Leqembi franchise.
This article is for informational purposes only and does not constitute investment advice.
