Key dosing differences between Eli Lilly’s Kisunla and Biogen’s Leqembi are about to come to a head in the Alzheimer’s market as patients end their 18-month course of Lilly’s product.
The first patients to begin Eli Lilly’s Alzheimer’s therapy Kisunla after its approval in July 2024 are beginning to hit the 18-month mark when they can transition off the therapy. Biogen is standing poised to capture them with Leqembi as the feedback comes in from the physician community about maintenance therapy.
“Physicians are asking, what do we do?” said Alisha Alaimo, head of North America, on Biogen’s first quarter earnings call Wednesday. “Patients in general, who are on either of the products, want to stay on product. There is a fear of coming off and having a decline in their cognition.”
So Biogen is considering how patients can switch to Leqembi, which won FDA approval in January 2023, becoming the first of a new wave of disease-modifying Alzheimer’s treatments.
Kisunla and Leqembi have been jockeying for the same market. A key difference between the two is that Kisunla is meant to be dosed until amyloid is cleared from the brain as seen via PET imaging. Leqembi, on the other hand, is dosed indefinitely.
This dosing difference created some regulatory challenges for Lilly, which missed the chance at an accelerated approval because the data submitted only had patients on the study drug for 12 continuous months. At the time, Lilly said this was by design, as the drug is meant to clear amyloid plaques—and the data showed it was doing just that.
Now, this design—which Lilly heralded as innovative during the regulatory process—may come back to haunt the Indianapolis pharma, as it could give Biogen an edge in the market.
Alaimo said that the first quarter of this year is when the first tranche of Kisunla patients are expected to move off their 18-month treatment period. While the official numbers aren’t in yet, she said Biogen has been fielding tons of questions from the healthcare community about what to do next.
“We do have physicians that are looking at: Can we switch them to maintenance or to substitute maintenance of Leqembi?” Alaimo said.
The launch process for Leqembi has been tough, as physicians adjust to the required scans to confirm treatment eligibility, along with reimbursement issues and, of course, the behemoth Lilly as a rival.
But in Q1 2026, the drug grew 74% year-over-year to $168 million globally, including $86 million in the U.S. This result beat consensus of $140 million, according to analysts. The product is partnered with Japan’s Eisai, with profits split 50/50.
“Leqembi sales exceeded expectations significantly (+12% vs. cons.) as . . . Alzheimer’s continues to gain traction slowly over time,” BMO Capital Markets wrote in a Wednesday morning note.
New data show that 78% of patients continued on Leqembi 18 months after starting treatment and the majority continued on to a maintence regimen.
Leqembi has already been winning about 60% of patients, William Blair said in a Wednesday note. But patients have stated that once-monthly dosing with Kisunla is the key reason they choose it over Leqembi, according to the firm. Biogen’s drug is dosed twice weekly in hour-long infusion sessions for the first 18 months, before moving to once monthly. Lilly’s product must be dosed in a care setting.
Biogen has been working to “improve the care pathway,” according to CEO Chris Viehbacher. The company last year received approval for a subcutaneous version of Leqembi, called Iqlik, to be used as maintenance therapy given via at-home injections. After an initial 18 months, patients can transition to the at-home version. Biogen is now awaiting FDA approval of Iqlik’s use for induction, with a decision set for May 24.
This approval “would remove Kisunla’s dosing advantage,” William Blair said.
