WASHINGTON - The United States Food and Drug Administration (FDA) on Friday approved a new Alzheimer’s drug that may modestly slow the pace of cognitive decline early in the disease but also carries risks of swelling and bleeding in the brain.

The approval of the drug, lecanemab, to be marketed as Leqembi, is likely to generate considerable interest from patients and physicians.

Studies of the drug – an intravenous infusion administered every two weeks – suggest it is more promising than the scant number of other treatments available.

Still, several Alzheimer’s experts said it was unclear from the medical evidence whether Leqembi could slow cognitive decline enough to be noticeable to patients.

Even a recent report of findings from a large 18-month clinical trial, published in the New England Journal of Medicine and co-written by scientists from the lead company making the drug, concluded that “longer trials are warranted to determine the efficacy and safety of lecanemab in early Alzheimer’s disease”.

Eisai, a Japanese pharmaceutical company, led the development and testing of the drug.

It is partnering with US company Biogen, maker of the controversial Alzheimer’s drug Aduhelm, for its commercialisation and marketing, and the companies will split the profits equally.

Eisai said the list price for Leqembi (pronounced le-KEM-bee) would be $26,500 per year.

The price is slightly lower than Aduhelm’s but higher than that recommended by some analysts.

“Based on our draft results, that price would not meet typical cost-effectiveness thresholds,” said Dr David Rind, chief medical officer for the Institute for Clinical and Economic Review, an independent non-profit organisation that assesses the value of medicines.

In a preliminary report last month, the institute said that to be cost-effective for patients, the price should be set between US$8,500 (S$11,362) and US$20,600 a year.

“Given the large number of patients with Alzheimer’s disease, it is particularly important that new therapies be priced in line with their value to patients,” Dr Rind said on Friday.

In its decision, the FDA appeared to be acknowledging the vehement criticism that erupted when it approved Aduhelm in 2021 after both a committee of independent advisers and an FDA council of senior officials said there was not enough evidence that it worked.

Last week, an 18-month investigation by two congressional committees found that the approval process for Aduhelm was “rife with irregularities” and involved an unusually close collaboration with Biogen.

In response, the FDA said “the agency has already started implementing changes consistent with the committees’ recommendations”.

An FDA official involved in the review of Leqembi said that “there were many important lessons learnt” since the approval of Aduhelm.

With Leqembi, the FDA included narrower and more cautionary language on the drug label than it initially had with Aduhelm.

After an outcry from physicians and others, it changed the Aduhelm label a month after its approval.

The Leqembi label says the drug should be used only for patients in early and mild stages of Alzheimer’s disease, matching the status of patients in the clinical trials of the drug.

It instructs doctors not to treat patients without doing tests to confirm that they have one of the hallmarks of Alzheimer’s: a build up of the protein amyloid, which Leqembi (like Aduhelm) attacks.

“In the case of Leqembi, more detail and clarity on the most appropriate patient population for use of the drug, and greater explanation around safety” for brain swelling, brain bleeding and use of blood thinners with the drug are “now included in the label”, said the official, who spoke on condition of anonymity to describe agency deliberations.

The official said the FDA also requested more data on subgroups of patients characterized by age, gender, health status and other factors, and that it worked with the companies to include more diversity in the clinical trials. Participants in the Aduhelm clinical trials were overwhelmingly white, but in the Leqembi trials, about 25 per cent of US participants were Black or Hispanic.

Mr Ivan Cheung, chair and CEO of Eisai’s US operations, said in an interview that in discussing who should be eligible for the treatment, “we have worked very hard with the FDA to narrow the population down to a very specific one, the same as the clinical trials.”

About 1.5 million of the 6 million people with Alzheimer’s in the United States are estimated to be in the beginning phases of the disease, with diagnoses of either mild cognitive impairment or early-stage Alzheimer’s. How many will be treated with Leqembi will depend significantly on whether Medicare covers the drug.

Last year, the federal Centers for Medicare and Medicaid Services sharply limited Medicare coverage for Aduhelm, citing the treatment’s unclear benefit and safety risks and allowing payment only for participants in clinical trials. That meant very few patients could afford Aduhelm’s US$28,800-a-year price tag, and the drug has effectively been sidelined from the marketplace.

If the agency determines that Leqembi has clearer evidence of helping patients, Medicare could cover it for all eligible patients and only impose a requirement that the patients’ experience be tracked.

Like Aduhelm’s label, Leqembi’s includes warnings about brain swelling and brain bleeding and notes that patients with a gene mutation that increases the risk of developing Alzheimer’s have a greater risk of brain swelling with the treatment.

Leqembi’s label also includes cautionary language about taking blood thinners while on the treatment, which has been raised as a concern with anti-amyloid drugs but was not addressed on Aduhelm’s label. “Additional caution should be exercised” when considering whether to give blood thinners to a Leqembi patient, the label says.

Concerns about safety have been stoked by news reports of the deaths of three patients who experienced brain swelling and brain bleeding, two of whom were being treated with blood thinners. Those patients participated in a large phase 3 trial of the drug, during which they were not told whether they received it or a placebo. But their deaths occurred after that phase of the trial, when they were knowingly being treated with lecanemab in what’s known as an open-label extension study. NYTIMES