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Eisai’s Alzheimer's Drug Offers New Hope

Eisai’s new drug lecanemab has shown small but significant benefits for people with early Alzheimer’s disease.

Last week, Eisai announced that their clinical trial for lecanemab had yielded incredibly encouraging results. The study met its primary endpoint, showing a “highly statically significant reduction of clinical decline” in those with early Alzheimer’s disease (AD), whilst also meeting all its key secondary endpoints.   

Lecanemab, an investigational anti-amyloid beta (A?) protofibril antibody, fundamentally works by removing the protein amyloid from the brain. A? denotes the peptides that are the main constituent of amyloid plaques found in the brains of people with Alzheimer’s. Lecanemab is one of several drugs developed to target amyloid in recent years, but it is the first to result in a reduced rate of mental decline among patients.   

The trial, Clarity AD, was conducted globally with 1795 participants who have either mild AD or mild cognitive impairment due to AD, collectively known as early AD. Participants were given an intravenous infusion of either lecanemab or a placebo bi-weekly. The patients then underwent brain scans and regular interview-based tests called CDR-SB, assessing cognitive and functional performance in several key areas, including memory, judgement and problem solving, and personal care.  

Eisai’s announcement stated that “from as early as six months, across all time points, the treatment showed highly statistically significant changes in CDR-SB from baseline compared to placebo.” Moreover, after 18 months, those taking lecanemab saw their CDR-SB score decline 27% more slowly than those in the placebo group.   

"An important milestone for Eisai in fulfilling our mission to meet the expectations of the Alzheimer's community."

The drug is, of course, not without its side effects. The major downside is the development of amyloid-related imaging abnormalities, or ARIA, a condition characterised by swelling and/or bleeding in the brain. 21.3% of those who were administered lecanemab experienced ARIA, with 17% developing ARIA-H, a more severe form of the condition. However, it should be noted that 9% of those who received the placebo still developed ARIA, with 8.3% developing ARIA-H. Overall, Eisai said that lecanemab’s ARIA incidence profile was within expectations.  

Another concern is the nature of drug administration; with an intravenous infusion given every two weeks, patients had to make regular hospital visits and undergo frequent monitoring scans, a process which has been recognised as taxing for many. As a result, Eisai is working on a version of lecanemab which can be administered as a subcutaneous injection. This would be easier to administer and could also reduce side effects.   

Haruo Naito, Chief Executive Officer of Eisai, described the trial’s results as “an important milestone for Eisai in fulfilling our mission to meet the expectations of the Alzheimer’s community.” Eisai will now discuss the data with regulatory bodies worldwide and is hoping to obtain early approval for lecanemab so that those with early AD may have access to therapy as soon as possible. 

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