Dementia is a condition that results in progressive memory or thinking problems. It is now the most common cause of death in Australia. There are many different causes of dementia, but Alzheimer’s disease accounts for about 60–80% of all cases.
Last week, Australia’s Therapeutic Goods Administration (TGA) approved a new drug for early Alzheimer’s disease: lecanemab, sold under the brand name Leqembi. This follows the approval of a similar drug, donanemab, earlier this year. While lecanemab has been shown to slow the progression of disease in some people who receive an early diagnosis, it comes with a high price tag that will put it out of reach for many Australians.
### How Does It Work?
Lecanemab belongs to a class of drugs known as monoclonal antibodies. When our bodies encounter foreign invaders, such as bacteria or viruses, our immune system produces antibodies—proteins that bind to the invader and mark it for destruction by other immune cells.
A monoclonal antibody is produced in a lab to bind to a specific target. In this case, the target is the amyloid protein, which is the microscopic hallmark of Alzheimer’s disease. Once the immune system captures the antibody, it can then remove amyloid from our brains, helping to limit ongoing damage.
### How Effective Is It?
The recent approval is based on a large clinical trial involving 1,734 participants over 18 months, funded by the drug company Eisai. The trial showed a significant slowing of disease progression in patients with either early Alzheimer’s or mild cognitive impairment due to early Alzheimer’s changes in the brain.
Before the trial, all patients had positron emission tomography (PET) scans confirming the presence of amyloid protein in their brains. Those who received the active drug progressed 27% less compared to those given a placebo over the 18 months. This was measured using the Clinical Dementia Rating Sum of Boxes, a scale assessing both cognition and function.
Over the study period, this amounts to about five months less decline in the group who received lecanemab. For patients continuing treatment, there is evidence of sustained benefit for as long as four years.
Participants who received lecanemab also showed large reductions in amyloid levels in the brain, as measured by PET scans. By the end of the trial, most participants were below the threshold that typically indicates the presence of Alzheimer’s, although the treatment did not reverse their symptoms.
### What Are the Side Effects?
Safety concerns have been raised by regulators. The TGA initially rejected lecanemab’s approval in October last year due to concerns over its risk-benefit profile.
In the trial, 12.6% of participants receiving the drug experienced brain swelling. The rate was higher—32.6%—in those with two copies of an Alzheimer’s-promoting gene, apolipoprotein E4 (ApoE4). Among those with brain swelling, 22% experienced side effects such as headaches, dizziness, blurred vision, and balance problems. These symptoms were generally mild.
However, a small number of participants who were also on blood-thinning medications suffered serious brain bleeds, resulting in death. The remaining 78% of those with brain swelling were asymptomatic.
Due to the risk of brain swelling, patients taking lecanemab require MRI scans every three months to monitor their brains. Additionally, 17.3% of those on the active drug experienced small brain bleeds (microhemorrhages) compared to 9.0% on placebo.
Following the initial rejection, new safety and outcome data extending to four years of treatment were presented during an appeal process, leading to the recent approval.
### How Much Does It Cost?
Australia’s Pharmaceutical Benefits Scheme (PBS) does not currently subsidize lecanemab. The drug costs approximately A$40,000 per year, placing it beyond the reach of many people who might benefit.
Treatment guidelines recommend dosing every two weeks for an 18-month period, followed by monthly maintenance doses. There are also additional costs related to necessary monitoring—such as doctor visits, MRI scans, and PET scans.
The Pharmaceutical Benefits Advisory Committee (PBAC) has not yet assessed lecanemab for PBS listing. It is worth noting that the PBAC rejected an application for donanemab in July, citing concerns that its benefits were too small and uncertain to justify the treatment burden on both patients and the healthcare system.
Since lecanemab works in a similar way to donanemab, with comparable costs, effectiveness, and risks, these considerations are highly relevant.
### Bottom Line
Lecanemab can only be used in the early stages of Alzheimer’s disease. If you or a loved one are experiencing early signs—such as consistent short-term memory loss or confusion about days and dates—it is important to seek medical advice promptly. Early diagnosis is key to understanding your treatment options.
If you are considering lecanemab or donanemab, it is crucial to know that these drugs are not cures for Alzheimer’s. They may slow disease progression but do not improve existing symptoms.
Lecanemab will not benefit individuals whose dementia is caused by conditions other than Alzheimer’s, nor will it help those with Alzheimer’s whose disease has advanced beyond the earliest stages.
https://knowridge.com/2025/10/what-is-lecanemab-the-newly-approved-alzheimers-drug-can-it-really-slow-down-dementia/