# Anti-amyloid antibodies

Anti-amyloid antibodies (AAA), are a class of monoclonal antibodies developed to treat Alzheimer's disease. The first drug in the class to be developed, in the early 2000s, is bapineuzumab, but it did not show effectiveness in later-stage trials. The first drug to be approved by the US Food and Drug Administration (FDA) is aducanumab—in 2021.

## Approved drugs

As of 2022, none of these drugs has been approved by the European Medicines Agency.

### Aducanumab

Aducanumab, sold under the brand name Aduhelm, is an anti-amyloid drug designed to treat Alzheimer's disease. It is a monoclonal antibody that targets aggregated forms (plaque) of amyloid beta (Aβ) found in the brains of people with Alzheimer's disease to reduce its buildup. It was developed by Biogen and Eisai. Aducanumab is given via intravenous infusion.
Aducanumab was approved for medical use in the United States by the Food and Drug Administration (FDA) in June 2021, in a controversial decision that led to the resignation of three advisers to the FDA in the absence of evidence that the medication is effective. The FDA stated that it represents a first-of-its-kind treatment approved for Alzheimer's disease and that it is the first new treatment approved for Alzheimer's since 2003. Aducanumab's approval is controversial for numerous reasons including ambiguous clinical trial results regarding efficacy, the high cost of the medication and the very high rate of serious adverse events. The FDA considers it to be a first-in-class medication.
In November 2020, a panel of outside experts for the FDA concluded that a pivotal study of aducanumab failed to show strong evidence that the medication worked, citing questionable efficacy and multiple red flags found with the data analysis. There were also significant health risks associated with the medication; brain swelling or brain bleeding was found in 41% of patients enrolled in the studies. Nevertheless, the medication was approved under the FDA's accelerated approval pathway, and the FDA requires Biogen to perform follow-up reviews to assure the medication is a safe and effective treatment for Alzheimer's disease. The Office of Inspector General, US Department of Health and Human Services was asked to investigate interaction between the drug company and the FDA prior to the medication's approval.

### Lecanemab

Lecanemab, sold under the brand name Leqembi, is a monoclonal antibody medication used for the treatment of Alzheimer's disease. Lecanemab is an amyloid beta-directed antibody. It is given via intravenous infusion to patients with mild cognitive impairment or mild dementia. In clinical trials, it demonstrated modest efficacy in reducing relative cognitive decline compared to placebo. The most common side effects of lecanemab include headache, infusion-related reactions, and amyloid-related imaging abnormalities, a side effect known to occur with the class of antibodies targeting amyloid.

### Donanemab

Donanemab, sold under the brand name Kisunla, is a monoclonal antibody used for the treatment of Alzheimer's disease. Donanemab was developed by Eli Lilly and Company.
The most common side effects include amyloid-related imaging abnormalities and headache.

## Efficacy

A 2023 review found that "Anti-Aβ drugs have relatively low efficacy in preventing cognitive decline, and they reduce pathological productions with acceptable safety." A 2022 review finds "a statistically significant but slight clinical effect of these drugs emerges in patients with early AD after 18 months" and states, "The risk/benefit ratio of this class of drugs in early AD remains so far questionable after 18 months."
From a 2023 statement by the European Association of Neurology and the European Psychiatric Association, "Anti-Aβ antibodies represent a significant advance in the treatment of AD, but their effectiveness is moderate and much work remains to be done to improve their efficacy, safety and accessibility."
In a 2023 commentary, the authors express concern that the results of the trials, which are based on scoring by patients and their caregivers, of these drugs could be confounded by unblinding produced by adverse effects. They also support running studies designed to distinguish between disease-modifying and symptomatic effects.
A 2024 study suggests that the cognitive benefits of monoclonal antibody treatments for Alzheimer’s disease may result from increases in Aβ42 levels, rather than solely from the removal of amyloid plaques. This challenges traditional amyloid-focused hypotheses, highlighting the need for further research into the role of Aβ42 and the risk/benefit balance of these treatments.

## Adverse effects
### Amyloid related imaging abnormalities

Amyloid-related imaging abnormalities (ARIA) are a serious adverse effect; with higher rates of ARIA associated with higher amyloid clearance. There are two categories of ARIA, based on signal changes believed to be associated with vasogenic edema (ARIA-E) and microhemorrhages (ARIA-H).

### Accelerated brain volume loss

Brain volume loss is a symptom of Alzheimer's disease and is accelerated by anti-amyloid drugs developed to treat it. One meta-analysis found that people with mild cognitive impairment treated with anti-amyloid drugs would reach the brain volume associated with full Alzheimer's disease eight months earlier than those who received no such treatment. The significance of the brain volume loss caused by these drugs is unknown.
The mechanism is not understood. Amyloid-related imaging abnormalities (ARIA) have been suggested as a possible cause of the accelerated brain volume loss. Others say it may be attributed to the reduction in amyloid plaques.
Accelerated brain volume loss has been reported with lecanemab, aducanumab, donanemab, and other anti-amyloid drugs. Hippocampal, ventricular, and whole brain volumes are reported in studies and declines in all three have been found. However, the affected parts of the brain are not fully understood.

## Society and culture
### Drug development

The approved anti-amyloid antibodies were developed after years of unsuccessful attempts to develop a disease-modifying treatment for Alzheimer's disease.

### Cost

Concerns have been raised about the high cost of the drugs and accessibility to patients.