Lecanemab (Leqembi) for early-stage Alzheimer's disease

In Alzheimer's disease, more and more nerve cells in the brain die as time goes by. Deposits of small protein particles (known as amyloid plaques) are also found in the brains of those affected. Some experts suspect that these protein deposits damage the nerve cells.

Lecanemab is an antibody that targets these protein deposits in the brain: It binds to the beta-amyloid protein and is thought to prevent the build-up of further deposits in this way. With the help of the immune system, it is also thought to partially break down protein that has already been deposited.

These effects of the medication are believed to slow down the progression of the disease. One thing is clear, though: Lecanemab cannot cure Alzheimer's or stop the progression.

Lecanemab is only suitable for people who have early-stage Alzheimer's disease. It is not approved for people whose disease has already progressed further.

The main signs of early-stage Alzheimer's disease are problems with memory and thinking. The forgetfulness can be mild and have hardly any (or no) effect on everyday life. The medical term for this is mild cognitive impairment (MCI). But it may already be worse, making it harder to live an independent life. Then it is considered to be mild Alzheimer's dementia.

Before starting treatment with lecanemab, people must have an MRI scan ( magnetic resonance imaging) in order to rule out other problems such as swelling or bleeding in the brain. If you would like to have treatment with lecanemab, you can only do so if you agree to other conditions, too:

• You must allow your data to be collected in a European registry. The treatment outcomes of all people in Europe who use this medication are collected here. That way, scientists can find out how often side effects occur, for example.
• You must agree to have regular MRI scans to see if there are any signs of problems like swelling in the brain.

Because of the possible serious side effects and special aspects of treatment with lecanemab, your doctor must give you particularly thorough information about it. The manufacturer has produced detailed written information for this purpose. This includes a special card ("Patientenkarte" in German) with the most important information on lecanemab and the associated risks. It is given to all people who are planning to have treatment with this medication, before the treatment starts. You should always carry the card with you and show it every time you go to a doctor's practice or pharmacy. The doctor will also give you the package insert for lecanemab.

Doctors diagnose Alzheimer's disease if the person clearly has the typical symptoms (impaired memory and thinking problems) and other causes are unlikely.

In addition, the person must be shown to have the typical protein deposits in their brain. This is done using biomarkers. It often involves taking a sample of cerebrospinal fluid through a lumbar puncture (spinal tap). But it can also be done using amyloid positron emission tomography (amyloid PET imaging). Amyloid PET is an imaging technique that uses a weak radioactive substance to see beta-amyloid protein deposits in the brain.

Lecanemab can only be used in people with early-stage Alzheimer's disease who have a maximum of one copy of a specific version of a gene, known as ApoE4. This is because people who have two copies of ApoE4 (rather than only one copy, or no copies) are more likely to have serious side effects when using lecanemab. These include potentially life-threatening swelling and bleeding in the brain.

We all have two copies of the ApoE gene. It plays a role in fat metabolism. But there are three different versions (variants) of the gene, known as E2, E3 and E4. Each of the parents passes on one variant to their child. Depending on which variant they pass on, their child might have one, two or no copies of the E4 variant.

Doctors can use a genetic test to find out whether the person has any copies of the ApoE4 gene variant – and if so, how many. This is done by taking a sample of blood and examining it in a laboratory. The genetic test is not yet a routine test.

Research has shown that people are more likely to get Alzheimer's disease (at a younger age, too) if they have two ApoE4 genes rather than just one ApoE4 gene and one ApoE3 gene, for example. If someone is found to have the ApoE4 gene, it could be a good idea to find out whether, for example, their children and siblings also carry the gene. These relatives could also have a higher risk of developing Alzheimer's disease later in life. So knowing that you have the gene can have consequences for other members of your family, too. Because of this, the doctor has to tell you all about this before you have the genetic test.

Lecanemab is given as an infusion (a drip) every two weeks. The infusion takes about one hour. After the first infusion, you will be monitored for about two-and-a-half hours to see if you have any negative reactions to it.

The dosage depends on the person's body weight: 10 milligrams (mg) of lecanemab are used per kilogram of body weight. For the infusion, the drug is diluted in saline solution.

The person must have MRI scans during treatment with lecanemab: before the 5^th, 7^th and 14^th dose. These scans are done to look for signs of swelling or bleeding in the brain. More MRI scans are done if there are symptoms such as headaches, confusion, nausea, vision problems, dizziness or difficulty walking.

Treatment with lecanemab is stopped if the disease progresses to middle-stage (moderate) Alzheimer's dementia. To be able to assess this, the person's memory and thinking skills are tested about every six months, along with other signs of Alzheimer's.

Doctors will also consider stopping the treatment if there is an increased risk of bleeding in the brain during the treatment. This may be the case if, for example, the person needs an anticoagulant or a thrombolytic (a drug designed to dissolve blood clots) to treat something like a stroke or pulmonary embolism.

In Germany, the pros and cons of lecanemab (compared to other treatments that are already being used for Alzheimer's) are currently being examined more closely. This is because new drugs undergo something known as an early benefit assessment after they are approved and enter the German market.

The Joint Federal Committee (G-BA) has commissioned the Institute for Quality and Efficiency in Healthcare (IQWiG) to do this: IQWiG is currently assessing the pros and cons of lecanemab for patients, compared to the current standard treatments. For this purpose, manufacturers must provide all the data they have on the new drug – including previously unpublished research findings.

The results of IQWiG's assessment are expected to be published on December 1, 2025. We will then update this article. Knowing about the pros and cons can help people to make an informed decision about whether or not to have treatment with lecanemab.