Pronunciation: leh-kem’-bee
Generic name: lecanemab
Dosage form: injection for infusion
Drug class: Miscellaneous central nervous system agents

Medically reviewed by Melisa Puckey, BPharm. Last updated on Jan 28, 2025.

What is Leqembi?

Leqembi (lecanemab) is used for Alzheimer’s disease to help slow the decline in memory, thinking, and behavior in patients who have mild cognitive impairment (MCI) or mild dementia. Leqembi infusion works by reducing amyloid beta plaques in the brain, which helps slow down the worsening of dementia symptoms.

In a clinical trial (Clarity AD), Leqembi patients experienced a 27% slower rate of cognitive decline over 18 months compared to those who received a placebo.  Leqembi helps control Alzheimer’s disease but does not cure it. 

Leqembi infusion is given every 2 weeks and takes approximately 1 hour, after 18 months of treatment, this may be extended to every 4 weeks.

How does Leqembi work?

Alzheimer’s disease is a type of dementia that affects memory, thinking, and behavior, which can eventually grow severe enough to interfere with daily tasks. One of the causes of Alzheimer’s disease is thought to be abnormal buildup in the brain of a protein (amyloid) into clumps or plaques which makes it harder for brain cells to communicate with each other and results in the symptoms of Alzheimer’s disease. 

Leqembi infusion works by selectively targeting amyloid beta proteins before they form plaques and also helps to remove plaques that have already formed. By helping to reduce amyloid beta plaque buildup, Leqembi infusion helps to slow the decline of Alzheimer’s Disease.

Leqembi mechanism of action is as an amyloid beta-directed antibody against aggregated soluble and insoluble forms of amyloid beta.

Who can use Leqembi?

Leqembi approval is to treat Alzheimer's disease in patients who have:

• mild cognitive impairment or mild dementia due to Alzheimer's disease, and
• presence of amyloid beta pathology.

Leqembi FDA approval was granted on January 6, 2023, to Eisai Inc.

Leqembi side effects

Common Leqembi side effects 

The most common side effects of Leqembi infusion are:

• infusion-related reactions, which can be serious
• headache
• swelling in areas of the brain, with or without small bleeding spots in or on the brain's surface (ARIA).

Infusion-related reactions. Infusion-related reactions occurred in 26% of Leqembi patients compared to 7% of placebo patients. Symptoms of infusion reactions are:

• fever
• flu-like symptoms (chills, generalized aches, feeling shaky, and joint pain),
• nausea and vomiting,
• low blood pressure (hypotension),
• high blood pressure (hypertension),
• and oxygen desaturation. 

Managing infusion-related reactions. If you have an infusion-related reaction the infusion rate may be reduced, or the infusion may be stopped, and appropriate therapy may be started as clinically indicated. Before future infusions, preventative (prophylactic) treatment with antihistamines, acetaminophen, nonsteroidal anti-inflammatory drugs, or corticosteroids may be considered.

The most common side effects occurred in 10% or more of patients and were higher than the side effect incidence compared to placebo.

Serious Leqembi side effects and warnings

Leqembi carries a Boxed Warning for Amyloid-related imaging abnormalities.

Amyloid Related Imaging Abnormalities or “ARIA”. This medicine can cause a condition called ARIA which does not usually cause any symptoms but serious symptoms can occur. ARIA is most commonly seen as temporary swelling in areas of the brain that usually resolves over time. Some people may also have small spots of bleeding in or on the surface of the brain, and infrequently, larger areas of bleeding in the brain can occur. Most people with this type of swelling in the brain do not get symptoms, however, some people may have symptoms, such as headache, confusion, dizziness, vision changes, nausea, difficulty walking, or seizures.

Some people have a genetic risk factor (homozygous apolipoprotein E gene carriers) that may cause an increased risk for ARIA. Talk to your healthcare provider about testing to see if you have this risk factor.

Some medicines can increase the risk for larger areas of bleeding in the brain in patients taking this medicine. Talk to your healthcare provider to see if you are on any medicines that increase this risk.

Your healthcare provider will do magnetic resonance imaging (MRI) scans before and during your treatment with this medicine to check you for ARIA. Call your healthcare provider or go to the nearest hospital emergency room right away if you have any of the symptoms listed above.

Serious allergic reactions. Swelling of the face, lips, mouth, or tongue, hives, or difficulty breathing has happened during a Leqembi infusion. Tell your healthcare provider if you have any symptoms of a serious allergic reaction during or after your infusion.

Infusion-related reactions. Infusion-related reactions are a common side effect that can be serious. 

These are not all the possible side effects of Leqembi. For more information, ask your healthcare provider or pharmacist, or see the below for more detailed information on side effects. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

Leqembi cost

Leqembi's cost will depend on your insurance coverage and Leqembi Copay eligibility. For links to enrollment forms for the Copay Cards and Patient Assistance Program (PAP) see the Leqembi Prices, Coupons, Copay Cards, and Patient Assistance page.

Before receiving this medicine

Do not receive this medicine if you are allergic to the active ingredient lecanemab or any of the inactive ingredients in this medicine. See below for a list of inactive ingredients. 

Tell your healthcare provider about all of your medical conditions, including if you:

• are pregnant or intending to become pregnant
• are breastfeeding or intending to breastfeed. 

Pregnancy

It is not known if this medicine will harm your unborn baby. Tell your healthcare provider if you become pregnant during Leqembi treatment.

Breastfeeding

It is not known if Leqembi passes into breast milk. Talk to your healthcare provider about the best way to feed your baby while receiving this medicine.

How will I receive this medicine?

Leqembi is administered by a healthcare provider through an intravenous (IV) infusion, which involves inserting a needle into a vein in your arm.

• Leqembi is given every 2 weeks for the first 18 months, and then this may be extended to every 4 weeks.
• Each infusion will last about 1 hour.

You may receive medications before your infusion, such as antihistamines, anti-inflammatories, or steroids, to reduce your risk of having an infusion-related reaction. Tell your healthcare provider right away if you get symptoms of an infusion-related reaction. See infusion-related reaction symptoms in the side effects section.

Leqembi dose information

Usual Leqembi Dose for Alzheimer’s Disease (Adult):

• The recommended Leqembi dosage is 10 mg/kg.
• The injection is diluted and then administered as an intravenous infusion over approximately one hour, once every two weeks for the first 18 months, and then this may be extended to every 4 weeks.

Leqembi is available as:

•  500 mg/5 mL (100 mg/mL) in a single-dose vial.
•  200 mg/2 mL (100 mg/mL) in a single-dose vial.

Leqembi Package Insert 

Review the Leqembi Package Insert (PI) for more detailed information about this medicine. The PI contains more comprehensive information on Indications and Usage, Dosage and Administration, Clinical Pharmacology, Clinical Studies, Drug Interaction, and more. Discuss any medical questions you have with your doctor or other health care provider. This is not all the information you need to know about this medicine for safe and effective use, and it does not take the place of talking to your doctor about your treatment.

The Package Insert is sometimes called the Prescribing Information (PI) or the FDA label.

What other drugs will affect this medicine?

Tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.

Especially tell your healthcare provider if you take medicines to reduce blood clots from forming (antithrombotic medicines, including aspirin). Ask your healthcare provider for a list of these medicines if you are not sure.

Know the medicines you take. Keep a list of them to show your healthcare provider and pharmacist when you get a new medicine.  

Ingredients

Active ingredient: lecanemab-irmb.
Inactive ingredients: arginine hydrochloride, histidine, histidine hydrochloride monohydrate, polysorbate 80, and water for injection.

Storage

Unopened Vial Storage:

• Store in a refrigerator at 2°C to 8°C (36°F to 46°F).
• Store in the original carton to protect from light.  
• Do not freeze or shake.

After vial dilution

• Immediate use is recommended 
• If not administered immediately, store refrigerated at 2°C to 8°C (36°F to 46°F) for up to 4 hours, or at room temperature up to 30°C (86°F) for up to 4 hours.
• Do not freeze.

Leqembi Manufacturer

Leqembi manufacturer Eisai Inc. Nutley, NJ 07110.

Leqembi Biosimilars

Biosimilar and interchangeable products are biological products that are highly similar to and have no clinically meaningful differences from the reference product.

Reference products

These are biological products that have already been approved by the FDA, against which biosimilar products are compared. There is 1 for Leqembi.

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Further information

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