Lecanemab (Leqembi) can cause various side effects while treating early Alzheimer's disease.

I. What are the common side effects?

1. Infusion-related reactions

(1) Occur in approximately 26% of patients receiving intravenous infusion, with 75% occurring during the first infusion.

(2) Most are mild or moderate, presenting as fever, flu-like symptoms (chills, body aches, tremors, joint pain), nausea, vomiting, blood pressure fluctuations, and decreased oxygen saturation.

(3) About 1% of patients discontinue treatment due to this.

2. Amyloid-related imaging abnormalities (ARIA)

(1) Includes ARIA-E (brain edema/effusion) and ARIA-H (hemosiderin deposition, manifesting as microhemorrhages and superficial siderosis).

(2) Most ARIA are asymptomatic or resolve spontaneously, but can be fatal.

3. Headache

Incidence approximately 11%, usually mild to moderate, often occurring early after infusion.

4. Superficial siderosis of the central nervous system

Incidence approximately 6%, a manifestation of ARIA-H, indicating hemosiderin deposition on the brain surface.

5. Rash

Incidence approximately 6%, may present as erythema, injection site rash, urticaria, etc.

6. Injection site reactions (subcutaneous injection)

(1) When using an auto-injector, local reactions include erythema, induration, swelling, warmth, pain, pruritus, bruising, and hematoma.

(2) Systemic injection reactions (headache, fever, fatigue) are rare and mild to moderate.

7. Other relatively common reactions

(1) Nausea/vomiting incidence approximately 6%, atrial fibrillation approximately 3%.

(2) Approximately 38% experience transient lymphopenia and 22% experience transient neutrophilia after the first infusion.

II. Ways to alleviate side effects

1. Management of infusion-related reactions

(1) If a reaction occurs during infusion, healthcare providers may slow or pause the infusion and provide symptomatic treatment.

(2) Prophylactic medications may be considered before subsequent infusions: antihistamines (e.g., diphenhydramine), acetaminophen, NSAIDs, or corticosteroids.

(3) Severe reactions require immediate discontinuation of infusion and emergency management.

2. Monitoring and management of ARIA

(1) Baseline brain MRI is mandatory before treatment, with repeat MRI within one week prior to the 3rd, 5th, 7th, and 14th infusions.

(2) Decision to temporarily discontinue dosing based on ARIA type, imaging severity, and clinical symptoms: Asymptomatic mild-to-moderate ARIA-E may continue dosing; moderate-to-severe or symptomatic ARIA-E requires temporary discontinuation, with reassessment for resumption after MRI shows resolution (typically repeat MRI in 2-4 months).

3. Management of headache

(1) Acetaminophen (paracetamol) can be taken for relief.

(2) Avoid aspirin or other NSAIDs (unless prescribed by a doctor) as they may increase bleeding risk.

4. Rash and injection site reactions

(1) Local reactions may be managed with cold compresses and application of non-irritating moisturizing cream.

(2) For severe or persistent rash, antihistamines or topical corticosteroid creams may be used after consulting a doctor.

(3) Avoid scratching.

5. General supportive measures

(1) Ensure adequate rest and proper hydration on the day of infusion.

(2) If fever or flu-like symptoms occur, rest, hydrate, and take acetaminophen.

(3) Seek medical attention if symptoms are severe or persistently unresolved.

6. Bleeding risk precautions

(1) Because anticoagulants can significantly increase the risk of cerebral hemorrhage, close monitoring is required if used concomitantly.

(2) Seek immediate emergency care if any signs of intracranial bleeding occur (sudden severe headache, nausea/vomiting, altered mental status, limb weakness).

III. Storage conditions

1. Intravenous infusion vial

(1) Unopened vials must be refrigerated at 2°C to 8°C, stored in the original carton to protect from light.

(2) Do not freeze or shake.

(3) Diluted infusion solution may be stored refrigerated (2-8°C) or at room temperature (up to 30°C) for a maximum of 4 hours. Do not freeze.

2. Subcutaneous auto-injector

(1) Unopened auto-injectors must be refrigerated at 2°C to 8°C, stored in the original carton to protect from light.

(2) Do not freeze.

3. General precautions

(1) Do not shake any dosage form.

(2) Single-dose container for single use only; discard any unused portion.