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Anti-Amyloid Immunotherapy (IgG1 Monoclonal Antibody) Pregnancy: Not applicable — AD indication in elderly. Avoid in women of childbearing potential — no human data.

Lecanemab (Anti-Amyloid Monoclonal Antibody)

Brand names: Leqembi

Adult dose

Dose: 10 mg/kg IV every 2 weeks
Route: IV infusion over 1 hour
Frequency: Every 2 weeks (ongoing)
Max: 10 mg/kg per infusion
Targets soluble amyloid-beta protofibrils. FDA approved January 2023 (traditional approval July 2023). Under MHRA review (2024). Indicated for early AD with confirmed amyloid pathology (PET or CSF). Requires APOE4 genotyping before use — higher ARIA risk in APOE4 homozygotes. Serial MRI monitoring mandatory.

Paediatric dose

Route:
Not applicable — Alzheimer's disease indication in adults only.

Dose adjustments

Renal

No dose adjustment required in mild-moderate renal impairment. Limited data in severe renal impairment.

Hepatic

No dose adjustment required.

Clinical pearls

  • CLARITY AD trial (van Dyck et al. NEJM 2023): lecanemab 10 mg/kg vs placebo over 18 months — 27% slowing in CDR-SB score decline; statistically significant. First phase 3 RCT to show meaningful disease modification in early AD. NNT to prevent one unit of CDR-SB decline over 18 months = approximately 10
  • ARIA monitoring protocol: MRI before starting, at weeks 26 and 52, then as clinically indicated. Symptomatic ARIA requires dose suspension; asymptomatic ARIA: reduce infusion frequency or suspend pending radiological resolution
  • Patient selection is critical: only early AD (MCI or mild dementia, CDR 0.5–1) with confirmed amyloid positivity by PET or CSF biomarkers. Patients with moderate-severe AD were EXCLUDED from trial — no evidence of benefit in this group
  • APOE4 status: APOE4/4 homozygotes have approximately 45% ARIA-E rate — FDA label includes genetic counselling recommendation before prescribing; APOE4/4 patients should be counselled extensively about risks vs modest benefits

Contraindications

  • APOE4 homozygotes (very high ARIA risk — approximately 45% ARIA incidence; requires careful benefit-risk discussion)
  • Active intracranial haemorrhage
  • Anticoagulation therapy (significantly increases ARIA-H risk)
  • MRI contraindications (monitoring requirement)

Side effects

  • ARIA-E (amyloid-related imaging abnormalities — oedema): 12.6% in CLARITY AD trial; mostly asymptomatic
  • ARIA-H (microhaemorrhages and superficial siderosis): 17.3% in CLARITY AD
  • Infusion-related reactions: 26% (first infusion; pre-medication recommended)
  • Headache
  • Fall and contusion risk (ARIA-related)
  • Serious ARIA requiring hospitalisation: ~3%

Interactions

  • Anticoagulants (warfarin, DOACs — increased ARIA-H risk; avoid or extreme caution)
  • Antiplatelets (aspirin, clopidogrel — increased ARIA-H risk)

Monitoring

  • MRI brain (baseline, week 26, week 52, then as indicated — ARIA surveillance)
  • APOE4 genotyping before initiation
  • Infusion site and vital signs during administration
  • Neurological status (new headache, visual changes, confusion = possible ARIA)
  • Cognitive assessments (CDR-SB, MMSE) — benefit monitoring

Reference: BNFc; BNF 90 (pending MHRA approval); van Dyck et al. NEJM 2023 (CLARITY AD trial); FDA Prescribing Information Leqembi 2023; Alzheimer's Association Guidelines 2023. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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