Anti-Amyloid Immunotherapy (IgG1 Monoclonal Antibody) Pregnancy: There are no adequate data on use in pregnant women to evaluate for a drug-associated risk of major birth defects, miscarriage or other adverse maternal or fetal outcomes; no animal studies have been conducted to assess reproductive or developmental toxicity (US label section 8.1).

Lecanemab (Anti-Amyloid Monoclonal Antibody)

Brand names: Leqembi

Lecanemab is an anti-amyloid monoclonal antibody used in early symptomatic Alzheimer's disease to slow clinical progression by clearing cerebral amyloid.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 10 mg/kg (starting dosage)

Route: Intravenous infusion over approximately one hour, after dilution in 250 mL of 0.9% sodium chloride injection

Frequency: Once every 2 weeks

After 18 months the starting dosage may be continued, or a transition to a maintenance regimen may be considered: intravenous 10 mg/kg once every 4 weeks over approximately one hour, OR subcutaneous 360 mg once every week using the LEQEMBI IQLIK autoinjector. If transitioning from starting to maintenance dosage, give the first maintenance dose two weeks after the last starting dose; when switching between maintenance routes, initiate 1 week after the last maintenance dose. Confirm the presence of amyloid beta pathology before initiating treatment. Obtain a recent baseline brain MRI before initiating, and an MRI within approximately one week before the 3rd, 5th, 7th and 14th infusions. Dosing interruption is required for amyloid related imaging abnormalities (ARIA-E and ARIA-H) according to the label's severity tables; suspend dosing for intracerebral haemorrhage greater than 1 cm in diameter until MRI demonstrates radiographic stabilisation and symptoms resolve. No eMC/UK SPC posology was available in this source bundle - dose taken from US prescribing information and must be verified against UK labelling. No drug interactions section was present in the source bundle.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Serious hypersensitivity to lecanemab-irmb or to any of the excipients of LEQEMBI or LEQEMBI IQLIK; reactions have included angioedema and anaphylaxis

Side effects

Infusion-related reactions
Amyloid related imaging abnormality - microhaemorrhages (ARIA-H)
Amyloid related imaging abnormality - oedema/effusion (ARIA-E)
Headache
Hypersensitivity reactions (including angioedema and anaphylaxis)

Clinical monograph

How it works

It is a monoclonal antibody that preferentially binds soluble amyloid-beta protofibrils and promotes clearance of amyloid, reducing plaque burden.

Prescribing in practice

Amyloid-related imaging abnormalities (ARIA) with cerebral oedema and microhaemorrhage are the principal safety concern, requiring baseline and follow-up MRI, with heightened risk in ApoE e4 carriers.
Confirmation of amyloid pathology and assessment for haemorrhage risk are required before starting, with treatment given by infusion under specialist supervision.
Concomitant anticoagulation increases the risk of serious intracerebral haemorrhage and must be carefully weighed.

Monitoring

Scheduled MRI surveillance for ARIA, together with monitoring for infusion-related reactions and clinical response, is required throughout treatment.

Counselling the patient

You will need regular brain scans to look for swelling or small bleeds.
Report new headache, confusion, weakness or visual disturbance without delay.
The treatment is intended to slow decline, not cure the disease.

Evidence & guidelines

Phase 3 trial data demonstrate that lecanemab reduces amyloid and modestly slows cognitive and functional decline in early Alzheimer's disease.

Reference: van Dyck et al. NEJM 2023 (CLARITY AD trial); FDA Prescribing Information Leqembi 2023; Alzheimer's Association Guidelines 2023; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways