Eculizumab

Mechanism of action

◆Complement component C5 (plasma protein)Eculizumab

ⓘ The figure shows human complement C5 with the binding fragment (variable domains) of eculizumab itself; as an antibody it has no small-molecule ligand.

Eculizumab binds complement C5 and prevents its cleavage into C5a and C5b. Without C5b, the terminal membrane attack complex cannot form, so intravascular haemolysis in PNH and complement-driven thrombotic microangiopathy in atypical HUS stop. The same blockade removes a key defence against Neisseria meningitidis.

1. Eculizumab binds complement C5 in the plasma
2. C5 can no longer be split into C5a and C5b
3. The membrane attack complex does not form
4. Red cells and vessel walls are spared complement attack

Indications

• Paroxysmal nocturnal haemoglobinuria (PNH) Paroxysmal nocturnal haemoglobinuria →
• Atypical haemolytic uraemic syndrome (aHUS) Hemolytic uremic syndrome (HUS) →
• Generalised myasthenia gravis with acetylcholine-receptor antibodies Myasthenia gravis →
• Neuromyelitis optica spectrum disorder with aquaporin-4 antibodies Neuromyelitis optica spectrum disorder →

Adverse effects

Common

• Headache
• Runny nose, sore throat, cough
• Nausea, vomiting, diarrhoea
• Joint, muscle or limb pain
• Tiredness, dizziness, trouble sleeping

Contraindications

• Active (unresolved) meningococcal infection
• Not vaccinated against meningococcus, unless antibiotic cover is given until the vaccine has had time to work
• Hypersensitivity to eculizumab

Key interactions

Meningococcal vaccines

Given at least 2 weeks before the first dose (boosters as advised); they reduce but do not remove the infection risk

Pneumococcal and Haemophilus influenzae type b vaccines (children)

Children are vaccinated against these before treatment, because complement also helps clear them

What is monitored

• Vaccination record checked before every course
• Blood tests for haemolysis (PNH) or platelets, LDH and kidney function (aHUS) during treatment
• After stopping: about 8 weeks of lab follow-up in PNH and about 12 weeks in aHUS

Administration and safety

• Intravenous infusion by a health professional, over at least 35 minutes; observed for 1 hour afterwards
• Only through prescribers enrolled in a risk-management (REMS) programme
• The infusion is slowed or stopped if a reaction occurs
• Biosimilar names (suffixes -aeeb, -aagh) refer to the same molecule: check the product before each infusion

Pregnancy and breastfeeding

Pregnancy or plans for pregnancy are reported to the treating team, who weigh the risks; a pregnancy during treatment is reported at once.

Nursing care

• Confirm meningococcal vaccination (or antibiotic cover) before the first dose
• Check temperature and ask about infection signs before each infusion
• Teach the patient to carry the safety card during treatment and for 3 months after, and to seek care at once for fever or headache
• Stress that missed doses are reported right away

Pharmacokinetics

Absorption

Intravenous infusion only

Distribution

Stays mainly in the blood, like other IgG antibodies

Elimination

Broken down like other proteins; the effect lasts between infusions

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Connections

← Back to the class: Complement inhibitors

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Eculizumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.