Complement inhibitors
Antibodies and peptides that block a step of the complement cascade, used in PNH, atypical HUS and some autoimmune nerve and muscle diseases.
What they are
Complement is part of innate immunity: a chain of plasma proteins that ends in a pore (the membrane attack complex) able to burst cells. In paroxysmal nocturnal haemoglobinuria red cells lack their protective shield and are destroyed; in atypical haemolytic uraemic syndrome complement damages small vessels. C5 inhibitors (eculizumab, ravulizumab) stop the final step; pegcetacoplan acts earlier, on C3.
Mechanism of action
C5 inhibitors bind C5 and stop its cleavage into C5a and C5b, so the lytic pore never forms. A C3 inhibitor binds C3 higher up the cascade and also blocks the coating of cells with C3 fragments. Because complement is key to killing Neisseria, every member raises the risk of meningococcal infection.
Target: Complement proteins C5 or C3
Drugs in this class
- EculizumabA humanised antibody against complement C5 that stops red-cell destruction in PNH and vessel damage in atypical HUS…Complement component C5 (plasma protein)
- RavulizumabA longer-acting antibody against complement C5, related to eculizumab, for PNH, atypical HUS, myasthenia gravis and…Complement component C5 (plasma protein)
- PegcetacoplanA complement C3 inhibitor injected under the skin for PNH and some C3-driven kidney diseases; it raises the risk of…Complement component C3 (plasma protein)
Others in the class
- sutimlimab
- avacopan
- zilucoplan
- crovalimab
- iptacopan
- danicopan
- pozelimab
Test yourself
Think of the answer, then tap the question to see it.
Which infection is the main danger of complement inhibitors?
Meningococcal (Neisseria meningitidis) infection.
Which complement protein do eculizumab and ravulizumab bind?
C5, which stops formation of the membrane attack complex.
Why is lab monitoring continued after a C5 inhibitor is stopped in PNH?
Red cells can break down again (haemolysis) once the blockade wears off.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Eculizumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025).
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Representative model, for educational purposes only.