An anti-von-Willebrand-factor antibody injection
Caplacizumab
A specialist injected medicine used in hospital for the rare blood emergency acquired thrombotic thrombocytopenic purpura.
What is Caplacizumab?
Caplacizumab is a specialist injected medicine used to treat acquired thrombotic thrombocytopenic purpura (aTTP), a rare and serious emergency in which tiny clots form throughout the small blood vessels and the platelet count drops dangerously. It is given alongside plasma exchange and medicines that calm the immune system, and it helps stop the harmful clotting more quickly. It is started in hospital by a specialist team. The main side effect is bleeding, so any new or unusual bleeding must be reported straight away. It is given by injection.
Education and reference only. This is a plain-language guide to Caplacizumab — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Caplacizumab is a prescription-only medicine used to treat acquired thrombotic thrombocytopenic purpura (aTTP), a rare and life-threatening disorder. In aTTP, a protein called von Willebrand factor makes platelets stick together and form tiny clots throughout the small blood vessels, which can damage organs and cause the platelet count to fall sharply. Caplacizumab is an antibody-based medicine that blocks this process. It is used together with plasma exchange and immune-calming treatment and is started in hospital under specialist supervision, then continued for a period as the person recovers.
How it works
Caplacizumab attaches to von Willebrand factor, the protein that, in aTTP, drives platelets to clump together and form damaging clots in the smallest blood vessels. By blocking this interaction, it stops new tiny clots forming, which helps protect the organs and allows the platelet count to recover more quickly while the underlying immune problem is treated. Because it works on the clotting system, the same action that helps control aTTP can also make bleeding more likely, so it is used carefully and for a defined period alongside the other parts of treatment.
Company & origin
Originated / developed by: Sanofi.
A specialist hospital medicine used in the UK to treat the rare blood-clotting emergency acquired thrombotic thrombocytopenic purpura (aTTP).
Practical use
How to take Caplacizumab
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is started in hospital, with the first part given by the specialist team alongside plasma exchange.
- Later injections may be given under the skin, and you may be taught how to do these at home as advised.
- Report any bleeding that will not stop, blood in your urine or stools, or unusual bruising straight away.
- Tell any healthcare professional you take it before surgery, dental work or invasive tests, as it may need to be paused.
- Do not stop it early without advice, as completing the planned course helps prevent the condition flaring again.
Weighing it up
Advantages & disadvantages of Caplacizumab
Advantages
- Helps control the dangerous clotting of aTTP more quickly when added to standard treatment.
- Allows the platelet count to recover sooner alongside plasma exchange and immune-calming medicines.
- Can often be continued as an at-home injection once the person is stable, after suitable training.
Disadvantages
- Its main side effect is bleeding, which can sometimes be serious.
- It is a specialist hospital-initiated treatment and is only one part of a wider package of care.
- It may need to be paused around surgery or procedures, which has to be planned carefully.
Practical use
Good to know
Caplacizumab is an emergency hospital treatment and is always used as one part of a package that also includes plasma exchange and medicines to calm the immune system; it is not used on its own. The most important thing to know is that its main side effect is bleeding, because it works on the clotting system. Any bleeding that does not stop, blood in the urine or stools, unusual bruising, heavy periods or bleeding from the gums or nose should be reported promptly. It may need to be paused around surgery, dental procedures or invasive tests. The early part of treatment is given in hospital, and people are often taught how to give later injections at home, with clear advice on what to watch for.
Who should not take it / use with caution
- It is used with great caution in people who already have a high risk of bleeding or active bleeding.
- It may need to be stopped temporarily before planned surgery, dental work or invasive procedures.
- It is given only under specialist supervision as part of full aTTP treatment, not on its own.
Monitoring
- Regular blood counts to track recovery of the platelet count.
- Close watching for any signs of bleeding throughout treatment.
- Planning around any surgery or procedures, with the medicine paused if needed.
Side effects
- Bleeding is the main side effect, including nosebleeds, bleeding gums, bruising or heavier periods.
- Headache, tiredness and reactions at the injection site can occur.
- Rarely, more serious bleeding, which must be reported and treated urgently.
Key interactions
- Other blood-thinning or anti-platelet medicines, such as aspirin or anticoagulants, add to the risk of bleeding.
- Any medicine that affects clotting is reviewed carefully by the specialist team before it is combined.
- Tell your team about all medicines, including those bought over the counter, because of the bleeding risk.
Available as: An injection given under the skin, with the first part started in hospital.
Answers
Caplacizumab: frequently asked questions
What is caplacizumab used for?
It is used to treat acquired thrombotic thrombocytopenic purpura (aTTP), a rare blood-clotting emergency, alongside plasma exchange and immune-calming medicines.
What is the main side effect?
Bleeding is the main side effect because it works on the clotting system; report any bleeding that will not stop or unusual bruising straight away.
Is it used on its own?
No, it is always one part of a wider treatment that includes plasma exchange and medicines to calm the immune system.
Can I give the injection at home?
Once you are stable, you may be taught to give later injections at home, with clear advice on what to watch for.
What if I need an operation?
Tell your team, as it may need to be paused before surgery, dental work or invasive procedures to reduce bleeding risk.
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.