Caplacizumab

How it works

It binds the A1 domain of von Willebrand factor, blocking its interaction with platelet glycoprotein Ib and thereby preventing the ultra-large von Willebrand factor–platelet microthrombi that drive organ ischaemia in TTP.

Prescribing in practice

• Bleeding is the predominant adverse effect because it directly impairs platelet adhesion; it should be interrupted around invasive procedures and used cautiously with other antithrombotic agents.
• It is given in addition to — not instead of — plasma exchange and immunosuppression, and is typically continued for a period after plasma exchange ends to prevent relapse.
• Von Willebrand factor activity is suppressed during treatment, so it should be withheld and von Willebrand factor concentrate considered if major bleeding occurs.

Monitoring

Monitor platelet count for treatment response and watch closely for mucocutaneous and other bleeding throughout therapy.

Counselling the patient

• It is given by injection as part of a combined treatment for TTP.
• Report any bleeding, including nosebleeds, gum bleeding or heavy bruising, without delay.
• Tell the team before any dental or surgical procedure so it can be paused.

Evidence & guidelines

Caplacizumab is recommended by NICE for acquired thrombotic thrombocytopenic purpura, with efficacy demonstrated in the HERCULES trial.