New treatment for severe haemophilia B approved

Written by Jessica Bomford, May 21, 2025

Marstacimab, a new treatment for severe haemophilia B which can be injected under the skin, has been approved for use in England.

The new product will be available to anyone aged 12 or over (weighing at least 35kg) with severe haemophilia B. It is not currently available to people with inhibitors.

NICE, the body that considers clinical and cost effectiveness of new treatments, published final draft guidelines on 21 May which recommend Pfizer’s marstacimab for use in the NHS in England. Once final guidelines are published, it could start to be prescribed in early autumn. Availability of this product through the NHS in Wales, Scotland and Northern Ireland should follow. 

‘A positive development’

Conan McIlwrath, Chair of the Haemophilia Society, said: ‘A subcutaneous treatment option for severe haemophilia B is a positive development which will open up some much-needed choice for people living with the condition. This will hopefully help people move towards more individualised treatment plans, based on what best supports the life they choose to live.’ 

Steve Wilkinson, 55, who has severe haemophilia B, gave his perspective as a patient expert as part of NICE’s decision-making on marstacimab. He said: ‘For the next generation, this sub cutaneous treatment feels like a big step forward. I hope there will be a license soon for people with inhibitors and for younger children. It is vital that people with severe haemophilia B who currently have limited treatment options are able to access new treatments such as this.’

Once a week injections

Marstacimab is an antibody which works by targeting tissue factor pathway inhibitor (TFPI), a protein that prevents blood clotting. Lowering TFPI increases the amount of thrombin your body produces which improves blood clotting.  It can be injected under the skin using a pre-filled syringe or pen. On average, injections would be needed once a week.

Around 255 people live with severe haemophilia B in England, of whom an estimated 205 will be eligible for treatment with marstacimab.  

Although marstacimab can be used for haemophilia A as well as haemophilia B it has only been approved for treatment for haemophilia B. A subcutaneous non-factor product, Emicizumab, is already available for adults and children with haemophilia A.

Helen Knight, director of medicines evaluation at NICE, said: ‘Marstacimab’s clinical and cost-effectiveness compared with current treatment, together with its once-weekly dosing by injection under the skin means it has the potential to significantly improve the quality of life of people with severe haemophilia B.’

Additional trials are taking place

There are trials currently underway with the hope that marstacimab’s license will be extended to people with inhibitors and children aged under 12 in the future. 

If you are interested in this treatment, please talk to your haemophilia centre to discuss your options once it becomes available later this year.