Treatment with marstacimab for people with severe hemophilia A or B: a plain language summary

This is a summary of the results from two clinical studies of treatment for men with severe hemophilia A or B. The studies were published in the British Journal of Haematology. People with hemophilia either have low amounts of clotting factors or are missing certain clotting factors in their blood. The severity of hemophilia is found out by a blood test. There are medicines that people with hemophilia can take to replace the missing clotting factor. However, sometimes the body thinks the clotting factor used to treat hemophilia is a foreign substance and produces antibodies to destroy it (called inhibitors) which may slow down or stop blood clotting. The studies showed that men with hemophilia had fewer bleed events while taking marstacimab than before this treatment. The results were similar for all doses of marstacimab tested. Overall, the side effects with marstacimab were generally acceptable. Two men had to stop taking marstacimab because of side effects in the short-term study. The most common side effects were high blood pressure and injection site reactions. Most of these reactions were mild or moderate. These studies showed that marstacimab could help prevent bleeding in men with hemophilia A or B, with or without inhibitors. The results of this study may differ from those of other studies. Physicians should make treatment decisions based on all available evidence and not just on the results of a single study. Larger studies of marstacimab involving more people with hemophilia A or B have started.