Long-term, weekly prophylactic treatment with the investigational human monoclonal antibody marstacimab is well tolerated and effective in preventing bleeding episodes in patients with severe hemophilia, with or without inhibitors, according to a multicenter, open-label study recently published in the British Journal of Haematology.

“In the present study, we extended marstacimab prophylaxis for up to 365 days to evaluate its long-term safety, tolerability, and efficacy as prophylactic treatment to prevent or reduce the frequency of bleeding events in adults with severe haemA [hemophilia A] or haemB [hemophilia B] with or without inhibitors,” the study’s authors explained.

Long-term marstacimab treatment maintained the efficacy observed in a 3-month parent study, regardless of the weekly maintenance dose (150 or 300 mg), the presence of inhibitors, and the hemophilia type (ie, A or B). Mean on-study annualized bleeding rates decreased from 14.0 to 22.0 bleeding episodes/participant/year pretreatment to 0 to 3.6 bleeding episodes/participant/year after marstacimab treatment. Among the participants who completed the study, one-half had no bleeding event.

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Seven (70%) participants in each dosing regimen (ie, 300 mg/150 mg or 300 mg) experienced treatment-emergent adverse events, including injection site reactions, injection site hematoma, and hemarthrosis. One participant had 2 serious adverse events, including a grade 3 cerebral hemorrhage and a grade 2 generalized tonic-clonic seizure, which were not considered treatment related. No thrombotic event was reported.

The study included 20 male patients (age range, 19-57 years old) with severe hemophilia. Most were enrolled from a previous phase Ib/II study. Participants were distributed among 6 treatment cohorts and received either once-weekly
300 mg marstacimab or a 300 mg loading dose followed by once-weekly 150 mg doses, for up to 365 days.


Mahlangu J, Luis Lamas J, Cristobal Morales J, et al. Long-term safety and efficacy of the anti-tissue factor pathway inhibitor marstacimab in participants with severe haemophilia: Phase II study results. Br J Haematol. Published online October 11, 2022. doi:10.1111/bjh.18495