First Experience with Marstacimab Monitoring

Introduction The inhibition of tissue factor pathway inhibitor (TFPI) is a new approach to normalize coagulation in patients with hemophilia A and B. TFPI inhibitors indirectly improve the generation of factor Xa, and subsequently factor IIa, which leads to sufficient hemostasis. Hence, thrombin generation (TG) is the perfect candidate for therapy monitoring. Here, we want to present our first data in three patients receiving TFPI inhibitor marstacimab (Pfizer). Method Three patients were included (age 54-64), two with severe hemophilia B and one with moderate hemophilia B (residual activity 3%). All patients were treated according to the manufacturer’s guideline. Thrombin generation was assessed immediately before the first application (baseline) of marstacimab and regularly after therapy started. Thrombin generation was assessed with ST Bleedscreen and ST Thromboscreen (ST Genesia, Stago) and Technoclone TGA (RC high) on the Ceveron analyzer. Results Thrombin generation improves significantly under therapy with marstacimab, in all assays by a factor of 4 to 5 compared to the baseline value. The results are similar between all methods. The patient with the lowest baseline TG achieved about 80% of normal TG (thrombin peak), the other patients between 130% and 140%. So far, no clinical event, bleeding or thrombosis, has been reported by the patients. Conclusion Thrombin generation is a suitable tool for the monitoring of TFPI inhibitor marstacimab. To which extent the data reflect clinical outcome is not clear at this moment; more and longer monitoring is required to answer that question. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany