This clinical trial is focused on studying the effectiveness and safety of a treatment called Marstacimab for children and teenagers with a condition known as Hemophilia. Hemophilia is a rare bleeding disorder where the blood doesn’t clot properly, leading to excessive bleeding. The study includes participants with two types of hemophilia: Hemophilia A, which involves a deficiency in a protein called factor VIII, and Hemophilia B, which involves a deficiency in factor IX. The trial is open to participants under 18 years of age, with severe forms of these conditions, whether or not they have developed inhibitors, which are antibodies that can interfere with treatment.

The purpose of the study is to compare the new treatment, Marstacimab, with the standard treatment that participants have been receiving over the past year. Marstacimab is administered as a solution for injection using a pre-filled pen, which is a device that allows the medication to be injected under the skin. The study will last for about 48 weeks, during which participants will receive regular doses of Marstacimab. The trial aims to see if Marstacimab can reduce the number of bleeding episodes and improve the overall health of the joints, which are often affected by bleeding in people with hemophilia.

Throughout the study, the safety of Marstacimab will be closely monitored, including any side effects or reactions at the injection site. The trial will also assess the impact of the treatment on the participants’ quality of life, using questionnaires designed for different age groups. This research is important for understanding how well Marstacimab works in young people with hemophilia and whether it can become a new option for managing this condition.