A new clinical trial will assess the safety and efficacy of the investigational therapy marstacimab in treating pediatric hemophilia. The estimated study start date is November 15, 2022.

Participants will receive prophylactic marstacimab as a subcutaneous shot once a week for a 12-month period. The first dose will be administered at the study site, while the remaining can be given at home.

The study will also include a 1-month period for screening and a 1-month follow-up period. During the 14 months of study, participants will be invited to visit the study site at least 10 times. Alternatively, 2 visits can be completed at the participant’s home if all necessary conditions are verified. In addition, participants will be contacted by telephone approximately every 2 months.

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Primary outcome measures include the annualized bleeding rate of treated bleeding events from baseline to the end of 12-month treatment period, the incidence of adverse events and serious adverse events, the incidence and severity of thrombotic events, thrombotic microangiopathy, disseminated intravascular coagulation/consumption coagulopathy events, and injection site reaction, immunogenicity, and the incidence of severe hypersensitivity and anaphylactic reactions. The findings will be compared with a historical period in which participants were not taking marstacimab.

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The trial will enroll 100 male participants with a diagnosis of severe hemophilia A or moderately severe to severe hemophilia B. First, the study will open enrollment to adolescent participants (age range, 12-17 years), then to children (age range, 6-11 years), and last to younger children (age range, 1-5 years old). The study is not yet recruiting.

Participants must have the required minimum weight to participate in the study. Moreover, they must have a diary and/or medical records documenting exogenous factor VIII or factor IX replacement or bypass over the 12 months prior to the time of consent.

The clinical trial is sponsored by Pfizer.


A clinical trial of study medicine (marstacimab) in pediatric patients with hemophilia A or hemophilia B (BASIS KIDS). ClinicalTrials.gov. November 10, 2022. Updated November 10, 2022. Accessed November 15, 2022.