Marstacimab recommended for EU approval for hemophilia A and B
Therapy, expected to be branded Hympavzi, under review in Europe and US
Note: This story was updated Oct. 15, 2024, to note results from the subset of patients with inhibitors participating in BASIS are now expected next year.
A European Medicines Agency (EMA) committee has issued a positive opinion recommending the approval of marstacimab in the European Union for preventing bleeding episodes in people with severe hemophilia A or hemophilia B without inhibitors.
The European Commission will now review the recommendation, made by the EMA’s Committee for Medicinal Products for Human Use (CHMP), with a final decision on the therapy’s approval expected in the coming months.
If approved, the treatment, developed by Pfizer, should be available under the brand name Hympavzi as a 150 mg solution for subcutaneous, or under-the-skin, injection, according to the EMA. The company also has submitted a request to the U.S. Food and Drug Administration asking for the therapy’s approval, with a decision expected in that country this year.
“The benefit of Hympavzi is the prevention of bleeding in severe haemophilia A or severe haemophilia B patients when given as prophylaxis,” or preventive treatment, the EMA’s overview states.
Marstacimab shown in BASIS trial to reduce bleed rates
Hemophilia A and B are caused by mutations that disrupt the activity of blood clotting proteins: factor VIII in type A and factor IX in type B. Standard treatment usually involves replacement therapy, in which a functional version of the faulty or missing clotting factor is delivered to patients.
However, these treatments usually involve frequent intravenous, or into-the-vein, infusions, which imposes a treatment burden on patients. Further, some individuals with hemophilia may develop antibodies against the delivered clotting proteins — known as inhibitors — which reduce the treatment’s efficacy.
Marstacimab is an antibody-based therapy designed to block the activity of tissue factor pathway inhibitor, a protein that normally helps prevent the formation of blood clots. Given as a preventive treatment once a week, marstacimab is expected to promote blood clotting and reduce or prevent bleeding in people with hemophilia.
CHMP’s positive opinion, which specifically applies to hemophilia A or B patients weighing at least 35 kg (about 77 pounds) with no preexisting antibodies against clotting factors, was supported by data from the Phase 3 BASIS trial (NCT03938792). The results showed that marstacimab significantly reduced bleed rates in adults and adolescents without inhibitors, compared with standard therapies.
In this first part of the trial, patients without inhibitors received their current replacement therapy for six months, followed by marstacimab, given at a 300 mg loading dose and then 150 mg weekly, for about one year. Marstacimab was found to reduce annualized bleed rates by 35% relative to preventive replacement therapy, and by 92% compared with on-demand replacement treatment.
The therapy was generally safe and well tolerated, with the most common side effects including injection site reactions, headache, high blood pressure, and itching.
Results from patients with inhibitors are expected by the end of 2025.
Patients who complete this trial may enroll in an open-label extension study (NCT05145127) to continue receiving marstacimab for up to seven years. Available data so far indicate consistent benefits for up to 1.5 years.
Another Phase 3 clinical trial, called BASIS KIDS (NCT05611801), is investigating the safety and efficacy of marstacimab in children with severe hemophilia A and moderately severe to severe hemophilia B, with or without inhibitors. That trial is expected to be completed in 2028.
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