FDA, EMA Accept Regulatory Submission for Marstacimab Treatment of Hemophilia A, B

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The submissions to both agencies were based upon positive results from the BASIS trial that had been presented at the American Society of Hematology Annual Meeting.

Pfizer Inc. announced that the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) had accepted its submission for the Biologics License Application (BLA) of marstacimab for hemophilia A or hemophilia B patients without Factor VIII (FVIII) or Factor IX (FIX) inhibitors.1

Announced December 12, the new anti-tissue factor pathway inhibitor (anti-TFPI) candidate is now under review. There is also a Prescription Drug User Fee Act (PDUFA) action date planned by the FDA for the fourth quarter of 2024, as well as a planned decision by the European Commission by the initial quarter of 2025.

“Marstacimab has demonstrated that it may be an efficacious treatment option with once-weekly, subcutaneous flat-dose administration via an auto-injector pen, for appropriate patients, if approved,” James Rusnak, MD, PhD, Chief Development Officer and senior vice president of Internal Medicine and Infectious Diseases at Pfizer, said in a statement. “This is critical as intravenous infusions are typically required for people living with these diseases today.”

If it receives approval in the EU and US, marstacimab would be poised to become the first weekly subcutaneous therapy available for those with hemophilia B and represent the first flat-dose treatment for those with hemophilia A or B.

Pfizer’s BLA submissions had been based upon positive phase 3 findings in the BASIS trial, with the results being presented at the 2023 American Society of Hematology (ASH) Annual Meeting.2

The global BASIS study was done to look into the annual bleed rate (ABR) over a 12-month period in about 145 patients aged 12 to <75 that have severe hemophilia A or moderately severe to severe hemophilia B, with or without inhibitors. Around 15% of those participating in the research were adolescents aged 12 to <18 years.

The investigators’ work involved a 6-month observational phase in which they compared treatment with a run-in period for subjects on factor replacement or on bypass therapy. This was later followed by a 12-month active treatment phase.

In this later phase, subjects were given prophylaxis with marstacimab, beginning with a 300 mg subcutaneous loading dose. This was then followed by 150 mg subcutaneously once-per-week, with the potential for dose escalation up to 300 mg once-per-week.

Among the major findings, the investigators found the drug demonstrated a 35% decrease in annualized bleeding rates among participants compared to routine prophylaxis, as well as a 92% reduction compared to on-demand treatment in those with hemophilia A and B without inhibitors.

Additionally, the investigators reported that their long-term extension study resulted in a sustained and consistent reduction in subjects’ bleeding rates over an additional 16 months of follow-up.

“We look forward to progressing the review of this novel therapy with the FDA, EMA, and global regulatory authorities to bring this important medicine to patients globally,” Rusnak said in the same statement.


  1. FDA and EMA Accept Marstacimab Regulatory Submissions for the Treatment of Hemophilia A and B. Pfizer.; 2023. Available at:
  2. Marstacimab Phase 3 Data Presented at ASH 2023 Demonstrate Significant Bleed Reduction in Hemophilia A and B.; 2023. Available at: