BAY 81-8973, a full-length recombinant factor VIII treatment for hemophilia A, is effective for bleed prevention and treatment in previously untreated and minimally treated severe hemophilia patients, according to a recent study published in the journal Thrombosis and Haemostasis.

For the purpose of this phase 3, multicenter, open-label, uncontrolled study, researchers recruited 53 eligible patients aged less than 6 years with hemophilia A. Forty-three patients received prophylactic doses of BAY 81-8973 at least once per week between September 2012 and September 2019.

The primary efficacy endpoint was the annualized bleeding rate (ABR) within 48 hours after the infusion of BAY 81-8973. The study authors also evaluated treatment-related adverse events and immunogenicity. Moreover, immune tolerance induction treatment in an optional extension phase was also offered to those participants who developed inhibitors.

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According to the results, the median annualized bleeding rate was 0.0 (0.0-1.8) among patients without inhibitors (n=20) and 0.0 (0.0-2.2) in all patients. The most frequent treatment-related adverse event was the development of inhibitors. Out of 12 patients who underwent immune tolerance induction treatment in the extension phase, 6 achieved a negative inhibitor titer.

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“The inhibitor incidence observed during the study was strongly influenced by a cluster of inhibitor cases and may be a chance finding or due to unknown confounding risk factors,” Ljung and colleagues noted.

“While a clear conclusion on the immunogenicity risk of BAY 81–8973 cannot be made from the results of this study, the overall benefit and risk of treatment with BAY 81– 8973 remains within expectations for rFVIII products and is supported by ongoing, long-term safety surveillance,” they concluded. “Finally, immune tolerance can be achieved with BAY 81–8973.”

Frequent bleeds associated with severe forms of hemophilia can lead to progressive joint damage, deformity, and disability. The main treatment and standard of care for people with hemophilia—regular prophylaxis with FVIII replacement therapy—is found most effective when initiated at an early age.


Ljung R, Chan AKC, Glosli H, et al. BAY 81-8973 efficacy and safety in previously untreated and minimally treated children with severe hemophilia A: the LEOPOLD kids trialThromb Haemost. Published January 20, 2023. doi:10.1055/s-0042-1757876