A study by researchers at the Hemophilia and Thrombosis Center, University of Colorado, Aurora, found that patients with hemophilia A who are on emicizumab treatment continue to have bleeding events, the majority of which are related to trauma. 

Patients on the treatment should therefore be closely monitored for bleeding or other adverse outcomes, according to the authors of the study published in Research and Practice in Thrombosis and Haemostasis last week. 

Emicizumab is an antibody that binds to activated factors IX and X and simulates the action of factor VIII (FVIII). Results of clinical trials have shown that it leads to low bleeding rates in patients with hemophilia A.

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The treatment was approved by the US Food and Drug Administration (FDA) in 2018 and is increasingly used in the treatment of hemophilia A. However, the need for prophylactic treatment with FVIII during the loading period, flexibility in the frequency of treatment, side effects, and management of bleeding events remain uncertain.

Here, a team of researchers led by Christopher J Ng, MD, conducted a retrospective chart review and structured phone interviews to better understand the early impact of emicizumab on patients with hemophilia A. They analyzed 68 patients with hemophilia A, aged 0 to 80 years, who were on emicizumab treatment for a median of 213 days.

They found that most adverse reactions associated with the use of emicizumab were skin reactions. There were no anaphylactic reactions or thrombosis. Bleeding events showed wide variability, with 25 of the 68 patients having no bleeds, while 5 had more than 8 bleeds per year. These often occurred in the first 10 weeks of taking emicizumab and were mostly traumatic musculoskeletal bleeds. However, no time period was without bleeding events.

There were also wide variations in prescribing practices and factor prophylaxis overlap dosing regimens, with some patients being prescribed emicizumab every week, while others were prescribed the treatment every 2 weeks and some had alternative dosing frequencies.

The researchers stated, “We report our real-world experience using emicizumab in a large US hemophilia treatment center with pediatric and adult patients,” adding that their findings call for more studies to better understand the long-term effects of the treatment.


Warren BB, Chan A, Manco-Johnson M, et al. Emicizumab initiation and bleeding outcomes in people with hemophilia A with and without inhibitors: a single-center report. Res Pract Thromb Haemost. 2021;5(5):e12571. doi:10.1002/rth2.12571