Fitusiran Shows Promise as Prophylactic Therapy for Hemophilia A, B


The monthly prophylactic injection reduces bleeds by interfering with the production of specific proteins for both types of hemophilia with or without inhibitors.

Fitusiran Shows Promise as Prophylactic Therapy for Hemophilia A, B

Fitusiran, a monthly prophylactic injection, has shown promising results in reducing bleeds in patients with hemophilia A or B, according to two separate randomized controlled trials. This is a significant development for those living with hemophilia, as it offers an effective prophylactic treatment option that works for both types of hemophilia and for patients with or without inhibitors.

Prophylactic treatments are aimed at reducing spontaneous bleeding by regularly administering drugs that enhance hemostasis. However, current prophylactic options may not be an effective approach for patients with inhibitors because there are risks of triggering an immune reaction against replacement clotting factor treatment.

The lead investigator of one of the studies, Guy Young, MD, Children’s Hospital Los Angeles, University of Southern California Keck School of Medicine, stated current options for treating patients with hemophilia B are limited to on-demand therapies that address a bleed that's already occurred.

Fitusiran is a new type of treatment known as small interfering RNA (siRNA) therapy that interferes with the production of specific proteins. It targets antithrombin, a protein that reduces blood clotting, and increases clotting ability.

“Our study looks at the efficacy of the first siRNA therapy used to treat hemophilia with inhibitors. The data is encouraging and suggests it may be the first prophylactic treatment – meaning it can be given to prevent bleeds rather than to treat them after they have already occurred – that works for both hemophilia A and B patients with inhibitors," Young said in the statement.

While these data present the potential to revolutionalize hemophilia treatment, the drug is not approved for use outside of clinical trials.

"The most common adverse effect was increased alanine aminotransferase, which is seen with many medications and indicates liver inflammation. Importantly, most of these elevations were temporary and did not result in discontinuation of fitusiran," he continued.

"In this context, it suggests that fitusiran did not result in any long-term liver damage, but this adverse effect needs continued assessment in this and other trials of fitusiran. Regulators will need to assess the benefits and risks of the drug when deciding whether to approve its use and for which patients it is suitable.”

Young also noted that two patients in the study experienced blood clotting, which is a risk for these types of treatments. However, in the second study led by Alok Srivastava, MD, Christian Medical College, Vellore, there were no reported instances of blood clotting.

"Our study looks at the use of fitusiran in patients with hemophilia A or B without inhibitors and complements the findings from the study looking at fitusiran with inhibitors - also finding that it is very effective in preventing bleeds," Srivastava stated.

Both studies saw 0 bleeding - the first study was compared with 16.8 and the second study comparator group was 21.8.

"With this drug being administered just once a month or even less frequently, there is a marked reduction in treatment burden. This means patients with hemophilia could manage their condition with fewer trips to the hospital, which can cause worry and be disruptive to daily life," Srivastava continued. "This would lead to an improved quality of life as documented in the study."


Monthly injections of fitusiran reduces bleeds in patients with haemophilia A and B. News release. The Lancet. March 29, 2023. Accessed April 3, 2023.

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