Qfitlia (Fitusiran): A Novel siRNA-based Treatment for Haemophilia  

Qfitlia (Fitusiran), a novel siRNA-based treatment for haemophilia has received FDA approval. It is a small interfering RNA (siRNA) based therapeutic that interfere with natural anticoagulants such as antithrombin (AT) and tissue factor pathway inhibitor (TFPI). It binds to AT mRNA in the liver and blocks AT translation thereby reduce antithrombin and improve thrombin generation. It is administered as subcutaneous injection starting once every two months. The dose and frequency of injections are adjusted using the INNOVANCE Antithrombin companion diagnostic that ensure antithrombin activity in the target range. The fixed dose is not approved. The new treatment is significant for patients because it is administered less frequently than other existing options.  

Qfitlia (fitusiran) has been approved in the USA (on 28 March 2025) for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adult and children 12 years of age and older with hemophilia A or hemophilia B, with or without factor VIII or IX inhibitors (neutralizing antibodies). The new treatment is significant because it is administered less frequently (starting once every two months) than other existing options.  

Bleeding disorders in haemophilia are caused due to inadequacy of clotting factors. Haemophilia A is caused due to deficiency of clotting factor VIII (FVIII), while haemophilia B is due to low levels of factor IX (FIX). Lack of functional factor XI is responsible for haemophilia C. These conditions are treated by infusing commercially prepared clotting factor or a non-factor product as functional replacement of the missing factor.  

Octocog alfa (Advate), which is a ‘genetically engineered using DNA technology’ version of clotting factor VIII, is commonly used for the preventive as well as on-demand treatment of haemophilia A. For haemophilia B, nonacog alfa (BeneFix), which is an engineered version of clotting factor IX is commonly used.   

Hympavzi (marstacimab-hncq) was approved in the USA (on 11 October 2024) and in the EU (on 19 September 2024) as a new drug for prevention of bleeding episodes in individuals with hemophilia A or hemophilia B. It is a human monoclonal antibody that prevents bleeding episodes by targeting the naturally occurring anticoagulation protein called “tissue factor pathway inhibitor” and reduces its anticoagulation activity thereby increasing the amount of thrombin. This is first, non-factor and once-weekly treatment for hemophilia B. 

Another monoclonal antibody, Concizumab (Alhemo) was approved in the USA (on 20 December 2024) and in the EU (on 16 December 2024) for prevention of bleeding episodes in patients with hemophilia A with factor VIII inhibitors or hemophilia B with factor IX inhibitors. Some haemophilia patients on “clotting factor medicines” for treatment their bleeding disorder condition develop antibodies (against the clotting factor medicines). The antibodies formed inhibit the action of “clotting factor medicines” making them less effective. Concizumab (Alhemo), administered daily as subcutaneous injection, is meant to treat this condition which has traditionally been treated by inducing immune tolerance through daily injections of clotting factors. 

While mpavzi (marstacimab-hncq) and Concizumab (Alhemo) are monoclonal antibodies, the new treatment Qfitlia (fitusiran) is a small interfering RNA (siRNA) based therapeutic that interfere with natural anticoagulants such as antithrombin (AT) and tissue factor pathway inhibitor (TFPI). It binds to AT mRNA in the liver and blocks AT translation thereby reduce antithrombin and improve thrombin generation.  

Qfitlia (fitusiran) is administered as subcutaneous injection starting once every two months. 

The dose and frequency of injections are adjusted using the INNOVANCE Antithrombin companion diagnostic that ensure antithrombin activity in the target range. The fixed dose is not approved. Notwithstanding this, the new treatment is significant for patients because it is administered less frequently than other existing options. 

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References:  

1. FDA News Release – FDA Approves Novel Treatment for Hemophilia A or B, with or without Factor Inhibitors. Posted 28 March 2025. Available at  https://www.fda.gov/news-events/press-announcements/fda-approves-novel-treatment-hemophilia-or-b-or-without-factor-inhibitors  

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Related article: 

• Concizumab (Alhemo) for Hemophilia A or B with Inhibitors  (29 December 2024) 

• Hympavzi (marstacimab): New Treatment for Hemophilia (12 October 2024)  

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