Fitusiran: what if we rebalanced coagulation?

By Ana Espino | Published on April 17, 2026 | 4min read


Hemophilia is a genetic bleeding disorder caused by a deficiency in factor VIII (hemophilia A) or factor IX (hemophilia B), leading to spontaneous or prolonged bleeding. It primarily affects males due to its X-linked inheritance and represents a chronic condition that significantly impacts quality of life.

Current treatments are mainly based on replacement therapy with coagulation factors, administered either on demand or prophylactically. Although effective, these treatments have several major limitations: high cost, frequent intravenous injections that are burdensome for patients, and the development of neutralizing antibodies (inhibitors) that can reduce their effectiveness.

These limitations highlight current challenges: improving adherence, reducing treatment burden, and providing effective options for patients with inhibitors. In this context, this study was conducted to present fitusiran, the first approved small interfering RNA (siRNA) therapy for hemophilia, and to evaluate its mechanism of action, clinical efficacy, and potential to transform disease management.

Can hemophilia be controlled differently ?

The study is based on the analysis of data from several phase III clinical trials (ATLAS-INH, ATLAS A/B, and ATLAS-OLE), including patients with hemophilia A or B, with or without inhibitors. These trials compare prophylactic fitusiran with standard treatments (bypassing agents or on-demand coagulation factor therapy).

Fitusiran works through an innovative mechanism: it targets the SERPINC1 gene in the liver to reduce antithrombin production. This reduction increases thrombin activity and restores coagulation balance, independently of factor VIII or IX deficiency and regardless of the presence of inhibitors.

Clinical trial results show a significant reduction in the annualized bleeding rate (ABR) in patients treated with fitusiran:

• in patients with inhibitors: substantial reduction compared to bypassing agents (5.1 vs 19.1),
• in patients without inhibitors: marked reduction compared to standard treatments (9.0 vs 31.4).

Another major advantage is the simplicity of the dosing regimen, with infrequent subcutaneous administration (every two months with individualized adjustment), potentially improving treatment adherence.

However, adverse effects have been reported, including thrombotic events, liver and biliary disorders, as well as infections. These risks led to adjustments in the dosing regimen, based on monitoring antithrombin activity to maintain a balance between efficacy and safety.

Rethinking coagulation

Hemophilia remains a chronic disease requiring long-term management, with significant therapeutic constraints. The main challenges involve reducing treatment burden, managing inhibitors, and improving patients’ quality of life.

This study aimed to present fitusiran as a novel and innovative therapeutic approach based on RNA interference. The results show that fitusiran represents a major advancement, offering a mechanism independent of coagulation factors and a significant reduction in bleeding, while simplifying treatment.

However, some limitations remain, particularly the risks of thrombosis and liver toxicity, as well as the lack of long-term data on safety and effectiveness in real-world settings.

Nevertheless, the outlook remains promising. Fitusiran could sustainably transform hemophilia management and pave the way for other RNA interference–based therapies, provided its long-term safety profile is confirmed.




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About the author – Ana Espino
PhD in Immunology, specialized in Virology  
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.