FDA Approves Fitusiran For Prophylactic Hemophilia A, B Treatment Regardless of Inhibitor Status

The FDA has approved fitusiran (Qfitlia; Alnylam Pharmaceuticals, Sanofi), a first-in-class antithrombin-targeting small interfering RNA (RNAi) drug, for the prophylactic treatment of adult and pediatric patients aged 12 years and older with hemophilia A or B, regardless of inhibitor status, according to a news release from the FDA.¹

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“Today’s approval of [fitusiran] is significant for patients with hemophilia because it can be administered less frequently than other existing options,” Tanya Wroblewski, MD, deputy director of the Division of Non-Malignant Hematology in the FDA's Center for Drug Evaluation and Research, said in the news release. "This new treatment option highlights our continued efforts to improve the lives of patients with hemophilia.”¹

Though it does not replace the missing clotting factor in patients with hemophilia A or B, fitusiran instead reduces the amount of antithrombin, which increases the amount of thrombin in the body and allows for more effective blood clotting. The treatment is administered subcutaneously, starting once every 2 months, with doses and frequency adjusted using the FDA-approved INNOVANCE Antirhombin companion diagnostic test. Importantly, fitusiran has a boxed warning for thrombotic events and gallbladder disease, and features a warning regarding liver toxicity.¹

Fitusiran has demonstrated effectiveness at reducing annualized bleeding rates in multiple clinical trials. Investigators of one phase 3 clinical trial (NCT03417245) found that fitusiran was more effective in the long term than on-demand treatment with factor concentrates at reducing mean annualized bleeding rate in patients 12 years or older with severe hemophilia A or B without inhibitors. In this trial, patients were treated with fitusiran for approximately 9 months, indicating sustained effectiveness.²

Another trial (NCT03417102) sought to further investigate fitusiran's effectiveness at reducing annualized bleeding rate. With a similar population and end points to the prior trial, the investigators found that the annualized bleeding rate was significantly lower in patients receiving fitusiran, with a 90.8% observed reduction. Importantly, 66% of individuals treated with fitusiran had 0 treated bleeds, compared with 1 in the standard care group.²

Fitusiran is subcutaneously administered to patients to prevent bleeds and rebalance hemostasis through the lowering of antirhombin, which is a protein that inhibits blood clotting. According to Sanofi, fitusiran utilizes novel conjugate technology that allows for subcutaneous dosing and increased potency and durability. Given the low treatment burden associated with fitusiran, this approval could enable treatment for patients across the globe with hemophilia A or B regardless of their inhibitor status.³

Now that fitusiran is FDA-approved, pharmacists stand to play a major role in utilizing the therapy for the treatment of hemophilia A and B. Pharmacists must be appropriately educated on fitusiran's indications and be prepared to counsel patients on their eligibility and proper dosing. Patients must also be educated on the appropriate administration of fitusiran in order to have the most effective course of treatment.²

REFERENCES

1. FDA. FDA approves novel treatment for hemophilia A or B, with or without factor inhibitors. News Release. Released March 28, 2025. Accessed March 28, 2025. https://www.fda.gov/news-events/press-announcements/fda-approves-novel-treatment-hemophilia-or-b-or-without-factor-inhibitors

2. Gallagher A. Fitusiran is a drug to watch in the hematology space in 2025. Pharmacy Times. Published February 1, 2025. Accessed March 7, 2025.

3. Sanofi. Press release: ISTH: Sanofi advances leadership in hemophilia with new data for ALTUVIIIO and fitusiran. News Release. Released June 21, 2024. https://www.pharmacytimes.com/view/fitusiran-is-a-drug-to-watch-in-the-hematology-space-for-2025Accessed March 7, 2025. https://www.globenewswire.com/news-release/2024/06/21/2902104/0/en/Press-Release-ISTH-Sanofi-advances-leadership-in-hemophilia-with-new-data-for-ALTUVIIIO-and-fitusiran.html