Qfitlia (fitusiran)

An siRNA therapy that lowers antithrombin levels to restore clotting balance in hemophilia A and B patients, with or without inhibitors, aged 12 and older. Given as a subcutaneous injection starting once every 2 months, with the dose and schedule adjusted based on blood antithrombin levels.

Fitusiran uses RNA interference to reduce the body's production of antithrombin, a protein that normally slows down clotting. In healthy people, antithrombin keeps clotting in check. But in hemophilia, where clotting factors are already low, antithrombin makes the problem worse. By reducing antithrombin, fitusiran tips the balance back toward normal clotting.

Qfitlia has a boxed warning for serious blood clots and for gallbladder disease (gallstones and gallbladder inflammation, sometimes needing surgery). The clot risk is higher when antithrombin levels stay below 15%, with an indwelling venous catheter, and after surgery if bleed management guidelines are not followed. It can also raise liver enzymes, so liver tests are done at the start, monthly for at least 6 months and after dose increases. The most common side effects were viral infections, nasopharyngitis (cold symptoms) and bacterial infections; injection site reactions also occurred. Antithrombin activity is checked with an FDA-cleared test to guide dosing.

Given as a subcutaneous injection, starting at 50 mg once every 2 months. Blood antithrombin levels are checked at months 1, 3, 5 and 6 and after any dose change, and the dose or schedule is adjusted (for example to monthly, or to a lower dose) to keep antithrombin between 15% and 35%. Can be self-administered at home after training. Works for both hemophilia A and B, making it a versatile treatment option.

Yes, Fitusiran (Qfitlia) is FDA approved (2025) for the treatment of Hemophilia A and Hemophilia B.

Fitusiran is the first siRNA (RNA interference) therapy for hemophilia. While emicizumab mimics Factor VIII and anti-TFPI drugs block a clotting inhibitor, fitusiran silences antithrombin production at the RNA level, reducing a natural anticoagulant to restore clotting balance. Most patients start with 1 injection every 2 months, adjusted based on antithrombin blood levels.

Yes. Fitusiran is approved for hemophilia A and B patients with or without inhibitors. Because it targets antithrombin rather than replacing specific clotting factors, it works regardless of which factor is deficient.

Thromboembolic events are a known risk because fitusiran reduces antithrombin, which normally prevents excessive clotting. The label carries a boxed warning for blood clots and also for gallbladder disease. Antithrombin levels are checked with an FDA-cleared test and the dose is adjusted to keep them between 15% and 35%, because levels below 15% raise clot risk. Patients should promptly report symptoms like leg swelling, chest pain, shortness of breath, or pain in the upper belly.

Fitusiran is given as a subcutaneous injection starting once every 2 months. Depending on antithrombin blood levels, the doctor may change it to a different dose or to once a month. Patients can self-administer at home after proper training.

Fitusiran was developed through a partnership between Sanofi and Alnylam Pharmaceuticals, the pioneer in RNA interference therapeutics. It leverages Alnylam's siRNA technology platform to silence antithrombin gene expression in liver cells.

Antithrombin activity is measured at months 1, 3, 5 and 6 after starting and after any dose change. Liver tests are done at baseline, monthly for at least 6 months and after dose increases, then periodically. Doctors also watch for signs of blood clots and gallbladder disease. The treating physician will schedule periodic blood tests to ensure safety throughout treatment.

The Phase 3 ATLAS program showed significant reduction in annualized bleeding rates across hemophilia A and B patients with and without inhibitors, leading to FDA approval in March 2025. The program included multiple trials covering different hemophilia populations.