FDA Approves First Prophylactic Therapy for Hemophilia A or B With or Without Inhibitors

The FDA has approved Sanofi’s Qfitlia (fitusiran) as the first therapy in the United States to treat hemophilia A or B with or without inhibitors for patients ages 12 and older, according to a news release.

“Qfitlia delivers the fewest doses of any prophylactic therapy in hemophilia, and its unique mechanism allows it to be used to treat all types of hemophilia, including those with inhibitors and hemophilia B, where unmet medical needs remain,” Guy Young, M.D., director of the Homeostasis and Thrombosis Center at Children's Hospital, Los Angeles, said in the news release. “By targeting antithrombin, which can be reliably measured with an FDA-cleared blood assay, Qfitlia is proven to help rebalance hemostasis and improve bleed rates and protection.”

Hemophilia is a bleeding disorder in which blood does not clot properly. It can be dangerous because it can cause spontaneous bleeding or prolonged bleeding after surgery or injuries, according to the Centers for Disease Control and Prevention. There are two types of hemophilia: A and B. Hemophilia A, sometimes called “classic hemophilia,” is caused by a lack or low level of clotting factor VIII. Hemophilia B, which is sometimes called Christmas disease, is caused by a lack or low level of clotting factor IX .

In both types, some people develop antibodies, called inhibitors, to clotting factor treatments. According to the Hemophilia Federation of America, approximately 30% of people with severe hemophilia A will develop inhibitors sometime in their life, but only 2% to 3% with hemophilia B do. The consequences of hemophilia B inhibitors can be serious, though. About half of patients with hemophilia B inhibitors will develop an anaphylactic reaction to infused factor IX, which can be life-threatening.

This disease is caused by a mutation in the genes on the X chromosome and is more common in males because they only have one X chromosome. Females have two X chromosomes and therefore have a “back up” if there is a mutation in one of them. Hemophilia occurs in approximately 1 out of every 5,000 male births.

Hemophilia becomes difficult to treat if the patient develops an antibody called an inhibitor, which prevents medication from working. Cost of care for these patients increases because they must use more of a clotting factor or a different type. They also are more prone to joint disease and other complications, potentially resulting in a lower quality of life.

The mean annual cost of hemophilia A and B was $206,027 and $179,747, respectively, according to a study that examined insurance claims data, published in Journal of Managed Care Specialty Pharmacy. For patients with inhibitors, annual costs exceeded $400,000.

Qfitlia, approved on March 28, 2025, is an antithrombin-directed small interfering ribonucleic acid that lowers antithrombin, a protein that inhibits blood clotting. This increases thrombin generation and restores homeostasis, the news release explains.

This approval was based on the results from the ATLAS phase 3 studies where effectiveness was measured using annualized bleeding rates when compared with clotting factor concentrate on-demand. In patients without inhibitors, Qfitlia resulted in a bleed reduction of 71%, and in patients with inhibitors, Qfitlia patients saw a 73% reduction. In addition, 47% of patients on Qfitlia experienced one or fewer bleeds during the study.

Adverse reactions occurred in at least 10% of the 286 patients tested, the most common being viral infection, nasopharyngitis and bacterial infection.

The starting dose of Qfitlia is a 50 milligram subcutaneous injection administered once every two months via a single-dose prefilled pen.

The cost of Qfitlia will be similar to other prophylactic hemophilia treatments, but the overall cost will be less because Qfitlia offers the fewest doses on the market, the release states.

The HemAssist program will launch alongside Qfitlia and provide patient resources such as insurance and financial assistance.