Late last week, the FDA approved Qfitlia (fitusiran) for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adult and pediatric patients (12 years of age and older) with hemophilia A or hemophilia B, with or without factor VIII or IX inhibitors (neutralizing antibodies).
“Today’s approval of Qfitlia is significant for patients with hemophilia because it can be administered less frequently than other existing options,” said Tanya Wroblewski, MD, deputy director of the Division of Non-Malignant Hematology in the FDA’s Center for Drug Evaluation and Research. “This new treatment option highlights our continued efforts to improve the lives of patients with hemophilia.”
Qfitlia is a small interfering RNA (siRNA) drug. RNAi (RNA interference)—a process of gene silencing recognized with the 2006 Nobel Prize for Physiology or Medicine—is a rapidly growing area of drug development. Qfitlia joins six other FDA-approved drugs in the growing category of siRNA drugs.
“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 with inhibitors and hemophilia B, where unmet medical needs remain,” noted Guy Young, MD,
director, Hemostasis and Thrombosis Center at Children’s Hospital, Los Angeles. “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 A and hemophilia B are genetic bleeding disorders caused by a dysfunction or deficiency of coagulation factor VIII (FVIII) or IX (FIX), respectively. Patients with these hemophilias are unable to clot properly and may bleed for a longer time than normal after injury or surgery. They may also have spontaneous bleeding in muscles, joints, and organs, which can be life-threatening. These bleeding episodes are typically managed by either on-demand, episodic treatment or prophylaxis using products containing FVIII or FIX, or a product that mimics a factor.
Qfitlia does not replace the missing clotting factor. Rather, it reduces the amount of the antithrombin protein, leading to an increase in thrombin, an enzyme critical for blood clotting.
Qfitlia is administered subcutaneously starting once every two months. The dose and frequency of injections are adjusted using the FDA-cleared INNOVANCE Antithrombin companion diagnostic test. This companion diagnostic is intended to monitor and—by informing dosing and frequency of injections—achieve antithrombin activity in the target range to reduce the risk of bleeding and to reduce the risk of excessive blood clotting. The FDA granted clearance of the INNOVANCE Antithrombin test to Siemens Healthcare Diagnostics.
Qfitlia’s efficacy and safety were assessed in two multicenter, randomized clinical trials which enrolled a total of 177 adult and pediatric male patients with either hemophilia A or hemophilia B. In the two randomized trials, participants received either a fixed dose of Qfitlia monthly or their usual on-demand treatment (bypassing agents or clotting factor concentrates) as needed for nine months. The fixed dose of Qfitlia is not approved because it led to excessive clotting in some patients.
Participants subsequently entered a long-term extension study in which they received an adjustable dose of Qfitlia based on periodic measurements of antithrombin activity. This antithrombin-based dosing regimen is the approved dosage regimen. Efficacy of Qfitlia using the antithrombin-based dosing regimen was established by comparing patients on this dosing regimen of Qfitlia during the long-term extension study to the on-demand control data from the two randomized clinical trials.
The primary measure of efficacy of Qfitlia was the estimated annualized bleeding rate of treated bleeds. In the participants with inhibitors who received the antithrombin-based dosing regimen of Qfitlia, there was a 73% reduction in estimated annualized bleeding rate compared to those who received on-demand treatment with bypassing agents. In participants without inhibitors who received the antithrombin-based dosing regimen of Qfitlia, there was a 71% reduction in estimated annualized bleeding rate compared to those who received on-demand treatment with clotting factor concentrates.
Qfitlia has a boxed warning for thrombotic events (blood clotting) and gallbladder disease (with some patients requiring gallbladder removal). Qfitlia also has a warning about liver toxicity and the need to monitor liver blood tests at baseline and then monthly for at least six months after initiating treatment with Qfitlia or after a dose increase of Qfitlia.
The most common side effects of Qfitlia are viral infection, common cold symptoms (nasopharyngitis), and bacterial infection.
The FDA granted Qfitlia Orphan Drug and Fast Track designations for this application and granted the approval of Qfitlia to Sanofi.