Small Study Shows Safety, Efficacy of Prophylactic rIX-FP in Previously Untreated Hemophilia B

Findings from a small study are suggesting that recombinant fusion protein linking coagulation factor IX (FIX) with albumin (rIX-FP) is tolerable and effective in patients with hemophilia B who have not previously received treatment.

Hemophilia B | Image Credit: © MQ-Illustrations - stock.adobe.com

Published in Thieme Open, the study, explained the researchers, adds new insight into the feasibility of rIX-FP as preventive or on-demand treatment for patients with hemophilia B.

“In previous studies, rIX-FP has shown a favorable safety profile and effective treatment of bleeds in adult and pediatric patients who had been previously treated with FIX replacement therapy,” wrote the group. “rIX-FP has also demonstrated improved [pharmacokinetic] profiles in comparison with standard half-life factor replacement products, which offers improved protection against bleeds. This also allows the option to extend dosing intervals up to every 21 days in well-controlled adult patients, to reduce the burden on patients and their families without compromising efficacy.”

Findings from this new study demonstrate the safety and efficacy of rIX-FP among a group of treatment-naive patients often characterized by young age. Being able to effectively control bleeding has particular importance for maintaining joint health in young, active patients. These patients, noted the researchers, are particularly vulnerable to severe bleeding and development of inhibitors after factor replacement.

Twelve patients with moderately severe or severe hemophilia B were included in the study, throughout which they received 25 to 75 IU/kg of rIX-FP either weekly or as needed. The median age of patients was 0 years, and majority of patients were under the age of 6 years.

Over the 24-month period, 1 of the 12 previously untreated patients developed FIX inhibitors—the study’s primary end point. The 8% incidence was similar to that seen in previous studies (9.3%).

“The 11-year-old patient who developed an inhibitor was ultimately discontinued after 39 [exposure days] due to hypersensitivity reactions to treatment,” detailed the researchers. “This patient had large deletions within exons 7 and 8 of the F9 gene, which have previously been identified as a risk factor for inhibitor development, as noted in a recent study which found that patients with large structural deletions had a higher risk (33.3%) of inhibitor development.”

The researchers also found similar estimated mean incremental recovery (IR) among the 8 patients receiving a 50 IU/kg dose of treatment among their patients and previous study populations. Among their study population, the researchers observed a mean IR—the study’s other coprimary end point—of 1.23. Previous research has shown a mean IR of 1.38 among patients with rIX-FP. The group noted that the IR seen with rIX-FP is higher than that previously seen with other FIX treatments, including rFIX (mean, 0.94) and pdFIX (mean, 1.10).

Throughout the study period, 8 patients had an adherence rate of at least 80%. With routine prophylaxis, there were no major bleeds were reported, and 9 patients maintained an AsBR of 0. There were 10 patients who completed at least 6 months of prophylaxis with rIX-FP, among whom there was a median annualized bleeding rate of 1.1.

Most treatment-emergent adverse events (TEAEs) occurring throughout the study were mild and resolved, and the most common TEAE was infection or infestation. There were 135 TEAEs, just 5 of which, occurring among 2 patients, were attributed to rIX-FP. Two of these events occurred during prophylaxis treatment and the other 3 occurred during intensified treatment that was off protocol.

Reference

Lemons R, Wang M, Curtin J, et al. Safety and efficacy of recombinant fusion protein linking coagulation factor IX with albumin (rIX-FP) in previously untreated patients with hemophilia B. TH Open. 2024;8(1):e155-e163.