Extending recombinant factor IX Fc fusion protein dosing interval to 14 or more days in patients with hemophilia B

BACKGROUND: In the phase 3 B‐LONG study (NCT01027364), prophylaxis with recombinant factor IX Fc fusion protein (rFIXFc) every 7 to >14 days was associated with low annualized bleed rates (ABRs) in males aged ≥12 years with severe hemophilia B. The long‐term safety and efficacy of rFIXFc prophylaxis was confirmed in the B‐YOND study (NCT01425723), an extension of the B‐LONG clinical trial. OBJECTIVE: The aim of this post‐hoc analysis was to evaluate the efficacy of a ≥14‐day rFIXFc dosing interval in patients treated prophylactically during B‐LONG or B‐YOND. METHODS: The analysis included 22 patients aged ≥12 years who received prophylactic rFIXFc with a ≥14‐day dosing interval at any time during B‐LONG or B‐YOND up until the second interim analysis of B‐YOND (September 2015). RESULTS: The median (interquartile range [IQR]) rFIXFc exposure on the ≥14‐day dosing interval was 3.4 (1.8‐4) years. Patients treated with a ≥14‐day dosing interval were well controlled with a median (IQR) overall ABR of 1.6 (0.6‐2.7) and a median (IQR) spontaneous ABR of 0.7 (0.3‐1.1) in 18 evaluable patients. A rFIXFc dosing interval of ≥14 days was well tolerated, with no new safety concerns identified. CONCLUSION: Most patients on rFIXFc prophylaxis, with a dosing interval of ≥14 days, remained well controlled; ABRs were consistent with those reported in the overall study population. A ≥14‐day dosing interval can be utilized in some well controlled individuals and reduces the burden imposed by frequent prophylactic injections while maintaining adequate bleed suppression.