Objective The introduction of factor replacement products with enhanced half-life has helped patients with haemophilia B to overcome one of the limitations of standard factor IX (FIX) products by allowing less frequent infusions. rIX-FP is one such FIX product, that provides a prolonged dosing interval in patients with haemophilia B. A phase III extension study evaluated the long-term efficacy and safety of rIX-FP prophylaxis in adult patients with haemophilia B, including a subset of patients treated on a 21-day dosing regimen.

•rIX-FP can be used effectively for surgical management in hemophilia B patients•Most surgeries can be well managed using a single pre-operative dose of rIX-FP•Surgical procedures can be performed with low FIX consumption using rIX-FP•No inhibitors or adverse events related to treatment were reported

Scientific Research Question: To investigate the long-term safety and efficacy of rIX-FP in previously treated patients (PTPs) over approximately 3 years.

Essentials Performance of the one‐stage clotting (OSC) assay varies with the clotting activator used. Recombinant FIX‐albumin fusion protein (rIX‐FP) was reliably monitored with most OSC reagents. rIX‐FP shows comparable reagent‐dependent variability to other rFIX products in the OSC assay. Actin® FS and kaolin‐based reagents underestimated rIX‐FP activity by around 50% in the OSC assay.