Recombinant single‐chain factor VIII in severe hemophilia: Long‐term safety and efficacy in previously treated patients in the AFFINITY extension study

BACKGROUND: rVIII‐SingleChain is a recombinant single‐chain factor VIII used to treat people with hemophilia A. OBJECTIVES: The aim of this extension study was to investigate the long‐term safety and efficacy of rVIII‐SingleChain prophylaxis in ≥200 previously treated patients (PTPs) with hemophilia A with ≥100 exposure days (EDs). METHODS: In total, 222 patients were enrolled, of which 204 rolled over from prior rVIII‐SingleChain studies. The median age was 21 years (range, 2–65 years), including 155 patients ≥12 years and 67 patients <12 years. Patients continued with their previously assigned dose and regimen, or switched at the investigator’s discretion. Patients were treated for a mean duration of 31 months (range, 1–47 months), the mean ED was 342 (standard deviation, 135.5), and 212 (95.5%) patients achieved >100 EDs. When the study ended, most patients were on either a prophylaxis regimen of 34.9 (17–62) IU/kg, 3×/week (N = 88; 39.6%), or 37.2 (13–65) IU/kg, 2×/week regimen (N = 72; 32.4%). RESULTS: Hemostatic efficacy was rated excellent or good in 87.1% of assessed bleeds. The median (range) annualized bleeding rate was 1.21 (0.0–42.6), and the annualized spontaneous bleeding rate (AsBR) was 0.32 (0.0–33.0) for prophylaxis regimens. Median AsBR was similar for patients treated 3×/week and 2×/week (0.31 and 0.30, respectively). Surgical hemostatic efficacy was rated excellent or good in 100% of surgeries. No inhibitors, anaphylactic reactions, or thromboembolic events were reported in PTPs. CONCLUSION: These results confirm the safety and efficacy of rVIII‐SingleChain as a long‐term prophylaxis treatment modality for PTPs with severe hemophilia A.