Real-World Bleeding Outcomes, Weekly Factor Consumption Doses, Annualized Factor Costs in Severe-Type Patients with Hemophilia a (PwHA) before and after Switching to Extended Half-Life rFVIII-Fc Prophylaxis

Introduction: Stand half-life (SHL) rFVIII had been used in patients with hemophilia A (PwHA) for episodic treatment (ET) and prophylaxis therapy (PT) for years. Extended half-life (EHL) rFVIII had been available since 2014, also available in Taiwan since 2018, and resulted in markedly increased willingness for PT because it reduced injection burden. We aimed to investigate the real-world bleeding outcomes, weekly factor doses, and factor costs of severe-type PwHA with pre-switch SHL rFVIII and post-switch EHL rFVIIIFc prophylaxis in Taiwan, and made a pre-switch and post-switch comparison.

Methods and Materials: There were totally 51 non-inhibitor, severe-type PwHA, with complete bleeding records before and after switching from SHL rFVIII to EHL rFVIII-Fc, enrolled from two hemophilia centers during Nov, 2018－July, 2019. Most of them had various degree of one to more major joints arthropathy, except children. The medical charts were retrospective reviewed and data were collected, including body features and factor regimen, etc. Patients' annualized bleeding/joint-bleeding rate (ABR/AJBR), weekly doses (WD), annualized factor costs (AFC) were obtained from the chart records of pre-switch 12 months and post-switch at least more-than 6-month until July, 2019. Data from scheduled operation or hospitalization due to trauma or accidence were excluded.

Results: There were 8 boys and 43 adults, the median age of all PwHA when switching was 35.6 years (10.5-62). Before switching, these 51 PTP treated with SHL rFVIII who received ET (ET group), irregular prophylaxis (IP group), and regular prophylaxis (RP group) were 19 (37.3%), 7 (13.7%), and 25 (49%), respectively. Bleeding records of 51 PTP treated with SHL rFVIII were traced back with 11.8±0.9 months. After switching to rFVIII-Fc, 3 PwHA receiving ET were excluded, and bleeding records of 48 received RP were obtained with 14.7±4.6 months. Pre-switch and post-switch prophylaxis rate were 62.7% (32/51) and 94.1% (48/51), respectively. For comparison of pre-switch and post-switch outcomes: Median ABR was reduced from 48, 12, and 4 to 1.15, 1.9, and 1.5 for ET, IP, and RP group, respectively. Median AJBR was reduced from 32, 11, and 4 to 0.95, 0.7, and 1.2 for ET, IP, and RP group, respectively. Median WD was increased from 38.4, 52.9, and 63.6 IU/kg/wk to 84.6, 84.5, and 84.9 IU/kg/wk for ET, IP, and RP group, respectively. Median AFC was increased from 4,141,800, 4,064,000 and 5,129,700 NTD to 7,042,325, 5,835,450, and 5,762,810 NTD for ET, IP, and RP group, respectively. Comparing pre-switch and post-switch outcomes of children and adults who received pre-switch and post-switch prophylaxis, median ABR was reduced from 3 and 5 to 1.35 and 1.85 for children and adults, respectively. Median AJBR was reduced from 3 and 4 to 1.35 and 1.15 for children and adults, respectively. Median WD was increased from 58.8 and 58.3 IU/kg/wk to 87.85 and 83.85 IU/kg/wk for children and adults, respectively. Median AFC was increased from 4,104,225 and 5,879,025 NTD to 4,419,800 and 6,024,916 NTD for children and adults, respectively. For all PwHA, zero ABR accounted for 5.9% (3/51) with pre-switch SHL rFVIII treatment and for 20.8% (10/48) with post-switch rFVIII-Fc prophylaxis. Zero AJBR accounted for 9.8% (5/51) with SHL rFVIII treatment and for 33.3% (16/48) with rFVIII-Fc prophylaxis. For PwHA with pre- and post-switch prophylaxis, zero ABR accounted for 12.5% (1/8) and 8.3% (2/24), respectively, for children and adults on SHL rFVIII prophylaxis and 25% (2/8) and 25% (6/24) respectively, for children and adults on rFVIII-Fc prophylaxis. Zero AJBR accounted for 12.5% (1/8) and 16.7% (4/24), respectively, for children and adults on SHL rFVIII prophylaxis and 25% (2/8) and 37.5% (9/24) respectively, for children and adults on rFVIII-Fc prophylaxis.

Conclusion: In real-world setting, for pre-switch ET group, switch to rFVIII-Fc prophylaxis made both mean ABR and AJBR reduced >95%, and mean WD increased >50%. For pre-switch IP group, switch to rFVIII-Fc prophylaxis made both mean ABR and AJBR reduced >80%, and mean WD increased >35%. For pre-switch RP group, switch to rFVIII-Fc prophylaxis made both mean ABR and AJBR also reduced >45%, and mean WD increased >20%. The proportions in zero ABR and zero AJBR as post-switch rFVIII-Fc prophylaxis were increased. No matter in ET, IP, or RP group, after switching to RP with rFVIII-Fc, improvement for bleeding outcomes was quite evident.