Outcomes in participants switching from FVIII replacement therapy to efanesoctocog alfa prophylaxis in XTEND-1: a post hoc analysis

Background: Efanesoctocog alfa is a first-in-class high-sustained factor VIII (FVIII) replacement therapy. In the phase III XTEND-1 (NCT04161495) study, once-weekly efanesoctocog alfa prophylaxis (50 IU/kg) was well-tolerated and achieved high-sustained factor levels in the normal to near-normal range (>40%) for most of the week. Objective: To report outcomes in previously treated participants with severe haemophilia A aged ⩾12 years from an observational study who switched to efanesoctocog alfa prophylaxis during XTEND-1. Design: Paired assessment of participants from an observational study who enrolled in the phase III XTEND-1 study. Methods: Seventy-eight participants switched from marketed standard half-life (SHL) or extended half-life (EHL) FVIII prophylaxis to once-weekly efanesoctocog alfa prophylaxis (50 IU/kg). Endpoints included annualized bleed rates (ABRs), treatment of bleeding episodes, injection frequency and FVIII consumption. Results: Pre-study, 44 (56%) and 34 (44%) participants received SHL FVIII or EHL FVIII prophylaxis, respectively. In the overall population, a significant reduction in ABR from 2.96 to 0.69 (p < 0.0001) was observed following the switch to efanesoctocog alfa prophylaxis as well as reductions in spontaneous, traumatic, joint and spontaneous joint ABRs (p < 0.0001). Significant reductions in mean weekly injection frequency were observed, from 2.8 to 1.0 in the SHL FVIII cohort (p < 0.0001) and from 1.8 to 1.0 in the EHL FVIII cohort (p < 0.0001). Mean annualized factor consumption reduced by 47% in the SHL FVIII cohort and 30% in the EHL FVIII cohort. Conclusion: Collectively, the results of this post hoc analysis demonstrate the benefits of once-weekly efanesoctocog alfa prophylaxis over SHL or EHL FVIII prophylaxis on bleed rates, injection frequency and consumption. Trial registration: Observational study: 242HA201/OBS16221; XTEND-1: NCT04161495 (https://clinicaltrials.gov/study/NCT04161495).