Efanesoctocog Alfa Population Pharmacokinetics and Repeated Time‐To‐Event Analysis of Bleeds in Adults, Adolescents, and Children with Severe Hemophilia A

Efanesoctocog alfa is a first-in-class high-sustained factor VIII (HSF) replacement therapy for treatment of hemophilia A. This article presents population pharmacokinetics (PopPK) of efanesoctocog alfa and repeated time-to-event (RTTE) analysis of bleeding episodes in adults/adolescents (≥12 years of age) and children (<12 years). The final PopPK dataset contained pooled data from 277 patients (4405 post-dose factor VIII [FVIII] activity records) from two Phase 1/2a studies (NCT03205163; EudraCT 2018-001535-51), and three Phase 3 studies, XTEND-1 (NCT04161495), XTEND-Kids (NCT04759131), and XTEND-ed (NCT04644575). The PopPK model developed was a linear one-compartment model including body weight effect on clearance and volume of central compartment; Asian race was identified as a statistically significant covariate on clearance. The final PopPK model adequately described the FVIII activity-time profiles in adults, adolescents, and children with once-weekly (QW) efanesoctocog alfa 50 IU/kg, consistent with experience in XTEND-1 and XTEND-Kids. Bleeding episodes in participants in XTEND-1 and XTEND-Kids were characterized by an RTTE model with a Weibull base hazard and effect of FVIII activity modeled by a power effect. The RTTE model showed the probability of being bleed-free in 1 year with efanesoctocog alfa 50 IU/kg QW regimen was >70% across all age groups, consistent with the observed clinical outcomes in the Phase 3 trials of highly effective protection from bleeding episodes in patients with severe hemophilia A, which validates the model's prediction of the long-term bleed hazard.