A revised classification of FVIII concentrates: rationale and novel metrics

Factor VIII (FVIII) replacement remains central to the management of hemophilia A. Extended half-life (EHL)-FVIII concentrates, developed through Fc-fusion or PEGylation, extend terminal half-life and overall exposure area under the curve (AUC) by ∼30% compared with standard half-life (SHL) products but remain limited by the von Willebrand factor (VWF)-imposed half-life ceiling. A newly engineered high-sustained-activity/ultralong half-life FVIII (HSA/UL-FVIII) eliminates VWF binding through multiple structural modifications, achieving a fourfold longer half-life, a sixfold greater AUC than SHL-FVIII, and FVIII activity within the nonhemophilia range for several days following once-weekly dosing. Using population pharmacokinetic (PK) modeling, we simulated single-dose and steady-state FVIII activity-time profiles in 1000 virtual patients treated with SHL-, EHL-, or HSA/UL-FVIII. Time spent and area above clinically relevant FVIII thresholds clearly differentiated HSA/UL-FVIII from EHL products. These data support updating FVIII product classification and highlight the value of new PK-based metrics, including time-above-threshold and segmented AUC, in evaluating next-generation FVIII therapies.