PO040 | PHARMACODYNAMIC CHARACTERIZATION OF THROMBIN GENERATION IN SEVERE HEMOPHILIA A PATIENTS ON EMICIZUMAB PROPHYLAXIS: A REAL-WORLD LONGITUDINAL STUDY

M. Bergamaschi, A. Pallotta, M. Biglietto, S. Sorella, S. Ligia, E. Baldacci, A. Chistolini, C. Santoro, R. Mormile | Department of translational and precision Medicine, Sapienza, University of Rome, Italy

Background and Aims. Emicizumab, a humanized bispecific antibody mimicking FVIII cofactor activity, has significantly redefined the therapeutic landscape of severe Hemophilia A (HA). However, its constitutive activity leads to profound analytical interference in conventional contact-phase-dependent clotting assays, limiting their clinical utility for monitoring. This study employs the Thrombin Generation Assay (TGA) to investigate global hemostatic remodeling, quantify the restoration of hemostatic potential, and evaluate the correlation between pharmacodynamic parameters and plasma drug concentrations in a real-world setting.
Methods. We studied a cohort of 15 patients with severe HA on Emicizumab, including 4 with high-titer inhibitors. TGA was performed during the loading phase and at steady state using the Calibrated Automated Thrombogram (CAT) on platelet-poor plasma spiked with PPP-Reagent (5 pM TF and 4 µM phospholipids); a dedicated Thrombin Calibrator was used to correct for inner filter effects. Data were compared with: 1) 11 untreated HA patients not receiving Emicizumab and 2) 11 healthy controls. Six kinetic-quantitative parameters (ETP, Peak, Lag Time, ttPeak, Velocity Index, and StartTail) were determined. Statistical analysis included the Wilcoxon signed-rank test for longitudinal comparisons, the Mann-Whitney U-test for independent groups, and Spearman’s rank correlation combined with logarithmic regression to model the dose-response relationship with plasma drug levels (measured via modified one-stage clotting assay).
Results. The analysis demonstrates an immediate restoration of the hemostatic potential. Notably, ETP levels reached after the first loading dose were remarkably similar to those observed at steady state (915.41 vs. 936.23 nM·min, p=0.07), providing a laboratory-based rationale for the early discontinuation of FVIII replacement therapy. At steady state, ETP values were statistically comparable to healthy controls (936.23 vs. 1067.34 nM·min, p=0.33), showing a recovery from the severe baseline defect (613.08 nM·min, p<0.01). No significant differences were found between patients with and without inhibitors (p=0.57). A solid dose-response correlation was confirmed between Emicizumab levels and quantitative parameters: ETP (ρ=+0.205, p=0.025) and Peak (ρ=+0.246, p=0.007). Conversely, the kinetic profile remained altered, showing a significant and dosage-independent prolongation of Lag Time, ttPeak, and StartTail (p<0.02).
Conclusions. Emicizumab prophylaxis induces a stable remodeling of the coagulation profile in severe HA. Quantitative parameters, ETP and Peak, show a significant association with plasma drug concentrations, confirming their utility in evaluating the biological response to treatment. The rapid recovery of ETP after the first dose suggests the clinical feasibility of early FVIII replacement therapy discontinuation. Regarding coagulation kinetics, a unique signature with delayed initiation was observed; however, the clinical significance of this kinetic remodeling warrants further investigation. Overall, Emicizumab effectively bridges the native hemostatic gap, providing immediate and predictable protection, Figure 1 Longitudinal Thrombin Generation curves. Reconstructed median curves. Note the rapid ETP restoration after the 1st dose and the specific steady-state kinetic profile (delayed lag time/lower peak).