Objectives:
Emicizumab, a novel bispecific humanized monoclonal antibody promotes coagulation by bridging FIXa and FX to replace the function of missing activated FVIII, and has potential to address unmet medical needs in pediatric persons with hemophilia A (PwHA) with inhibitors. This study assessed efficacy, safety and pharmacokinetics of once-weekly subcutaneous emicizumab prophylaxis in pediatric PwHA with inhibitors.
Methods:
The study (NCT02795767) enrolled PwHA with inhibitors aged <12 years (or 12–17 years if <40 kg) previously treated with bypassing agents to receive emicizumab prophylaxis for ≥52 weeks. Emicizumab was administered subcutaneously at 3 mg/kg/week for 4 weeks, followed by 1.5 mg/kg/week thereafter. Efficacy objectives included bleed rate, and comparison of the bleed rate on emicizumab prophylaxis vs historical bleed rate obtained from a prospective, non-interventional study (NIS; NCT02476942). The NIS collected detailed, high-quality real- world data on bleeds and safety outcomes from a cohort of pediatric PwHA with inhibitors treated according to local, routine clinical practice. Participants from the NIS could subsequently enter the HAVEN 2 study, which permitted intra-individual comparisons.
Summary:
This interim analysis included 20 PwHA with inhibitors aged 3–12 years (median 8.5); 19 aged <12 years were included in the efficacy analyses. The median observation time was 12.1 weeks (range 7–14). In total, 18/19 (94.7%) participants had zero treated bleeds and 12/19 (63.2%) did not bleed while on study. Overall, 14 bleeds were reported in 7 participants, with none occurring in a joint or muscle. No participants have required up- titration of emicizumab. A substantial reduction in ABR on study vs ABR on prior treatment with bypassing agents (non-interventional study) was observed in 8 participants included in the intra-individual comparison; all 8 participants reported zero bleeds with emicizumab prophylaxis (efficacy period 85–99 days). Emicizumab was well tolerated; most common AEs were mild injection-site reactions (15%) and nasopharyngitis (15%). Three unrelated serious AEs were observed (mouth hemorrhage, appendicitis, catheter site infection). No thromboembolic or thrombotic microangiopathy events were reported. No anti-drug antibodies were detected. Mean trough emicizumab concentrations of >50 μg/mL were achieved after 4 loading doses of 3 mg/kg/week and sustained with maintenance doses of 1.5 mg/kg/week, and were consistent across age groups and body weight.
Conclusion:
Emicizumab prophylaxis was well tolerated and prevented/reduced bleeds in pediatric PwHA with inhibitors. Clinically meaningful reductions in ABR were observed compared with ABR on prior treatment with bypassing agents. The pharmacokinetic profile of emicizumab was similar to that seen in adolescent/adult PwHA with inhibitors. These interim data show the potential for emicizumab to reduce the disease and treatment burden for pediatric PwHA with inhibitors.