Background
Phase III RCT, N=109, congenital hemophilia A (any severity) with history of high-titer FVIII inhibitor (≥5 BU/mL), ≥12 y/o, previously on episodic (arms A, B) or prophylactic (arm C) bypassing agents. Emicizumab is a bispecific monoclonal antibody bridging factors IXa and X, mimicking missing FVIIIa; half-life 4-5 wks. It lowers aPTT and falsely elevates one-stage and human-reagent chromogenic FVIII assays; bovine-reagent chromogenic assays required for monitoring.
Interventions and follow up
Arm A: emicizumab 1.5 mg/kg qwk*
Arm B: no emicizumab prophylaxis (episodic bypassing agent)
Arm C: prior bypassing-agent prophylaxis switched to emicizumab 1.5 mg/kg qwk*
Arm D: emicizumab prophylaxis for patients unable to enroll in arms A-C before closure
Primary endpoint: annualized rate of treated bleeding events over ≥24 weeks
*Loading: emicizumab 3.0 mg/kg qwk ×4 in all patients.
Arm B: no emicizumab prophylaxis (episodic bypassing agent)
Arm C: prior bypassing-agent prophylaxis switched to emicizumab 1.5 mg/kg qwk*
Arm D: emicizumab prophylaxis for patients unable to enroll in arms A-C before closure
Primary endpoint: annualized rate of treated bleeding events over ≥24 weeks
*Loading: emicizumab 3.0 mg/kg qwk ×4 in all patients.
Results
Annualized treated bleeding rate (A vs B vs C): 2.9 (1.7-5.0) vs 23.3 (12.3-43.9) vs 5.1 (2.28-11.22)
RR A vs B: 0.13, P<.001 (87% reduction)
Median bleeding events (A vs B vs C): 0.0 (0.0-3.7) vs 18.8 (13.0-35.1) vs 0.0 (0.0-1.7)
Zero bleeds/yr (A vs B vs C): 62.9% vs 5.6% vs 69.4%
Arm C intra-patient (24 pts; emicizumab vs prior bypassing-agent prophylaxis): 3.3 vs 15.7, 79% difference, P<.001
RR A vs B: 0.13, P<.001 (87% reduction)
Median bleeding events (A vs B vs C): 0.0 (0.0-3.7) vs 18.8 (13.0-35.1) vs 0.0 (0.0-1.7)
Zero bleeds/yr (A vs B vs C): 62.9% vs 5.6% vs 69.4%
Arm C intra-patient (24 pts; emicizumab vs prior bypassing-agent prophylaxis): 3.3 vs 15.7, 79% difference, P<.001
Adverse events
Injection-site reactions (A/B/C/D): 23.5% vs 7.7% vs 10.2% vs 14.3%
URI: 20.6% vs 0 vs 4.1% vs 0
Headache: 8.8% vs 7.7% vs 12.2% vs 28.6%
Thrombotic/TMA events: TMA in 1 (arm A) and 1 (arm C); skin necrosis 1 (arm A); superficial thrombophlebitis (arm A); cavernous sinus thrombosis 1 (arm C). All in patients receiving multiple aPCC infusions.
URI: 20.6% vs 0 vs 4.1% vs 0
Headache: 8.8% vs 7.7% vs 12.2% vs 28.6%
Thrombotic/TMA events: TMA in 1 (arm A) and 1 (arm C); skin necrosis 1 (arm A); superficial thrombophlebitis (arm A); cavernous sinus thrombosis 1 (arm C). All in patients receiving multiple aPCC infusions.
Conclusions
Emicizumab prophylaxis reduced bleeding by 87% vs no prophylaxis in inhibitor-positive hemophilia A. Concomitant aPCC drives thrombotic/TMA risk. Cost: 60 mg/0.4 mL vial $7,579.20; ~$345,000-$690,000/yr depending on weight.
Key Limitations
Open-label; small no-prophylaxis comparator (arm B); intra-patient comparison (arm C) non-randomized; thrombotic/TMA signal with concomitant aPCC; high cost; assay interference complicates monitoring.
Clinical Context
First registrational trial leading to FDA approval of emicizumab for hemophilia A with inhibitors (2017). Established subcutaneous prophylaxis as standard for inhibitor patients; protocols now caution against concomitant aPCC use.