Key Points

  • Low ABRs were maintained with long-term emicizumab prophylaxis; bleeding into target joints decreased substantially & no new ones formed.

  • Emicizumab had a favorable long-term safety profile, with no unexpected safety signals, or treatment-related deaths observed.

Prophylaxis with emicizumab-a subcutaneously administered, bispecific, humanized, monoclonal antibody-promotes effective hemostasis in persons with hemophilia A (PwHA). The primary efficacy, safety and pharmacokinetics of emicizumab were reported previously, but long-term data were limited. Here, data from 401 pediatric and adult PwHA with/without factor VIII inhibitors who were enrolled in the Phase III HAVEN 1, HAVEN 2, HAVEN 3, and HAVEN 4 studies have been pooled to establish a long-term efficacy, safety and pharmacokinetic profile. Across a median (interquartile range) efficacy period of 120.4 (89.0-164.4) weeks (data cut-off May 15, 2020), the model-based treated annualized bleed rate (ABR) was 1.4 (95% confidence interval, 1.1-1.7). ABRs declined and then maintained at <1 in an analysis of 24-week treatment intervals; at Weeks 121-144 (n=170) the mean treated ABR was 0.7 (0-5.0). During Weeks 121-144, 82.4% of participants had zero treated bleeds, 97.6% had ≤3 treated bleeds, and 94.1% reported zero treated target joint bleeds. Bleeding into target joints decreased substantially. Emicizumab was well tolerated, and no participants discontinued due to adverse events beyond the five previously described. This data-cut includes the previously reported 3 thrombotic microangiopathies (1 in the PwHA with fatal rectal hemorrhage), and 2 thromboembolic events, all associated with activated prothrombin complex concentrate use; and additionally, a myocardial infarction and a venous device occlusion. With 970.3 patient-years of exposure, emicizumab prophylaxis maintained low bleed rates in PwHA of all ages with/without FVIII inhibitors and remains well tolerated, with no new safety concerns identified. Clinical trials registered as NCT02622321, NCT02795767, NCT02847637, NCT03020160.

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