A Phase IV, Multicenter, Open-Label Study of Emicizumab Prophylaxis in Persons with Hemophilia a with or without FVIII Inhibitors Undergoing Minor Surgical Procedures

Introduction: Emicizumab is a subcutaneously administered, bispecific, humanized monoclonal antibody that bridges factor (F)IXa and FX to restore the function of missing activated FVIII in persons with hemophilia A (PwHA). This study (NCT03361137) was designed to evaluate the safety and efficacy of emicizumab prophylaxis in PwHA with or without FVIII inhibitors undergoing minor surgical procedures without additional prophylaxis with bypassing agents (BPAs; for patients with FVIII inhibitors) or FVIII (for patients without FVIII inhibitors).

Methods: This Phase IV, multicenter, single-arm, open-label study enrolled PwHA of any age, with or without FVIII inhibitors, who were scheduled to undergo minor surgical procedures. Patients were required to have received a minimum of four loading doses of emicizumab (3mg/kg once weekly for 4 weeks) prior to surgical procedure; subsequent maintenance doses of emicizumab were 1.5mg/kg once weekly, 3mg/kg every 2 weeks, or 6mg/kg every 4 weeks. Patients were required to be adherent to emicizumab prophylaxis. Treatment with emicizumab was scheduled to continue for at least 1 month after surgery. No other prophylactic treatment with coagulation factor was permitted. Outcome measures included incidence of excessive bleeding intra-operatively and until discharge from surgery, use of BPAs or FVIII to control bleeding (intra- and post-operatively), incidence of adverse events (AEs), and the percentage of patients with complications requiring hospitalization or return to surgery. Excessive bleeding was defined as a rating of fair to poor on the hemostatic rating scale and translates to an intra- and/or post-operative blood loss of ≥25% over expectation for a patient without hemophilia prior to discharge from surgery. Patients were followed for 28 days following discharge from surgery.

Results: Between June 28, 2018 and March 13, 2020, 14 PwHA undergoing minor surgeries were enrolled (with FVIII inhibitors n=11; without FVIII inhibitors n=3); one PwHA with FVIII inhibitors enrolled but did not have surgery and discontinued prematurely, therefore the surgery analysis population comprised 13 patients (with FVIII inhibitors n=10; without FVIII inhibitors n=3). The majority (78.6%) of those enrolled were <18 years of age and all surgeries were either central venous access device (CVAD) removal (n=11) or dental procedures (n=2; Table 1). Of the 10 patients with FVIII inhibitors, one CVAD removal led to excessive bleeding during surgery with a need for BPA therapy, two patients undergoing CVAD removal received BPA therapy during surgery but had no reported excessive bleeding, three (two CVAD removals, one dental extraction) had post-operative bleeding that required use of a BPA (Table 2). Seven patients with FVIII inhibitors had zero bleeds after discharge from surgery. None of the three PwHA without FVIII inhibitors had excessive bleeding necessitating FVIII treatment during surgery or until discharge; two CVAD removals resulted in zero bleeds post-operatively and one dental extraction led to a post-operative bleed that did not require treatment. No serious AEs, thromboembolic events (TEs), thrombotic microangiopathies (TMAs) or deaths were reported during the study. Overall, 10 AEs occurred in five patients with FVIII inhibitors (headache n=3, limb injury, procedural pain, pyrexia, constipation, device occlusion, adhesiolysis, and hematoma, all n=1); no AEs were reported in patients without FVIII inhibitors. There were no AEs leading to dose modification, interruption or withdrawal of treatment, and no patient in either group had surgical complications requiring hospitalization or a return to surgery. The study was terminated early due to low enrollment and the limited variety of surgery types.

Conclusions: In this study of mostly pediatric PwHA with and without FVIII inhibitors receiving emicizumab prophylaxis, minor surgeries were safely performed. The majority of surgeries were performed without additional prophylactic coagulation factor, however the small sample size should be considered here. There were no serious AEs, TEs, TMAs, or deaths. These findings are consistent with results from previous studies of patients undergoing minor surgery while receiving emicizumab prophylaxis.