Emicizumab Use in Infancy: A Survey of United States Pediatric Hemophilia Treatment Center Medical Directors

Introduction: Emicizumab, a bispecific antibody directed against activated factor IX and factor X, is a subcutaneous non-factor prophylactic option for individuals with hemophilia A (HA). The safety and efficacy of emicizumab has been demonstrated in both adult and pediatric patients. It was approved by the United States (U.S.) Food and Drug Administration for routine prophylaxis to prevent or reduce bleeding episodes in individuals with HA, ages newborn and older, both with (2017) and without (2018) factor VIII (FVIII) inhibitors. Despite this approval, data on emicizumab in infants are limited. The HAVEN 2 pediatric clinical trial had only two infants under 24 months of age, though interim analysis of the HAVEN 7 trial demonstrated emicizumab efficacy and safety in infants. Thus, the optimal use of emicizumab in infants under 12 months of age remains unclear. The objective of this study was to understand the rationale and treatment decisions regarding initiation of emicizumab prophylaxis in children under 12 months of age among pediatric Hemophilia Treatment Center (HTC) Medical Directors in the U.S.

Methods: An electronic survey was conducted from April to May 2023 of U.S. HTC Medical Directors via REDCap. Invitations were sent to all individuals listed as HTC Directors at pediatric medical centers on the Center for Disease Control and Prevention database. The survey included two hemophilia patient case scenarios associated with 15 multiple-choice questions and additional free-text options. The first case was of a 9-month-old male with severe HA, without prior bleeding history or exposure to FVIII, who presented for his initial visit to an HTC. The second case was a 3-month-old male with severe HA receiving FVIII replacement therapy for an intracranial hemorrhage. This study was approved by the Baylor College of Medicine Institutional Review Board.

Results: Overall, 33 of 97 (34%) pediatric HTC Medical Directors participated in the survey. One survey was minimally completed and excluded for a total of 32 surveys included in the final analysis. The majority of participants had over 15 years of experience caring for patients with HA (n=21, 65.6%) and represented HTCs with over 250 patients (n=22, 68.8%; Table 1). For previously untreated or minimally treated infants (Case 1), 96.9% of responses (n=31) stated they would consider starting emicizumab prophylaxis; 45.2% (n=14) would consider initiating it as young as 1 week of age. The most common reason cited for starting emicizumab in an infant was to prevent an intracranial hemorrhage (n=17, 53.1%) followed by the desire to avoid central line placement (n=7, 21.9%). The majority of respondents did not wait for a minimum number of factor exposure days prior to starting emicizumab (n=31, 96.9%) nor did they report regularly exposing infants to FVIII concentrate until 50 EDs are reached (n=29, 90.6%). After the initial loading phase, the majority of respondents selected an emicizumab dosing regimen of every 2 weeks (n=19, 59.4%). There was a varied approach to monitoring for inhibitor development after starting emicizumab; 40.6% (n=13) reported monitoring at regular intervals between every 6 to 24 months, whereas 46.8% (n=15) did not report following a set schedule and instead obtain FVIII inhibitor testing only after FVIII exposure (Table 2).

For infants receiving FVIII replacement for treatment of an intracranial hemorrhage (Case 2), 96.9% (n=31) of participants stated they would transition to emicizumab as a prophylactic agent. Over half (n=16, 51.6%) stated they would initiate emicizumab during the treatment period for the hemorrhage rather than waiting until therapy completion. For providers that use emicizumab in moderate hemophilia, emicizumab was reported to be used routinely by 27.3% (n=6) and on a case-by-case basis in 40.9% (n=9, Table 2) in infants with moderate HA.

Conclusion: Pediatric HTC Medical Directors in the U.S. report commonly utilizing emicizumab in infants under 12 months of age despite the lack of robust data in this age group. This practice is consistent with recommendations by the National Hemophilia Foundation's Medical and Scientific Advisory Council. With the completion of clinical trials focused on infants with HA, along with additional long-term outcomes data, more specific guidance around initiation, follow-up and monitoring may be available to inform the optimal management for these patients.