PB0201 - The first four years of life with severe Hemophilia A: Outcomes using early prophylaxis with factor VIII (FVIII) versus a FVIII mimetic.

Background: Using the factor VIII (FVIII) mimetic, emicizumab, bleeding rates have been dramatically decreased. The optimal age to initiate emicizumab is unknown.

Aims: of this study were to compare outcomes of children treated with early prophylaxis either with factor VIII or emicizumab at age 4 years.

Methods: This study was an analysis of a consented prospective cohort of infants with severe Hemophilia A. Prophylaxis agent and timing of initiation were determined by parents and primary hematologists. Outcomes of initial prophylaxis with FVIII or emicizumab (defined as starting before 5 FVIII exposures) were compared at 48 months. Data included prophylaxis agent, age at initiation, total FVIII exposures, number of total and joint bleeding events, joint function, FVIII inhibitor formation and titer, central line placement and central line complications. Joint function was measured using the hemophilia joint health score (HJHS, higher scores worse). Descriptive data were reported as mean, standard deviation, median and range. Groups were compared with independent samples t-tests and Fisher’s exact tests.

Results: Fifteen babies born between 2012 and 2019 started prophylaxis with FVIII and thirteen babies born between 2017 and 2019 started prophylaxis with emicizumab (results are displayed on Table 1). Emicizumab treated children had fewer FVIII exposures, fewer total and joint bleeding events, lower HJHS scores and fewer inhibitors. Life-threatening bleeding occurred in 3 infants in the FVIII group. Initial emicizumab prophylaxis avoided central lines and central line complications.

Conclusion(s): In young children with severe Hemophilia A outcomes at 48 months were superior in those on emicizumab compared with FVIII prophylaxis. Outcomes determined at the same age, following the same clinic treatment and during comparable eras increase the strength of evidence. Currently we begin emicizumab as early as the first week of life, and as this cohort ages, outcomes of very early prophylaxis using a FVIII mimetic will be assessed.