Introduction and Objectives:
In the phase 3 B-LONG and Kids B-LONG studies, subjects with severe hemophilia B receiving rFIXFc prophylaxis had low annualized bleeding rates (ABRs), with decreased weekly factor consumption and fewer infusions compared with pre- study FIX treatment. This report evaluated the effect of rFIXFc on subjects’ physical activity across a variety of age groups using a subject-reported assessment.
Methods:
Eligible subjects for B-LONG (≥12 y) and Kids B-LONG (<12 y) were previously treated males with severe hemophilia B (≤2 IU/dL endogenous FIX activity). Subjects in B- LONG were enrolled into 1 of 4 treatment arms: Arm 1, weekly prophylaxis; Arm 2, individualized interval prophylaxis; Arm 3, episodic treatment; or Arm 4, perioperative management (not included in this analysis). All subjects in Kids B-LONG started on weekly prophylaxis. There were no restrictions regarding physical activity. Physical activity assessments were conducted at Weeks 4, 16, 26, 39, 52, and end of study (B-LONG) and Weeks 3, 12, 24, 36, 50, and end of study (Kids B-LONG). At each visit after their first rFIXFc dose, subjects were asked to rate their activity level relative to their prior study visit as: more (or more intensive), fewer (or less intensive), or about the same amount of physical activities. To summarize each subject’s change in physical activity over the course of the study compared to baseline, subjects’ reports were classified into four groups: less, the same, more, or undetermined.
Results:
Overall, 123 and 30 subjects enrolled in B-LONG and Kids B-LONG, respectively. The majority of subjects in B-LONG reported more or the same amount of physical activity, and few subjects reported less physical activity during the study (less, the same, more, undetermined in Arm 1 [n=60], 7%, 42%, 35%, 17%; Arm 2 [n=25], 16%, 28%, 48%, 8%; Arm 3 [n=27], 15%, 26%, 30%, 30%, respectively). Results were generally similar for subjects in Kids B-LONG (for subjects aged <6 y [n=15], 13%, 27%, 47%, 13%; for subjects aged 6 to <12 y [n=15], 7%, 13%, 67%, 13%).
Conclusions:
ABRs were low in B-LONG and Kids B-LONG despite similar or increased physical activity levels reported by the majority of subjects. These results suggest that people with severe hemophilia B across a variety of age groups may maintain or increase their physical activity levels with rFIXFc, while also reducing infusion frequency and weekly factor consumption, without compromising efficacy.