Photo courtesy of Biogen
rFIXFc components
Interim results from the B-YOND trial suggest prophylactic treatment with a recombinant factor IX Fc fusion protein (rFIXFc) can provide long-term safety and efficacy, according to researchers.
B-YOND is an extension study for adults and adolescents who completed the B-LONG study and children who completed the Kids B-LONG study.
In both trials, researchers tested rFIXFc in patients with hemophilia B.
The median duration of rFIXFc treatment has surpassed 3 years for the adults and adolescents enrolled in B-YOND and exceeded 1.5 years for children in this trial.
Researchers said the median annualized bleeding rates (ABRs) have been low in these patients, and none of the patients have developed inhibitors.
“The interim data from B-YOND confirm the safety profile of [rFIXFc] and show that adult, adolescent, and pediatric subjects maintained low annual bleed rates with prophylactic dosing of [rFIXFc] every 1 to 2 weeks,” said principal investigator John Pasi, MD, PhD, of Barts and the London School of Medicine and Dentistry in London, UK.
“These results come from the longest-term study of an extended half-life therapy for hemophilia B and provide physicians across the globe with important insights and information about the treatment of hemophilia B.”
The results were published in Thrombosis and Haemostasis.
The research was sponsored by Bioverativ Therapeutics Inc., the company developing rFIXFc (also known as eftrenonacog alfa and by the brand name Alprolix) in collaboration with Sobi. rFIXFc is approved to treat hemophilia B in the US, European Union, and other countries.
Treatment
B-YOND has enrolled 116 patients with hemophilia B who completed B-LONG (n=93) or Kids B-LONG (n=23). The patients were placed in 1 of 4 treatment groups (but could change at any point):
- Weekly prophylaxis—20 to 100 IU/kg every 7 days (50 adults/adolescents, 19 children)
- Individualized prophylaxis—100 IU/kg every 8 to 16 days (30 adults/adolescents, 5 children)
- Modified prophylaxis, which was defined as further dosing personalization to optimize prophylaxis (13 adults/adolescents, 1 child)
- Episodic treatment, which was available only to adults and adolescents (n=15).
In the weekly prophylaxis group, the median dosing interval was 7.0 days for adults, adolescents, and children. The average weekly prophylactic dose was 49.5 IU/kg in adults/adolescents, 64.4 IU/kg in kids younger than 6, and 63.1 IU/kg in kids ages 6 to 11.
In the individualized prophylaxis group, the median dosing interval was 13.7 days for adults and adolescents and 10.0 days in pediatric patients (ages 6 to 11 only). The average weekly prophylactic dose was 50.2 IU/kg in adults/adolescents, and 66.6 IU/kg in kids ages 6 to 11.
In the modified prophylaxis group, the median dosing interval was 6.9 days for adults and adolescents and 4.1 days in the single pediatric patient (who was older than 6). The average weekly prophylactic dose was 61.7 IU/kg in adults/adolescents and 157.9 IU/kg in the pediatric patient.
From the start of B-LONG to the B-YOND interim data cut, adults/adolescents had a median of 39.5 months of cumulative rFIXFc treatment and a median of 162 cumulative exposure days.
From the start of Kids B-LONG to the data cut, pediatric patients had a median of 21.9 months of cumulative rFIXFc treatment and a median of 94 cumulative exposure days.
ABRs
As of the interim data cut, the overall median ABR was 2.3 for adults/adolescents in both the weekly and individualized prophylaxis groups.
The median ABR was 2.4 for adults/adolescents in the modified prophylaxis group and 11.3 for those receiving on-demand treatment.
Among children under age 6 (n=9), the median ABR in the weekly prophylaxis group was 0. (None of the younger children had individualized or modified prophylaxis.)
For children ages 6 to 11, the median ABR was 2.7 in the weekly prophylaxis group (n=10) and 2.4 in the individualized prophylaxis group (n=5). The patient in the modified prophylaxis group had an ABR of 3.1.
Safety
The researchers said rFIXFc was well-tolerated, and the adverse events (AEs) reported were typical of the population studied.
AEs were reported in 75.9% of patients. The most common were headache (n=14, 12.1%) and common cold (n=13, 11.2%), and the majority of AEs were considered unrelated to rFIXFc.
Three adult/adolescent patients experienced AEs during B-YOND that were considered treatment-related, including noncardiac chest pain, hematuria, and obstructive uropathy. All 3 events resolved.
One patient experienced breath odor during B-LONG that was considered treatment-related. And 1 patient reported decreased appetite during Kids B-LONG that was considered treatment-related. Neither of these events resolved.
There were 39 serious AEs in 23 patients (19.8%). All but 1 of these events were considered unrelated to rFIXFc.
The treatment-related serious AE was renal colic in a patient originally enrolled in the B-LONG study. The patient had a medical history of previous clot colic. The event resolved and did not lead to study discontinuation.
There have been no reports of serious allergic reactions or anaphylaxis associated with rFIXFc, no vascular thrombotic events, and no deaths.
