The treatment of pediatric patients with severe hemophilia A treated with extended half-life recombinant factor VIII (rFVIIIFc) resulted in a lower annualized bleeding rate  (ABR) compared with on-demand therapy and with an incidence of inhibitors within the expected range, according to the results of the phase 3 A-LONG trial published in the journal Blood.

The open-label, phase 3 A-LONG trial randomly assigned pediatric patents younger than 6 years old with previously untreated, severe hemophilia A to receive rFVIIIFc prophylaxis or on-demand therapy. The primary endpoint was inhibitor development and secondary endpoints included ABR, total number of exposure days, and annualized rFVIIIFc consumption.

At baseline, the median age was 7.0, with 78% of patients aged younger than 1 year. There were 76.7% of patines who were White, 1.9% who were Black or African American, 4.9% who were Asian, and 1.9% who were Native Hawaiian or other Pacific Islander. Of these patients, 16.5% were Hispanic or Latino. There were 80% of patients with a high-risk F8 mutation and 19% had a family history of inhibitor development.

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The median exposure days was 91 in the prophylaxis group compared with 4 in the on-demand group. There were 73% of patients who achieved a compliance of 80% or greater for dose and dosing interval. “Overall inhibitor development was within the expected range,” the authors wrote in their report.

The inhibitor incidence was 27.7% among all rFVIIIFc-treated patients. Inhibitor development was similar among patients with at least 10 days of exposure compared with 20 or more or 50 or more exposure days at 31.1%, 31.5%, and 32.6%, respectively. The development of inhibitors occurred within a median of 9 exposure days.

Prophylaxis resulted in an ABR of a median of 1.49 compared with 2.24 in the on-demand group.

The rate of treatment-emergent adverse events (TEAEs) was similar between the groups. Serious TEAEs occurred in 46.9% and 38.2% of patients in the on-demand and prophylaxis arms, respectively. The most common adverse event was inhibitor development. There were no treatment-related deaths.

The authors concluded that “rFVIIIFc was well-tolerated and effective for the control and prevention of bleeds in this pediatric previously untreated patient population.”

Disclosures: This study was supported by Sanofi and Sobi. Please see the original reference for a full list of disclosures.


Königs C, Ozelo MC, Dunn A, et al. First study of extended half-life rFVIIIFc in previously untreated patients with hemophilia A: PUPs A-LONG final results. Blood. 2022;139:3699-3707. doi: 10.1182/blood.2021013563