Safety of Recombinant Activated Factor VII (rFVIIa) in Patients with Congenital Hemophilia with Inhibitors: Overall Dose Exposure and Intervals Following >240 Mcg/Kg Doses Across Trial, Registry and Diary Studies,

Recombinant FVIIa (rFVIIa) is indicated for the treatment of bleeding episodes in hemophilia patients with inhibitors at a dose of 90 mcg/kg every 2–3 hours, or as a single 270 mcg/kg rFVIIa dose (outside US). As patient response and bleeds are variable, treatment is often individualized by the center and by the patient/caregiver administering rFVIIa. With home treatment, it is difficult to ascertain how often patients use higher doses (>90 mcg/kg), and whether these doses are associated with increased risk of thromboembolic events (TEs). The aim of this analysis was to understand the safety of higher rFVIIa doses and the intervals to subsequent doses.

Data for rFVIIa on-demand (OD) bleed treatment in inhibitor patients were obtained from 6 sources: 2 prospective randomized studies; 1 prospective observational US diary study (DOSE); the US-based Hemostasis and Thrombosis Research Society (HTRS) Registry; the international ONE Registry; and the HemoRec registry (Czech data only). Data on prophylactic (PPX) rFVIIa use was obtained from 3 sources: 1 prospective randomized trial; 1 retrospective chart review study (PRO-PACT); and the HemoRec registry (Czech data). Data on intervals between high initial/subsequent doses and any further bypassing agent dose in OD treatment were analyzed from 3 sources that reported time of administration (DOSE, ONE and HemoRec). All studies had data safety monitoring in the form of explicit surveillance, positive affirmations of lack of adverse events, or chart reviews. Overlap in patient participation in studies could not be ruled out; however, all data are believed to be non-overlapping due to study timelines. Demographics, rFVIIa dosing, and frequency of TEs were analyzed and reported using descriptive statistics.

A total of 481 inhibitor patients reported using 61,734 rFVIIa doses either for OD treatment or PPX. Most patients had hemophilia A (87%) and were Caucasian (79%). Age ranged from <1 to 64 years (40% >18y). All data sources included the use of rFVIIa doses higher than current US-recommendations. Overall, 52.2% of doses (45.9% in adults) were >120 mcg/kg, the highest dose referenced from previous clinical trials in the US package insert.

For the152 patients from DOSE, ONE and HemoRec included in the dosing interval analyses, age ranged from <1 to 64 y (45% >18y). Patients received 3,042 rFVIIa doses for 1,017 bleeds. These included 361 initial rFVIIa doses (36%) >240 mcg/kg, including 136 followed by a second dose of bypassing agent (130 with rFVIIa; 15 with pd-aPCC). There were 670 doses >240 mcg/kg used throughout treatments (22%), including 327 followed by a subsequent dose (311 with rFVIIa; 23 with pd-aPCC). Most subsequent doses (79%) occurred after >8 hrs.

A review of 61,734 cumulative rFVIIa doses in studies with explicit safety monitoring demonstrates the use and safety of rFVIIa doses >90 mcg/kg in inhibitor patients. When doses >240 mcg/kg were followed by other bypassing agent doses, the dosing interval was >8 hrs after 79% of doses and >24 hrs after 53% of doses. Unlike MedWatch and passive surveillance where underreporting is common, we expect that the explicit surveillance in these studies would adequately identify TE events. Thus, the lack of TEs supports the overall low TE occurrence (0.28%) reported in the original registration trials in inhibitor patients using ≤90 mcg/kg. These data reinforce that the arterial thrombosis risk identified in meta-analyses outside of licensed indications (critical bleeds) are unique to those populations and do not apply to inhibitor patients. Furthermore, higher doses may provide an opportunity to improve bleed treatment with less frequent injections and decreased follow-up infusions.

Shapiro:Novo Nordisk inc.: Consultancy, Research Funding, Speakers Bureau. Off Label Use: rFVIIa use in indicated population of congential hemophilia with inhibitors at doses that differ from those in the prescribing information. Neufeld:Novo Nordisk Inc.: Consultancy, Research Funding. Blanchette:Novo Nordisk: Consultancy. Chambost:Novo Nordisk: Consultancy. Salaj:Novo Nordisk: Consultancy. Gut:Novo Nordisk Inc.: Employment. Cooper:Novo Nordisk Inc.: Employment.