Association Of Bleeding Tendency With Time Under Target FIX Activity Levels In Severe Hemophilia B Patients Treated With Recombinant Factor IX Fc Fusion Protein

Introduction The goal of prophylactic treatment with coagulation factor replacement in hemophilia patients has been to convert severe hemophilia, defined as Methods A 3-compartmental population PK model of rFIXFc was developed based on activity-time profiles in 12 subjects from a Phase 1/2a study and 123 subjects (>12 years) from B-LONG, collected over ≤ 52 weeks of treatment (Diao L, EAHAD 2013). Individual post-hoc PK parameters were then derived to construct continuous FIX activity-time profiles for each dose administered over the course of the study for all subjects in B-LONG. The cumulative time under target 1%, 3%, and 5% FIX level for each individual on study was calculated and normalized to obtain annualized time under the respective target FIX level. Negative binomial regression models were used to evaluate associations between the number of bleeding events (overall, spontaneous, traumatic, and joint) and annualized time (days) under 1%, 3%, and 5% of FIX activity for all subjects in B-LONG. Models were adjusted for age, body mass index, baseline HIV and HCV status, FIX genotype, number of bleeding episodes in the 12 months prior to study entry, and each subject9s time on study. Results The multivariable negative binomial regression analysis estimated that overall bleeding events increased with increased time spent under 1% of FIX activity (p Conclusions This is the first study to demonstrate a correlation between increased time spent under a target therapeutic FIX activity level (1%, 3% or 5%) and increased bleeding tendency, as well as a reduced probability of being bleed-free in patients treated with rFIXFc, suggesting that rFIXFc can provide protection from bleeding in a manner similar to endogenous FIX. These findings also confirm the importance of a minimum therapeutic threshold of 1% and provide additional support for establishing effective rFIXFc prophylaxis using population PK simulation. Disclosures: Shapiro: Baxter: Consultancy, Global steering committees Other, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novo Nordisk: Consultancy, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Global steering committees, Global steering committees Other, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Inspiration: Consultancy, Membership on an entity’s Board of Directors or advisory committees, Research Funding; CSL Behring: Research Funding; Biogen Idec: Research Funding. Potts: Biogen Idec: Employment. Li: Biogen Idec: Employment. Valentino: Baxter Healthcare: Consultancy; Bayer: Consultancy; Biogen Idec: Consultancy; GTC Biotherapeutics: Consultancy; Inspiration Biopharmaceuticals: Consultancy; Novo Nordisk: Consultancy. Diao: Biogen Idec: Employment, Equity Ownership. Wang: Biogen Idec: Employment. Robinson: Biogen Idec: Employment. Pierce: Biogen Idec: Employment, Equity Ownership. Jiang: Biogen Idec: Employment; Biogen Idec: Equity Ownership.