Prophylaxis with recombinant factor IX Fc fusion protein reduces the risk of bleeding and delays time to first spontaneous bleed event in previously untreated patients with haemophilia B: A post hoc analysis of the PUPs B-LONG study.

OBJECTIVES: Haemophilia B (HB), characterised by deficient factor IX (FIX), leads to spontaneous bleeds. Severe cases require prophylactic FIX replacement. This post hoc analysis assessed the first spontaneous bleeds among previously untreated patients (PUPs) with HB treated with recombinant FIX Fc fusion protein (rFIXFc) (NCT02234310) to identify factors influencing bleeds. METHODS: Subjects included paediatric PUPs with HB (≤2 IU/dL endogenous FIX). Analyses described treatment patterns (on demand [OD] vs. prophylaxis) and prophylaxis type (started on vs. switched to prophylaxis). Kaplan-Meier analyses assessed the time to first spontaneous bleed, including median time to event and fitting models with predictors for treatment regimen and/or baseline age. RESULTS: PUPs B-LONG enrolled 33 subjects. Baseline age did not influence the time to first spontaneous bleed for any rFIXFc regimen. Those who started on prophylaxis with rFIXFc (n = 11), compared with those treated OD (n = 22), had an extended time to first spontaneous bleed. Starting prophylaxis afforded a 93% reduced risk of first spontaneous bleed versus starting OD (hazard ratio [95% confidence interval]: 0.071 [0.009-0.592]) (p = .015). CONCLUSION: rFIXFc prophylaxis, particularly starting early, reduced the risk of bleeding and delayed time to first spontaneous bleed compared with rFIXFc OD. Hence, initial treatment regimens impact bleed patterns in paediatric PUPs.

Matching-Adjusted Indirect Comparison of Recombinant Factor IX Albumin Fusion Protein Versus Recombinant Factor IX Fc Fusion Protein for Weekly Prophylactic Treatment of Hemophilia B.

INTRODUCTION: Prophylactic treatment of hemophilia B with recombinant factor IX (rFIX) molecules with enhanced pharmacokinetics including rIX-FP (albutrepenonacog alfa; Idelvion©) and rFIXFc (eftrenonacog alfa; Alprolix©) have commonly been used in the clinic. In the absence of head-to-head comparative trials, the aim of this study was to estimate the efficacy of rIX-FP versus rFIXFc using matching-adjusted indirect comparisons (MAICs). METHODS: MAIC analyses leveraged individual patient data from the PROLONG-9FP trial and published summary-level data from the B-LONG trial for subjects who received weekly prophylaxis regimens. Individual patient data were used to assign weights and balance subjects from PROLONG-9FP with subjects from B-LONG on baseline disease severity, age, prior FIX regimen, and body mass index (BMI). Six efficacy outcomes were analyzed including annualized bleeding rate (ABR), annualized spontaneous bleeding rate (AsBR), annualized joint bleeding rate (AjBR), and the proportion of subjects without bleeding events (for total, spontaneous, and joint bleeding events). RESULTS: After adjustment for baseline disease severity, age, prior FIX regimen, and BMI, rIX-FP was associated with a statistically significant decrease in AsBR (rate ratio [RR] 0.42; 95% confidence interval [CI] 0.22, 0.82; P = 0.0107), and the proportion of patients without bleeding events (odds ratio [OR] 3.24; 95% CI 1.41, 7.45; P = 0.0057), spontaneous bleeding events (OR 3.47; 95% CI 1.56, 7.73; P = 0.0023), and joint bleeding events (OR 2.41; 95% CI 1.10, 5.26; P = 0.0274) compared with rFIXFc. Prophylactic treatment with rIX-FP was also associated with a numerically lower ABR (RR 0.75; 95% CI 0.32, 1.75; P = 0.5095) and AjBR (RR 0.82; 95% CI 0.37, 1.82; P = 0.6178). CONCLUSION: The MAICs demonstrated that weekly prophylaxis treatment of severe hemophilia B with rIX-FP resulted in favorable efficacy outcomes as compared to rFIXFc. These findings suggest rIX-FP may offer improved clinical benefits over rFIXFc.

Efficacy of rFIXFc versus N9-GP Prophylaxis in Patients with Hemophilia B: Matching-Adjusted Indirect Comparison of B-LONG and PARADIGM 2 Trials.

Purpose: For patients with hemophilia B, extended half-life factor IX (FIX) products are available for prophylaxis and for treating bleeds. Different methods are used to extend the half-lives of recombinant FIX Fc fusion protein (rFIXFc) and nonacog beta pegol (N9-GP). This affects their biodistribution and plasma FIX levels, although differences do not always correlate with clinical outcomes. A matching-adjusted indirect comparison (MAIC) of prophylaxis with rFIXFc and N9-GP was performed, based on licensed dosing in the European Union. Patients and Methods: Combined rFIXFc data from the weekly and individualized interval prophylaxis arms of the B-LONG clinical trial, and N9-GP data from the 40 IU/kg once-weekly prophylaxis arm of PARADIGM 2 were used in a MAIC. Individual patient data for rFIXFc (n=87) were matched to aggregated data for N9-GP (n=29). Estimated annualized bleeding rates (ABRs) for rFIXFc were recalculated using a Poisson regression model with adjustment for over-dispersion, and compared with ABRs reported for N9-GP, using incidence rate ratios (IRRs) with 95% confidence interval (CI). Results: There was no evidence of significant differences in estimated ABRs between prophylaxis with rFIXFc and N9-GP. Analysis of pooled rFIXFc weekly and interval-adjusted dosing compared with N9-GP 40 IU/kg once weekly produced estimated ABRs of 2.59 versus 2.51 (IRR 1.03; 95% CI 0.56-1.89), as well as 1.34 versus 1.22 (IRR 1.10; 95% CI 0.42-2.91) and 1.13 versus 1.29 (IRR 0.88; 95% CI 0.47-1.63) for overall, spontaneous, and traumatic bleeding events, respectively. Conclusion: The study did not reveal any significant differences in the efficacy of rFIXFc and N9-GP prophylaxis. Given differences in trough levels (rFIXFc dosing was targeted to achieve a trough 1-3 IU/dL above baseline versus a reported estimated N9-GP mean trough of 27.3 IU/dL), interpreting plasma FIX levels as potential surrogate efficacy markers requires consideration of compound-specific pharmacokinetic profiles.

Real-World Effectiveness of rFIXFc Prophylaxis in Patients with Haemophilia B Switched from Standard Half-Life Therapy in Three European Countries.

INTRODUCTION: The current study describes real-world clinical outcomes and factor usage among patients with haemophilia B switching from standard half-life factor IX (SHL FIX) treatment to recombinant factor IX Fc fusion protein (rFIXFc) prophylaxis in European treatment centres. METHODS: This non-interventional, retrospective, multicentre chart review evaluated medical records from adult and paediatric patients with haemophilia B in Denmark, Germany and the UK. Patients had documented SHL FIX treatment, on-demand or prophylaxis, for ≥ 6 months before starting rFIXFc prophylaxis, and subsequent data for ≥ 6 months afterwards (up to 24 months). Primary endpoints included annualised bleeding rates (ABRs), prophylactic factor consumption and injection frequency. RESULTS: Data from 30 patients (24/30 [80.0%] with severe disease) showed overall mean (standard deviation, SD) ABRs of 4.7 (6.3) on SHL FIX treatment and 1.7 (2.3) after switching to rFIXFc prophylaxis. The reduction in mean (SD) ABRs was greater when switching from SHL FIX on-demand treatment (n = 6), with a decrease from 10.5 (9.9) to 2.6 (4.5), than when switching from SHL FIX prophylaxis (n = 24), with a decrease from 3.3 (4.3) to 1.5 (1.4). Among prior SHL FIX prophylaxis patients, switching to rFIXFc prophylaxis increased the proportion of those with zero bleeds from 21.7% to 45.8% during the 6 months before and after switching, respectively. In the total population, five of six target joints (83.3%) present when patients started rFIXFc prophylaxis subsequently resolved. In patients switching from SHL FIX prophylaxis to rFIXFc prophylaxis, mean (SD) weekly injection frequency was reduced by 1.0 (0.7) and mean (SD) factor consumption was reduced by 27.7 (49.6) IU/kg/week. CONCLUSION: This study demonstrates the effectiveness of rFIXFc prophylaxis in real-world clinical practice. Improvements in both clinical effectiveness and factor usage associated with rFIXFc prophylaxis may potentially reduce patient burden and improve quality of life.

Cost-effectiveness analysis of recombinant factor IX Fc fusion protein compared with recombinant factor IX for the treatment of moderate-severe to severe hemophilia B in China.

OBJECTIVE: To evaluate the lifetime cost-effectiveness of recombinant factor IX Fc fusion protein (rFIXFc) and recombinant factor IX (rFIX) for the treatment of hemophilia B (HB) in China. METHODS: We developed a decision-analytic Markov model including three health states: alive, requiring surgery, and dead. This model estimated the lifetime cost and quality-adjusted life-years (QALYs) of prophylaxis in childhood, followed by on-demand treatment in adulthood for moderate-severe to severe HB patients from China's healthcare system perspective. Efficacy data derived from pivotal clinical trials, clinical guideline recommendations, and expert consultation were applied to two scenarios (full dose and low dose). One-way sensitivity analysis and probabilistic sensitivity analysis (PSA) were performed to assess the robustness of the model. OUTCOMES: Lifetime cost, QALYs, and the incremental cost-effectiveness ratio were calculated, and the results were compared with willingness-to-pay (WTP) thresholds of one to three times the gross domestic product per capita of China in 2021 ($12,551-$37,653). RESULTS: RFIXFc was associated with lower cost and more QALYs than rFIX in both scenarios, which suggested that it is a dominant strategy (more effective and cheaper) for moderate-severe to severe HB in China. In the full-dose scenario, rFIXFc saved more money and yielded more QALYs than in the low-dose scenario (low doses are the typical clinical reality in China). PSA demonstrated that rFIXFc had an over 90% probability of being cost-effective with full-dose and low-dose treatment at WTP thresholds of $12,551-$37,653. CONCLUSIONS: Compared with rFIX, rFIXFc appears to be a cost-effective option for the lifetime management of moderate-severe to severe HB patients in China.

Managing surgery in hemophilia with recombinant factor VIII Fc and factor IX Fc: Data on safety and effectiveness from phase 3 pivotal studies.

Background: Surgical procedures impose hemostatic risk to people with hemophilia, which may be minimized by optimal factor (F) replacement therapy. Methods: This analysis evaluates the efficacy and safety of extended half-life factor replacement recombinant FVIII and FIX Fc fusion proteins (rFVIIIFc and rFIXFc) during surgery in phase 3 pivotal (A-LONG/Kids A-LONG and B-LONG/Kids B-LONG) and extension (ASPIRE and B-YOND) studies. Dosing regimens were determined by investigators. Injection frequency, dosing, blood loss, transfusions, and hemostatic response were assessed. Results: Forty-five major (n = 31 subjects) and 90 minor (n = 70 subjects) procedures were performed in hemophilia A; 35 major (n = 22) and 62 minor (n = 37) procedures were performed in hemophilia B. Unilateral knee arthroplasty was the most common major orthopedic procedure (hemophilia A: n = 15/34; hemophilia B: n = 8/24). On the day of surgery, median total dose in adults/adolescents was 81 IU/kg for rFVIIIFc and 144 IU/kg for rFIXFc; most major procedures required ≤2 injections (including loading dose). Through days 1-14, most major procedures had ≤1 injection/day. Hemostasis was rated excellent (rFVIIIFc: n = 39/42; rFIXFc: n = 29/33) or good (n = 3/42; n = 4/33) in evaluable major surgeries, with blood loss comparable with subjects without hemophilia. Most minor procedures in adults/adolescents required one injection on the day of surgery, including median loading dose of 51 IU/kg (rFVIIIFc) and 80 IU/kg (rFIXFc). No major treatment-related safety concerns were identified. No subjects developed inhibitors or serious vascular thromboembolic events. Conclusions: rFVIIIFc and rFIXFc were efficacious and well tolerated for the management of perioperative hemostasis across a wide spectrum of major and minor surgeries in hemophilia.

Surgical outcomes in patients with haemophilia A or B receiving extended half-life recombinant factor VIII and IX Fc fusion proteins: Real-world experience in the Nordic countries.

INTRODUCTION: Perioperative dosing recommendations vary across Nordic haemophilia treatment centres (HTCs) for extended half-life (EHL) factor concentrates in haemophilia A/B (HA/HB) patients. AIM: To summarise Nordic real-world surgical experiences with EHL recombinant factor VIII/IX Fc (rFVIIIFc/rFIXFc) fusion proteins using retrospective data from clinical records at four HTCs in Finland, Sweden and Norway. METHODS: Factor dosing and surgical outcomes were recorded from HA/HB patients who underwent surgery and were treated with rFVIIIFc/rFIXFc. Perioperative factor dosing regimens were clinician-determined based on local practises. RESULTS: Twenty five surgeries were performed on 20 patients, all covered by bolus injections except one minor HA surgery; eight minor surgeries were in paediatric patients. Median preoperative rFVIIIFc dose for major HA surgeries (n = 8) was 48 IU/kg (range: 35-57), with total consumption up to Day 14 of 427 IU/kg (196-568). For the two major HB surgeries (in one patient), preoperative rFIXFc doses were 50 IU/kg and 20 IU/kg; total consumption up to Day 14 was 130 IU/kg and 40 IU/kg. Median preoperative rFVIIIFc/rFIXFc bolus doses for minor HA (n = 10) and HB (n = 4) surgeries were 50 IU/kg (24-79) and 47 IU/kg (40-71), with total consumption up to Day 5 of 138 IU/kg (49-404) and 100 IU/kg (43-125), respectively. Intraoperative and postoperative haemostatic responses were rated as at least good/excellent for 24/25 surgeries, with bleeding episodes reported in only three surgeries. CONCLUSION: Nordic real-world experiences suggest that EHL products can be used safely and effectively for peri-operative haemostasis. Further research is required to develop local dosing guidelines for optimised treatment schedules.

Apixaban and eftrenonacog alfa treatment in a patient with moderate hemophilia B and cardiovascular disease.

In developed countries, the life expectancy of patients with hemophilia (PwH) is now close to that of the unaffected male population. This means that these patients are at risk of developing age-related comorbidities, including cardiovascular disease. Managing cardiovascular disease in PwH patients can be particularly challenging, due to their high bleeding risk. To our knowledge, this is the first report of a male patient with moderate hemophilia B and hypertensive ischemic heart disease complicated by arrhythmia due to nonvalvular atrial fibrillation, who was treated with apixaban and left atrial appendage closure while receiving concomitant anti-hemorrhagic prophylaxis with eftrenonacog alfa.

Efficacy of rFIXFc versus rIX-FP for the Treatment of Patients with Hemophilia B: Matching-Adjusted Indirect Comparison of B-LONG and PROLONG-9FP Trials.

PURPOSE: In patients with hemophilia B, treatment with extended half-life (EHL) recombinant factor IX allows for longer dosing intervals while providing equal or superior bleeding protection compared with standard half-life products. This enables flexible, individualized treatment schedules, which reduce the burden of prophylaxis and improve patient outcomes. This analysis compared the efficacy of recombinant factor IX Fc fusion protein (rFIXFc) and recombinant factor IX albumin fusion protein (rIX-FP), two EHL therapies approved for prophylaxis and treatment of bleeding in hemophilia B. PATIENTS AND METHODS: Matching-adjusted indirect treatment comparison (MAIC) was used to adjust the between-treatment differences in baseline characteristics. Individual patient data for rFIXFc (B-LONG) were matched to aggregated data for rIX-FP (PROLONG-9FP) followed by statistical comparison for estimated annualized bleeding rate (ABR) using a Poisson regression model with adjustment for over dispersion. Data were analyzed according to treatment regimen prior to study entry: prior prophylaxis (rFIXFc, n=48; rIX-FP, n=40) or prior episodic treatment (n=43 and n=19, respectively). Relative treatment effects are presented as incidence rate ratios (IRR) with 95% confidence intervals (CI). RESULTS: After adjustment for baseline characteristics, estimated ABR observed for rFIXFc and rIX-FP was not significantly different in patients on prior prophylaxis (1.87 versus 1.58; IRR 1.18, 95% CI 0.67-2.10) or prior episodic (2.25 versus 2.22; IRR 1.01 95% CI 0.40-2.57) regimens. CONCLUSION: This MAIC analysis shows that the estimated ABR for rFIXFc-treated patients from B-LONG was similar to that of rIX-FP-treated patients from PROLONG-9FP and, therefore, indicates that the two EHL therapies provide similar efficacy when used as prophylaxis for patients with hemophilia B. Trough levels differ between the two products (1-3% [targeted] versus 20% [observed], respectively), suggesting that trough level is not a surrogate indicator when ABR is used as a criterion for clinical efficacy when comparing these FIX products in hemophilia B.

Real-world assay variability between laboratories in monitoring of recombinant factor IX Fc fusion protein activity in plasma samples.

INTRODUCTION: Monitoring of factor IX (FIX) replacement therapy in haemophilia B relies on accurate coagulation assays. However, considerable interlaboratory variability has been reported for one-stage clotting (OSC) assays. This study aimed to evaluate the real-world, interlaboratory variability of routine FIX activity assays used in clinical haemostasis laboratories for the measurement of recombinant FIX Fc fusion protein (rFIXFc) activity. METHODS: Human FIX-depleted plasma was spiked with rFIXFc at 0.80, 0.20 or 0.05 IU/mL based on label potency. Participating laboratories tested samples using their own routine OSC or chromogenic substrate (CS) assay protocols, reagents and FIX plasma standards. Laboratories could perform more than one measurement and method, and were not fully blinded to nominal activity values. RESULTS: A total of 142 laboratories contributed OSC results from 175 sample kits using 11 different activated partial thromboplastin time (aPTT) reagents. The median recovered FIX activity for the 0.80, 0.20 and 0.05 IU/mL samples was 0.72 IU/mL, 0.21 IU/mL and 0.060 IU/mL, respectively. Across all OSC reagents, interlaboratory variability (% CV) per aPTT reagent ranged from 9.4% to 32.1%, 8.2% to 32.6% and 12.2% to 42.0% at the 0.80, 0.20 and 0.05 IU/mL levels, respectively. CS results showed excellent median recoveries at all nominal levels (87.5% to 115.0%; n = 11) with low interlaboratory variability (CV 3.6% to 15.4%). CONCLUSION: This large, real-world data set indicates that rFIXFc activity in plasma samples can be accurately measured with the majority of routine OSC and CS assay methods. Given the variation in FIX assay procedures between sites, it is important that individual laboratories qualify their in-house methods for monitoring of rFIXFc activity.