Prevalence of factor IX inhibitors among patients with haemophilia B: results of a large-scale North American survey

Plasma-derived factor VIIa and factor X mixture agent (MC710) prophylaxis in haemophilia B patients with inhibitors

INTRODUCTION

Haemophilia B patients with factor IX inhibitors have particularly unmet needs for conventional therapy.

AIM

Phase II/III clinical trial, multicentre, open-label, prospective, self-controlled study was conducted to assess MC710 prophylaxis in haemophilia B patients with inhibitors.

METHODS

We enrolled haemophilia patients who had received episodic or prophylactic treatment with bypassing agents up to that time. The participants continued their conventional therapy for 24 weeks and then MC710 was prophylactically infused intravenously every 2 or 3 days at 60 to 120 μg as FVIIa per kilogram of body weight for 24 weeks. The primary endpoint was the annual bleeding rate (ABR) requiring bypassing agents, which was compared intraindividually between the conventional therapy period and the MC710 prophylaxis period.

RESULTS

A total of 11 male haemophilia B patients were enrolled. The median ABR ratio for each participant (the prophylaxis period ABR divided by the conventional therapy period ABR) was .33 (2.1/6.5), range from .00 to 3.77. ABR ratios for 9 of the 11 patients ranged from .00 to .60, and 3 of the 9 patients had zero bleeding events during the prophylaxis period. Meanwhile, ABR ratios for the remaining two patients were 2.53 and 3.77, respectively. Although a fibrinogen decrease recovered by the dose reduction was reported for only one participant as the sole adverse drug reaction in this study, no thrombotic events or other safety concerns were reported.

CONCLUSION

MC710 prophylaxis is considered to be decrease the bleeding rate in haemophilia B patients with inhibitors without safety concerns.

Factor IX inhibitors in haemophilia B: A report of National Haemophilia Registry in China

INTRODUCTION

The development of inhibitors against factor FIX (FIX) is the most serious complication of FIX replacement therapy in haemophilia B (HB) patients. Currently, only few cohorts of HB inhibitor patients have been reported worldwide.

AIM

This Chinese nationwide study of HB inhibitor patients explored their risk factors for FIX inhibitor development and experience on their management.

METHODS

We retrospectively analysed patient characteristics, F9 genotypes, treatment strategies and outcomes of HB inhibitor patients registered to the Chinese National Registry and Patient Organization Registry.

RESULTS

Forty-four unique HB inhibitor patients were identified in 4485 unique HB patients registered by year 2021 to the two Registries. Inhibitor diagnosis were usually delayed and the low prevalence (.98%) may suggest some inhibitor patients were not identified. Their median age at inhibitor diagnosis was 7.5 (IQR, 3.0-14.8) years. Most patients (95.5%) had high-titre inhibitors. Allergic/Anaphylactic reactions occurred in 59.1% patients. Large deletions and nonsense mutations were the most common F9 mutation types in our FIX inhibitor patients. Patients with large F9 gene deletions were more likely to develop inhibitors (p = .0002), while those with missense mutations had a low risk (p < .0001). Thirteen (29.5%) patients received immune tolerance induction (ITI) therapy using low-dose prothrombin complex concentrate regimens. Twelve completed ITI with three (25.0%) achieving success. Nephrotic syndrome developed in two (16.7%) patients during ITI.

CONCLUSION

This study reports the largest Chinese cohort of HB inhibitor patients. Large deletions were most significantly associated with inhibitor development. Low-dose ITI might be feasible for FIX inhibitor eradication.

Blood pressure in persons with haemophilia with a focus on haemophilia-specific risk factors

INTRODUCTION

Persons with haemophilia (PWH) have a higher prevalence of hypertension compared to the general population, which cannot be explained entirely by the usual cardiovascular risk factors. Neutralizing antibodies (inhibitors) against clotting factors might have some relation to cardiovascular disease in PWH. However, whether inhibitors facilitate hypertension is unknown.

AIM

We investigated the relationship between hypertension/blood pressure and inhibitors in PWH. Additional goals were to determine the relationships with haemophilia type, race, and viral status.

METHODS

Records were extracted retrospectively for PWH (age ≥18 years) between 2003 and 2014 from four Hemophilia Treatment Centers in North America and included demographics, weight, height, haemophilia type/severity, HCV and HIV infection status, hypertension, use of anti-hypertensive medications, and inhibitor status. We fitted semiparametric generalized additive models (GAMs) to describe adjusted curves of blood pressure (BP) against age.

RESULTS

Among 691 PWH, 534 had haemophilia A and 157 had haemophilia B, with a median age of 39 years (range 18 to 79). Forty-four PWH (6.5%) had a history of inhibitors, without evidence for a higher prevalence of hypertension or higher BP. A higher prevalence of hypertension and higher BP were noted for haemophilia A (vs. haemophilia B), coinfection with HCV/HIV (vs. uninfected), or moderate haemophilia (vs. severe haemophilia).

CONCLUSION

While there was no signal to suggest that a history of inhibitors is associated with hypertension, differences based on haemophilia type, severity, and viral infection status were identified, encouraging prospective investigations to better delineate haemophilia-specific risk factors for hypertension.

Eradication of FIX inhibitor in haemophilia B children using low-dose immune tolerance induction with rituximab-based immunosuppressive agent(s) in China

INTRODUCTION

Development of haemophilia B inhibitors (HBI) results in the ineffectiveness of FIX replacement therapy. Inhibitor eradication by immune tolerance induction (ITI) is therefore necessary. In HBI, ITI even at high FIX dose is less effective and has a higher risk of severe complications.

AIM

To characterize clinical features and outcome of ITI on HBI.

METHODS

This retrospective study was conducted in Haemophilia Paediatric Comprehensive Care Centre of China. We used low-dose ITI (25-50 FIX IU/kg/three-times-weekly to every-other-day) with domestic prothrombin complex concentrate (PCC), combined with two successive immunosuppressive (IS) regimens.

RESULTS

Sixteen HBI children, representing 5.7% of all and 14.4% of our severe registered HB patients, were enroled. Seven cases reported allergic reactions (ARs) proximal to inhibitor development. The historic peak inhibitor titre was median 54.2 (range 4.7-512) BU, and 15 (93.8%) had high-titre inhibitors. Twelve patients adherent to ITI were analysable. Of the nine ITI patients who received rituximab/prednisone (IS Regimen-1), four achieved tolerization in 1.4-43.3 months. Two subsequently relapsed but re-tolerized after a second course of IS Regimen-1. During ITI, the median treated bleed was .39/month (82.7% reduction from before ITI), and the incidence of AR and nephrotic syndrome (NS) complications was each at 22% (2/9). Three ITI patients received modified 'Beutel' protocol (IS Regimen-2) using multiple-IS-drugs, and two had rapid tolerization (.8 and 1.8 months).

CONCLUSIONS

Inhibitor eradication could be achieved by low-dose ITI protocol using PCC combined with IS. Larger studies are needed to confirm if ITI with IS Regimen-2 is more effective with less complications.

First open-label, single-arm, prospective study of real-world use of FIX replacement therapy in a predominantly pediatric hemophilia B population in China

BACKGROUND

Nonacog alfa (recombinant factor IX [FIX]) is approved in China for the control and prevention of bleeding events in patients with hemophilia B. This was the first study to assess prophylaxis and on-demand therapy with recombinant FIX replacement in a real-world setting in China. This study aimed to evaluate the safety and efficacy of nonacog alfa in Chinese patients with hemophilia B.

METHODS

In this open-label, multicenter study (clinicaltrials.gov identifier NCT02336178), patients received on-demand or prophylactic treatment with intravenous nonacog alfa for approximately 6 months or 50 exposure days, whichever occurred first. The primary safety outcome was medically important events (i.e., development of FIX inhibitors, allergic reactions, and thrombotic events). Key secondary efficacy outcomes included the annualized bleeding rate for on-demand treatment and prophylaxis, response to on-demand treatment, the number of infusions per bleeding event, and the number of breakthrough bleeding events within 48 hours of prophylaxis.

RESULTS

Seventy male patients (mean [standard deviation] age 7.8 [7.2] years) were enrolled (on-demand, n = 37; prophylaxis, n = 57 [24 patients were included in both groups]). Thirty-eight (54%) patients had up to 50 FIX exposure days before the study. The only medically important event was a transient low-titer FIX inhibitor (incidence 1.4%, 95% confidence interval, 0-7.7). The mean annualized bleeding rate was 26.3 for on-demand treatment and 6.5 for prophylaxis. A mean (standard deviation) of 1.5 (1.7) nonacog alfa infusions were given per bleeding episode; 78.8% of episodes resolved with 1 infusion. Response was "excellent" or "good" for 88% of the on-demand infusions. Twenty-three bleeding events (n = 11 patients) occurred within 48 hours of 2032 prophylaxis doses (1.13%).

CONCLUSION

In the real-world setting, nonacog alfa is safe and effective for on-demand treatment and for prophylaxis for patients with hemophilia B in China.

Treatment outcomes in persons with severe haemophilia B in the Nordic region: The B-NORD study

INTRODUCTION

Data on outcome in persons with haemophilia B (PwHB) are limited and mainly extrapolated from studies of haemophilia A (HA).

AIM

To characterize treatment outcomes in persons with severe HB in the Nordic region, with a focus on joint health, compared with matched controls with HA.

METHODS

PwHB attending haemophilia centres in Denmark, Finland, Norway and Sweden were enrolled and matched with controls with HA. Joint assessment using Haemophilia Joint Health Score (HJHS) and ultrasound according to Haemophilia Early Arthropathy Detection protocol (HEAD-US) was conducted. Adherence was evaluated using the Validated Haemophilia Regimen Treatment Adherence Scale (VERITAS).

RESULTS

Seventy-nine males with HB, with median age of 30 years (range 1-75), were enrolled. Eleven patients (14%) had a history of or current inhibitor. Twenty-nine PwHB (37%) reported joint bleeds during the prior year, and 35% had previously undergone joint surgery. Ninety-five per cent were on prophylaxis, and 70% used recombinant concentrates, with a median factor consumption of 3,900 IU/kg/year for standard half-life products. Only two patients had a VERITAS score corresponding to 'non-adherence'. Joint health, assessed with HJHS, showed a significant lower score among PwHB compared with HA controls, explained by a difference in the 18-49 age group, without observed differences in older or younger subgroups. The HEAD-US scores were overall low.

CONCLUSION

The Nordic cohort of PwHB is well treated by prophylaxis, but the goal of zero bleeds for all is not reached. Our findings suggest that patients with severe HB suffer from a milder arthropathy than patients with severe HA.

Inhibitor incidence in an unselected cohort of previously untreated patients with severe haemophilia B: a PedNet study

The incidence of factor IX (FIX) inhibitors in severe hemophilia B (SHB) is not well defined. Frequencies of 3-5% have been reported but most studies to date have been small, including patients with different severities, and without prospective follow up for inhibitor incidence. The study objective was to investigate the inhibitor incidence in patients with SHB followed up for to 500 exposure days (ED), the frequency of allergic reactions, and the relationship with genotypes. Consecutive previously untreated patients (PUP) with SHB enrolled into the PedNet cohort were included. Detailed data was collected for the first 50 ED, followed by the annual collection of the inhibitor status and allergic re-actions. The presence of inhibitors was defined by at least two consecutive positive samples. Additionally, data on FIX gene mutation was collected. One hundred and fifty-four PUP with SHB were included; 75% were followed up until 75 ED, and 43% until 500 ED. Inhibitors developed in 14 patients (seven high-titer). The median number of ED at inhibitor manifestation was 11 (interquartile range [IQR]: 6.5-36.5). The cumulative inhibitor incidence was 9.3% (95% Confidence Interval [CI]: 4.4-14.1) at 75 ED, and 10.2% (95% CI: 5.1-15.3) at 500 ED. Allergic reactions occurred in four (28.6%) inhibitor patients. Missense mutations were most frequent (46.8%) overall but not associated with inhibitors. Nonsense mutations and deletions with large structural changes comprised all mutations among inhibitor patients and were associated with an inhibitor risk of 26.9% and 33.3%, respectively. In an unselected, well-defined cohort of PUP with SHB, the cumulative inhibitor incidence was 10.2% at 500 ED. Nonsense mutations and large deletions were strongly associated with the risk of inhibitor development. The ‘PedNet Registry’ is registered at clinicaltrials.gov; identifier: NCT02979119.

Safety and effectiveness of Rixubis in patients with hemophilia B: a real-world, prospective, postmarketing surveillance study in South Korea

Background

Rixubis (recombinant factor IX, nonacog gamma) is indicated for the control and prevention of bleeding episodes, perioperative management, and routine prophylaxis in hemophilia B patients. This real-world, postmarketing surveillance study aimed to evaluate the safety and effectiveness of Rixubis in adult and pediatric hemophilia B patients in South Korea.

Methods

This prospective, observational, multicenter study (clinicaltrials.gov identifier NCT029 22231) was conducted in hemophilia B patients between April 2015 and April 2019, who were observed for up to 6 months after the initiation of Rixubis treatment. Safety was evaluated based on the number and severity of adverse events (AEs) and serious AEs (SAEs). Hemostatic effectiveness was assessed by physicians and patients by using a four-point scale and rated as excellent, good, fair, or no response based on treatment type.

Results

In all, 58 patients were enrolled from four centers by seven physicians during the study period. The safety and effectiveness analysis sets included 57 and 54 patients, respectively. Overall, 11 AEs were reported in eight patients (14.0%), of which three were SAEs and occurred in three patients (5.3%). All 11 AEs were reported as unexpected and mild in severity, with no anaphylactic reaction, and 10 AEs (90.9%) resolved. The majority of AEs (10) were unrelated to Rixubis. Of the 142 hemostatic effectiveness assessments, 123 (86.6%) were reported as good or excellent.

Conclusion

Rixubis demonstrated an acceptable safety and effectiveness profile in the treatment of bleeding, perioperative management, and prophylaxis in hemophilia B patients in a real-world setting in South Korea.

Natural history study of factor IX deficiency with focus on treatment and complications (B-Natural)

INTRODUCTION

Haemophilia B (HB) is less well studied than haemophilia A (HA); despite similarities between the two inherited bleeding disorders, important differences remain that require further research.

AIM

B-Natural is a multi-centre, prospective, observational study of HB, designed to increase understanding of clinical manifestations, treatment, quality-of-life (QoL), inhibitor development, immune tolerance induction (ITI) outcome, renal function and create a biorepository for future investigations.

METHODS

Participants include sibling pairs/groups without a current/history of inhibitors and singletons or siblings with a current/history of inhibitors followed for six months. Demographics, medical, social history and treatment were recorded. A physical examination including joint range of motion (ROM) was performed; QoL was assessed. Samples were collected for F9 gene mutation, HLA typing, non-inhibitory antibodies and renal function testing.

RESULTS

Twenty-four centres enrolled 224 individuals from 107 families including 29 with current/history of inhibitors. Of these, 68, 30.4%, had severe (<1% FIX level of normal); 114, 50.9%, moderate (1%-5%); and 42, 18.8%, mild (>5-<40%) disease. At enrolment, 53.1% had 50 + exposure days to exogenous FIX. Comparison of joint scores showed significant (P < .05) differences between those with severe (with/without inhibitors), and those with moderate/mild disease. The majority with severe disease, 80.0% with current/history of inhibitors and 64.3% of those without, were treated with prophylaxis.

CONCLUSION

B-Natural provides data supporting an increased understanding of HB and its impact throughout life. The need for optimal disease control to normalize physical and psychosocial outcomes is underscored, and further analyses will contribute to an increased understanding of critical issues in HB.

Preclinical evaluation of a next-generation, subcutaneously administered, coagulation factor IX variant, dalcinonacog alfa

Introduction

The rapid clearance of factor IX necessitates frequent intravenous administrations to achieve effective prophylaxis for patients with hemophilia B. Subcutaneous administration has historically been limited by low bioavailability and potency. Dalcinonacog alfa was developed using a rational design approach to be a subcutaneously administered, next-generation coagulation prophylactic factor IX therapy.

Aim

This study aimed to investigate the pharmacokinetic, pharmacodynamic, and safety profile of dalcinonacog alfa administered subcutaneously in hemophilia B dogs.

Methods

Two hemophilia B dogs received single-dose daily subcutaneous dalcinonacog alfa injections for six days. Factor IX antigen and activity, whole blood clotting time, and activated partial thromboplastin time were measured at various time points. Additionally, safety assessments for clinical adverse events and evaluations of laboratory test results were conducted.

Results

There was an increase in plasma factor IX antigen with daily subcutaneous dalcinonacog alfa. Bioavailability of subcutaneous dalcinonacog alfa was 10.3% in hemophilia B dogs. Daily subcutaneous dosing of dalcinonacog alfa demonstrated the effects of bioavailability, time to maximal concentration, and half-life by reaching a steady-state activity sufficient to correct severe hemophilia to normal, after four days.

Conclusion

The increased potency of dalcinonacog alfa facilitated the initiation and completion of the Phase 1/2 subcutaneous dosing study in individuals with hemophilia B.

Postmarketing safety and effectiveness of recombinant factor IX (nonacog alfa) in Japanese patients with haemophilia B

INTRODUCTION

In 2010, nonacog alfa became the first recombinant factor IX (rFIX) available in Japan for patients with haemophilia B.

AIM

To determine real-world safety (adverse events, incidence of inhibitors) and effectiveness of nonacog alfa in Japan.

METHODS

This multicentre, prospective, observational, postmarketing surveillance study enrolled previously treated and untreated patients (PTPs and PUPs, respectively) who were observed for 1 and 2 years, respectively, after initiating nonacog alfa therapy. Safety and effectiveness were assessed for each treatment type. Annualized bleeding rate (ABR) and incremental recovery of rFIX were also evaluated.

RESULTS

Overall, 312 of 314 patients enrolled from 173 sites were eligible for the safety analysis set (PTPs, 281; PUPs, 28; other, 3). Mean age was 25.4 (PTPs) and 14.8 (PUPs) years. Haemophilic severity ranged from mild to severe, and 133 (42.6%) patients had haemophilic arthropathy. Of 285 patients (PTPs, 257; PUPs, 28) in the effectiveness set, 112 received on-demand treatment for 1161 bleeding episodes (effectiveness rate, 93.7%) and 185 received routine prophylaxis (effectiveness rate, 95.5%). No spontaneous bleeding was observed in 52.4% of patients during prophylactic treatment. Median ABR was lower during routine prophylaxis (2.0) vs the rest of the observation period (8.3). A weak negative correlation was found between body weight and the reciprocal of rFIX recovery. Eleven adverse drug reactions occurred in 7 PTPs (2.2% [7/312]); recurrence of inhibitor was observed in 1 patient, but no new inhibitor developed in PTPs or PUPs.

CONCLUSION

Nonacog alfa therapy is safe and effective in the real-world scenario in Japan.

Haemophilia B: impact on patients and economic burden of disease

Worldwide, haemophilia is the most common hereditary bleeding disorder. The incidence of haemophilia B, however, is considerably less than haemophilia A and consequently appears to have received less attention in the research literature. This article aims to summarise the available evidence documenting the patient and economic burden associated with haemophilia B and current methods of disease management. Both the immediate and long-term clinical consequences of haemophilia B can have significant implications for patients in terms of functional limitations and diminished health-related quality of life (HRQOL). Evidence demonstrates that primary prophylaxis is the optimal strategy for replacing missing clotting factor IX (FIX) and managing haemophilia B. Use of recombinant FIX (rFIX) over plasma-derived FIX (pd-FIX) is also generally preferred for safety reasons. Prophylaxis using currently available rFIX products, however, requires a demanding regimen of intravenous infusions 2–3 times a week which may have significant implications for adherence and ultimately the long-term efficacy of such regimens. Only limited assessments of the cost-effectiveness of prophylactic versus on-demand FIX treatment regimens have been conducted to date. Prophylaxis, however, is generally more costly as greater quantities of FIX are consumed. Any reduction in FIX replacement dosing frequency is expected to improve patient adherence and contribute to improved clinical outcomes, further supporting the costeffectiveness of such interventions. Although a rare disease, as economic constraints for healthcare increase, generating further information regarding the key clinical, patient and economic outcomes associated with haemophilia B will be essential for supporting improvements in care for people with haemophilia B.

Immune Modulatory Cell Therapy for Hemophilia B Based on CD20-Targeted Lentiviral Gene Transfer to Primary B Cells

Gene-modified B cells expressing immunoglobulin G (IgG) fusion proteins have been shown to induce tolerance in several autoimmune and other disease models. However, lack of a vector suitable for gene transfer to human B cells has been an obstacle for translation of this approach. To overcome this hurdle, we developed an IgG-human factor IX (hFIX) lentiviral fusion construct that was targeted to specifically transduce cells expressing human CD20 (hCD20). Receptor-specific retargeting by mutating envelope glycoproteins of measles virus (MV)-lentiviral vector (LV) and addition of a single-chain variable fragment specific for hCD20 resulted in gene delivery into primary human and transgenic hCD20 mouse B cells with high specificity. Notably, this protocol neither required nor induced activation of the B cells, as confirmed by minimal activation of inflammatory cytokines. Using this strategy, we were able to demonstrate induction of humoral tolerance, resulting in suppression of antibody formation against hFIX in a mouse model of hemophilia B (HB). In conclusion, transduction of receptor-specific retargeted LV into resting B cells is a promising method to develop B cell therapies for antigen-specific tolerance induction in human disease.

Survey of the anti-factor IX immunoglobulin profiles in patients with hemophilia B using a fluorescence-based immunoassay

Essentials Studies characterizing neutralizing antibodies (inhibitors) in hemophilia B (HB) are lacking. The current study describes anti-factor (F) IX antibody profiles in 37 patients who have HB. Anti-FIX IgG4 levels exhibited a strong positive correlation with Nijmegen-Bethesda results. These data will help to more clearly define, predict, and treat alloantibody formation in HB.

SUMMARY

Background Hemophilia B (HB) is an inherited bleeding disorder caused by the absence or dysfunction of coagulation factor IX (FIX). A subset of patients who have HB develop neutralizing alloantibodies (inhibitors) against FIX after infusion therapy. HB prevalence and the proportion of patients who develop inhibitors are much lower than those for hemophilia A (HA), which makes studies of inhibitors in patients with HB challenging due to the limited availability of samples. As a result, there is a knowledge gap regarding HB inhibitors. Objective Evaluate the largest group of patients with inhibitor-positive HB studied to date to assess the relationship between anti-FIX antibody profiles and inhibitor formation. Methods A fluorescence immunoassay was used to detect anti-FIX antibodies in plasma samples from 37 patients with HB. Results Assessments of antibody profiles showed that anti-FIX IgG1-4 , IgA, and IgE were detected significantly more often in patients with a positive Nijmegen-Bethesda assay (NBA). All NBA-positive samples were positive for IgG4 . Anti-FIX IgG4 demonstrated a strong correlation with the NBA, while correlations were significant, yet more moderate, for anti-FIX IgG1-2 and IgA. Conclusions The anti-FIX antibody profile in HB patients who develop inhibitors is diverse and correlates well with the NBA across immunoglobulin (sub)class, and anti-FIX IgG4 is particularly relevant to functional inhibition. The anti-FIX fluorescence immunoassay may serve as a useful tool to confirm the presence of antibodies in patients who have low positive NBA results and to more clearly define, predict, and treat alloantibody formation against FIX.

New developments in the management of moderate-to-severe hemophilia B

Hemophilia B is an X-linked genetic deficiency of coagulation factor IX (FIX) activity associated with recurrent deep tissue and joint bleeding that may lead to long-term disability. FIX replacement therapy using plasma-derived protein or recombinant protein has significantly reduced bleeding and disability from hemophilia B, particularly when used in a prophylactic fashion. Although modern factor replacement has excellent efficacy and safety, barriers to the broader use of prophylaxis remain, including the need for intravenous (IV) access, frequent dosing, variability in individual pharmacokinetics, and cost. To overcome the requirement for frequent factor dosing, novel forms of recombinant FIX have been developed that possess extended terminal half-lives. Two of these products (FIXFc and rIX-FP) represent fusion proteins with the immunoglobulin G1 (IgG1) Fc domain and albumin, respectively, resulting in proteins that are recycled in vivo by the neonatal Fc receptor. The third product has undergone site-specific PEGylation on the activation peptide of FIX, similarly resulting in a long-lived FIX form. Clinical trials in previously treated hemophilia B patients have demonstrated excellent efficacy and confirmed less-frequent dosing requirements for the extended half-life forms. However, gaps in knowledge remain with regard to the risk of inhibitor formation and allergic reactions in previously untreated patient populations, safety in elderly patients with hemophilia, effects on in vivo FIX distribution, and cost-effectiveness. Additional strategies designed to rebalance hemostasis in hemophilia patients include monoclonal-antibody-mediated inhibition of tissue factor pathway inhibitor activity and siRNA-mediated reduction in antithrombin expression by the liver. Both of these approaches are long acting and potentially involve subcutaneous administration of the drug. In this review, we will discuss the biology of FIX, the evolution of FIX replacement therapy, the emerging FIX products possessing extended half-lives, and novel “rebalancing” approaches to hemophilia therapy.

Central venous access device (CVAD) complications in Haemophilia with inhibitors undergoing immune tolerance induction: Lessons from the international immune tolerance study

INTRODUCTION

Central venous access devices (CVADs) are frequently required as stable long-lasting venous access in children with haemophilia, especially those requiring immune tolerance induction (ITI) for inhibitors. CVAD infection is one of the most frequently reported catheter-related complications in this patient population.

AIM

Detailed review of CVAD complications from the International ITI (I-ITI) study and analysis of potential risk factors for such complications.

METHODS

Retrospective analysis of prospectively obtained data from the I-ITI study primarily focused on CVAD-related complications.

RESULTS

A total of 115 children were recruited and 183 CVADs were placed in 99 subjects resulting in 121,206 CVAD-days observed on-study. A total of 124 CVAD infections were reported in 41 of 99 (41%) subjects with an overall infection rate of 0.94 per 1000 CVAD-days (interquartile ranges 0-1.7). A similar number of infections were observed in the two treatment arms (median: 2 and 3 in high dose and low dose respectively). Infections occurred more frequently in the presence of external catheters than with fully implanted catheters (P = 0.026). Infected patients were significantly younger at the time of CVAD insertion (median age: 22 vs. 25 months, P = 0.020). Patients with Gram-positive infections were also significantly younger than those with Gram-negative infections (median age: 17 vs. 25 months, P < 0.0001).

CONCLUSION

CVAD infection was the most common complication observed in children with severe haemophilia and inhibitors in the frame of the I-ITI study. Younger age at CVAD insertion and external CVAD were associated with higher risk for infection. ITI outcome was unaffected by CVAD infections.

Efficacy and safety of a recombinant factor IX (Bax326) in previously treated patients with severe or moderately severe haemophilia B undergoing surgical or other invasive procedures: a prospective, open-label, uncontrolled, multicentre, phase III study

Haemostatic management of haemophilia B patients undergoing surgery is critical to patient safety. The aim of this ongoing prospective trial was to investigate the haemostatic efficacy and safety of a recombinant factor IX (rFIX) (Bax326) in previously treated subjects (12-65 years, without history of FIX inhibitors) with severe or moderately severe haemophilia B, undergoing surgical, dental or other invasive procedures. Haemostatic efficacy was assessed according to a predefined scale. Blood loss was compared to the average and maximum blood loss predicted preoperatively. Haemostatic FIX levels were achieved peri- and postoperatively in 100% of subjects (n = 14). Haemostasis was 'excellent' intraoperatively in all patients and postoperatively in those without a drain, and 'excellent' or 'good' at the time of drain removal and day of discharge in those with a drain employed. Following the initial dose, the mean FIX activity level rose from 6.55% to 107.58% for major surgeries and from 3.60% to 81.4% for minor surgeries. Actual vs. predicted blood loss matched predicted intraoperative blood loss but was equal to or higher than (but less than 150%) the maximum predicted postoperative blood loss reflecting the severity of procedure and FIX requirements. There were no related adverse events, severe allergic reactions or thrombotic events. There was no evidence that BAX326 increased the risk of inhibitor or binding antibody development to FIX. BAX326 was safe and effective for peri-operative management of 14 subjects with severe and moderately severe haemophilia B.

Mutation analysis of a cohort of US patients with hemophilia B

Hemophilia B (HB) is a disorder resulting from genetic mutations in the Factor 9 gene (F9). Genotyping of HB patients is important for genetic counseling and patient management. Here we report a study of mutations identified in a large sample of HB patients in the US. Patients were enrolled through an inhibitor surveillance study at 17 hemophilia treatment centers. A total of 87 unique mutations were identified from 225 of the 226 patients, including deletions, insertions, and point mutations. Point mutations were distributed throughout the F9 gene and were found in 86% of the patients. Of these mutations, 24 were recurrent in the population, and 3 of them (c.316G>A, c.1025C>T, and c.1328T>A) accounted for 84 patients (37.1%). Haplotype analysis revealed that the high recurrence arose from a founder effect. The severity of HB was found to correlate with the type of mutation. Inhibitors developed only in severe cases with large deletions and nonsense mutations. None of the mild or moderate patients developed inhibitors. Our results provide a resource describing F9 mutations in US HB patients and confirm previous findings that patients bearing large deletions and nonsense mutations are at high risk of developing inhibitors.

Prevalent inhibitors in haemophilia B subjects enrolled in the Universal Data Collection database

Several risk factors for inhibitors have recently been described for haemophilia A. It has been assumed that similar risk factors are also relevant for haemophilia B, but there is limited data to confirm this notion. The aim of this study was to determine the prevalence of and risk factors associated with inhibitors in haemophilia B. The database of the Universal Data Collection (UDC) project of the Centers for Disease Control for the years 1998-2011 was queried to determine the prevalence of inhibitors in haemophilia B subjects. In addition, disease severity, race/ethnicity, age, factor exposure and prophylaxis usage were evaluated to determine their impact on inhibitor prevalence. Of the 3785 male subjects with haemophilia B enrolled in the UDC database, 75 (2%) were determined to have an inhibitor at some point during the study period. Severe disease (OR 13.1, 95% CI 6.2-27.7), black race (OR 2.2, 95% CI 1.2-4.1), and age <11 years (OR 2.5, 95% CI 1.5-4.0) were found to be significantly associated with having an inhibitor. There was insufficient data to determine if type of factor used and prophylaxis were associated with inhibitors. Inhibitors in haemophilia B are much less prevalent than haemophilia A, especially in patients with mild disease. Similar factors associated with inhibitors in haemophilia A also seem to be present for haemophilia B. The information collected by this large surveillance project did not permit evaluation of potential risk factors related to treatment approaches and exposures, and additional studies will be required.

Inhibitors in haemophilia B: the Italian experience

The prevalence of inhibitors in haemophilia B is significantly lower than that of patients with haemophilia A. However, the peculiar occurrence of allergic reactions associated with the onset of inhibitor in haemophilia B (HB) may render immune tolerance a risky procedure. We have carried out a detailed survey among all the Italian Hemophilia Centers to analyse all the patients with HB and inhibitors. A total of eight patients were reported among 282 living patients (2.8%) with severe factor IX (FIX) deficiency (FIX < 1 U dL(-1)). In addition, two deceased patients were also identified. Six patients carried nonsense mutations while in four partial or complete gene deletions were detected. Three patients (one deceased) had history of allergic/anaphylactic reaction upon substitutive treatment, which in one case was recurrent and resolved after switching to plasma derived FIX. Immune tolerance was adopted in five patients and in four complete response was achieved while in the remaining it was partial. No nephrotic syndrome was observed. Our data confirm that inhibitors in HB occur in patients with null mutations or complete/partial gene deletion. Immune tolerance can be achieved also in HB patients, without allergic reactions or nephrotic syndrome upon replacement therapy.

A survey of the management of newborns with severe hemophilia in Canada

OBJECTIVE

To determine the practice patterns of Canadian hematologists and neonatologists/paediatricians who care for newborns with hemophilia, with regard to vitamin K administration, use of empirical clotting factor replacement therapy, neuroimaging and timing of hematology consultation.

METHODS

Hematologists and neonatologists/paediatricians, identified from membership lists of Canadian professional organizations, were provided electronic and/or paper versions of the survey instrument. Questions were posed in the context of specific clinical scenarios. Differences in response proportions between groups were compared for selected questions.

RESULTS

There were 171 respondents among 616 eligible persons who were sent the survey; 58 respondents had recent experience managing a newborn with hemophilia. There was a consensus not to provide empirical treatment to well newborns after uncomplicated deliveries, to provide empirical treatment to symptomatic newborns and to obtain neuroimaging for symptomatic newborns. Systematic differences between hematologists and neonatologists/paediatricians existed with regard to the timing of hematology consultation when the diagnosis of hemophilia had not been confirmed antenatally, the route of vitamin K administration for newborns with hemophilia and the choice of product to use for empirical treatment of a symptomatic newborn.

CONCLUSIONS

The observed lack of consensus regarding important management decisions indicates a need for ongoing research in the care of newborns with hemophilia. Systematic differences between hematologists and neonatologists/paediatricians suggest a role for improved communication and collaboration between these two groups of practitioners.

Haemophilia B: current pharmacotherapy and future directions

INTRODUCTION

Hemophilia B is a rare hereditary hemorrhagic disorder characterized by deficiency of the clotting factor IX (FIX). Hemophilia B patients experience mild to severe bleeding complications according to the degree of FIX defect. Nowadays, the most challenging complication of individuals with hemophilia B is the development of alloantibodies, which render the standard replacement therapy with FIX concentrates ineffective, exposing them to a significantly increased morbidity and mortality.

AREAS COVERED

This review summarizes the most important events leading to the development of the current FIX products available for the treatment of hemophilia B patients. In addition, it focuses on the more recent advances in the production of new FIX molecules aimed at improving the clinical management of such patients.

EXPERT OPINION

Although the availability of plasma-derived FIX concentrates has greatly improved the clinical management of hemophilia B patients, the introduction of FIX products using recombinant DNA technology has represented the most significant therapeutic progress in hemophilia B therapy, ensuring an advanced level of safety. The development of rFIX products with extended half lives will further improve the therapeutic armamentarium for hemophilia B patients.

A prospective registry of European haemophilia B patients receiving nonacog alfa, recombinant human factor IX, for usual use

Nonacog alfa, a recombinant factor IX (FIX) used for the treatment of haemophilia B, was approved in Europe in 1998. In accordance with European Medicines Agency requirements, a registry study was conducted from 2002 to 2009. A reformulated iso-osmotic version was approved for European use in 2007. This study was conducted to evaluate the safety of nonacog alfa in a usual care setting, and provide clinical trial and postmarketing surveillance data support. This open-label, non-interventional, prospective observational cohort study (registry) comprised 52 sites in nine European countries. Patients with haemophilia B receiving nonacog alfa in either formulation for prevention or treatment were followed on a usual care schedule. A total of 218 patients were enrolled, of whom 66 (30.3%) were <18 years of age. Haemophilia severity was evenly distributed, with baseline FIX activity of <1%, 1-5% and >5% in 33.3%, 36.6% and 30.1% of patients, respectively. One hundred thirty-eight patients received the original formulation alone; 80 switched to or received only the new formulation. There was a low incidence of events of special interest (ESIs), with less-than-expected therapeutic effect in five patients (2.2%), inhibitor development in two (0.9%), thrombosis in one (0.5%) and allergic events in eight (3.7%). These accounted for the majority of the 15 serious AEs reported in six patients. Six patients discontinued because of AEs, primarily related to hypersensitivity. Nonacog alfa was shown to be safe for the treatment of haemophilia B, with a low incidence of serious AEs and ESIs.

Inhibitors of propagation of coagulation (factors VIII, IX and XI): a review of current therapeutic practice

The management of patients with congenital haemophilia who develop alloantibodies against factors of the propagation phase of blood coagulation, commonly known as inhibitors, is the most important challenge facing haemophilia caregivers at present, as this complication not only compromises the efficacy of replacement therapy but also consumes an enormous amount of economic resources. Development of inhibitors further complicates the clinical course of severe haemophilia, with a prevalence of up to 30% in patients with haemophilia A (factor VIII deficiency) and up to 5% in those with haemophilia B (factor IX deficiency) and haemophilia C (factor XI deficiency). While the short-term goal of treatment of patients who develop alloantibodies is the control of bleeding, the eradication of the inhibitor is the main long-term goal. The management of severe bleeding episodes and the eradication of the autoantibody are also the mainstays of treatment of patients with acquired haemophilia, a rare but life-threatening haemorrhagic condition characterized by the development of inhibitory autoantibodies against coagulation factor VIII. The most recent options available for treating patients with congenital haemophilia complicated by inhibitors and acquired haemophilia because of autoantibodies against factor VIII are summarized in this review article.

Haemophilia in Spain

To determine the prevalence of haemophilia A and B and their complications in Spain, and to characterize the health care network providing support to haemophiliac patients. The study examines clinical and genetic characteristics, treatment options, and complications observed during the course of the disease. Cross-sectional multi-centre study. The study population were patients with HA and HB in active follow-up at any Spanish hospital by December 2006. We studied 2400 haemophiliacs, 2081 (86.7%) HA and 319 (13.3%) HB patients. Illness was severe in 32.3% of patients, moderate in 16.4%, and mild in 51.3%. Genetic screening was carried out in 32.6% of the patients. Treatment administered in 2006 consisted of coagulation factor concentrates in 60% of patients. Until December 2006, 45.8% of severely ill patients were taking prophylaxis. The mean number of bleeding episodes in 2006 was four for patients not receiving primary prophylaxis and 1.3 for those taking primary prophylaxis. Thirty percent of patients had established haemophiliac arthropathy in at least one joint; 16.8% of patients were HIV-infected and 34.8% HCV-infected. Inhibitors were detected in 10% of severe HA patients and in 6.5% of severe HB patients. Immune tolerance induction therapy was started in 34 patients. This is the first comprehensive study on the epidemiology of haemophilia in Spain. It will enable us to draw comparisons with neighbouring countries, to assess the quality of care provided to haemophiliacs in Spain, and to provide evidence-based guidance for the even provision and improvement of such care.

Safety and efficacy of investigator-prescribed BeneFIX prophylaxis in children less than 6 years of age with severe haemophilia B

Prophylaxis is increasingly prescribed in treatment of haemophilia and its benefit is believed to be most significant for the youngest patients as haemophilic arthropathy may be prevented if prophylaxis is initiated prior to recurrent haemarthroses. While clinical prophylaxis data are readily available for haemophilia A, analogous data for haemophilia B are relatively limited. A prospective clinical study of recombinant factor IX (BeneFIX; rFIX), designed to allow investigator prescribed prophylaxis according to customary practices, was conducted in children <6 years old with severe haemophilia B. Nearly all children were prescribed prophylaxis (22/25; 88%) for all or part of their study participation. Favourable efficacy and safety profiles were reported. Routine prophylaxis with 1 or 2 rFIX infusions per week over an average of greater than 6 months of therapy resulted in near complete prevention of spontaneous breakthrough haemorrhages (<1 per year), with most children (77%) having none, including seven patients (32%) who had no bleeding episodes at all. Haemorrhages in joints were less common than those outside joints (27% vs. 73% of haemorrhages). In a patient population that included children with multiple prior haemarthroses, 68% of children had no joint bleeding. Breakthrough haemorrhages resolved with 1 or 2 infusions in 89% of episodes. The absence of changes in prophylaxis infusion schedules suggests that 1 or 2 rFIX infusion(s) per week were well-tolerated by these young patients, including those with (41%) and without (59%) central venous access devices. Safety was established by the low incidence of treatment-related adverse events.

Inhibitors in factor IX deficiency a report of the ISTH-SSC international FIX inhibitor registry (1997-2006)

Haemophilia B is an X-linked disorder resulting in coagulation factor IX deficiency. Patients with severe deficiency (<1% factor IX activity) may have significant bleeding complications similar to patients with haemophilia A or factor VIII deficiency. The development of inhibitory antibodies to the missing coagulation factor is a major complication in patients with haemophilia. While the incidence of inhibitors in patients with haemophilia A is higher than that in haemophilia B, the occurrence of allergic and or anaphylactic reactions with the development of inhibitors is unique to haemophilia B patients. Since haemophilia B is a rare bleeding disorder and the incidence of inhibitors is an even rarer entity, a registry was established by Dr Indira Warrier under the auspices of the FVIII/FIX subcommittee of the International Society of Thrombosis and Haemostasis, to gather information on the occurrence and characteristics of patients with inhibitors and also the incidence of allergic and anaphylactic reactions in this group of patients. This is the first report from this registry and helps us to gather some insight on haemophilia B patients with inhibitors and complications related to inhibitor development and difficulties with immune tolerance.

Current use of by-passing agents in Europe in the management of acute bleeds in patients with haemophilia and inhibitors

The ultimate goal of treatment for patients with inhibitory antibodies should be to permanently eradicate the inhibitor by immune tolerance induction therapy (ITI). However, ITI procedures fail in a substantial number of patients and in many countries ITI is not even offered owing to its high cost. How patients with inhibitors are managed in different European countries is evaluated with a special focus on the use of by-passing agents, i.e. recombinant FVIIa (rFVIIa) and activated prothrombin complex concentrates (aPCC), as well as the type of monitoring performed. Investigators from 22 large haemophilia centres participating within the network of the European Haemophilia Therapy Standardisation Board (EHTSB) were asked to complete a questionnaire. rFVIIa was routinely used in all centres for both children and adults at dosages ranging from 90 to 250 mug kg(-1) at an interval of 2-4 h. aPCC was used in 85% of the centres in adults and in 25% of the centres in children with haemophilia A at dosages of 50-100 IU kg(-1) every 6-12 h. The corresponding figures for children and adults with haemophilia B were 40% and 15% of the centres, respectively. Higher dosages of both agents were considered in the case of life-threatening bleeds. General recommendations were developed, based on the information provided by the survey. The results clearly indicate the need for well-designed comparative studies to optimize the use of by-passing agents.

Inhibitor development in haemophilia B: an orphan disease in need of attention

Factor IX (FIX) inhibitors develop in 1.5-3% of haemophilia B patients. Due to its low incidence compared with that in haemophilia A, few comparable data exist on host and treatment-related risk factors, and immunological processes associated with FIX inhibitor development. Moreover, the safety and efficacy of bypass therapy as well as the outcome predictors of successful inhibitor eradication have been poorly characterised. The lack of a useful evidence-based approach to the diagnosis and management of FIX inhibitors complicates their significant morbidity due to the frequency of allergic reactions that often herald antibody development. This review discusses what is currently known about the epidemiology, natural history and immunology of anti-FIX antibody development. It addresses several special considerations in the approach to the treatment of bleeding and inhibitor eradication. A case is made for moving forward with an integrated international collaboration for the further study of the nature and treatment of this problem.

Failure of rituximab to induce immune tolerance in a boy with severe haemophilia A and an alloimmune factor VIII antibody: a case report and review of the literature

We report the use of rituximab (MabThera); Roche Grenzach-Wyhlen, Germany) in a 6-year-old boy with severe haemophilia A and a high titre alloimmune factor VIII (FVIII) antibody, which had failed to respond to standard immune tolerance therapy. Rituximab was administered in 4 weekly doses with concurrent high-dose i.v. immunoglobulin (Flebogamma); Grifols, Barcelona, Spain) followed by daily high-dose recombinant FVIII concentrate (Recombinate); Baxter, CA, USA). Despite a fall in CD20 positive cell count to undetectable levels the inhibitor persisted. We discuss the possible reasons for failure of immune tolerance induction and review the literature concerning the use of rituximab for this indication.

Differences between patients', physicians' and pharmacists' preferences for treatment products in haemophilia: a discrete choice experiment

The provision of health care to patients with haemophilia through replacement of the deficient coagulation factor is the result of a complex interaction between patients, physicians and policy makers, each carrying their individual sets of preferences. Preferences of patients, physicians and pharmacists towards perceived viral safety, risk of inhibitor development, infusion frequency during prophylaxis, pharmaceutical dosage form, distribution modes and price were evaluated by conjoint analysis, using a discrete choice experiment. Overall 178 patients', 69 physicians and 58 pharmacists completed the study. Patients, physicians and pharmacists displayed preferences: (i) similar in direction and strength for risk of inhibitors and frequency of prophylaxis, (ii) similar in direction, but not in strength for perceived viral safety and price, with patients showing lower strength compared with physicians and pharmacists, and (iii) dissimilar in direction and/or strength for: (i) dosage form, which tested important only for pharmacists and (ii) distribution mode, which tested important for patients and physicians only. Our study provides evidence of the differences between different stakeholders in the preferences towards haemophilia replacement therapy, indicating that different opinions should be taken into account when planning optimal care.

Surgery in haemophilic patients with inhibitor: 20 years of experience

Surgery in haemophilic patients with inhibitor against factor (F)VIII or FIX is high risk. Surgery may be performed with the administration of sufficiently high dose of FVIII in patients with low-response inhibitor or who, despite having a high response, present a low inhibitor titre at the time of surgery. The use of high doses of FX is more complicated in patients with a low-titre FIX inhibitor, as there is a high risk of anaphylactic reactions. In the case of patients with high-titre inhibitors, several treatments have been proposed, such as porcine FVIII, recombinant FVIIa (rFVIIa), and activated prothrombin complex concentrate (APCC). We present our 20 years' experience in the treatment and subsequent management of haemophilic patients with inhibitor in surgery and evaluate the results obtained with the products available for haemostatic control in 64 surgical procedures. The efficacy we obtained with FVIII is good in 100% of the cases described; we had no haemorrhagic complication (HC) in the 18 procedures in which it was used (three major and 15 minor surgery). With APCC we obtained excellent results with only one HC in a synoviorthesis in the form of bleeding and haematomas out of 32 procedures. Good results were obtained with rFVIIa with few haemorrhagic episodes. Thus, in major surgery there was one HC out of three cases. In minor surgery, greater efficacy was observed using extremely large doses of rFVIIa (> or =120 mg kg(-1) 2 h(-1)) because of the shorter half-life of this factor in this type of patients.

Germline mosaicism resulting in the transmission of severe hemophilia B from a grandfather with a mild deficiency

We report a family in which the normal pattern of X-linked inheritance of hemophilia B (Factor IX deficiency) is complicated by mosaicism in the proband's maternal grandfather. The proband, an infant with severe Factor IX deficiency, was initially thought to be a sporadic case. Testing of other family members identified his mother as a carrier of the disorder, and his asymptomatic maternal grandfather as having very mild FIX deficiency. The causative familial mutation was identified as a two base pair deletion (AG within codons 134-135) in the Factor IX gene. The grandfather was shown to be "heterozygous" for the deletion. Karyotype analysis confirmed him to be 46XY thereby ruling out Klinefelter syndrome. The proband's aunt, who as the daughter of a man with hemophilia is theoretically an obligate carrier, was found not to carry this familial mutation, and thus not to be a carrier of hemophilia B. The grandfather must therefore be an X chromosome somatic and germline mosaic, with consequent segregation of the affected and non-affected Factor IX genes. This observation underlines the importance of confirming carrier status even in those individuals assumed to be obligate carriers, and has implications for genetic counseling.

Factor concentrate usage in persons with hemophilia in New York State

BACKGROUND

Persons with a congenital deficiency of FVIII or F IX (hemophilia A and hemophilia B, respectively) receive factor concentrate to treat or prevent bleeding.

STUDY DESIGN AND METHODS

A population-based study of all persons with hemophilia residing in New York State at any time during 1993 through 1998 was conducted. All available medical records for each patient were reviewed to determine type of therapy.

RESULTS

Case finding yielded 1160 cases, for a prevalence of 63.9 per 1 million population in 1998. Recombinant factor concentrates were used by 56 percent of patients. Patients with severe disease used more (158,234 IU/patient) factor concentrate than did patients with moderate disease (46,315 IU) or mild disease (5794 IU). Over half (57%) of all factor concentrate was prescribed for patients with severe disease on prophylactic therapy. Patients undergoing immune tolerance therapy used the most per person-455,116 IU each. Hemophilia treatment centers provided factor concentrate for 62 percent of all patients who used factor and 73 percent of patients with severe disease.

CONCLUSION

Hemophilia patients, especially patients with severe disease, use large amounts of expensive factor concentrates to prevent and to treat bleeding episodes. Specialized hemophilia treatment centers play a key role in the care of these patients.

Breastfeeding does not influence the development of inhibitors in haemophilia

Our aim was to test the hypothesis that breastfeeding may reduce development of inhibitors in male infants with haemophilia by inducing an oral immune tolerance to factor VIII. To achieve that goal, we performed a structured epidemiological survey comprising all males born with severe haemophilia A (in all 100 patients, 19 with inhibitors) or haemophilia B (in all 16 patients, six with inhibitors) in Sweden in 1980-99. Our results show no protective effect of breastfeeding.

Experience with use of recombinant activated factor VII

Recombinant activated factor VII (rFVIIa) has recently been introduced for improving haemostasis in haemophiliac patients developing alloantibodies (inhibitors) to factor VIII (FVIII) or factor IX (FIX). We describe the successful management of haemorrhagia with rFVIIa in five different situations: an episode of surgical bleeding in a patient with haemophilia A and non-surgical haemorrhages in four patients with haemophilia A, acquired haemophilia, congenital severe FV defect and pseudo-acquired haemophilia, respectively. In each case, rFVIIa was effective and safe. There is no doubt that rFVIIa is useful in the therapeutic management of patients with antibodies to FVIII or FIX. However, the treatment is expensive and a cost-effectiveness analysis would be useful.

Human recombinant factor IX: safety and efficacy studies in hemophilia B patients previously treated with plasma-derived factor IX concentrates

Human plasma-derived factor IX (pdFIX) concentrates are routinely used to treat patients with hemophilia B, an X-linked bleeding disorder that affects 1 in 30 000 males, but concerns remain regarding transmission of blood-borne pathogens. Therefore, the safety and efficacy of recombinant human factor IX (rFIX) were evaluated. A 20-center international trial was conducted in previously treated patients with severe or moderate (< 5 IU/dL factor IX activity) hemophilia B. Participants received rFIX for pharmacokinetic studies, treatment of or prophylaxis against hemorrhage, or surgical hemostasis, and were assessed at 3-month intervals for 2 years. Fifty-six subjects were treated. Mean incremental rFIX recovery was 0.75 IU/dL per IU/kg, 30% lower than expected for pdFIX, although the mean half-life was similar. Pharmacokinetic parameters were stable over time. Somewhat lower recoveries were seen in subjects younger than 15 years of age and in those with no detectable factor IX antigen. A total of 7362 infusions of rFIX were administered. All 1796 hemorrhages were controlled, 80.9% of which required only one rFIX infusion. Effective hemostasis was also achieved in prophylactic and surgical settings. One individual developed a low titer (1.2 Bethesda unit) transient inhibitor that spontaneously resolved. rFIX was not associated with serious adverse events, thrombogenicity, or virus transmission. rFIX is safe and effective for the treatment of hemophilia B. Despite a lower recovery compared with pdFIX, rFIX controlled hemorrhage in a wide variety of settings and may provide a safety advantage in terms of risk from blood-borne pathogens.