Inhibitors in hemophilia patients: current status and management

Nothing short of a revolution: Novel extended half-life factor VIII replacement products and non-replacement agents reshape the treatment landscape in hemophilia A

Hemophilia A, an X-linked genetic disorder, is characterized by a deficiency or dysfunction of clotting Factor VIII. The treatment landscape has substantially changed by introducing novel extended half-life factor VIII (EHL-FVIII) replacement therapies such as efanesoctocog Alfa and non-factor replacement therapy such as emicizumab. These agents signal a shift from treatments requiring multiple weekly infusions to advanced therapies with long half-lives, offering superior protection against bleeding and improving patient adherence and quality of life. While EHL-FVIII treatment might lead to inhibitor development in some patients, non-factor replacement therapy carries thrombotic risks. Therefore, ongoing research and the generation of robust clinical evidence remain vital to guide the selection of optimal and cost-effective first-line therapies for hemophilia A patients.

The future of bypassing agents for hemophilia with inhibitors in the era of novel agents

Bypassing agents are presently the standard of care for the treatment of bleeding episodes in patients with hemophilia and high-titer inhibitors and are also used for bleed prevention. Only two bypassing agents are available to patients, and these products trace their lineage to the 1970s (activated prothrombin complex concentrates) and the 1980s (recombinant factor VIIa). Given the limited repertoire of available products, clinicians have relied on experience, empirical observation, registry data and individualized care to improve clinical outcomes on a case-by-case basis. Research over the past two decades has culminated in a greatly improved understanding of human coagulation; resulting from this, new products have been developed that offer treatment options and mechanisms of actions that differ from current bypassing agents. The most advanced in clinical development is emicizumab, a bispecific antibody that mimics the function of FVIIIa in the intrinsic Xase complex and is indicated for once-weekly or every-other-week prophylactic dosing in inhibitor patients. Other non-traditional products in clinical development include fitusiran and antibodies directed against tissue factor pathway inhibitor. As non-factor-based therapies become more widely utilized over time, the use of bypassing agents may be expected to decrease; however, bypassing agents will remain essential for the foreseeable future. As such, clinical development of bypassing agents continues, with some products (e.g. eptacog beta) under regulatory review. In this review we examine the optimal use of bypassing agents and their mechanism of action. We also discuss newer products and how these might theoretically be administered in conjunction with traditional bypassing agents.

Cost and effectiveness of treatments for mild-to-moderate bleeding episodes in haemophilia patients with inhibitors in Korea

First-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Korea is currently activated prothrombin complex concentrate (aPCC) with recombinant activated factor VII (rFVIIa) as second-line therapy or as a last resort. The aim of this study was to estimate the cost and effectiveness of aPCC vs. rFVIIa for treating mild-to-moderate bleeds in inhibitor patients from the Korean reimbursement authorities' perspective. Clinical outcomes and resource utilization data (number of doses, average dose, number of outpatient visits, inpatient stays, ambulance transport and concomitant medications) were collected from an observational study involving four Korean paediatric haemophilia centres. Cost-effectiveness was modelled using a decision analysis approach and sensitivity analyses undertaken. rFVIIa was a more effective haemostatic therapy (87.1% efficacy in bleed resolution) than aPCC (64.0%). rFVIIa effected more rapid haemostasis, resolving bleeding in a mean of 6.6 h vs. 25.2 h for aPCC. Fewer rFVIIa doses were required per bleed vs. aPCC (means 1.7 and 2.3). Mean total direct medical costs from bleed initiation to cessation were estimated at Korean Won (KRW)12 460 thousand (US$12 311) for rFVIIa given as first-line therapy and KRW18 304 thousand (US$18 085) for aPCC given as first-line therapy. Sensitivity analyses confirmed the cost-effectiveness of rFVIIa vs. aPCC given as first-line therapy. In Korea, use of rFVIIa as first-line therapy for treatment of mild-to-moderate bleeding episodes in inhibitor patients is both clinically effective and cost-effective compared with initial aPCC treatment. rFVIIa should be considered as the first-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Korea.

Use of FEIBA for invasive or surgical procedures in patients with severe hemophilia A or B with inhibitors

Achieving hemostasis in patients with hemophilia A or B is complicated by the presence of inhibitors and is made even more difficult when these individuals require surgery. Over a 4-year period, 6 patients with inhibitors to factor VIII and 1 patient with inhibitors to factor IX underwent surgery or invasive procedures at our institution. A total of 26 procedures were performed, primarily using the bypassing agent FEIBA for bleeding control. Excellent hemostasis was obtained in all cases, adding to accumulating data indicating that FEIBA is safe and effective in hemophilia patients with inhibitors who require surgery.

Biophysical delivery of peptides: applicability for cancer therapy

There is a current trend towards evaluation of molecular agents for treatment of a variety of ailments, including cancer. One class of such biomolecules is proteins, and their shortened versions, peptides. Use of peptidic entities has been hindered by poor bioavailability in vivo and the high cost involved in mass-producing these macromolecular drugs. The need for localized delivery is being met with the development of various biophysical means, which include devices and aids, mainly transdermal and invasive implants. In addition, various cell-based delivery modalities, which include the use of spore-forming bacteria and stem cells, are being explored. This review discusses these methods in turn, and examines ways by which these can be enhanced for peptide delivery to tumors.

Application of current knowledge to the management of bleeding events during immune tolerance induction

The development of inhibitors to factor VIII is the most serious adverse event associated with the treatment of haemophilia A, predisposing patients to uncontrollable haemorrhage, disability and premature death. Eradication of inhibitors via immune tolerance induction (ITI) is effective in the majority of patients, but may require months to years to achieve success. In the interim, the treatment and prevention of acute bleeding episodes are primary foci of care. Regrettably, there is a paucity of information regarding management of bleeding episodes in inhibitor patients undergoing tolerization. Until specific data from ongoing clinical trials are available to provide more guidance in this patient group, it is reasonable and useful to rely on the broader base of medical literature pertaining to patients not being tolerized to deduce strategies for controlling acute and perioperative bleeding episodes in inhibitor patients during ITI.

Italian guidelines for the diagnosis and treatment of patients with haemophilia and inhibitors

The Italian Association of Haemophilia Centres reviewed and finally approved in November 2004 the new Italian Guidelines for the diagnosis and treatment of patients with clotting factor inhibitors. The recommendations have been based on the identification of levels of clinical evidence derived from the systematic review carried out in 2003 by the School of Health and Related Research, the University of Sheffield, UK, and further integrated by clinical studies published from 2003 to 2004. The Italian guidelines consist of six major domains concerning inhibitor definition, epidemiology, risk factors, diagnosis, inhibitor eradication, management of bleeding episodes, in patients with congenital and acquired coagulation disorders, with 121 statements, 59 synthesis and 54 recommendations. We report here recommendations and open issues concerning the diagnosis and monitoring of inhibitors, inhibitor eradication and the management of bleeding in patients with haemophilia A and B.

T cell recognition of the A2 domain of coagulation factor VIII in hemophilia patients and healthy subjects

Hemophilia A patients treated with coagulation factor VIII (FVIII), and also some healthy subjects, may develop anti-FVIII antibodies (Ab), whose synthesis is driven by FVIII-specific CD4+ T cells. Some Ab block the procoagulant function of FVIII (inhibitors). Many inhibitors recognize epitopes on the FVIII A2 domain. Here, we have sought to identify A2 epitopes recognized by CD4+ T cells. We tested the proliferative response of CD4+ blood lymphocytes (BL) from hemophilia patients and healthy subjects, to overlapping synthetic peptides spanning the A2 domain sequence. Many A2 peptides induced proliferative responses of CD4+ BL from one or more subjects. The peptide-induced responses were strongest in hemophilia patients with inhibitors, weakest in healthy subjects. A2 peptides comprising residues 371-400, 621-650 and 671-690 elicited frequent and strong responses in hemophilia A patients, and especially in those with inhibitors. Healthy subjects recognized frequently only the sequence 371-400. A three-dimensional model of the A2 domain suggests that these CD4+ epitope sequences have structural features typical of 'universal' CD4+ T epitopes.

Comparative thrombotic event incidence after infusion of recombinant factor VIIa versus factor VIII inhibitor bypass activity

Thrombosis is a rare but well-recognized potential complication of Factor VIII Inhibitor Bypass Activity (FEIBA) infusion. Recombinant factor VIIa (rFVIIa) is increasingly used as an alternative to FEIBA; however, the thrombotic safety profile of rFVIIa remains incompletely characterized. To determine the incidence rates of thrombotic adverse events (AEs) after infusion of rFVIIa and FEIBA. Data from the MedWatch pharmacovigilance program of the US Food and Drug Administration, as supplemented by published case reports, were used in conjunction with estimated numbers of infusions available from manufacturers to assess comparative incidence of thrombotic AEs in patients receiving rFVIIa or FEIBA in the period from April 1999 through June 2002. Reported thrombotic AEs were rare, with incidence rates of 24.6 per 10(5) infusions (CI, 19.1-31.2 per 10(5) infusions) for rFVIIa and 8.24 per 10(5) infusions (CI, 4.71-13.4 per 10(5) infusions) for FEIBA. Thrombotic AEs were significantly more frequent in rFVIIa than FEIBA recipients (incidence rate ratio, 2.98; CI, 1.71-5.52). The most commonly documented single type of thrombotic AE after rFVIIa infusion was cerebrovascular thrombosis, while myocardial infarction was the most frequent type in patients receiving FEIBA. Contrasting AE reporting patterns between rFVIIa and FEIBA may have contributed to the observed difference in thrombotic event incidence. Nevertheless, this comprehensive pharmacovigilance assessment does not support superior thrombotic safety of rFVIIa and suggests that thrombotic AE risk may be higher in rFVIIa than FEIBA recipients.

Epitope repertoire of human CD4(+) T cells on the A3 domain of coagulation factor VIII

Severe hemophilia A patients treated with factor (F)VIII may develop antibodies (Ab) that block FVIII function (inhibitors). Autoimmune inhibitors may develop in subjects without congenital hemophilia, and cause acquired hemophilia. Hemophiliacs without inhibitors and healthy subjects may also have small amounts of antiFVIII Ab. FVIII-specific CD4(+) T cells induce antiFVIII Ab synthesis. Here, we have examined their epitope repertoire in hemophilia patients and healthy subjects. We used overlapping synthetic peptides, spanning the sequence of the FVIII A3 domain, to challenge blood CD4(+) T cells in proliferation assays. The epitopes recognized in hemophilia A patients with or without inhibitors, acquired hemophilia patients, or healthy subjects overlapped, yet had characteristic differences. Most members of one or more study groups recognized the sequence regions 1691-1710, 1801-1820, 1831-1850, and 1941-60. In the proposed three-dimensional structure of the A3 domain, these sequences are largely exposed to the solvent and flanked by flexible sequence loops: these are structural features characteristic of 'universal' CD4(+) T epitopes. Hemophilia A patients with inhibitors recognized prominently only the sequence 1801-1820, which overlaps a known inhibitor binding site. This is consistent with the possibility that CD4(+) T cells recognizing epitopes within residues 1801-1820 have a role in inducing inhibitor synthesis. In contrast, CD4(+) T cells sensitized to sequences 1691-1710 and 1941-60, which are recognized by healthy subjects and hemophilia A patients without inhibitors, might curb inhibitor synthesis.

Successful induction of immune tolerance to enzyme replacement therapy in canine mucopolysaccharidosis I

Immune responses can interfere with the effective use of therapeutic proteins to treat genetic deficiencies and have been challenging to manage. To address this problem, we adapted and studied methods of immune tolerance used in canine organ transplantation research to soluble protein therapeutics. A tolerization regimen was developed that prevents a strong antibody response to the enzyme alpha-l-iduronidase during enzyme replacement therapy of a canine model of the lysosomal storage disorder mucopolysaccharidosis I. The tolerizing regimen consists of a limited 60-day course of cyclosporin A and azathioprine combined with weekly i.v. infusions of low-dose recombinant human alpha-l-iduronidase. The canines tolerized with this regimen maintain a reduced immune response for up to 6 months despite weekly therapeutic doses of enzyme in the absence of immunosuppressive drugs. Successful tolerization depended on high plasma levels of cyclosporin A combined with azathioprine. In addition, the induction of tolerance may require mannose 6-phosphate receptor-mediated uptake because alpha-l-iduronidase and alpha-glucosidase induced tolerance with the drug regimen whereas ovalbumin and dephosphorylated alpha-l-iduronidase did not. This tolerization method should be applicable to the treatment of other lysosomal storage disorders and provides a strategy to consider for other nontoleragenic therapeutic proteins and autoimmune diseases.

Recognition of coagulation factor VIII by CD4+ T cells of healthy humans

Hemophilia A patients treated with coagulation factor (F)VIII may develop an anti-FVIII immune response. Anti-FVIII antibodies may occur also in healthy subjects. To understand the extent to which an immune response to FVIII occurs in healthy subjects, we investigated the proliferative response of blood CD4+ T cells from 90 blood donors to FVIII and to pools of overlapping synthetic peptides spanning the sequences of individual FVIII domains (A1-A3, C1-C2). Most subjects responded to FVIII and several FVIII domains. Men had stronger responses to FVIII than women, and older subjects than younger subjects. The domain-induced responses were weaker than the FVIII-induced responses, yet their intensity in individual subjects correlated with that of the response to FVIII. We examined whether Th1 and/or Th2 cells responded to FVIII in 68 subjects, by determining the CD4+ T cells that secreted interferon-gamma (IFN-gamma) or interleukin (IL)-5 after stimulation with FVIII: 25 subjects had FVIII-specific IFN-gamma-secreting cells, and seven of them had also FVIII-specific IL-5-secreting cells. None had only IL-5-secreting cells. Thus, a CD4+ T cell response to FVIII, which first involves Th1 cells, is common among subjects with a normal procoagulant function.

Human CD4+ T-cell epitope repertoire on the C2 domain of coagulation factor VIII

Approximately 25% of severe hemophilia A patients develop antibodies (Ab) that neutralize the procoagulant function of factor (F)VIII (inhibitors). Autoimmune FVIII inhibitors may develop in individuals without congenital FVIII deficiency and cause acquired hemophilia. Low titers of anti-FVIII Ab may be present in hemophilia A patients without inhibitors and in healthy blood donors. FVIII-specific CD4+ T-cells drive the synthesis of anti-FVIII Ab. We examined the epitope repertoire of CD4+ T-cells from 15 healthy subjects, 10 hemophilia A patients without inhibitors, 11 hemophilia A patients with inhibitors, and six acquired hemophilia patients. Blood CD4+ T-cells were challenged in proliferation assays with a panel 16 overlapping synthetic peptides, spanning the sequence of the FVIII C2 domain. The sequence region 2291-2330 contained the most frequently and strongly recognized peptides in each of the four subject groups. Crystallographic B factor data and the location of these peptides within the three-dimensional structure of the C2 domain confirm that this region has a high degree of solvent exposure and flexibility within the peptide backbone, which are structural features typical of immunodominant universal CD4+ epitopes. Furthermore, this sequence region overlaps inhibitor-binding sites, suggesting that CD4+ T-cells recognizing peptide sequences within this region might be involved in inhibitor synthesis. The sequence regions 2191-2210 (recognized strongly by each study group except hemophilia A patients with inhibitors) and 2241-2290 (recognized primarily by acquired hemophilia patients and healthy subjects) share the same structural features, and also overlap inhibitor-binding sites. Although similar, there appear to be important differences in the CD4+ epitope repertoires of congenital and acquired hemophilia patients.

Optimization of storage conditions for diluted working solutions of porcine factor VIII and performance of the Bethesda assay for the determination of antiporcine FVIII inhibitor titres

The use of porcine factor VIII (FVIII) (Hyate:C, Ipsen) has proven to be very successful in treating patients with FVIII inhibitors. The best way to predict the usefulness of porcine FVIII therapy, and/or to estimate the appropriate treatment dose in a given patient, is to measure the patient inhibitor titre against porcine FVIII with the Bethesda assay, using porcine FVIII as the source of FVIII in the assay. The goals of the present study were to (1) find the optimal storage temperature, diluent and concentration for a working solution of porcine FVIII to be used as the source of FVIII for the porcine Bethesda assay, (2) assess the reliability of the labelled FVIII units in the preparation of such working solutions of porcine FVIII and (3) compare the inhibitor titres determined by the Bethesda assay using both porcine and human standard reference curves for measuring residual FVIII. The results of the present study demonstrate that a ready-to-use working solution of 1 U mL(-1) of Hyate:C diluted in human FVIII deficient plasma, either containing or deficient in von Willebrand factor antigen, is stable for up to 12 months, at -20 degrees C. The preparation of the 1 U mL(-1) working solution could be reliably calculated based on the units indicated on the vial label. Finally, using the human standard curve yields similar results to using the porcine standard curve for measuring any titre of allo- or auto-antibody against FVIII in the Bethesda assay, using Hyate:C as the source of FVIII. These findings are of practical value when performing a porcine FVIII-based Bethesda assay.

Unexpected bleeding disorders

Patients with known coagulation deficiencies, either congenital or acquired, may bleed spontaneously with trauma or with surgical intervention. In contrast, however, are the unchallenged patients who bleed in a variety of clinical settings that demand rapid diagnosis so that appropriate therapy can be instituted. In the first section Dr. Louis M. Aledort demonstrates a series of vignettes of actual cases who presented with unexpected bleeding or a screening laboratory abnormality prior to a needed surgical intervention. Settings include dental, oral surgical, obstetrical, surgical and gynecological. The differential diagnoses of these cases are discussed. In the second section Dr. David Green also uses vignettes to demonstrate how the laboratory is used to differentiate the various clinical entities. The choice and priority of required tests indicated by the settings, history, site and type of bleeding, and the syllogisms used to define the abnormality are stressed. In the third section, Dr. Jerome Teitel reviews in detail the therapeutic armamentarium available to the clinician and presents algorithms for the management of these bleeding disorders.

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.

CD4+ T cells specific for factor VIII as a target for specific suppression of inhibitor production

The studies we reviewed here have begun to clarify the complex cellular mechanisms involved in the immune response to fVIII, and the circumstances under which fVIII inhibitors develop. Further characterization and comparison of the immune response to fVIII in both hemophilia patients and healthy subjects will help to further elucidate these mechanisms. The murine hemophilia model will hopefully provide further insights into the mechanisms of inhibitor formation, and prove to be a suitable tool for the design and testing of therapeutic strategies aimed at preventing the development of fVIII inhibitors.

Safety of factor VIII inhibitor bypass activity (FEIBA): 10-year compilation of thrombotic adverse events

Published and unpublished spontaneously reported thrombotic adverse events (AEs) in factor VIII inhibitor bypass activity (FEIBA(R)) recipients were compiled for the most recent 10-year period during which FEIBA(R) units equivalent to 3.95 x 105 typical infusions were distributed worldwide. A total of 16 thrombotic AEs were documented over the 10-year period, corresponding to an incidence of 4.05 per 105 infusions (95% CI, 2.32-6.58 per 105 infusions). Disseminated intravascular coagulation (n=7) and myocardial infarction (n=5) were the most frequent thrombotic AEs. One fatality occurred in an 87-year-old metastatic cancer patient. In 13/16 (81%) patients known risk factors were present, most commonly FEIBA(R) overdose in 8/16 (50%), obesity in 3/16 (19%) and serum lipid abnormalities in 2/16 (12%). These findings indicate that thrombotic AEs in FEIBA(R) recipients are very rare. Recognition of risk factors and avoidance of FEIBA(R) overdosage may avert thrombotic AEs.

Apathetic Graves' disease and acquired hemophilia due to factor VIIIc antibody

Acquired hemophilia due to autoantibody to Factor VIII coagulant (Factor VIIIc) is a rare event which may be observed in patients with different autoimmune diseases. To our knowledge, this association has been reported only once in patients with autoimmune thyroid disease. Here we describe a patient presenting with a severe hemorrhagic disorder due to Factor VIIIc antibody in whom biochemical screening for thyroid diseases led to a diagnosis of hyperthyroid Graves' disease not associated to overt clinical features. This case underlines the importance of carrying out a complete screening for autoimmunity, including thyroid autoimmune disease, in all patients with apparently isolated serum Factor VIIIc inhibitors.

Clinical trial to investigate the pharmacokinetics, pharmacodynamics, safety, and efficacy of recombinant factor VIIa in Japanese patients with hemophilia with inhibitors

A multicenter and open-labeled clinical trial of human recombinant factor VIIa (rFVIIa) was conducted in Japanese patients with severe hemophilia A or B with inhibitors. The trial consisted of 2 parts. In study 1, the pharmacokinetics, pharmacodynamics, and safety of a single dose of 120 microg/kg of rFVIIa were investigated in 8 patients. In the subsequent study 2, the hemostatic effect and safety of rFVIIa were evaluated during a 24-week period in 10 patients. In study 1, the mean maximum FVII-coagulant activity (FVII:C) was found to occur after 10 minutes; activity then decreased rapidly and returned to the baseline within 24 hours after a single intravenous infusion of rFVIIa. The mean half-life of FVII:C was 3.5 hours. The activated partial thromboplastin time and prothrombin time in the patients were immediately shortened but returned to the baseline within 24 hours after dosing. In study 2, 86 microg/kg to 120 microg/kg of rFVIIa (mean, 97 microg/kg) was administered 1 to 85 times to 10 patients. A total of 58.0% (91/157) of bleeding episodes were treated excellently or effectively, with 5 (3.2%) ineffective episodes. There was no apparent trend in the relationship of the hemostatic effect with bleeding sites, mean dose, or number of injections. The efficacy rate, however, was significantly higher (90.0%) in bleeding episodes treated within 3 hours than in those treated at longer intervals (31.0%). No treatment-related adverse events were observed, and there was no evidence of antibody formation to rFVIIa. In conclusion. rFVIIa is an effective and well-tolerated option for treatment of bleeding episodes in hemophilia patients with inhibitors.

Making a therapeutic choice: human versus recombinant fractions - can we do it?

New manufacturing methods have resulted in production of higher purity human-derived products and recombinant factors with less human- or animal-derived reagents or stabilizers for the treatment of congenital coagulation disorders. In addition, new viral inactivation processes are being used to reduce the chance of viral contamination. Preferred treatment approaches are moving toward using newer-generation agents. At the same time, rationale exists for continuing fractionation of all types of products, based on considerations including cost, product availability, safety issues, and specific clinical situations for which a recombinant or high-purity product is not available. These issues and others are reviewed in the context of making a therapeutic choice.

Frequency of inhibitor development in severe haemophilia A children treated with cryoprecipitate and low-dose immune tolerance induction

The frequency of factor VIII inhibitor development was evaluated in a hundred severe haemophilia A patients < 18 years of age (mean 10.4 +/- 5.1 years); 25 were previously untreated patients (PUPs), with a mean age of 11.2 +/- 2.9 months. All were followed up for 3 years from December 1996. Immune tolerance (IT) was induced with low-dose factor VIII (FVIII); 25-50 IU kg(-1) every other day for the 10 haemophiliacs who developed persistent inhibitors. The incidence of inhibitors for PUPs was 3/25 (12%; 95% confidence interval [CI], 0. 7-24.7%) and were detected after 4, 15 and 20 exposure days (mean 13 +/- 8.2 days; 95% CI, 3.7-22.2%). Children with maximum inhibitor levels of > 40 Bethesda units (BU) per mL (n=4) received IT therapy as 25 U kg(-1) FVIII in the form of cryoprecipitate every other day for 1-4 months (mean 2.4 +/- 1.6 months; 95% CI, 0.8-3.9%), which was successful in all of them. FVIII (50 U kg(-1)) was given every other day for six patients with maximum inhibitor level > 40 BU mL(-1) for 3-9 months (mean 5.4 +/- 3.2 months; 95% CI, 2.9 -7.9%) with success in 4/6 (66.6%; 95% CI, 28.8-104.3%). Patients who showed a good IT response had an inhibitor level < or = 30 BU mL(-1), were < or = 9 years of age at inhibitor development with few exposure days to FVIII and had an early immune tolerance. In conclusion, inhibitor development in severe haemophilia A children exclusively treated with cryoprecipitate is low. Early low-dose IT induction for high responders may be achieved successfully if inhibitor level is < or = 50 BU mL(-1).

Immune tolerance induction in the treatment of paediatric haemophilia A patients with factor VIII inhibitors

The development of an inhibitor to transfused factor VIII (FVIII) is a serious treatment-related problem in haemophiliac children. The management of patients with high titre FVIII inhibitors is difficult, and immune tolerance induction (ITI) is the only method available for the eradication of these inhibitors. The results of the ITI regimen used at the Children's Hospital of Michigan Haemophilia Treatment Center are described and discussed. ITI was attempted in 14 children with severe haemophilia A (13 high responders, one low responder), with daily doses of FVIII alone. FVIII dosage was chosen according to the patient's historical peak inhibitor titre. ITI included three phases; induction phase, dose reduction phase and maintenance phase. During the first phase, the starting dose was 50 or 100 U kg-1 d-1; during the second phase the FVIII dosage was reduced gradually to 25 U kg-1 every other day according to the inhibitor titre, FVIII recovery and/or half-life study. In the third (maintenance) phase, the children received either prophylactic therapy or episodic therapy for 12 months. The inhibitor elimination was defined as the time taken to achieve a negative inhibitor assay with no anamnestic response and normal FVIII recovery and/or normal half-life. Immune tolerance was achieved in 11 of 14 patients (79%) patients within a median time of 6 months; two children are still on therapy, three failed ITI. We observed either failure or prolongation of immune tolerance if the historical peak titre or the maximum titre during ITI was >200 BU. The success rate of our low dose ITI regimen is not different from that reported by other investigators and the inhibitor elimination time is similar to some of the studies reported previously.

Long-lasting remission and successful treatment of acquired factor VIII inhibitors using cyclophosphamide in a patient with systemic lupus erythematosus

Acquired deficiency of clotting factor VIII (FVIII) is a rare bleeding diathesis seldom encountered in systemic lupus erythematosus (SLE). Reduction of FVIII activity by autoantibodies can cause potentially life-threatening situations. Herein, an SLE patient with a positive lupus anticoagulant (LAC) test who abruptly developed metrorrhagia 4 yr after diagnosis is reported. Coagulation tests revealed FVIII activity reduced to 3% and a prolonged aPTT. FVIII inhibitor(s) were found to be as high as 3.0 Bethesda Units. Plasmapheresis, immunoglobulins, prednisolone and FVIII plasma concentrates induced the cessation of metrorrhagia, but the clotting tests were barely improved. One month later, extensive ecchymosis appeared and worsened, despite re-administration of the previous therapy. Pulse cyclophosphamide followed by oral administration was then started with normalization of coagulation parameters and long-lasting disease remission.

Use of prothrombin complex concentrates and activated prothrombin complex concentrates as prophylactic therapy in haemophilia patients with inhibitors

Haemophilia patients with inhibitors are treated for acute bleeding with prothrombin complex concentrates (PCCs) or activated prothrombin complex concentrates (aPCCs). Despite this therapy, patients with high-level inhibitors are at increased risk of developing devastating joint disease. This paper examines available information that supports the study of PCCs and/or aPCCs as prophylactic therapy for haemophilia patients with inhibitors. This strategy would require that PCCs or aPCCs be administered repetitively in a dose that is sufficient to prevent haemarthrosis without causing thrombogenic events, or causing anamnestic response in inhibitor titre. PCC doses ranging from 30 to 50 U kg-1 every other day for up to 8 months have resulted in subjective improvement both in bleeding associated with target joints and in the management of chronic joint inflammation. aPCC doses as low as 50-100 U kg-1 every other day have been useful in postsurgical prophylaxis. The risk of developing a myocardial infarction or clinically relevant disseminated intravascular coagulation is linked to total dosages of either PCCs or aPCCs greater than 200 U kg-1 day-1. It is uncertain what anamnestic response would result from prophylaxis, but with typical therapy the aPCCs cause such a response in only a small percentage of patients. Based on these findings, a clinical trial of these products used in doses of 50-100 U kg-1 every other day would appear to be warranted in patients who have permanent inhibitors and frequent joint bleeding.

Treatment options for bleeding episodes in patients undergoing immune tolerance therapy

Inhibitors to factor VIII develop in 4-20% of haemophilia A patients, with the percentage rising to 52% in certain subpopulations. The management of inhibitor patients is directed toward stopping acute haemorrhages, providing short-term haemostasis before and after surgery, and inducing immune tolerance to factor VIII (immune tolerance therapy or ITT). Several different protocols have been used for ITT, but they are all centred around ongoing exposure to high doses of factor VIII. High responders (those patients with a large increase in inhibitor level after exposure to factor VIII) are the prime candidates for ITT, but low responders may also benefit from this treatment. It is often necessary to treat bleeding episodes during ITT, because elimination of inhibitors may require many years of therapy. Treatment of haemorrhages in inhibitor patients is reviewed for both low and high responders during ITT and in the absence of ITT. The choice of clotting agent for inhibitor patients who have not yet responded to ITT depends on current and past inhibitor levels, the severity of the haemorrhage, the site of the haemorrhage or the setting in which it occurs (e.g. surgical), and the extent of inhibitor cross-reactivity with porcine factor VIII. Patients with high-titre inhibitors experiencing a critical haemorrhage are generally best managed with bypassing agents (AUTOPLEX T or FEIBA VH), porcine factor VIII or rFVIIa.

Management of haemophilia in patients with high-titre inhibitors: focus on the evolution of activated prothrombin complex concentrate AUTOPLEX T

Numerous therapeutic strategies have been applied to the management of patients with inhibitors to factors VIII or IX. Different treatment approaches are analysed including prothrombin complex concentrates (PCCs), activated prothrombin complex concentrates (aPCCs), porcine factor VIII concentrate, inhibitor neutralization, immune tolerance therapy, immunosuppressive regimens and recombinant factor VIIa. Clinical data are reported in the analysis of several treatments. PCCs and aPCCs have gained widespread acceptance as the standard first-line approach for patients with inhibitors. The aPCC AUTOPLEX T has achieved a high response rate with a low level of thrombotic events. Four case studies are presented in which AUTOPLEX T has been used successfully. Administration of platelet concentrate or, in elective surgery, waiting for inhibitor levels to decline are useful adjuncts to some treatments. The optimal treatment depends on the patient's inhibitor status--low responder (minimal or no increase in inhibitor levels upon administration of replacement clotting factor) or high responder (replacement clotting factor generates inhibitor production). A suggested algorithm for treating high-responder inhibitor patients is presented.

Clinical efficacy of prothrombin complex concentrates and recombinant factor VIIa in the treatment of bleeding episodes in patients with factor VII and IX inhibitors

An overview is given on APCCs and recombinant FVIIa for the treatment of bleeding episodes in hemophiliacs with FVIII or FIX inhibitors or in patients with acquired hemophilia. The initial dose of activated plasma-derived PPCs, mainly FEIBA, is up to 100 U/kg body weight, and the maintenance dosage is up to 100 U/kg body weight twice daily. The single dosage of recombinant FVIIa is about 60-90 microg/kg body weight, which has to be repeated every 2 to 6 hours depending on the bleeding situation.

The impact of inhibitors on the cost of clotting factor replacement therapy in Haemophilia A in Canada

A retrospective case controlled study was performed to determine the comparative costs of clotting factor concentrate therapy for haemophilia A patients with and without inhibitors. We examined treatment records for a 3.5-year period for nine patients with factor VIII inhibitors and nine noninhibitor control patients matched for age and severity of disease. Inhibitor patients used FEIBA, porcine factor VIII, recombinant factor VIIa, and recombinant factor VIII over the study period. Controls used recombinant factor VIII and small amounts of monoclonal antibody purified plasma-derived factor VIII and DDAVP. The total and mean cost for treating the nine inhibitor patients was 2.25-fold greater than the cost for treating the controls. However, in six of the nine pairs the replacement product costs were actually less for the control patient than for the inhibitor patient, and the median cost of concentrates was comparable in the two groups (CDN$150 686 and $133 342 for inhibitor and control patients, respectively). This discrepancy was largely accounted for by a single inhibitor patient who required frequent hospitalizations for severe bleeding episodes. This individual, who did not receive an immune tolerance protocol, accounted for 62% of the total costs for the entire inhibitor group. In summary, over the study period the cost of haemostatic therapy for most inhibitor patients did not exceed that of control patients. However, due to the high per-unit cost of the products used to treat inhibitor patients, the effect of individual outliers greatly magnifies the overall costs of treating patients with this complication.

Unsolved problems in haemophilia

Diagnosis and therapy for the vast majority of haemophiliacs in the world remain beyond their reach. Health care costs for hemophilia replacement products keep rising. Global inequities for financing health care result in most hemophiliacs being undertreated. The transfusion-transmitted disease, factor VIII inhibitors, is common. Its predictability escapes detection. Management has progressed substantially and offers many therapeutic modalities. Programs for prophylaxis or immune tolerance induction are impossible for most patients. Thus, the challenge for haemophiliacs is to attain these goals.

Inhibitor development and substitution therapy in a developing country: Turkey

Prevalence of inhibitor in developing countries, such as Turkey, where fresh frozen plasma (FFP) is still in use due to high cost of concentrates, is unknown. To determine the frequency of inhibitors in Turkish haemophiliacs exposed to blood products, 53 haemophilia A patients (age range 1-20; median: 11 years) and 12 haemophilia B patients (age range 3-20; median: 10 years), were evaluated; 31 haemophilia A patients (23 severe) received plasma-derived concentrates and 22 patients (10 severe) only FFP. No haemophilia B patients developed inhibitor, compared with seven of 53 (13%) haemophilia A patients, all with a severe defect (7/33; 21%) and treated with concentrates (7/23; 30%), whereas severe patients treated with FFP showed a lower risk to develop inhibitors (0/10, P = 0.07). Inhibitors were detected after 8-125 exposure days (median: 52). Intermediate-purity concentrates and pasteurization seemed to be linked with a higher risk of inhibitor compared to high-purity concentrates and solvent-detergent inactivation for seven patients with inhibitor. In four of seven inhibitor patients low-dose concentrate was administered at 25 IU kg-1 twice weekly and inhibitor disappeared in 1-4 months. This regimen might be recommended for immune tolerance in developing countries for its lower cost.

Zero incidence of inhibitor development in previously treated haemophilia A, HIV-negative patients upon exposure to a plasma-derived high-purity and double viral inactivated factor VIII concentrate

Thirty-six haemophilia A, HIV-negative, previously treated patients were changed therapy to a highpurity and double-inactivated (solvent/detergent and dry-heating) previously unused factor VIII concentrate. The mean age of these patients was 27 years at the time of the change. Twenty-three patients were severe haemophiliacs (FVIII:C < 0.02 IU mL-1), seven moderate (FVIII:C between 0.02 and 0.05 IU mL-1) and six mild (FVIII:C > 0.05 IU mL-1). The mean follow-up with this single product was 16 months, with 82 accumulated exposure days and the mean consumption was 117,300 IU of FVIII corresponding to a mean of six batches per patient. No patient developed FVIII inhibitors (upper limit of the CI95: 7.98%), resulting in an incidence rate of 0/48 patient-years (upper limit of the CI95: 77/1000 patient-years). The change in therapy to this new factor VIII concentrate was not associated with the appearance of inhibitors.