Complications associated with the treatment of haemophiliacs with inhibitors

To examine the safety profile of products used to treat inhibitor patients unresponsive to factor VIII, a review of published clinical experience was performed. The products evaluated were activated prothrombin complex concentrates (aPCCs), such as AUTOPLEX® T, porcine factor VIII and recombinant activated factor VII (rVIIa). Safety characteristics included potential for transmission of infectious agents, anamnesis, thrombogenicity, thrombocytopenia and allergic reactions. While viral transmission has been virtually eliminated, the risk is theoretically higher with plasma-derived products such as aPCC and porcine factor VIII than with rVIIa, although contamination of cultured cells is a concern. Anamnesis occurs with aPCCs and porcine factor VIII, and may induce resistance to further therapy with porcine factor VIII. Thrombosis and disseminated intravascular coagulation are very infrequently reported in patients exposed to aPCCs and rVIIa, and never with porcine factor VIII. The latter is occasionally associated with thrombocytopenia, but this uncommonly limits treatment with this agent. Lastly, allergic reactions occur with about equal frequency with all products, but anaphylaxis is mainly a concern after administration of porcine factor VIII. In conclusion, products currently available are reasonably safe. Considerations such as efficacy, availability, ease of administration and cost must also be considered in making treatment choices.     

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.     

Recombinant factor VIIa versus aPCCs in haemophiliacs with inhibitors: treatment and cost considerations

For haemophiliacs with factor VIII inhibitor titres greater than approximately 5 Bethesda Units, haemostasis is best achieved with activated prothrombin complex concentrates (aPCCs, AUTOPLEX®T and FEIBA®) and the recently approved recombinant factor VIIa (rFVIIa). The optimal treatment should be determined by consideration of efficacy, safety, availability, cost and convenience. The current evidence does not allow definitive conclusions to be drawn regarding the relative efficacy of aPCCs and rFVIIa. The principal safety concerns are transmission of viral or other pathogens, thrombogenicity and immunogenicity. The two aPCCs are derived from human plasma and therefore carry the potential for transmitting viruses. This risk is negligible for rFVIIa, although this product could theoretically transmit animal pathogens. The aPCCs are clinically safe in most applications. Likewise, rFVIIa should be considered potentially thrombogenic, though with a low risk. The aPCCs contain detectable factor VIII and can therefore be immunogenic, but in practice this rarely affects their efficacy. The costs of single doses of aPCCs and rFVIIa are similar, but a treatment course of rFVIIa typically requires more doses. Treatment with rFVIIa may be more cumbersome owing to the requirement for more frequent administration. In addition, as for any product for which there is only a single supplier, availability could be vulnerable in some circumstances.     

Therapeutic choices for patients with hemophilia and high-titer inhibitors.

Effective treatment of bleeding episodes in hemophilia with high titer inhibitors (HTI) remains a challenge, despite the fact that the therapeutic armamentarium has expanded considerably over the past few years. Treatment safety has improved with the availability of porcine factor VIII (FVIII) and bypassing products such as recombinant factor VIIa (rFVIIa), and plasma‐derived activated Prothrombin Complex Concentrates (aPCCs) that are virally inactivated. The major drawbacks of rFVIIa and aPCCs are their unpredictable hemostatic effect, lack of laboratory assays to monitor efficacy and dosing frequency, and the risk of thrombosis. The proceedings of a one‐day workshop of physicians who specialized in treating patients with hemophilia held in Vienna on May 13, 2000 have been summarized. In making a decision regarding the choice of product, physicians often consider the type of bleeding episode (life or limb threatening), age of the patient, volume of the reconstituted product, previous exposure to plasma derived products, cost, efficacy, and safety. For plasma naïve patients, to achieve rapid hemostasis a majority of the panelists used porcine FVIII (for patients who lack porcine inhibitory antibodies) or rFVIIa. For patients previously treated with plasma derived factors, in addition to the above concentrates, aPCCs were recommended. Although no data exists regarding safety and efficacy, switching products was routinely practiced either because of availability or cost. Furthermore, the panelists were uncertain about the efficacy of bypassing agents in the prevention of joint disease in inhibitor patients. The workshop participants felt that future research offers the best solution to resolve some of the dilemmas faced by clinicians and may help individualise treatment in a hemophilia patient with a high titer inhibitor. Am. J. Hematol. 67:240–246, 2001. © 2001 Wiley‐Liss, Inc.     

Managing acute bleeds in the patient with haemophilia and inhibitors: options, efficacy and safety

Summary.  The options available for treating the patient with haemophilia and inhibitors undergoing surgery or with other acute bleeds include high-dose factor VIII (FVIII) (human or porcine), prothrombin complex concentrates (PCCs), activated PCCs (aPCCs), recombinant activated factor VII (rFVIIa), and factor replacement combined with immunoadsorption or immunosuppression. Human FVIII is effective in patients with low-titre inhibitors. Porcine FVIII is currently not available, and PCCs and aPCCs, although effective, have been associated with a high incidence of adverse events. Immunoadsorption and immunosuppression offer excellent long-term solutions, but the duration of these techniques makes them less attractive for use in acute settings. Recombinant FVIIa has demonstrated excellent efficacy and safety, even in patients refractory to other therapies.     

Recombinant factor VIIa: a universal hemostatic agent?

Recombinant factor VIIa (rVIIa) has proved effective for the treatment and prevention of hemorrhage in patients with inherited hemophilia A and B who develop inhibitors to factor VIII or IX, and patients with acquired hemophilia A. More recently, there is evidence that rVIIa may also be effective in the control of abnormal bleeding in a variety of other conditions, such as inherited factor VII deficiency, thrombocytopenia, Glanzmann's thrombasthenia, and liver disease. In some of the reports, rVIIa appeared to be effective in controlling massive hemorrhage in which there was no response to conventional measures. It is now considered by some to be potentially the first universal hemostatic agent. However, further prospective, controlled, and adequately powered clinical studies are clearly required. It will be of particular interest to determine the efficacy of rVIIa in conditions such as severe thrombocytopenia, severe von Willebrand disease, severe defects in platelet activation, and severe deficiencies of factors V, X, II, and fibrinogen in which effectiveness would seem to be unlikely based on our current understanding of mechanisms of action of rVIIa.     

Inhibitor antibodies to factor VIII and factor IX: management

Inhibitor antibodies directed against factor VIII or factor IX present challenges to the clinician. Fortunately, several management options are available, although each has disadvantages as well as advantages. Alloantibodies against factor VIII (which develop in 25 to 50% of children with severe hemophilia A, as well as in a small percentage of children with mild or moderate hemophilia A) may be low titer and transient or may be high titer. Most patients with high-titer problematic inhibitors now try to eliminate the inhibitor by using one of several immune tolerance induction (ITI) regimens. For treatment of bleeding episodes in patients who have high-titer (> or = 5 Bethesda units) inhibitors, one can use a prothrombin complex concentrate (PCC) (preferably an activated PCC [APCC]), recombinant (r) factor VIIa, or porcine factor VIII. The choice of product is generally dependent on the type and severity of the patient's bleeding, degree of cross-reactivity of the patient's inhibitor with porcine factor VIII, physician familiarity with the product, product availability, and cost. In persons with hemophilia B, alloantibodies occur in only 1 to 3% of severely affected individuals. However, in roughly half of those who develop inhibitors, anaphylaxis or severe allergic reactions occur on infusion of any type of factor IX-containing product. This phenomenon usually develops after relatively few exposures to factor IX; thus it is recommended that the first 10 to 20 infusions of factor IX given to children with severe hemophilia B be given in a setting equipped for treatment of shock. For treatment of bleeding episodes in patients with severe allergic reactions, rF VIIa is the treatment of choice. ITI has been less successful in hemophilia B patients with inhibitors than in those with hemophilia A, and in a subgroup of patients with severe allergic reactions who were desensitized to factor IX and then tried on ITI, results were even poorer. Additionally, several developed nephrotic syndrome while on ITI. For hemophilia B patients with inhibitors who do not have allergic reactions to factor IX, bleeding episodes can be treated with PCC or APCC or with rF VIIa. Autoantibodies directed against factor VIII are rare but can occur in a variety of settings. They occur mainly in adults, and bleeding is often severe and life threatening. Although some factor VIII autoantibodies disappear spontaneously, most require immunosuppression. Corticosteroids and cyclophosphamide are generally recommended. For treatment of bleeding, therapeutic options include (human) factor VIII concentrates, porcine factor VIII, APCC, and rFVIIa. The choice of product is generally determined by the consulting hematologist's familiarity with the product, product availability and cost, as well as response to treatment.     

Porcine factor VIII provides clinical benefit to patients with high levels of inhibitors to human and porcine factor VIII

The development of an inhibitor against Factor VIII is an important complication of haemophilia and occurs in approximately 31% of patients [1]. Despite various approaches to their management, the presence of these inhibitors remains a major cause of morbidity and mortality. Inhibitors may be low level [<5 Bethesda Units (BU)] or high level [>10 BU]. Low-level inhibitors usually remain low and do not respond to administered factor VIII with a rise of the inhibitor titre; high-level inhibitors, in contrast, are characterized by a rapid rise in titre following treatment with factor VIII. Modalities of treatment of acute bleeding episodes in patients with inhibitors include 'overcoming' the inhibitor with very large doses of factor VIII, 'bypassing' the inhibitor blockade with products such as activated prothrombin complex concentrates or recombinant factor VIIa, 'removing' the inhibitor by plasmapheresis or immunoabsorption and 'repressing' it with immunosuppressive drugs and immune tolerance induction. An alternative approach is to use a porcine factor VIII concentrate which does not cross-react with the human factor VIII inhibitor. Following treatment with porcine factor VIII, functional factor VIII can be detected and the therapeutic levels correlate with cessation of bleeding. The use of porcine factor VIII may, however, result in the development of antiporcine factor VIII antibodies, limiting its use. Experience in patients with high-titre inhibitors indicates that porcine factor VIII therapy could be used in the presence of factor VIII inhibitors [2-11], including inhibitors to porcine factor VIII [5,7], and that haemostasis may be obtained in the absence of detectable levels of circulating factor VIII [7,11].     

Continuous infusion of recombinant factor VIIa in patients with haemophilia and inhibitors: Experience in the Netherlands and Belgium.

Background: Initial clinical experience with recombinant factor VIIa (rVIIa) for treatment of haemophilia patients with inhibitors against factor VIII or IX has been obtained by administration of rVIIa by repeated intravenous bolus injections. However, continuous infusion of rVIIa may be a more appropriate administration method if prolonged treatment is indicated.Methods: We have surveyed and analysed the initial experience with continuous infusion of rVIIa in the Netherlands and Belgium.Results: Five hospitals treated 7 haemophilia patients with inhibitors on 9 different occasions (4 bleedings, 5 surgical interventions) by continuous infusion of rVIIa over a total of 59 days. Haemostatic coverage was considered effective in 8 out of 9 cases and partially effective in 1 case. Continuous infusion of rVIIa was aimed at rVIIa target plasma levels of 10 U/ml and a decrease in prothrombin time (PT) of 3 s compared to control levels. This was obtained by an initial bolus injection of 90 μg/kg prior to continuous infusion of rVIIa at doses between 30–6 μg/kg/h (mean 17.5 μg/kg/h). A conventional one-stage factor VII coagulation assay, often used in combination with a PT, was satisfactory in monitoring rVIIa treatment. The additional clinical value of anti-fibrinolytic and anti-thrombophlebitic treatment was unclear.Conclusion: In our experience, rVIIa appeared to be efficacious and safe when administered by continuous infusion. Continuous infusion of rVIIa is more convenient than bolus injections of rVIIa, easy to monitor and provides a cost reduction of >50%. These advantages make continuous infusion an attractive administration method for prolonged treatment with rVIIa.     

Continuous infusion of monoclonal antibody-purified factor VIII: Rational approach to serious hemorrhage in patients with allo-/autoantibodies to factor VIII

Hemorrhage in a patient with factor VIII inhibitor is associated with increased morbidity and mortality. Treatment with factor IX complex concentrates or recombinant factor VIIA (rVIIa) may not control bleeding and may induce thrombosis. In this study, continuous infusion of a monoclonal antibody-purified factor VII concentrate (Monoclate-P) was used successfully in two hemophilic patients with factor VIII alloantibodies and one nonhemophilic patient with a factor VIII autoantlbody. In two patients, hemorrhage was life-threatening, and, in one, bleeding did not stop with repeated infusions of activated factor IX complex concentrates. The patients' ages ranged from 4 to 15 years, and the inhibitor levels from 6 to 300 Bethesda units/ml. Clinical hemostasis was excellent, and In vivo recovery of infused factor VIII was achieved. When an excess of monoclonal factor VIII was added to the inhibitor plasma in vitro, a stable level of residual factor VIII activity was noted after an initial rapid loss. This second-order reaction occurs in plasmas of patients with type I factor VIII inhibitors. In one patlent, we showed that the saturation dose of the factor VIII inhibitor predicted in vivo recovery of factor VIII:C. These data emphasize the importance of characterizing the kinetic reactions of the factor VIII inhibitor. Furthermore, we confirm previous reports that continuous infusion of monoclonal factor VIII is a safe and effective treatment of patients with factor VIII inhibitors in whom hemorrhage Is either life-threatening or refractory to standard treatment. © 1994 Wiley-Liss, Inc.     

Inhibitors in young boys with haemophilia.

The development of an inhibitor antibody to factor VIII (or factor IX) in a child with haemophilia presents a major challenge to the paediatric haematologist. This article provides an overview of the incidence of inhibitor development in early childhood (30-52% in boys with severe haemophilia A), genetic risk factors, detection, high titre, low titre and transient inhibitors, and management. Treatment of patients with inhibitors is time-consuming and expensive. One should make every attempt to ensure that the boy's family has an understanding of inhibitors, treatment options, and just what is being recommended for their child and what this involves. Immune tolerance induction is successful in approximately 85% of boys with factor VIII inhibitors, but in only 40-50% of those with factor IX inhibitors. For treatment of bleeding episodes in children with high-titre (> or = 5 Bethesda Units) inhibitors, therapeutic options include activated prothrombin complex concentrates (APCC), rF VIIa, and (for factor VIII inhibitors) porcine factor VIII. The advantages and disadvantages of each are discussed. Although factor IX inhibitors are far less common (occurring in 2-3% of boys with haemophilia B), approximately 50% are accompanied by the occurrence of anaphylaxis or severe allergic reactions to any factor IX-containing product.     

Experience with highly purified porcine factor VIII in a patient with haemophilia A and a factor VIII inhibitor

Highly purified porcine factor VIII has been advocated for the treatment of bleeding episodes in patients with haemophilia who have inhibitors to factor VIII. This approach has been successful in a patient with an intermediate potency inhibitor showing little cross-reactivity to porcine material. As in some other reported cases, a severe allergic reaction occurred on one occasion but did not preclude the subsequent use of the porcine concentrate in carefully controlled conditions.     

Prophylactic effect of recombinant factor VIIa in factor VII deficient patients

Inherited factor VII (FVII) deficiency is a rare autosomal recessive disorder associated with a bleeding tendency. We describe three patients with congenital FVII deficiency who have been treated with activated recombinant factor VII (rVIIa). Two patients had novel mutations and were treated prophylactically with 1.2 mg rVIIa two to three times a week. Patients 1 and 2 had a severe bleeding tendency. The frequency and severity of bleeding decreased by treatment with rVIIa compared with similar treatment with plasma-derived FVII. The third patient with a moderate bleeding phenotype was treated on demand and showed no change in the frequency of bleeding upon treatment with rVIIa or plasma products. The beneficial effect of rVIIa cannot be explained by the rVIIa half-lives. Pharmacokinetical analysis showed rVIIa activity half-lives of 35, 50 and 54 min for patients 1, 2 and 3, respectively. In conclusion, prophylactic treatment of FVII deficient patients with rVIIa appears to be applicable, safe and successful, although the mechanism of action remains to be elucidated.     

Recombinant factor VIIa in the management of surgery and acute bleeding episodes in children with haemophilia and high responding inhibitors

The management of acute and surgical bleeding episodes in children with severe factor VIII or IX deficiency who develop high responding inhibitors presents a major therapeutic challenge to clinicians. Recombinant factor VIIa (rVIIa) is an effective, reliable and safe treatment that can be used to treat acute bleeding episodes prior to commencing an immune tolerance programme and to cover surgical procedures until the immune tolerance programme is successful. In a significant minority of patients, immune tolerance therapy is ineffective and an alternative haemostatic agent such as rVIIa is required for life-long treatment. The present study evaluated the use of rVIIa in a paediatric setting. Twelve children, aged 1-16 years, were treated successfully with rVIIa to prevent surgical bleeding in 20 surgical procedures (19 central venous access device insertion or removal, 1 dental extraction). Minor postoperative haematomata developed in 2 out of 20 cases after regular rVIIa therapy had been discontinued and resolved with a short course of rVIIa in both cases. Three children had six life- or limb-threatening bleeding episodes. All bleeding episodes resolved with regular rVIIa treatment although topical fibrin glue was needed in one child with a frenulum tear. One patient required two red cell transfusions for symptomatic anaemia resulting from two separate bleeding episodes. The rVIIa therapy was well tolerated and there was no evidence of treatment-related complications. We conclude that rVIIa is the treatment of choice for the management of surgery and acute life- or limb-threatening bleeding in children with haemophilia and high responding inhibitors.     

The diagnosis and management of factor VIII and IX inhibitors: a guideline from the United Kingdom Haemophilia Centre Doctors Organisation

The revised UKHCDO factor (F) VIII/IX Inhibitor Guidelines (2000) are presented. A schema is proposed for inhibitor surveillance, which varies according to the severity of the haemophilia and the treatment type and regimen used. The methodological and pharmacokinetic approach to inhibitor surveillance in congenital haemophilia has been updated. Factor VIII/IX genotyping of patients is recommended to identify those at increased risk. All patients who develop an inhibitor should be considered for immune tolerance induction (ITI). The decision to attempt ITI for FIX inhibitors must be carefully weighed against the relatively high risk of reactions and the nephrotic syndrome and the relatively low response rate observed in this group. The start of ITI should be deferred until the inhibitor has declined below 10 Bethesda Units/ml, where possible. ITI should continue, even in resistant patients, where it is well tolerated and so long as there is a convincing downward trend in the inhibitor titre. The choice of treatment for bleeding in inhibitor patients is dictated by the severity of the bleed, the current inhibitor titre, the previous anamnestic response to FVIII/IX, the previous clinical response and the side-effect profile of the agents available. We have reviewed novel dose-regimens and modes of administration of FEIBA (factor VIII inhibitor bypassing activity) and recombinant activated FVII (rVIIa) and the extent to which these agents may be used for prophylaxis and surgery. Bleeding in acquired haemophilia is usually treated with FEIBA or rVIIa. Immunosuppressive therapy should be initiated at the time of diagnosis with Prednisolone 1 mg/kg/d +/- cyclophosphamide. In the absence of a response to these agents within 6 weeks, second-line therapy with Rituximab, Ciclosporin A, or other multiple-modality regimens may be considered.     

Clinical experience with polyelectrolyte-fractionated porcine factor VIII concentrate in the treatment of hemophiliacs with antibodies to factor VIII

Circulating antibodies to factor VIII (anti-VIII, "inhibitors") occurring in patients with hemophilia neutralize porcine factor VIII less readily than human factor VIII in vitro. Over an 18-mo period, 8 patients with anti-VIII were treated with 45 courses (297 infusions) of polyelectrolyte-fractionated porcine factor VIII concentrate (PE porcine VIII). Where no anti-PE porcine VIII was detectable, mean post- infusion rise in plasma factor VIII was 1.29 U/dl/units infused/kg. Above 13 Old Oxford units of anti-PE porcine VIII and 48 Bethesda units of anti-human VIII, there were no postinfusion rises in plasma factor VIII. Where postinfusion rises were detected, clinical responses were good and conventional methods could be used to guide dosage. Ten percent of infusions were followed by febrile reactions, but these were usually mild and decreased in frequency and severity with increasing exposure. Multiple and prolonged courses of therapy were given to some patients without evidence of loss of clinical or laboratory efficacy. PE porcine VIII could provoke anamnestic rises of anti-VIII in susceptible patients, but appeared to have a lower immunogenic potential than human VIII. PE porcine VIII is a rational and effective therapeutic alternative for patients with anti-VIII, particularly those with intermediate level inhibitors who cannot be managed effectively using human factor VIII.     

Immunoblot cross-reactivity of factor VIII inhibitors with porcine factor VIII

Porcine factor VIII has been used successfully to treat factor VIII inhibitor patients whose plasmas have minimal cross-reactivity to porcine factor VIII. However, some inhibitor plasmas do inhibit porcine factor VIII, and the extent of procoagulant inhibition often increases after treatment with porcine factor VIII. Because there is no information about the porcine factor VIII epitopes with which these antibodies react, we have compared the immunoblot and enzyme-linked immunosorbent assay (ELISA) reactivities with porcine and human factor VIII for 20 inhibitor plasmas (11 from hemophilia A patients and 9 autoantibodies). Immunoblots identified binding to porcine factor VIII for only 2 of the 12 plasmas from patients who had not received porcine factor VIII, but this reactivity could not be predicted from the inhibitor titer to porcine factor VIII. Immunoblot reactivity with porcine factor VIII was detected for 7 of 8 inhibitor plasmas from patients who had been previously treated with porcine factor VIII, and the strength of this reactivity was generally related to the inhibitor titer. Of the 5 plasmas that were immunoblot positive with the porcine factor VIII A2 domain, 4 had inhibitor titers greater than 45 Bethesda units when tested with porcine factor VIII, whereas only 1 of 15 of the other plasmas had this level of inhibitor activity with porcine factor VIII. In contrast, immunoblot reactivity to the porcine factor VIII A1 domain did not correlate with the antiporcine VIII inhibitor titer. We also determined the effect of preincubation with human or porcine factor VIII on immunoblot reactivity. In one case, immunoblot reactivity with porcine factor VIII was absorbed with porcine, but not human, factor VIII, which is consistent with antibody formation after treatment with porcine factor VIII. In no cases did human factor VIII reduce the reactivity of inhibitor plasmas with the porcine A1 domain, suggesting that these antibodies are directed at unique porcine factor VIII determinants. The reactivity to porcine A2 in 2 plasmas probably represented cross-reactivity of similar A2 determinants, because it was absorbed by both human and porcine factor VIII. Although the ELISA assays with porcine factor VIII detected antibodies in some plasmas that could not be identified by inhibitor assay or immunoblot, the level of ELISA reactivity was generally consistent with the titers of the other assays.     

Update on the mechanism of action and future of activated prothrombin complex concentrates

Activated prothrombin complex concentrates (aPCCs) are an established treatment for bleeding in patients with inhibitors. These products are derived from prothrombin complex concentrates, purified from human plasma with dedicated activation steps included in their manufacturing process. Despite these activation steps, the majority of the prothrombin complex proteins remain as zymogens, with only a relatively small content of activated coagulation enzymes. Among these, the order of concentration based on activity units is the following: factor VIIa to factor Xa to thrombin to factor IXa. Studies in various in vitro and in vivo model systems indicate that the mechanism of action of aPCCs is primarily based on an enzyme-substrate complex consisting of factor Xa and prothrombin. These findings are complemented by others showing that prothrombin is a major procoagulant that is capable of triggering hemostasis under physiologic and pathophysiologic conditions. Despite the findings of the mechanism of action, aPCCs have a long history of successful clinical use, with established dosing regimens, and a relatively low risk of thromboembolic complications compared with other treatment options for patients with inhibitors.     

The use of porcine factor VIII concentrate (Hyate:C) in the treatment of patients with inhibitor antibodies to factor VIII. A multicenter US experience

The response to a highly purified concentrate of porcine factor VIII was evaluated in 45 bleeding episodes in 38 patients with high responding inhibitor antibodies to factor VIII. A total of 437 infusions were given. The patients came from 25 hemophilia centers in the United States. The majority had a life- or limb-threatening hemorrhage for which other modalities had not been successful. In 32 of 45 episodes, a good to excellent response was obtained. Adverse reactions were minimal, occurring in 17 treatment episodes, and were mostly treated with antihistamines and/or hydrocortisone. No clear predictor of clinical response to porcine factor VIII concentrate was identified, including pretreatment human and porcine inhibitor levels, percentage of cross-reactivity between the human and porcine antibodies, and the presence of measurable levels of factor VIII after the porcine factor concentrate was given. Anamnesis to porcine factor VIII did occur in some instances. Porcine factor VIII is a valuable modality in the treatment of serious hemorrhages in patients with inhibitors to factor VIII. Its use should be considered early in the course of severe hemorrhage in these patients.     

Efficacy of porcine factor VIII in the management of haemophiliacs with inhibitors

We report our experience with polyelectrolyte-fractionated highly purified porcine factor VIII concentrate (Hyate:C). Porcine factor VIII concentrate was used to treat 14 haemorrhagic episodes including seven severe haemarthroses, three severe haematomata, two episodes of oral bleeding, one traumatic and the other after multiple dental extractions and two life-threatening intestinal haemorrhages. Altogether 60 infusions of Hyate:C were given to five haemophiliacs with inhibitors. At the time of the first infusion with porcine factor VIII the anti-human inhibitor level ranged from 60 to 2-5 modified Bethesda units/ml (MBU 4 h incubation). The porcine cross-reactivity of these inhibitors was 25-6% and 5-4% of the human inhibitor level in two patients and scarcely measurable in the other three patients. We injected an amount of porcine factor VIII concentrate corresponding to the calculated porcine neutralizing units plus the units required for haemostasis. The clinical efficacy was excellent and no adverse effects were encountered, apart from two episodes of mild pyrogenic reactions well controlled by hydrocortisone. The anamnestic antibody response against human factor VIII was of slight degree in all cases, while the porcine cross-reactivity showed no significant variation. Our results emphasize the role of porcine factor VIII in the treatment of haemophiliacs with inhibitors.