The pharmacokinetics of clotting factor therapy

Clotting factor preparations are expensive and not readily available in all parts of the world. We are still facing shortages due to limited production. Thus, it is obvious that clotting factor therapy should be optimised as far as possible. The judicious use of pharmacokinetic principles should be one of the fundaments of dosing. There are several pitfalls in studies of clotting factor pharmacokinetics, such as discrepancies between assays, inadequate blood sampling protocols, problems to define the administered dose, uncertainty in the estimation of plasma volume for in vivo recovery calculation, and post-infusion activation of the clotting factor. Thus, while the pharmacokinetics of factor VIII is well characterised there are some discrepancies in the literature on factor IX. Recombinant factor VIIa is useful to treat haemorrhages in haemophilia complicated by inhibitors. The pharmacokinetics of VIIa has been investigated, however, the relationship between plasma level of VIIa and effect needs further exploration. Important applications of clotting factor pharmacokinetics include optimising the treatment and improving its cost-effectiveness during long-term prophylaxis as well as during bleeding episodes and surgery.     

Improved cost-effectiveness by pharmacokinetic dosing of factor VIII in prophylactic treatment of haemophilia A

The aim of the study was to investigate the feasibility of optimizing prophylactic dosing of factor VIII by the use of individual pharmacokinetic data. Twenty-one patients were enrolled in a randomized cross-over study on standard dosage regimens vs. dosing according to pharmacokinetic principles. The study period was 2×6 months. Using single-dose pharmacokinetic data for each patient, plasma factor VIII procoagulant activity (FVIII:C) curves following various doses and intervals were computer-simulated. From these calculations, a suitable dosage was chosen. FVIII:C was also repeatedly measured during study periods. Trough levels of FVIII:C, numbers of spontaneous joint bleedings and amounts of factor concentrate used during the two study periods were compared for each patient.
There was a close correlation between predicted and measured values of FVIII:C. As the half-lives of FVIII:C in the patients varied from 7.8 to 18.3 h, it was obviously beneficial to base the dosage on individual pharmacokinetic data. Fourteen patients completed both study periods. Mean trough level of exogenous FVIII:C was raised from 0.89 (SD 0.73) U dL⁻¹ during standard dosage to 2.2 (1.5) U dL⁻¹ during pharmacokinetic dosage. Concomitantly, mean 6-month consumption of factor VIII was decreased from 124 000 (SD 30 000) units to 84 000 (31 000) units. Numbers of reported bleedings were generally similar during both periods.
The study demonstrates the usefulness of individual pharmacokinetics as a tool for cost-effective utilization of factor VIII in the prophylactic treatment of haemophilia A.     

Use of pharmacokinetics in the coagulation factor treatment of patients with haemophilia

Dosing decisions for replacement coagulation factors in patients with haemophilia should be made on an individual patient basis, with the required dose dependent on factors including the clinical situation, the severity of the factor deficiency, and the location and extent of bleeding. Moreover, there is considerable variability in the pharmacokinetics of coagulation products that needs to be considered; in particular, with both factor (F) IX and FVIII products, there is considerable inter-patient variability in in vivo recovery and terminal half-life values. In the present report, we provide a practical guide to calculating and applying pharmacokinetic parameters relevant to the optimal dosing of coagulation products. We discuss the conduct of a pharmacokinetic study in an individual patient, how to calculate pharmacokinetic values from raw data and clinical situations where an individual pharmacokinetic study is helpful. We highlight the importance of considering an individual pharmacokinetic study in all patients starting a new coagulation product.     

Long‐acting recombinant factor IX Fc fusion protein (rFIXFc) for perioperative management of subjects with haemophilia B in the phase 3 B‐LONG study

In the phase 3 B‐LONG (Recombinant Factor IX Fc Fusion Protein [rFIXFc] in Subjects With Haemophilia B) study, rFIXFc demonstrated a prolonged half‐life compared with recombinant factor IX (rFIX), and safety and efficacy for prophylaxis and treatment of bleeding in subjects with moderately‐severe to severe haemophilia B. In this B‐LONG sub‐analysis, rFIXFc was evaluated for efficacy in subjects requiring major surgery. Dosing was investigator‐determined. Assessments included dosing, consumption, bleeding, transfusions and haemostatic response. A population pharmacokinetics model of rFIXFc was used to predict FIX activity. Twelve subjects underwent 14 major surgeries (including 11 orthopaedic surgeries); most subjects (11/12) received rFIXFc prophylaxis before surgery (range, ~2 weeks–12 months). Investigators/surgeons rated haemostatic responses as excellent (n = 13) or good (n = 1). In most surgeries (85·7%), haemostasis from the pre‐surgical dose until the end of surgery was maintained with a single rFIXFc infusion. Blood loss was consistent with similar surgeries in subjects without haemophilia. The strong correlation (R² = 0·9586, P < 0·001) between observed and population pharmacokinetic model‐predicted FIX activity suggests surgery did not impact rFIXFc pharmacokinetics. No unique safety concerns or inhibitors were observed. In conclusion, rFIXFc was safe and efficacious, with prolonged dosing intervals and low consumption, when used perioperatively in haemophilia B. Surgery did not appear to alter rFIXFc pharmacokinetics.     

In vivo recovery of factor VIII and factor IX: intra- and interindividual variance in a clinical setting

In vivo recovery (IVR) is traditionally used as a parameter to characterize the pharmacokinetic properties of coagulation factors. It has also been suggested that dosing of factor VIII (FVIII) and factor IX (FIX) can be adjusted according to the need of the individual patient, based on an individually determined IVR value. This approach, however, requires that the individual IVR value is more reliably representative for the patient than the mean value in the population, i.e. that there is less variance within than between the individuals. The aim of this investigation was to compare intra- and interindividual variance in IVR (as U dL1 per U kg1) for FVIII and plasma-derived FIX in a cohort of non-bleeding patients with haemophilia. The data were collected retrospectively from six clinical studies, yielding 297 IVR determinations in 50 patients with haemophilia A and 93 determinations in 13 patients with haemophilia B. For FVIII, the mean variance within patients exceeded the between-patient variance. Thus, an individually determined IVR value is apparently no more informative than an average, or population, value for the dosing of FVIII. There was no apparent relationship between IVR and age of the patient (1.5-67 years). For FIX, the mean variance within patients was lower than the between-patient variance, and there was a significant positive relationship between IVR and age (13-69 years). From these data, it seems probable that using an individual IVR confers little advantage in comparison to using an age-specific population mean value. Dose tailoring of coagulation factor treatment has been applied successfully after determination of the entire single-dose curve of FVIII:C or FIX:C in the patient and calculation of the relevant pharmacokinetic parameters. However, the findings presented here do not support the assumption that dosing of FVIII or FIX can be individualized on the basis of a clinically determined IVR value.     

Pharmacokinetics, coagulation factor consumption and clinical efficacy in patients being switched from full-length FVIII treatment to B-domain-deleted r-FVIII and back to full-length FVIII

Summary.  Concerns have been raised regarding pharmacokinetic performance, efficacy and safety of B-domain-deleted recombinant FVIII (BDD rFVIII). The objective of this study was to perform a retrospective survey of half-life measurements, efficacy and safety in patients with severe haemophilia A, switching treatment from full-length factor VIII (FL FVIII) to BDD rFVIII and then back to FL FVIII. We hypothesized that half-life of FVIII would be equal regardless of product and that total factor consumption and bleeding frequency would be indistinguishable. We report on inhibitor development and outcome following surgery. Patients with severe haemophilia A, exposed to BDD rFVIII were identified from a database. A retrospective analysis of laboratory data and medical notes was undertaken. No significant difference was detected between the half-life measurements during the switch from FL FVIII (T/2 median 9.15 h, range 6.4–22) to BDD rFVIII (T/2 median 9.7, range 4.7–16.8) and back to FL FVIII (T/2 median 9.0, range 5.0–19.5). There was no significant difference in coagulation factor usage (BDD rFVIII median 4803 IU kg⁻¹ year⁻¹, range 659–11 304; FL FVIII median 5349, range 1691–10 146), nor bleeds. Eleven received BDD rFVIII to cover surgical procedures, with no reports of excess bleeding. Thirty-three patients received significant exposure to BDD rFVIII and one developed a low titre inhibitor. BDD rFVIII was found to be equivalent to other FVIII products in terms of pharmacokinetics, clinical efficacy and safety in this study group.     

Management of a premature infant with moderate haemophilia A using recombinant factor VIII

The birth of a very premature infant with haemophilia A is a rare event. In this case report the problems posed in the management of a child with a factor VIII level of 0.03 IU mL-1 born at 28 weeks of gestation and weighing 1590 g are considered. The value of recombinant factor VIII, the pharmacokinetics of factor VIII in this situation and the importance of close cooperation between paediatricians and haematologists are discussed.     

Enhancement of factor VIIa haemostatic efficacy by formulation with PEGylated liposomes

Summary.  Recombinant activated factor VII (rFVIIa) is an effective treatment of the haemophilia patient with inhibitors and acquired haemophilia. However, on account of its relatively short half-life (HL), achieving therapeutic efficacy with FVIIa requires repeated injections. The development of a long-acting FVIIa product would therefore be beneficial. The formulation of factor VIII with PEGylated liposomes (PEGLip) was previously shown to extend the bleeding-free period in haemophilia patients. We report here an enhancement of haemostatic efficacy by similarly formulating FVIIa with PEGLip. Surface plasmon resonance analysis indicated that FVIIa binds non-covalently but with high affinity and specificity to PEGLip. A one-stage clotting assay demonstrated that formulation of FVIIa with PEGLip does not affect FVIIa activity and stability. A pharmacokinetic study in rats demonstrated that PEGLip formulation of FVIIa extends circulation time and results in higher FVIIa levels several hours after injection. Thromboelastography experiments indicated that PEGLip-FVIIa induces faster clot formation and higher clot stability than standard formulated FVIIa. These results suggest that formulation of FVIIa with PEGLip may lead to a safe and effective long-acting FVIIa that improves the care of haemophilic patients with inhibitors and acquired haemophilia.     

Pharmacokinetics of factor VIII and factor IX

Summary.  A survey of principal pharmacokinetic (PK) studies on factor VIII (FVIII) and factor IX (FIX) plasma- and rDNA-derived concentrates, analysed by means of the PKRD program, has been performed. Notwithstanding the accurate definition of the study design, released in 1991 by the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (SSC-ISTH), a large variability of PK parameters has been pointed out. In the majority of the PK studies, the size of the population is small. In this situation, a careful individualization of haemophilia therapy is strongly recommended. The tailored prediction of loading and maintenance dosages and the need for strict control of trough FVIII/IX levels are mandatory not only to decrease the risk of bleeds but also to spare financial resources. Recently, the old problem of FVIII assay standardization has again become a concern among physicians, especially after the introduction of B-domain deleted rFVIII concentrate. The discrepancies between the widely used one-stage clotting assay and the chromogenic substrate assay seem to be solved by the introduction of a product-specific laboratory standard.     

Pharmacoeconomics of factor dosing in the haemophilia population

Summary.  Treatment of haemophilia is extremely costly due to the short biological half-life of infused factor and pricing issues. This paper examines the impact of different dosing schedules on factor consumption, via a review of literature on dosing regimens used for prophylaxis with a focus on pharmacokinetics (PK).
Pharmacokinetics were found to have an important role for pharmacoeconomics in factor dosing both for assessment of the treatment and for developing new treatment protocols but the clinical response to treatment must always guide the dosing schedule. In order to better understand pharmacoeconomics during prophylaxis, controlled prospective studies are needed but much can also be learned from studies of existing cohorts that have been treated for decades.     

Prophylactic dosing of factor VIII and factor IX from a clinical pharmacokinetic perspective

Summary.  The high cost and limited availability of factor concentrates make dosing of factor VIII (FVIII) or factor IX (FIX) a crucial issue in the prophylactic treatment of haemophilia. It has often been recommended that this treatment should aim to maintain a minimum plasma level of 1% of normal coagulation factor activity (FVIII:C or FIX:C). The dosage needed is commonly given as 25–40 U kg⁻¹ three times weekly for FVIII or twice weekly for FIX. However, these guidelines are valid only with several qualifications. First, the actual trough levels required may vary considerably between patients. The clinical severity of haemophilia may depend on more factors than the endogenous level of FVIII:C or FIX:C. Secondly, interindividual variations in dose requirements are also due to variance in the pharmacokinetics of the coagulation factors. Pharmacokinetic calculations are useful to design optimal dosing schedules to achieve required trough levels of FVIII:C or FIX:C. Moreover, tailoring of the dosing of FVIII or FIX according to their disposition in the individual patient can markedly improve the cost-effectiveness of prophylactic treatment. However, the usefulness of in vivo recovery as a guide for prophylactic dosing seems questionable. It should be clearly understood that maintaining a certain trough level of FVIII:C or FIX:C is not an end in itself. Clinical outcome, not the achieved trough level, determines whether a dosage is adequate. Chiefly for economic reasons, the minimum effective dosage of coagulation factor should be determined and used in every patient. The dose requirement should also be re-evaluated at appropriate times.     

Multidose pharmacokinetics of factor IX: implications for dosing in prophylaxis

The aim of this study was to investigate the use of single-dose pharmacokinetic data for factor IX (FIX) to predict multidose pharmacokinetics and explore their use for pharmacokinetic dosing in prophylactic treatment of Haemophilia B. Eight patients with severe Haemophilia B were enrolled. Using single-dose pharmacokinetic data for each patient, plasma factor IX procoagulant activity (FIX:C) curves during prophylactic dosing were computer-simulated. The simulations were verified by repeated blood sampling and measurements of FIX:C. Theoretical dosing regimens to maintain a plasma trough level of 1.0 U dL⁻¹ of FIX:C were calculated. A 2 × 2 week cross-over study on standard dosing according to bodyweight vs. dosing every three days based on individual pharmacokinetics was carried out. FIX:C was measured during each treatment period. FIX:C data from the plasma sampling generally confirmed the single-dose pharmacokinetic data used. Pharmacokinetically tailored dosing of FIX could result in considerable savings of factor concentrate as compared to current standard dosing. The study demonstrates the applicability of individual pharmacokinetics as a tool for cost-effective utilization of FIX concentrates in the prophylactic treatment of Haemophilia B.     

Cross-reactivity to porcine factor VIII of factor VIII inhibitors in patients with haemophilia in Australia and New Zealand

Abstract Background: Inhibitory antibodies which neutralise factor VIII develop in 10–20% of individuals with inherited haemophilia A and rarely as autoantibodies in normal individuals to cause acquired haemophilia. The antibodies are directed against human factor VIII but cross-react to varying degrees with porcine factor VIII. Porcine factor VIII can be used for treatment in individuals with low cross-reactivity.
Aims: To determine the cross-reactivity of factor VIII inhibitors between human factor VIII and porcine factor VIII, in a population of patients with inherited and acquired haemophilia A. Also, to determine whether patients with inherited haemophilia and inhibitors have a higher incidence of factor VIII gene inversion in intron 22.
Methods: Samples and data sheets from 43 patients with inherited and ten with acquired haemophilia were submitted from hospitals in Australia and New Zealand. Inhibitor levels to human and porcine factor VIII were measured by the Bethesda method in 39 with inherited and nine with acquired haemophilia A.
Results: Of 39 patients with inherited haemophilia A, cross-reactivity was 0% in 17 patients,1–19% in six, 20–39% in 11 and 40–80% in five. In six of nine patients with acquired haemophilia cross-reactivity was 7%. In inherited severe haemophilia A, the frequency of the intron 22 inversion was not greater in 37 study patients than in 28 patients without an inhibitor.
Conclusions: Many patients in Australia and New Zealand with inhibitors to human factor VIII presently show a low or absent level of cross-reactivity to porcine factor VIII. These may respond to treatment with this concentrate at least in the short term. There remains a group of patients with high cross-reactivity who will respond only to recombinant factor Vila or prothrombin complex concentrates.     

A 6-year follow-up of dosing, coagulation factor levels and bleedings in relation to joint status in the prophylactic treatment of haemophilia

Summary. The primary aim of this study was to investigate the possible relationship between coagulation factor level and bleeding frequency during prophylactic treatment of haemophilia after stratification of the patients according to joint scores. The secondary aim was to obtain a systematic overview of the doses of coagulation factors prescribed for prophylaxis at the Malmö haemophilia treatment centre during a 6‐year period. A retrospective survey of medical records for the years 1997–2002 and pharmacokinetic study results from the 1990s was complemented by collection of blood samples for coagulation factor assay when needed. Information on the dosing and plasma levels of factor VIII or factor IX, joint scores and incidence of bleedings (joint bleeds and ‘other bleeds’) was compiled. The patients were stratified by age (0–6, 7–12, 13–18, 19–36 and >36 years) and joint score (0, 1–6 and >6). Individual pharmacokinetic parameters of plasma coagulation factor activities (FVIII:C and FIX:C) were estimated. Trough levels during the treatment were calculated, as well as the number of hours per week of treatment during which plasma FVIII:C/FIX:C fell below a 1, 2 or 3% target level. Fifty‐one patients with haemophilia A (two moderate, 49 severe) and 13 with haemophilia B (all severe) were included, yielding data for 364 patient‐years of treatment. There was a wide range of dosing schedules, the most common ones being three times a week or every other day for FVIII and twice a week or every third day for FIX. The overall relationship between FVIII:C/FIX:C levels and incidence of joint bleeding was very weak, even after stratification of the patients according to joint score. There was no relationship between coagulation factor level and incidence of other bleeds. In this cohort of patients on high‐dose prophylactic treatment, dosing was based more on clinical outcome in terms of bleeding frequency than on the aim to maintain a 1% target level of FVIII:C/FIX:C. Some patients did not bleed in spite of a trough level of <1% and others did in spite of trough levels >3%. The practical implication of our findings is that dosing in prophylactic treatment of haemophilia should be individualized. Thus, proposed standard regimens should be implemented only after careful clinical consideration, with a high readiness for re‐assessment and individual dose tailoring.     

Comparison of coagulant activity of factor VII and activated factor VII activity assays when used for determination of recombinant activated factor VII levels in plasma.

Two assays [coagulant activity of factor VII (FVII:C) and activated factor VII (FVIIa) activity] are currently available for the assessment of factor VII and FVIIa pharmacokinetics. This article presents the results of a comparison of the two assays when applied both in vitro as well as during clinical pharmacokinetic trials of recombinant FVIIa (rFVIIa) administered to healthy individuals and haemophilia patients. The in-vitro data showed that, for the FVII:C assay, plasma samples do not dilute in parallel. For the FVIIa activity assay, dilutions of samples are both parallel and linear with different dilutions of the calibrator. Moreover, intra-assay variation was found to be smaller for the FVIIa activity assay than for the FVII:C assay. When adding different amounts of rFVIIa (0-6 microg/ml) to normal plasma, a mean specific activity of rFVIIa of 48.6 U/mug was observed on applying the FVII:C assay; however, the specific activity decreased with increasing levels of rFVIIa. For the FVIIa activity assay, the mean specific activity was 45.4 IU/mug. Direct comparison of the two activity assays showed that no simple conversion between FVII:C and FVIIa activity measurements are possible. When applying the two assays for pharmacokinetic assessments in two clinical trials, statistically significant different estimates for the area under the curve, half-life, clearance and volume of distribution were obtained. In conclusion, for evaluation of rFVIIa pharmacokinetic properties, activity should be measured with the FVIIa activity assay - which is a more specific and reliable assay of the two available factor VII activity assays, especially when assessing low activity levels.     

Safety and efficacy of high-purity concentrates in haemophiliac patients undergoing surgery by continuous infusion

In this study we explore the feasibility of high-purity double-inactivated concentrates by continuous infusion for the treatment of haemophiliacs in a group of patients undergoing different surgical procedures. The patients were enrolled in the study on the basis of their transfusion history, which was well known due to their long-term follow up at our Haemophilia Center. We did not perform a pre-operative pharmacokinetic study because one of the aims of this study was to demonstrate that continuous infusion can become a first choice standard treatment in patients with haemophilia. Fourteen haemophilia A and one haemophilia B patients who needed at least 5 days of replacement therapy were monitored for haemostatic efficacy, post-operative factor VIII and factor IX levels and evaluated for safety and flexibility of the products. The infusion rate of 3 IU kg-1 h-1 was demonstrated to be sufficient to ensure haemostasis and patients did not need additional bolus infusion during the post-operative period. Our study demonstrates the safety and feasibility of high-purity concentrates in patients undergoing surgery by continuous infusion, also in the absence of a previous pharmacokinetic study.     

A clinical study assessing the pharmacokinetics,efficacy and safety of AlphaNine®, a high‐purity factor IX concentrate,in patients with severe haemophilia B

Summary. Effective treatment with factor IX (FIX) requires a thorough consideration of the properties of the concentrate to be used as replacement therapy, to date, the only available treatment for haemophilia B. The aim of the study was to determine the pharmacokinetics, clinical efficacy and safety in routine clinical use of AlphaNine^®, a high‐purity human FIX concentrate. This open, single‐arm, multicentre, non‐randomized trial included 25 subjects (age ≥ 12) with moderate/severe haemophilia B. Pharmacokinetics was assessed at baseline and after a 6‐month follow‐up. The degree of haemostasis control achieved was evaluated during a 12‐month follow‐up. Safety was evaluated in terms of tolerance, thrombogenicity, immunogenicity and viral safety. Mean recovery was 1.01 ± 0.19 IU dL^?1 per IU kg^?1 at baseline and 1.23 ± 0.34 IU dL^?1 per IU kg^?1 6 months later. Terminal half‐life was 34.5 ± 6.2 h and 33.7 ± 5.4 h, respectively. Ratios of each parameter between the two pharmacokinetic studies were all close to 1. A total of 1,576,890 IU AlphaNine^® were administered in 889 infusions (mean dose per infusion: 1774 IU; 3.2 infusions per month per patient). The main reasons for infusion were mild/moderate bleeding (62.3%) and prophylaxis (20.5% continuous, 15.6% intermittent). Overall, 93.0% of the efficacy assessments were rated as excellent/good and 88.8% of bleedings resolved after the first infusion. Twenty‐one adverse events were reported in eight patients, none of which was considered related to the study medication. AlphaNine^® showed a pharmacokinetic profile in agreement with that of other plasma‐derived FIX concentrates and provides safe and clinically effective substitution therapy for patients with haemophilia B.     

Pharmacokinetic study of a high-purity factor IX concentrate (Factor IX Grifols®) with a 6-month follow up in previously treated patients with severe haemophilia B

Summary. Optimal replacement treatment in haemophilia B patients requires a good understanding of the pharmacokinetics of factor IX (FIX). The aim of this study was to compare the pharmacokinetic profile of Factor IX Grífols^®, a highly purified human FIX concentrate with two specific pathogen inactivation/removal steps, to that of available FIX preparations. The study was an open, non‐randomized trial including 25 male subjects older than 12 years of age with severe haemophilia B. Pharmacokinetic profile of the FIX preparation regularly used by the subjects was determined as control. Pharmacokinetic profile of Factor IX Grifols^® was determined twice, one 7–15 days after control assessment and second after a 6 months period had elapsed. Results showed that all products had peak plasma levels of FIX:C within 30 min. Mean recovery was 1.3 ± 0.3 IU dL⁻¹ per IU kg⁻¹ for Factor IX Grifols^® and 1.0 ± 0.3 IU dL⁻¹ per IU kg⁻¹ for control products (P < 0.001). The mean terminal half‐life (t_1/2) for Factor IX Grifols^® was 26.7 h and 26.8 h for control product. Pharmacokinetic parameters after 6 months of treatment with Factor IX Grifols^® did not statistically differ from the parameters obtained with the first infusion. There were no adverse events related to Factor IX Grifols^® for the duration of the study. In conclusion, Factor IX Grifols^® has adequated pharmacokinetic properties comparable to the control plasma‐derived FIX and these parameters remain stable after 6 months of treatment. Factor IX Grifols^® can be an effective and safe plasma‐derived FIX concentrate for replacement therapy in haemophilia B patients.     

A Phase II clinical trial of a mixture of plasma‐derived factor VIIa and factor X (MC710) in haemophilia patients with inhibitors: haemostatic efficacy,safety and pharmacokinetics/pharmacodynamics

MC710, a mixture of plasma‐derived activated factor VII and factor X at a protein weight ratio of 1:10, is a novel bypassing agent for haemostasis in haemophilia patients with inhibitors. In a Phase II trial, we evaluated the haemostatic efficacy and safety of single doses of MC710, and investigated pharmacokinetic and pharmacodynamic parameters in nine joint bleeding episodes in six male haemophilia patients with inhibitors. This trial was a multi‐centre, open‐label, non‐randomized study of two doses (60 and 120 μg kg^?1 as FVIIa dose), allowing the re‐administration of different MC710 dosages to the same subjects. Haemostatic efficacy was assessed by evaluating reduction in pain and swelling, as well as increase in range of motion in a bleeding joint. The results of the study showed that in nine bleeding episodes, seven treatments were rated as ‘excellent’ or ‘effective’ according to investigator's rating system of efficacy at 8 h after administration. No serious or severe adverse events were observed after administration; furthermore, measurement of several diagnostic markers revealed no signs or symptoms of disseminated intravascular coagulation (DIC). The haemostatic potential of MC710 was confirmed at doses of 60 and 120 μg kg^?1 in this trial. MC710 is thus expected to be a safe and efficacious novel bypassing agent for controlling bleeding in haemophilia patients with inhibitors.     

Antibodies to factor VIIa in patients with haemophilia and high-responding inhibitors

The haemostatic effect of by-passing agents such as activated prothrombin complex concentrates (aPCC) and recombinant factor VIIa is inadequate in some patients with severe haemophilia and high-responding inhibitors. Theoretically, this could be due to antibody reactivity to procoagulant proteins other than the deficient factor. To evaluate this hypothesis, immunoglobulin (Ig) fractions from six multi-transfused patients (three haemophilia A and three haemophilia B) were purified on protein A sepharose and then subjected to immunoaffinity chromatography on factor IX sepharose and factor VIIa sepharose. All three Ig fractions from the haemophilia B patients, but not commercially available Ig, contained antibodies that bound to both gels. None of the haemophilia A patients had antibodies to factor IX but all three had antibodies towards factor VIIa. The immunoaffinity purified antifactor IX and VIIa antibodies from the haemophilia B patients inhibited thrombin formation in vitro using Feiba as active enzyme, but had no significant effect in the presence of NovoSeven. In contrast, no inhibitory effect was observed with the antifactor VIIa antibodies from the haemophilia A patients. Cross-reactivity to factor IX was seen for the antifactor VIIa antibodies from the patients with haemophilia B. Our findings show that antibody reactivity to other procoagulant factors such as factor VIIa exists in patients with high-responding inhibitors and that these antibodies may have an inhibitory potential that correlates to the amount of active enzyme present. The characterization of the antibody profile may facilitate an optimal treatment with by-passing agents in severe bleeding events.