Tranexamic acid as adjunct therapy to bypassing agents in haemophilia A patients with inhibitors

Haemophilia patients with inhibitors require bypassing agents (BPA) like activated prothrombin complex concentrate (aPCC) and recombinant activated factor VII (rFVIIa) to control bleeds. Adjunct tranexamic acid (TXA) may improve haemostasis. The objective of this study was to investigate safety and haemostatic effect of TXA given in combination with BPA. Healthy volunteers (N = 5) and haemophilia inhibitor patients (N = 6) were enrolled in a prospective case crossover design. Controls were treated with TXA 20 mg kg^?1 orally (O.R.) Patients were treated with aPCC 75 IU kg^?1 intravenous (I.V.) on day 1 followed by TXA 20 mg kg^?1 O.R. combined with aPCC 75 IU kg^?1 I.V. on day 2. A 14‐day washout occurred before crossover to rFVIIa 90 μg kg^?1 I.V. ±TXA. Safety evaluation and blood sampling processes were performed at baseline, 15, 30, 60, 120, 180 and 240 min post treatment. Primary outcome was maximum clot firmness (MCF) evaluated by whole blood thromboelastometry using a TF + tissue plasminogen activator‐based assay. Healthy controls showed a 20‐fold increase in MCF following TXA. Adjunct TXA to aPCC or rFVIIa induced a significant increase in MCF (P < 0.0001) reaching levels indistinguishable from healthy controls treated with TXA (P > 0.05). Infusion of aPCC or rFVIIa alone induced only 3–10 fold increase in MCF from baseline, with a decline in MCF starting after 60–120 min. TXA did not increase the endogenous thrombin potential. No clinical or laboratory signs of thromboembolic events, disseminated intravascular coagulation, or hypercoagulability were observed. Combination of aPCC or rFVIIa with TXA normalizes clot stability in haemophilia patients with inhibitor as compared to healthy controls. No clinical or laboratory adverse events were observed.     

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

Summary.  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.     

Prediction of the haemostatic effects of bypassing therapy using comprehensive coagulation assays in emicizumab prophylaxis-treated haemophilia A patients with inhibitors

In emicizumab prophylaxis, the concomitant therapy using bypassing agents (BPAs) is required for breakthrough bleeding and invasive procedures with attention to thrombotic complications. To predict coagulant effects of BPAs in emicizumab-treated patients with haemophilia A (PwHA) with inhibitor (PwHAwI), blood samples from emicizumab-treated PwHAwI (n = 8) and PwHA without inhibitor (n = 2) in phase 1/2 and HAVEN 1 study, spiked with activated prothrombin complex concentrates (aPCC) or recombinant factor VIIa (rFVIIa) ex vivo, and blood samples from emicizumab-treated PwHAwI-receiving BPAs were analysed by Ca²⁺-triggered rotational thromboelastometry (ROTEM) and ellagic acid/tissue factor-triggered clot waveform analysis (CWA). Spiked aPCC, corresponded to 10–100 U/kg, markedly shortened ROTEM parameters beyond the normal range, while spiked rFVIIa, corresponded to 90–270 μg/kg, shortened them within near-normal range. Each of the spiked BPA-improved adjusted maximum coagulation velocity of CWA to within or near the normal range. In blood samples at post-infusion of aPCC (44–73 U/kg) or rFVIIa (79–93 μg/kg), the parameters of both assays improved to approximately the normal range. Taken together, ex vivo results of spiking tests in ROTEM and CWA, except aPCC spiking test in ROTEM, were relatively consistent with in vivo ones, and could usefully predict the coagulant effects of concomitant bypassing therapy for emicizumab-treated PwHAwI.     

Evaluation of rFVIIa (NovoSeven) in Glanzmann patients with thromboelastogram

Summary.  Glanzmann thrombasthenia (GT) is a rare platelet function disorder characterized by a defect in fibrinogen binding to platelet membrane glycoprotein (GP) IIb/IIIa. Recombinant FVIIa (rFVIIa) is a haemostatic agent approved for the treatment of haemophilia patients with inhibitors, patients with acquired haemophilia and in EU also for treatment of factor VII (FVII)-deficient patients and GT patients with antibodies to GPIIb-IIIa. The present study was conducted to evaluate the use of the whole blood test system, rotational thrombelastometry (ROTEM), in measuring the overall haemostasis potential of rFVIIa in 28 GT patients treated with rFVIIa. The correlation of administered rFVIIa and time to start fibrin formation and clot dynamic/stability was assessed and correlation to the clinical response was elucidated. Assessments were performed on predose blood samples spiked with four different concentrations of rFVIIa and whole blood samples taken at 10 and 120 min following dosing. ROTEM parameters clotting time (CT), clot formation time (CFT) and maximum clot firmness (MCF) were measured. Both ex vivo and in vivo data showed beneficial effects on CT in the presence of rFVIIa, but no effect of added rFVIIa was seen on CFT and MCF. In conclusion, the use of thrombelastography at least in the modified form of ROTEM seems to be of limited use in predicting an adequate dose of rFVIIa in GT patients. A good clinical haemostatic response was recorded in spite of the limited changes in the ROTEM pattern supporting the conclusion that ROTEM should not be the method of choice for monitoring rFVIIa therapy in Glanzmann patients.     

Thrombin generation and fibrinolysis in anti‐factor IX treated blood and plasma spiked with factor VIII inhibitor bypassing activity or recombinant factor VIIa

Summary. Activated prothrombin complex concentrates (aPCC) and recombinant activated factor VIIa (rFVIIa) are two important therapies in haemophilia patients with inhibitors and improve clot stability. We hypothesized that potential differences in procoagulant and fibrinolytic actions of aPCC and rFVIIa may lie in the clot stability against fibrinolytic activation. We used thrombin generation, fluorescence detection and thromboelastometry in anti‐factor IXa (FIXa) aptamer‐treated whole blood (WB) and plasma to evaluate: (i) generation of thrombin and activated factor X (FXa) and (ii) viscoelastic properties of blood clots in the presence of tissue plasminogen activator (tPA) after addition of aPCC (0.4 U mL^?1) or rFVIIa (60 nm ). Peak thrombin generation increased from 85 ± 19 nm in aptamer‐treated plasma to 276 ± 83 nm and 119 ± 22 nm after addition of aPCC and rFVIIa respectively (P < 0.001). FXa activity increased within 20 min by 87 ± 6% and by 660 ± 97% after addition of aPCC and rFVIIa respectively (P < 0.001). TPA‐induced lysis time increased from 458 ± 378 s in aptamer‐treated WB to 1597 ± 366 s (P = 0.001) and 1132 ± 214 s (P = 0.075), after addition of aPCC and rFVIIa respectively. In this haemophilia model using the anti‐FIXa aptamer, the larger amount of thrombin was generated with aPCC compared with rFVIIa, while FXa generation was more rapidly increased in the presence of rFVIIa. Furthermore, clot formation in anti‐FIXa aptamer‐treated WB was less susceptible to tPA‐induced fibrinolysis after adding aPCC compared with rFVIIa.     

Tailoring haemostatic treatment to patient requirements – an update on monitoring haemostatic response using thrombelastography

Summary.  Currently, there is no single haemostasis laboratory test that has the capacity to accurately illustrate the clinical effects of procoagulant or anticoagulant interventions. Although the time course of thrombin generation in plasma and the endogenous thrombin potential (ETP) may be useful coagulation parameters, clotting involves components other than thrombin (e.g. platelets, fibrinogen). The continuous coagulation profiles of thrombelastography may provide a more accurate reflection of in vivo biology, covering initiation, development and final clot strength during whole blood clot formation. This method has helped to clarify the mechanism of action of whole blood clot formation, demonstrating the differences from clotting in plasma, and the importance of platelets and tissue factor titrations. It has also been used to investigate hypocoagulation (in haemophilia A, rare coagulation disorders, anticoagulant therapy and dilutional coagulopathy), hypercoagulation and the ex vivo testing of haemostatic interventions. Thrombelastography has been shown to reflect the clinical efficacy of activated prothrombin complex concentrate (aPCC) and recombinant activated factor VII (rFVIIa) in patients with haemophilia A with inhibitors and in patients with acquired haemophilia. Overall, tailoring laboratory assays to illustrate and correlate with clinical phenotypes is essential for effective coagulation monitoring. Applying an algorithm of preoperative, perioperative and postoperative tests, including thrombelastography, may enable physicians to achieve this.     

Bypass therapy assay testing as a strategy to reduce costs for treatment of haemophilia patients with inhibitors

Published studies suggest that bypass therapy assay testing can be used to predict treatment response and dosing requirements for haemophilia patients with inhibitors. The aim of this study was to evaluate the costs of utilizing and not utilizing bypass therapy assay testing before treating mild‐to‐moderate bleeding episodes on‐demand in haemophilia patients with inhibitors from a US third‐party payer perspective. In our exploratory decision tree model, the average patient was assumed to be an adult weighing 75 kg. Based on existing head‐to‐head clinical trials, the efficacy of activated prothrombin complex (aPCC) and recombinant factor VIIa (rFVIIa) was assumed to be equivalent and based on expert opinion of the haematologist in our study it was conservatively assumed that assay testing improves the efficacy of both the bypassing agents by 10%. Probabilistic and one‐way sensitivity analyses were used to determine the robustness of the results. Cost savings per bleeding episode were estimated at $6886 (95% CI = $4310–7978) for aPCC and $7647 (95% CI = $3134–10 388) for rFVIIa treatment. This translates in potential cost savings of 24.8% (95% CI = 15.5–28.8%) for aPCC use and 18.2% (95% CI = 8–24.7%) for rFVIIa use. Furthermore, if testing successfully predicts the optimum dose for concomitant therapy at the onset of bleeding, significant cost savings were observed compared with rFVIIa and aPCC therapies alone. Use of bypass therapy assay testing before treatment administration in haemophilia inhibitor patients can potentially reduce treatment costs significantly while optimizing dose and therapy response.     

A cost evaluation of treatment alternatives for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Brazil

Summary.  The first-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Brazil is currently activated prothrombin complex concentrate (aPCC), with recombinant activated factor VII (rFVIIa) used as second-line therapy or as a last resort. The aim of this study was to determine the cost and effectiveness of these treatments from the perspective of the Brazilian National Health Service. A decision analysis model was constructed to assess total direct medical costs (including drug costs, costs of outpatient or inpatient care, ambulance transportation and cost of concomitant medications) of first-line treatment with aPCC or rFVIIa. Clinical outcome and resource utilization data were obtained both retrospectively and prospectively and validated by the consensus of an expert panel of Brazilian haematologists. A total of 103 bleeds in 25 patients were included in the analysis. rFVIIa resolved bleeds more quickly (4.4 h) than aPCC (62.6 h) and was more effective (100% vs. 56.7% respectively). Mean total direct medical costs (from initiation to cessation of bleed) were estimated to be US$13 500 (aPCC) and US$7590 (rFVIIa). Extensive sensitivity analyses confirmed the cost-effectiveness of rFVIIa. Compared with aPCC, rFVIIa was more effective and less expensive when used as first-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Brazil. rFVIIa should be considered a first-line treatment for the management of these patients.     

Safety of recombinant activated factor VII (rFVIIa) in patients with congenital haemophilia with inhibitors: overall rFVIIa exposure and intervals following high (>240 μg kg−1) rFVIIa doses across clinical trials and registries

Recombinant activated factor VII (rFVIIa) is indicated for treatment of bleeding in congenital haemophilia with inhibitors (CHwI) using 90 μg kg^?1 every 2–3 h (EU and US) or a single 270 μg kg^?1 dose (EU only) with ~90% efficacy reported for both regimens. Dosing of rFVIIa varies, and home treatment makes assessment of frequency of doses >90 μg kg^?1, the intervals before additional treatment, and the risk for thromboembolic events (TEs) more difficult. This post hoc analysis assessed the safety and distribution of rFVIIa dosing in CHwI and the impact of >240 μg kg^?1 dosing on subsequent bypassing agent (BPA) dosing interval and frequency. Data regarding on‐demand or prophylactic rFVIIa dosing, TE incidence and subsequent BPA dosing after high rFVIIa doses were compiled from multiple sources incorporating safety surveillance. A total of 61 734 rFVIIa doses were reported in 481 patients treated for 3947 bleeds and for 43 135 prophylaxis days. Over half (52%) exceeded 120 μg kg^?1, 37% exceeded 160 μg kg^?1 and 15% exceeded 240 μg kg^?1. Subsequent doses of BPA(s) were administered after 38% of initial and 49% of any rFVIIa dose >240 μg kg^?1, and were most frequently administered ≥24 h after initial (40%) or any (53%) doses >240 μg kg^?1. No TEs were reported. The findings of this analysis show that rFVIIa doses >90 μg kg^?1 are utilized for ‘real‐world’ treatment of children and adults. When additional BPA was administered following an rFVIIa dose >240 μg kg^?1, reported intervals were prolonged, often ≥24 h. No safety issues were identified in the 61 734 doses analysed.     

Efficacy of recombinant activated factor VII vs. activated prothrombin complex concentrate for patients suffering from haemophilia complicated with inhibitors: a Bayesian meta-regression

Summary.  The optimal on-demand treatment of joint bleeds in haemophilia patients with inhibitors is a source of debate, with studies reporting various efficacy levels for different drugs and dosage regimens. To analyse, in a unified Bayesian meta-regression model, the published efficacy of recombinant activated factor VII (rFVIIa) and/or activated prothrombin complex concentrate (aPCC) as on-demand treatments for joint bleeds in haemophilia patients with inhibitors. A systematic search was carried out to identify studies reporting on dosage and efficacy of rFVIIa and aPCC in the treatment of joint bleeds in the target patient population. Data were abstracted and included in the model and adjusted for potential sources of heterogeneity. Pooled efficacy levels for typical rFVIIa and aPCC regimens were estimated. Seventeen studies, collectively reporting on >2000 joint bleeds, were included. Medication type combined with dosage was the only significant explanatory parameter. The model predicts that a typical regimen of 90 μg kg⁻¹ rFVII repeated every 3 h if needed results in cumulative joint bleed resolution of 66%, 88% and 95% after 12, 24 and 36 h, respectively. In comparison, a typical regimen of 75 IU kg⁻¹ aPCC repeated every 12 h if needed results in cumulative joint bleed resolution of 39%, 62% and 76%, respectively. These differences were statistically significant and were also robust in sensitivity analyses. This analysis suggests that a typical rFVIIa regimen will resolve joint bleeds more effectively than a typical aPCC regimen after 12, 24 and 36 h.     

Cost‐effectiveness of recombinant activated factor VII vs. plasma‐derived activated prothrombin complex concentrate in the treatment of mild‐to‐moderate bleeding episodes in patients with severe haemophilia A and inhibitors in Spain

Several analyses have shown that recombinant activated factor VII (rFVIIa) is a cost‐effective intervention compared with plasma‐derived activated prothrombin complex concentrate (pd‐aPCC) for the on‐demand treatment of mild‐to‐moderate bleeds in haemophilia patients with inhibitors. The aim of the study was to assess the cost‐effectiveness of rFVIIa vs. pd‐aPCC in the treatment of bleeding episodes in severe haemophilia A patients with inhibitors in Spain. A decision analytic model was designed to evaluate the costs and clinical outcomes of using rFVIIa or pd‐aPCC to treat mild‐to‐moderate joint bleeds in children (≤14 years old) and adults with inhibitors. Data were obtained from a published meta‐analysis and a panel of haemophilia experts. The analysis was conducted from the perspective of the Spanish National Healthcare System. One‐way sensitivity analyses were performed to assess the impact of model assumptions on study results. In the Treur meta‐analysis, rFVIIa resulted in cumulative joint bleed resolution of 88% and 95% after 24 and 36 h, respectively, compared with 62% and 76%, respectively, with pd‐aPCC (Treur et al. Haemophilia 2009; 15 : 420–36). Here, the mean cost per bleed was estimated at €8473 and €15 579 in children and adults treated with rFVIIa, vs. €8627 and €15 677 in children and adults treated with pd‐aPCC. rFVIIa treatment was found to be the dominating option (cheaper and more effective). The one‐way sensitivity analysis also confirmed that rFVIIa was less costly than pd‐aPCC. The model suggests that rFVIIa is a cost‐effective option compared with pd‐aPCC for the treatment of mild‐to‐moderate bleeding episodes in a Spanish setting.     

Thrombin generation and platelet activation induced by rFVIIa (NovoSeven®) and NN1731 in a reconstituted cell-based model mimicking haemophilia conditions

Summary.  Replacement therapy with factor VIII (FVIII) and factor IX (FIX) is routinely used in haemophilia patients with haemophilia A and B, respectively, while recombinant activated FVII (rFVIIa) has proven to induce haemostasis in haemophilia patients with inhibitors. To evaluate the effect of therapeutic intervention in patients with residual factor activities, the effects of increasing concentrations of rFVIIa or NN1731 on thrombin generation and platelet activation were measured in a cell-based model system mimicking severe, moderate and mild haemophilia A or B. Purified monocytes stimulated to express tissue factor and non-activated platelets from peripheral blood of healthy donors were incubated with a mixture of purified human coagulation factors in the absence or presence of increasing concentrations of FVIII or FIX. Sub-samples were analysed for thrombin activity and platelet activation measured as exposure of P-selectin by flow cytometry. Dose-dependent increases in thrombin generation and platelet activation were observed following increasing concentrations of rFVIIa or NN1731 in both haemophilia A- and B-like conditions. At 25 n m rFVIIa, which nears the peak levels in patient plasma after 90 μg kg⁻¹ intravenous dosing, the effects on maximum thrombin generation rate (maxTG) at 1–10% FVIII were comparable to those at 100% and 200% FVIII in the absence of rFVIIa. Normalization of maxTG required 500 n m rFVIIa and 25 n m NN1731 or 25–100 n m rFVIIa and 5 n m NN1731 in severe or moderate/mild haemophilia A and haemophilia B, respectively. This suggests that NN1731 holds its promise as a future bypassing agent for haemophilia patients with and without inhibitors.     

Platelet-dependent thrombin generation assay for monitoring the efficacy of recombinant Factor VIIa

Although the administration of recombinant coagulation factor VIIa (rFVIIa) is a well established treatment in haemophilia with inhibitory antibodies, monitoring the therapeutic efficacy is still a problem. This is because the complete haemostatic effect in vivo depends on negatively charged surfaces provided by exposed lipids from activated platelets which are not present in standard clinical assays using plasma. The thrombin generation assay, however, measures the endogenous thrombin potential (ETP) in platelet-rich plasma (PRP) and this assay might be useful for monitoring the haemostatic response to rFVIIa. We characterized the in vitro concentration-response relationship of rFVIIa and the thrombin generation parameters ETP, PEAK and TIME TO PEAK using platelet-rich plasma (PRP) and rFVIIa at concentrations between one and five times the therapeutic dose. We also studied the effect of inhibiting tissue-factor and the intrinsic coagulation pathway using excess TF-neutralizing antibodies and corn trypsin inhibitor (CTI), respectively. There was a sigmoid relationship between ETP and PEAK and the dose of rFVIIa. Increasing rFVIIa concentrations between 100 and 500 U/ml resulted in a progressive increase in ETP, whereas supratherapeutical concentrations led to a plateau phase. The plateau phase differed between patients, suggesting a biological variation in the maximum ETP. Neutralization of plasma TF with TF-Ab partially decreased FVIIa efficacy. The inhibitory effect of CTI on rFVIIa-induced thrombin generation via the intrinsic pathway was negligible. The thrombin generation assay using PRP is a useful test for determining the sufficient efficacy of rFVIIa in blood. Once a plateau level is reached, higher doses of rFVIIa have no additional effect on haemostatic efficacy. The variation in plateau levels between subjects indicates that there are inter-individual differences in the level of thrombin activity that can be generated. High doses of rFVIIa are effective even in the absence of TF.     

Tissue factor pathway inhibitor in activated prothrombin complex concentrates (aPCC) moderates the effectiveness of therapy in some severe hemophilia A patients with inhibitor

Some hemophilia A patients who have developed inhibitors are poorly responsive to activated prothrombin complex concentrates (aPCC) after daily dosage, but the mechanism(s) underlying this remain unknown. We examined two representative cases. In case 1, we found that changing to recombinant factor VIIa (rFVIIa) therapy was more effective, and the response to aPCC was restored within ~2 weeks. Tissue factor (TF)-triggered thrombin generation demonstrated a prolonged lag-time and decreased peak thrombin, and this impairment was focused on TF pathway inhibitor (TFPI). Plasma-free TFPI was elevated post-infusion of aPCC, while this was unaffected by rFVIIa. TFPI returned to normal range within 2–3 weeks. Plasmas obtained from patients with poor or good response to aPCC (aPCC-poor or aPCC-good), and good response to rFVIIa (FVIIa-good) demonstrated that free TFPI levels are increased in both aPCC groups, but not in FVIIa-good. TFPI levels pre- and post-infusion in aPCC-poor were significantly higher than those in aPCC-good. Addition of anti-TFPI antibody to the reaction samples demonstrated a greater increase of peak thrombin in aPCC-poor compared to aPCC-good, showing the higher TFPI activity in aPCC-poor. Free TFPI contained in aPCC corresponded to the increasing levels in plasma. In conclusion, TFPI in aPCC attenuated thrombin generation, and the reduced effectiveness of therapy in these circumstances appeared to be related to TFPI activity.     

First 20 years with recombinant FVIIa (NovoSeven)

Summary. This review describes the background for the development of recombinant FVIIa (rFVIIa; NovoSeven) for use in haemophilic patients with inhibitors. The first proof of principle for using pharmacological doses of FVIIa as a haemostatic agent was obtained by producing small amounts of pure plasma‐derived FVIIa, which showed encouraging effect in two patients with haemophilia A and inhibitors. To make pure FVIIa available for use in a larger number of patients, rFVIIa was produced that was approved for use in patients with inhibitors against coagulation factors (congenital haemophilia and acquired haemophilia) in 1996 (EU), 1999 (USA) and 2000 (Japan). The efficacy rate in severe bleedings and in major surgery including major orthopaedic surgery has been found to be around 90% in controlled studies, and no serious safety concerns have been demonstrated. The availability of rFVIIa has facilitated the performance of elective major surgery in haemophilia patients with inhibitors. Further steps along the vision of providing a treatment for inhibitor patients similar to non‐inhibitor patients have been the efficacy of rFVIIa in home‐treatment and recently the encouraging experience in prophylaxis. The concept of using pharmacological doses of rFVIIa as a haemostatic agent is a new one, which has caused difficulties in finding the correct dose. A step forward has been the demonstration that similar efficacy can be achieved after one single dose of 270 μg kg^?1 instead of three injections of a dose of 90 μg kg^?1. The higher clearance rate in children suggests that higher doses may be beneficial in children. The availability of rFVIIa has made advances in the understanding of coagulation processes possible. In a cell‐based in vitro model, it has been shown that rFVIIa binds to preactivated platelets if present in concentrations of 30 nm or higher. By doing so, it activates FX into FXa and enhances the thrombin generation on the activated platelet surface in the absence of FVIII/FIX. Through the increased thrombin generation, a firm, well‐structured fibrin haemostatic plug, which is resistant to premature lysis, is formed. By exploiting this mechanism of action, rFVIIa may also be effective in situations other than haemophilia, characterized by an impaired thrombin generation.     

Clot lysis phenotype and response to recombinant factor VIIa in plasma of haemophilia A inhibitor patients

Recombinant activated factor VII (rFVIIa) is a haemostatic agent that is used for the treatment of haemophilia A patients with inhibitors. However, clinical response to rFVIIa is variable and unpredictable with currently available assays. We investigated the anti‐fibrinolytic effects of rFVIIa in relation to thrombin generation (TG) and other haemostatic parameters in haemophilia A patients with inhibitors. After addition of rFVIIa to plasma, the clot‐lysis assay, TF‐dependent TG, TF‐independent TG and parameters involved in coagulation, anticoagulation and fibrinolysis were assessed. The clot‐lysis test distinguished two groups of patients: a group with a normal and a group with impaired anti‐fibrinolytic response to rFVIIa. Our results showed a dose‐dependent increase in TF‐dependent TG and TF‐independent TG in all individuals. There was a significant difference in TF‐independent TG parameters between the normal and impaired response groups. In addition, there was a difference between the normal and impaired response group in prothrombin time, which could be explained by significantly higher levels of coagulation factors in the normal response group, and soluble thrombomodulin. In conclusion, we observed different in vitro responses following rFVIIa addition in plasma of patients with haemophilia A and inhibitors, which could be partially attributed to levels of procoagulant proteins and soluble thrombomodulin.     

Elective surgery in patients with congenital coagulopathies and inhibitors: experience of the National Haemophilia Centre of Venezuela

Summary. Elective surgery in patients with congenital haemophilia with inhibitors carries a high risk of bleeding. However, inhibitor patients also have a high risk of haemarthroses and other orthopaedic complications, and surgery could improve their quality of life. Successful elective surgery has been reported in inhibitor patients under haemostatic cover with plasma‐derived activated prothrombin complex concentrate (pd‐aPCC) or recombinant activated factor VII (rFVIIa). Recombinant FVIIa has recently become available in Venezuela and, unlike pd‐aPCC, has not been associated with an anamnestic response. The aim of this study was to assess our experience using rFVIIa as a first‐line and sustained treatment in elective invasive surgical procedures at the National Haemophilia Centre in Venezuela. Surgical procedures were classified as major or minor, under haemostatic cover with rFVIIa. A total of 13 patients (12 with haemophilia A with high‐responding inhibitors and one with von Willebrand’s disease type 3) underwent a total of 19 surgical procedures under rFVIIa cover. Thirteen procedures were classified as major surgeries. Intraoperative haemostasis was achieved in the majority of patients. Only two patients required an additional dose of rFVIIa, at 30 min and 75 min, respectively, with good results. Postoperative haemostasis was considered effective in 16 of 18 (89%) of the procedures in haemophilia A patients. Treatment was considered to be ineffective in two patients because of excessive postoperative bleeding. Data from the study provide no safety concerns, and demonstrate that rFVIIa provides effective haemostatic cover in elective surgery in patients with inhibitors; research is ongoing to determine the optimal dose for such procedures.     

Experience of recombinant activated factor VII usage during surgery in patients with haemophilia with inhibitors

Inhibitor development is one of the most challenging complications of haemophilia management. Haemostatic control in patients with haemophilia with inhibitors can be difficult, and is especially risky in those undergoing surgical interventions. Most haemophilia patients with inhibitors suffer from chronic joint disease requiring surgical correction due to recurrent bleeding episodes. The aim of this study was to assess the use of recombinant activated factor VII (rFVIIa) as haemostatic therapy during orthopaedic surgery in haemophilia patients with inhibitors. A series of case reports was retrospectively collected to describe clinical experience of rFVIIa use in inhibitor patients undergoing a range of orthopaedic surgical procedures at a single centre. All surgeries were performed using standard methods. All patients received rFVIIa at a starting dose of 120 μg kg^?1 with the subsequent regimens depending on the type of surgery. rFVIIa provided effective haemostasis in 23 patients with haemophilia A and inhibitors (15 with high inhibitor titres) undergoing orthopaedic surgery. The majority (70%) of surgical procedures were major (joint and extra‐articular surgery). The doses and intervals of rFVIIa treatment used varied depending on the severity of bleeding, and the type (major or minor) or site of surgery. In all cases, administration of rFVIIa achieved good haemostasis. In all 23 patients with haemophilia with inhibitors, rFVIIa treatment in orthopaedic interventions proved to be an efficient haemostatic agent, providing effective intra‐operative and postoperative haemostasis.     

Stabilization of fibrin clots by activated prothrombin complex concentrate and tranexamic acid in FVIII inhibitor plasma

Summary. Defective hemostasis in haemophilia patients with FVIII inhibitors results in a dramatic decrease in thrombin generation forming unstable fibrin clots that are susceptible to fibrinolyisis. In this study we tested whether the combination of plasma derived activated prothrombin complex concentrate (pd‐aPCC) with tranexamic acid (TXA) may improve fibrin clot stability in FVIII inhibitor plasma. A microplate assay for clot lysis time was used to assess clot stability in FVIII inhibitor plasma. The effect of pd‐aPCC on clot stability was first tested using the commercial FVIII inhibitor plasma. TXA (5 ～ 10 mg mL^?1) increased clot lysis time, but pd‐aPCC (0.25 ～ 1.0 U mL^?1) had no effect on it. The combination of pd‐aPCC and TXA significantly increased clot lysis time compared with TXA alone. The effect appeared to be limited to fibrin clot resistance to fibrinolysis, as TXA was found to have no effect on thrombin generation induced by pd‐aPCC. The effect of pd‐aPCC and TXA on clot stability was then tested and verified in plasma samples from ten patients with severe haemophilia A and inhibitors. The combination of TXA (10 mg mL^?1) and pd‐aPCC (0.5 U mL^?1) significantly increased clot lysis time compared to TXA alone. Our results suggest that the combination of pd‐aPCC with TXA improves clot stability in FVIII inhibitor plasma without additional increases in thrombin generation.     

Dosing and effectiveness of recombinant activated factor VII (rFVIIA) in congenital haemophilia with inhibitors by bleed type and location: the experience of the Haemophilia and Thrombosis Research Society (HTRS) Registry (2004–2008)

Control of bleeding in patients with congenital haemophilia with inhibitors requires use of bypassing agents such as recombinant activated factor VII (rFVIIa). Due to the difficulties in performing prospective clinical trials in this small subgroup of patients with haemophilia and the need for postmarketing surveillance, a large‐scale database was developed by the Hemophilia and Thrombosis Research Society. This report comprises an analysis of the database with respect to assessing dosing and efficacy of rFVIIa by bleed type and location. Between January 2004 and November 2008, data from 129 inhibitor patients with 2041 rFVIIa‐treated bleeds were analysed. The bleeds were primarily spontaneous (58%) and traumatic (30%). The most common locations were joints (57%), muscle (20%), mucosal (7%) and subcutaneous (6%). Median total rFVIIa doses per bleeding episode for spontaneous and traumatic bleeds were 540 mcg kg^?1 (4 injections/2 days) and 300 mcg kg^?1 (2.5 injections/1 day) respectively. Median total rFVIIa dose (mean dose, number of injections) was 480 mcg kg^?1 (110 mcg kg^?1, 3) for joint; 557 mcg kg^?1 (120 mcg kg^?1, 4) for muscle; 360 mcg kg^?1 (120 mcg kg^?1, 3) for mucosal and 402 mcg kg^?1 (117 mcg kg^?1, 3) for subcutaneous. Overall efficacy ranged from 89% to 93%; bleeding stopped in 89% of spontaneous and 93% of traumatic bleeds, 90% of joint bleeds, and 89% of muscle, mucosal,and subcutaneous bleeds. Although spontaneous bleeds require slightly higher doses than traumatic bleeds, most bleeds were treated with a median of 3–4 injections (110–130 mcg kg^?1). Effectiveness of rFVIIa was consistently high across bleeding types and locations.