Individual thrombin generation and spontaneous bleeding rate during personalized prophylaxis with Nuwiq®(human-cl rhFVIII) in previously treated patients with severe haemophilia A

Multicenter evaluation of the hemostatic activity of emicizumab in patients with severe hemophilia A

BACKGROUND

Emicizumab has been approved for the prophylaxis of patients with hemophilia A with or without inhibitors. However, spontaneous and trauma-induced breakthrough bleeds have been reported in patients on emicizumab prophylaxis, and no laboratory assay has been validated to evaluate the hemostatic activity of emicizumab.

OBJECTIVES

The thrombin generation assay (TGA) could be a surrogate marker of the hemostatic efficacy of emicizumab. The correlation between TGA and the methods used to measure emicizumab blood concentration was evaluated in this study.

METHODS

TGA was modified by the use of a trigger reagent combining a very low concentration of tissue factor and activated factor (F)XI. Emicizumab quantification was performed by 3 methods: the modified 1-step FVIII assay and 2 methods based on liquid chromatography and mass spectrometry (LC-MS).

RESULTS

Using tissue factor/activated FXI-triggered TGA and platelet-poor plasma, a relationship was observed between the area under the thrombin generation curve (endogenous thrombin potential [ETP]) and the clinical response of patients to emicizumab. The ultrastructure of fibrin clots was consistent with ETP results and showed that emicizumab had a hemostatic activity equivalent to 20 to 30 IU/dL of FVIII. Finally, pharmacokinetic/pharmacodynamic analyses showed no correlation between ETP and LC-MS nor with modified 1-stage FVIII assay, but a statistically significant correlation between the LC-MS methods and the time-to-peak results of the TGA.

CONCLUSION

Using a modified TGA, this study showed that patients who experienced breakthrough bleeds while on emicizumab had a lower thrombin-generating capacity compared with others with good clinical response to emicizumab.

Pharmacokinetic-Pharmacodynamic Modelling in Hemophilia A: Relating Thrombin and Plasmin Generation to Factor VIII Activity After Administration of a VWF/FVIII Concentrate

BACKGROUND

Hemophilia A patients are treated with factor (F) VIII prophylactically to prevent bleeding. In general, dosage and frequency are based on pharmacokinetic measurements. Ideally, an alternative dose adjustment can be based on the hemostatic potential, measured with a thrombin generation assay (TGA), like the Nijmegen hemostasis assay.

OBJECTIVE

The objective of this study was to investigate the predicted performance of a previously developed pharmacokinetic-pharmacodynamic model for FVIII replacement therapy, relating FVIII dose and FVIII activity levels with thrombin and plasmin generation parameters.

METHODS

Pharmacokinetic and pharmacodynamic measurements were obtained from 29 severe hemophilia A patients treated with pdVWF/FVIII concentrate (Haemate P®). The predictive performance of the previously developed pharmacokinetic-pharmacodynamic model was evaluated using nonlinear mixed-effects modeling (NONMEM). When predictions of FVIII activity or TGA parameters were inadequate [median prediction error (MPE) > 20%], a new model was developed.

RESULTS

The original pharmacokinetic model underestimated clearance and was refined based on a two-compartment model. The pharmacodynamic model displays no bias in the observed normalized thrombin peak height and normalized thrombin potential (MPE of 6.83% and 7.46%). After re-estimating pharmacodynamic parameters, EC50 and Emax values were relatively comparable between the original model and this group. Prediction of normalized plasmin peak height was inaccurate (MPE 58.9%).

CONCLUSION

Our predictive performance displayed adequate thrombin pharmacodynamic predictions of the original model, but a new pharmacokinetic model was required. The pharmacodynamic model is not factor specific and applicable to multiple factor concentrates. A prospective study is needed to validate the impact of the FVIII dosing pharmacodynamic model on bleeding reduction in patients.

Patients with moderate hemophilia A and B with a severe bleeding phenotype have an increased burden of disease

BACKGROUND

Patients with moderate hemophilia express varying bleeding phenotypes.

OBJECTIVES

To assess the burden of disease in patients with moderate hemophilia and a mild or severe phenotype incorporating the thrombin generation profile.

METHODS

This sub-study of the 6th Hemophilia in the Netherlands study, analyzed data of adults with moderate hemophilia A or B. Patient characteristics and information on bleeding tendency, joint status, and quality of life were obtained from electronic patient files and self-reported questionnaires. A severe bleeding phenotype was defined as an annual bleeding rate ≥5, an annual joint bleeding rate ≥3, and/or the use of secondary/tertiary prophylaxis, and a mild phenotype vice versa. TG was measured with the Nijmegen Hemostasis Assay.

RESULTS

This study included 116 patients: 21% had a severe phenotype of whom 46% used prophylaxis. Patients with a severe phenotype treated on demand reported a higher median annual bleeding rate (7), annual joint bleeding rate (3), and more frequently an impaired joint (77%) than patients with a severe phenotype on prophylaxis (2; 0; 70%) or patients with a mild phenotype (0; 0; 47%). Furthermore, patients with a severe phenotype treated on demand experienced a more decreased quality of life. Despite similar factor activity levels, patients with a severe phenotype had a lower thrombin peak height and thrombin potential (0.7%; 0.06%) than patients with a mild phenotype (21.3%; 46.8%).

CONCLUSION

Patients with moderate hemophilia and a severe phenotype treated on demand displayed a high burden of disease as well as a low thrombin generation profile advocating them toward more intensive prophylactic treatment.

Blood-Induced Arthropathy: A Major Disabling Complication of Haemophilia

Haemophilic arthropathy (HA) is one of the most serious complications of haemophilia. It starts with joint bleeding, leading to synovitis which, in turn, can cause damage to the cartilage and subchondral bone, eventually inducing degenerative joint disease. Despite significant improvements in haemophilia treatment over the past two decades and recent guidelines from ISTH and WFH recommending FVIII trough levels of at least 3 IU/dL during prophylaxis, patients with haemophilia still develop joint disease. The pathophysiology of HA is complex, involving both inflammatory and degenerative components. Early diagnosis is key for proper management. Imaging can detect joint subclinical changes and influence prophylaxis. Magnetic resonance imagining (MRI) and ultrasound are the most frequently used methods in comprehensive haemophilia care centres. Biomarkers of joint health have been proposed to determine osteochondral joint deterioration, but none of these biomarkers has been validated or used in clinical practice. Early prophylaxis is key in all severe haemophilia patients to prevent arthropathy. Treatment is essentially based on prophylaxis intensification and chronic joint pain management. However, there remain significant gaps in the knowledge of the mechanisms responsible for HA and prognosis-influencing factors. Better understanding in this area could produce more effective interventions likely to ultimately prevent or attenuate the development of HA.

Sensitive Measurement of Clinically Relevant Factor VIII Levels in Thrombin Generation Assays Requires Presence of Factor XIa

BACKGROUND

 Hemophilia A (HA) is characterized by decreased or absent factor VIII (FVIII) activity. Current FVIII assays are based on clotting time and thus only provide information about the initiation of coagulation. In contrast, thrombin generation assays (TGAs) can be used to measure the full coagulation spectrum of initiation, propagation, and termination that provide information on the whole course of thrombin generation and inhibition. However, the commercially available TG kits lack sensitivity for measurements of hemophilia plasma within lower FVIII ranges, which is essential for explaining differences in bleeding phenotypes in hemophiliacs at clinically low levels of FVIII.

AIMS

 Optimization of the TGA for measurements of low FVIII levels in severe HA patients.

METHODS

 TGA measurements were performed in severe HA pooled plasma (n = 10). Investigations of several preanalytical and analytical variables of the assay were performed in a stepwise process and adjusted based on sensitivity toward intrinsic coagulation activation.

RESULTS

 TGA initiated by tissue factor (TF) alone at varying concentrations was unable to significantly differentiate between FVIII levels below 20%. In contrast, TGA activation with low concentrations of TF in presence of FXIa appeared to be highly sensitive for FVIII changes both in high and low ranges. In addition, a representative TGA curve at trough levels could only be produced using the dual TF/FXIa TGA.

CONCLUSION

 We propose a critical optimization for the setup of the TGA for measurements in severe HA plasma. The dual TF/FXIa TGA shows increased sensitivity, especially in lower FVIII ranges, which allows for better individual characterization at baseline, prediction of interventions, and follow-up.

Thrombin generation, bleeding and hemostasis in humans: Protocol for a scoping review of the literature

INTRODUCTION

Hemostasis and bleeding are difficult to measure. Thrombin generation assays (TGAs) can measure both procoagulant and anticoagulant contributions to coagulation. TGAs might prove useful for the study of bleeding disorders. There has been much progress in TGA methodology over the past two decades, but its clinical significance is uncertain. We will undertake a scoping review of the literature to synthesize available information on the application of TGAs towards the study of bleeding and hemostasis, TGA methodologies being used and to summarize available literature on associations between TGA parameters, bleeding and hemostatic outcomes.

METHODS AND ANALYSIS

MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials (CENTRAL) will be searched in collaboration with an information specialist. Title/abstract and full-text screening will be carried out independently and in duplicate; eligible study types will include randomized controlled trials, non-randomized studies, systematic reviews, and case series reporting TGA results and bleeding/hemostatic outcomes among humans. Mapping the information identified will be carried out with results presented using qualitative data analytical techniques.

ETHICS AND DISSEMINATION

This scoping review will use published, publicly available information. Research ethics approval will not be required. We will disseminate our findings using conference presentations, peer-reviewed publications, social media, and engagement with knowledge users. This review will outline knowledge gaps concerning TGAs, better delineate its applicability as a clinically relevant assay for bleeding. and seek to identify ongoing barriers to its widespread adoption in clinical research, and eventually, in the clinical setting.

TRAIL REGULATIONS

Registration ID with Open Science Framework: osf.io/zp4ge.

The road to implementation of pharmacokinetic-guided dosing of factor replacement therapy in hemophilia and allied bleeding disorders. Identifying knowledge gaps by mapping barriers and facilitators

Clinical guidelines and expert groups recommend the use of pharmacokinetic (PK)-guided dosing of factor replacement therapy for the treatment of bleeding disorders, especially for patients with hemophilia. Although PK-guided dosing is increasingly applied, it is generally not considered standard clinical practice. The aim of this scoping review is to map barriers and facilitators for the implementation of PK-guided dosing in clinical practice and to identify knowledge gaps. A literature search was performed and 110 articles were included that describe PK-guided dosing in patients with bleeding disorders, mostly hemophilia A. We defined two overarching themes, efficacy and feasibility, and discuss five topics within each theme. For each topic, barriers, facilitators and knowledge gaps were described. Although consensus was found with regard to some topics, contradicting reports were found for others, especially with respect to the efficacy of PK-guided dosing. These contradictions highlight the need for future research to elucidate current ambiguities.

In patients with hemophilia, a decreased thrombin generation profile is associated with a severe bleeding phenotype

Background

Heterogeneity in clinical bleeding phenotype has been observed in hemophilia patients with similar FVIII or FIX activity levels. Thrombin generation and plasmin generation, as a global hemostasis assay, may contribute to a better prediction of which patients are at an increased risk of bleeding.

Objectives

The objective of this study was to describe the association between clinical bleeding phenotype and thrombin generation and plasmin generation profiles in patients with hemophilia.

Methods

The Nijmegen Hemostasis Assay, which simultaneously measures thrombin and plasmin generation, was performed in plasma samples of patients with hemophilia participating in the sixth Hemophilia in the Netherlands study (HiN6). Patients receiving prophylaxis underwent a washout period. A severe clinical bleeding phenotype was defined as a self-reported annual bleeding rate of ≥5, a self-reported annual joint bleeding rate of ≥3, or the use of secondary/tertiary prophylaxis.

Results

In total, 446 patients, with a median age of 44 years, were included in this substudy. Thrombin generation and plasmin generation parameters differed between patients with hemophilia and healthy individuals. The median thrombin peak height was 1.0 nM, 25.9 nM, 47.1 nM, and 143.9 nM in patients with severe, moderate, and mild hemophilia and healthy individuals, respectively. A severe bleeding phenotype was observed in patients with a thrombin peak height of <49% and a thrombin potential of <72% compared to healthy individuals, and was independent of the hemophilia severity. The median thrombin peak height was 0.70% in patients with a severe clinical bleeding phenotype and 30.3% in patients with a mild clinical bleeding phenotype. The median thrombin potentials for these patients were 0.06% and 59.3%, respectively.

Conclusion

A decreased thrombin generation profile is associated with a severe clinical bleeding phenotype in patients with hemophilia. Thrombin generation in combination with bleeding severity may be a better tool to personalize prophylactic replacement therapy irrespective of hemophilia severity.

Thrombin generation and implications for hemophilia therapies: A narrative review

Thrombin plays an essential role in achieving and maintaining effective hemostasis and stable clot formation. In people with hemophilia, deficiency of procoagulant factor (F)VIII or FIX results in insufficient thrombin generation, leading to reduced clot stability and various bleeding manifestations. A correlation has been found between the bleeding phenotype of people with hemophilia and the extent of thrombin generation, with individuals with increased thrombin generation being protected from bleeding and those with lower thrombin generation having increased bleeding tendency. The amount, location, and timing of thrombin generation have been found to affect the formation and stability of the resulting clot. The goal of all therapies for hemophilia is to enhance the generation of thrombin with the aim of restoring effective hemostasis and preventing or controlling bleeding; current treatment approaches rely on either replacing or mimicking the missing procoagulant (ie, FVIII or FIX) or rebalancing hemostasis through lowering natural anticoagulants, such as antithrombin. Global coagulation assays, such as the thrombin generation assay, may help guide the overall management of hemostasis by measuring and monitoring the hemostatic potential of patients and, thus, assessing the efficacy of treatment in people with hemophilia. Nevertheless, standardization of the thrombin generation assay is needed before it can be adopted in routine clinical practice.

Thrombin generation assays to personalize treatment in bleeding and thrombotic diseases

Treatment of bleeding and thrombotic disorders is highly standardized and based on evidence-based medicine guidelines. These evidence-based treatment schemes are well accepted but may lead to either insufficient treatment or over-dosing, because the individuals' hemostatic properties are not taken into account. This can potentially introduce bleeding or thrombotic complications in individual patients. With the incorporation of pharmacokinetic (PK) and pharmacodynamic (PK-PD) parameters, based on global assays such as thrombin generation assays (TGAs), a more personalized approach can be applied to treat either bleeding or thrombotic disorders. In this review, we will discuss the recent literature about the technical aspects of TGAs and the relation to diagnosis and management of bleeding and thrombotic disorders. In patients with bleeding disorders, such as hemophilia A or factor VII deficiency, TGAs can be used to identify patients with a more severe bleeding phenotype and also in the management with non-replacement therapy and/or bypassing therapy. These assays have also a role in patients with venous thrombo-embolism, but the usage of TGAs in patients with arterial thrombosis is less clear. However, there is a potential role for TGAs in the monitoring of (long-term) antithrombotic therapy, for example with the use of direct oral anticoagulants. Finally this review will discuss controversies, limitations and knowledge gaps in relation to the introduction of TGAs to personalize medicine in daily medical practice.

Applicability of the Thrombin Generation Test to Evaluate the Hemostatic Status of Hemophilia A Patients in Daily Clinical Practice

Hemophilia A (HA) is a rare bleeding disorder caused by factor VIII (FVIII) deficiency due to various genetic mutations in the F8 gene. The disease severity inversely correlates with the plasma levels of functional FVIII. The treatment of HA patients is based on FVIII replacement therapy, either following a prophylactic or on-demand regime, depending on the severity of the disease at diagnosis and the patient’s clinical manifestations. The hemorrhagic manifestations are widely variable amongst HA patients, who may require monitoring and treatment re-adjustment to minimize bleeding symptoms. Notably, laboratory monitoring of the FVIII activity is difficult due to a lack of sensitivity to various FVIII-related molecules, including non-factor replacement therapies. Hence, patient management is determined mainly based on clinical manifestations and patient–clinician history. Our goal was to validate the ST Genesia^® automated thrombin generation analyzer to quantify the relative hemostatic status in HA patients. We recruited a cohort of HA patients from the Principality of Asturias (Spain), following treatment and at a stable non-bleeding phase. The entire cohort (57 patients) had been comprehensively studied at diagnosis, including FVIII and VWF activity assays and F8 genetic screening, and then clinically monitored until the Thrombin Generation Test (TGT) was performed. All patients were recruited prior to treatment administration, at the maximum time-window following the previous dose. Interestingly, the severe/moderate patients had a similar TGT compared to the mild patients, reflecting the non-bleeding phase of our patient cohort, regardless of the initial diagnosis (i.e., the severity of the disease), treatment regime, and FVIII activity measured at the time of the TGT. Thus, TGT parameters, especially the peak height (Peak), may reflect the actual hemostatic status of a patient more accurately compared to FVIII activity assays, which may be compromised by non-factor replacement therapies. Furthermore, our data supports the utilization of combined TGT variables, together with the severity of patient symptoms, along with the F8 mutation type to augment the prognostic capacity of TGT. The results from this observational study suggest that TGT parameters measured with ST Genesia^® may represent a suitable tool to monitor the hemostatic status of patients requiring a closer follow-up and a tailored therapeutic adjustment, including other hemophilia subtypes or bleeding disorders.

Risk factors for bleeding in people living with hemophilia A and B treated with regular prophylaxis: A systematic review of the literature

BACKGROUND

Knowledge about the risk for bleeding in patients with hemophilia (PWH) would be relevant for patients, stakeholders, and policy makers.

OBJECTIVES

To perform a systematic review of the literature on risk assessment models (RAMs) and risk factors for bleeding in PWH on regular prophylaxis.

METHODS

We searched Medline, Embase, the Cochrane Central Register of Controlled Trials, and the Cochrane Database of Systematic Reviews from inception through August 2019. In duplicate, reviewers screened the articles for inclusion, extracted data, and assessed the risk for bias using the Quality in Prognostic Studies (QUIPS) tool. A qualitative synthesis of the results was not performed due to high heterogeneity in risk factors, outcomes definition and measurement, and statistical analysis of the results.

RESULTS

From 1843 search results, 10 studies met the inclusion criteria. No RAM for the risk for bleeding in PWH was found. Most studies included only PWH A or both PWH A and B and were conducted in North America or Europe. Only one study had a low risk for bias in all the domains. Eight categories of risk factors were identified. The risk for bleeding was increased when factor levels were lower and in people with a significant history of bleeding or who engaged in physical activities involving contact.

CONCLUSIONS

Our findings suggest that plasma factor levels, history of bleeds, and physical activity should be considered for the derivation analysis when building a RAM for bleeding in PWH, and the role of other risk factors, including antithrombotic treatment and obesity, should be explored.

Thrombin generation for monitoring hemostatic therapy in hemophilia A: A narrative review

Patients with severe hemophilia A (HA) have an increased risk of spontaneous and trauma-related bleeding because of a congenital absence of factor VIII (FVIII). Most severe HA patients use prophylactic FVIII concentrate, the effect of which can be monitored with FVIII activity level measurement. However, FVIII activity level is less valuable in predicting the potential clinical bleeding risk. Some patients still experience breakthrough bleeds despite adequate FVIII trough levels, whereas others do not bleed with trough levels below threshold. This difference may be caused by inter-individual differences in pro- and anticoagulant factors, the so-called hemostatic balance. Thrombin generation assays (TGAs) measure the hemostatic balance as a whole. Thereby, the TGAs may be a better tool in the guidance and monitoring of treatment in HA patients. In addition, TGAs offer the opportunity to determine the response to bypassing agents and treatment with non-factor replacement therapy, in which FVIII activity assays are not suitable for monitoring. This review summarizes the current knowledge about monitoring different HA treatment modalities by TGA, as a single treatment option and when used in a concomitant fashion.

Combining factor VIII levels and thrombin/plasmin generation: a population pharmacokinetic-pharmacodynamic model for patients with hemophilia A

Aims

Prophylactic treatment of haemophilia A patients with factor VIII (FVIII) concentrate focuses on maintaining a minimal trough FVIII activity level to prevent bleeding. However, due to differences in bleeding tendency, the pharmacokinetic (PK)‐guided dosing approach may be suboptimal. An alternative approach could be the addition of haemostatic pharmacodynamic (PD) parameters, reflecting a patient's unique haemostatic balance. Our aim was to develop a population PK/PD model, based on FVIII activity levels and Nijmegen Haemostasis Assay (NHA) patterns, a global haemostatic assay that measures thrombin/plasmin generation simultaneously.

Methods

PK/PD measurements were collected from 30 patients treated with standard half‐life FVIII concentrate. The relationship between FVIII activity levels and the thrombin/plasmin generation parameters (thrombin potential, thrombin peak height and plasmin peak height), were described by sigmoidal E_max functions.

Results

The obtained EC₅₀ value was smallest for the normalized thrombin potential (11.6 IU/dL), followed by normalized thrombin peak height (56.6 IU/dL) and normalized plasmin peak height (593 IU/dL), demonstrating that normalized thrombin potential showed 50% of the maximal effect at lower FVIII activity levels. Substantial inter‐individual variability in the PD parameters, such as EC₅₀ of thrombin potential (86.9%) was observed, indicating that, despite similar FVIII activity levels, haemostatic capacity varies significantly between patients.

Conclusion

These data suggest that dosing based on patients' individual PK/PD parameters may be beneficial over dosing solely on individual PK parameters. This model could be used as proof‐of‐principle to examine the application of PK/PD‐guided dosing. However, the relation between the PD parameters and bleeding has to be better defined.

Evaluation of the equivalence of different intakes of Fruitflow in affecting platelet aggregation and thrombin generation capacity in a randomized, double-blinded pilot study in male subjects

BACKGROUND

The water-soluble tomato extract, Fruitflow® is a dietary antiplatelet which can be used to lower platelet aggregability in primary preventative settings. We carried out a pilot study to investigate the range of intakes linked to efficacy and to make an initial assessment of variability in response to Fruitflow®.

METHODS

Platelet response to adenosine diphosphate (ADP) agonist and thrombin generation capacity were monitored at baseline and 24 h after consuming 0, 30, 75, 150 or 300 mg of Fruitflow® in a randomized, double-blinded crossover study in male subjects 30-65 years of age (N = 12). Results were evaluated for equivalence to the standard 150 mg dose.

RESULTS

Results showed that the changes from baseline aggregation and thrombin generation observed after the 75 mg, 150 mg, and 300 mg supplements were equivalent. Aggregation was reduced from baseline by - 12.9 ± 17.7%, - 12.0 ± 13.9% and - 17.7 ± 15.7% respectively, while thrombin generation capacity fell by - 8.6 ± 4.1%, - 9.2 ± 3.1% and - 11.3 ± 2.3% respectively. Effects observed for 0 mg and 30 mg supplements were non-equivalent to 150 mg and not different from baseline (aggregation changed by 3.0 ± 5.0% and - 0.7 ± 10.2% respectively, while thrombin generation changed by 0.8 ± 3.0% and 0.8 ± 3.1% respectively).

CONCLUSIONS

The data suggest that the efficacious range for Fruitflow® lies between 75 mg and 300 mg, depending on the individual. It may be pertinent to personalize the daily intake of Fruitflow® depending on individual platelet response.

TRIAL REGISTRATION

ISRCTN53447583 , 24/02/2021.

Validation of factor VIII activity for monitoring standard and extended half-life products and correlation to thrombin generation assays

INTRODUCTION

Monitoring replacement therapy with standard and extended half-life (EHL) products is challenging, since one-stage assay (OSA) and chromogenic substrate assay (CSA) results may differ significantly. Recent recommendations include local validation of each new product with recovery within 20-30%, depending on activity level.

AIM

To validate factor VIII (FVIII) activity for monitoring products in clinical use on Atellica Coag and to correlate it with thrombin generation.

METHODS

Plasma samples spiked with Advate^® , Elocta^® , Adynovi^® , Nuwiq^® , NovoEight^® and Afstyla^® (0.05, 0.20, 0.50 and 0.80 IU/ml) were analysed using Atellica Coag 360 with CSA-1 (Coatest SP) and CSA-2 (FVIII chromogenic), and OSA (Actin FS). Thrombin generation was performed using two thrombin generation assays (TGA-1 (Thrombinoscope) and TGA-2 (Technothrombin).

RESULTS

All products at levels above 0.05 IU/ml, except Adynovi, showed acceptable recovery using CSA-1, whereas measurements using CSA-2 gave more results outside the target level. All products, except Afstyla, showed acceptable recovery using OSA. Correlation between CSA-1 and OSA was excellent (r² =1.0) with biases of 6-3​2%, depending on FVIII product. A clear dose-response was seen for all thrombin generation parameters and products using both methods, except at low levels for lag time using TGA-1. With CSA-1 as an independent variable, the correlations to thrombin peak (measured with TGA-2) were good (r²  = .8-.9).

CONCLUSION

Our data revealed good correlation and acceptable bias between CSA and OSA using our sets of reagents, methods and analyser in spiked samples. Thrombin generation gave good correlation to CSA-1 factor activity and is a possible complement to factor activity assays.

Study of thrombin generation with St Genesia to evaluate xaban pharmacodynamics: Analytical performances over 18 months

INTRODUCTION

ST Genesia is a new automated system enabling quantitative standardized evaluation of thrombin generation (TG), for example, in patients receiving anti-Xa direct inhibitors (xabans). Data on its analytical performances are scarce.

METHODS

Over an 18-month period, repeatability, reproducibility, and accuracy were assessed using STG-ThromboScreen (without or with thrombomodulin) or STG-DrugScreen reagents (corresponding to intermediate/high tissue-factor concentration, respectively), and controls. Furthermore, reproducibility was assessed using commercialized lyophilized and frozen normal pooled plasmas. Rivaroxaban and apixaban impacts on TG parameters were assessed using spiking experiments. Finally, a comparison with the Calibrated Automated Thrombogram method (CAT) (PPP reagent) was performed using plasma from healthy volunteers enrolled in the DRIVING-studyNCT01627665) before and after rivaroxaban intake.

RESULTS

For all dedicated quality control (QC) levels, inter-series coefficients of variations (CV) were <7% for temporal TG parameters, peak height (PH), and endogenous thrombin potential (ETP), whether results were normalized with a dedicated reference plasma STG-RefPlasma or not. Noteworthy, STG-RefPlasma used for normalization displayed substantially high PH and ETP. Mean biases between the observed and manufacturer's assigned QC values were mostly <7%. Both rivaroxaban/apixaban plasma concentrations were significantly associated with TG parameters. Finally, Bland-Altman plots showed a good agreement between ST Genesia-STG-ThromboScreen and CAT method within the explored range of values, although biases could be observed (PH: 16.4 ± 13.2%, ETP: 17.8 ± 11.9%).

CONCLUSION

ST Genesia^® enables the reliable measurement of TG parameters in both in vitro and ex vivo xaban plasma samples using either STG-ThromboScreen or STG-DrugScreen according to xaban concentrations. The use of reference plasma, despite not completely reflecting a normal pooled plasma behavior, likely improves standardization and inter-laboratory comparisons.

Pharmacodynamic monitoring of factor VIII replacement therapy in hemophilia A: Combining thrombin and plasmin generation

BACKGROUND

Clinical severity of hemophilia A (HA) varies, possibly due to interplay of many factors in the hemostatic pathway. Pharmacokinetic monitoring of factor VIII (FVIII) replacement therapy in HA patients consists of measuring FVIII activity levels and subsequent dose adjustment. The Nijmegen Hemostasis Assay (NHA) measures thrombin generation (TG) and plasmin generation (PG).

OBJECTIVE

To determine differences in TG and PG between HA patients before and during a pharmacokinetic study and identify best parameters to develop a pharmacodynamic model.

METHODS

Twenty-five HA patients (baseline FVIII < 1-9 IU/dL) underwent a pharmacokinetic study with a single dose of 25-50 IU/kg standard half-life FVIII concentrate. At baseline and after administration of FVIII TG and PG parameters were measured with the NHA.

RESULTS

FVIII activity level increased from median 1.0 IU/dL (interquartile range < 1.0-6.0) to 71 IU/dL (62-82) 15 minutes after administration and decreased to 15 IU/dL (10-26) at 24 hours. TG was enhanced simultaneously, with thrombin peak height (TPH) increasing from 22nM (15-35) to 222nM (159-255), and thrombin potential (TP) from 404nM/min (undetectable-876) to 1834nM/min (1546-2353). Twenty-four hours after infusion, TG parameters remained high (TPH 73nM [58.5-126.3]; TP 1394nM/min [1066-1677]) compared to FVIII activity level. PG showed hyperfibrinolysis in severe HA patients compared to mild patients and controls, which normalized after FVIII supplementation.

CONCLUSION

HA patients showed clear differences in baseline TG and PG despite having comparable FVIII activity levels. These results reveal a discrepancy between FVIII activity level and TG, in which the latter may be a better parameter to monitor individualized treatment in HA patients.

Monitoring standard and extended half-life products in hemophilia: Assay discrepancies for factor VIII and IX in pre- and postinfusion samples

BACKGROUND

Monitoring hemophilia treatment with extended half-life products is challenging for coagulation laboratories since factor assays may show substantial differences between results obtained with the one-stage assay (OSA) and the chromogenic substrate assay (CSA).

OBJECTIVES

The aim of this study was to evaluate and compare different factor assays and global coagulation methods.

METHODS

Factor VIII (FVIII) and IX (FIX) activities and global assay parameters were analyzed in pre- and postinfusion samples (5 patients 2 samples/product/method).

RESULTS

Samples containing FVIII products (NovoEight, Elocta, and Nuwiq) gave higher levels when measured with CSA compared to OSA. The correlation was excellent (r 2 ≥ .97) while biases of 42%-72% of mean (CSA-OSA) were obtained. With FVIII (OSA) as independent variable, the correlations to kaolin clot time (CT) and thrombin generation assay (TGA) peak were modest (r2  = .71-.72 and .64-.65, respectively), except for Nuwiq for which there was a poor correlation to TGA peak (r 2 = .08). Samples containing Alprolix, a FIX product, gave a smaller difference between activity levels (CSA-OSA), and the correlation was excellent (r 2 = .96). With FIX (CSA) as independent variable for both Alprolix and Refixia, the correlations to Innovin CT and TGA peaks were weak (r 2 = .33-.45 and .44-.76, respectively).

CONCLUSIONS

Our data show that factor activity assays differ between methods used and agents. These discrepancies indicate the value of having more than one type of assay available in the coagulation laboratory when monitoring hemophilia treatment with extended half-life products. Global assays gave complementary information indicated by the modest correlations to factor activities.

Clustering of Thrombin Generation Test Data Using a Reduced Mathematical Model of Blood Coagulation

Correct interpretation of the data from integral laboratory tests, including Thrombin Generation Test (TGT), requires biochemistry-based mathematical models of blood coagulation. The purpose of this study is to describe the experimental TGT data from healthy donors and hemophilia A (HA) and B (HB) patients. We derive a simplified ODE model and apply it to analyze the TGT data from healthy donors and HA/HB patients with in vitro added tissue factor pathway inhibitor (TFPI) antibody. This model allows the characterization of hemophilia patients in the space of three most important model parameters. The proposed approach may provide a new quantitative tool for the analysis of experimental TGT. Also, it gives a reduced model of coagulation verified against clinical data to be used in future theoretical large-scale modeling of thrombosis in flow.

A new paradigm for personalized prophylaxis for patients with severe haemophilia A

AIM

For patients with severe haemophilia A, guidelines recommend prophylactic treatment with FVIII, with dose calculations targeting a predetermined FVIII trough level. However, this pharmacokinetic (PK) approach is suboptimal, with some patients experiencing breakthrough bleeds. We aimed to improve FVIII dosing by incorporating the thrombin generation assay, a global haemostasis assay whose main pharmacodynamic (PD) parameter, endogenous thrombin potential (ETP), predicts spontaneous bleeding risk.

METHODS

We performed post hoc combined PK-PD modelling using data from 66 adults who received human-cl rhFVIII (Nuwiq^® , Octapharma AG) in a phase IIIb study. Time-to-event analyses simulated the probability of spontaneous bleeding for different FVIII exposures and baseline ETPs.

RESULTS

Ninety-one spontaneous bleeds occurred in 20/66 patients. The relationship between FVIII:C and ETP was non-linear, and the sigmoid Emax model adequately described the data. Individual PK-PD Bayesian estimation significantly improved predictive performance. Simulations showed that the mean spontaneous annual bleeding rate decreased with increasing baseline ETP or dosing: with ETP values of 200, 400 and 600 (nmol/L)·min annual bleeding rates were 2.36, 1.25 and 0.66, respectively, on 40 IU/kg human-cl rhFVIII every 3 days; and annual bleeding rates were 2.09, 1.10, and 0.60, respectively, on 60 IU/kg every 3 days.

CONCLUSION

Prophylactic FVIII dosing is more clinically meaningful when incorporating ETP alongside FVIII level. For the first time, FVIII dosing can be personalized with the aim of eliminating spontaneous breakthrough bleeds.