Comparative effectiveness of factor Xa non-vitamin K antagonist oral anticoagulants versus phenprocoumon in patients with non-valvular atrial fibrillation

BACKGROUND

Non-vitamin K antagonist oral anticoagulants (NOACs) have largely supplanted vitamin K antagonists (VKAs) for oral anticoagulation in non-valvular atrial fibrillation (NVAF). However, data on the real-world effectiveness of NOACs vs. phenprocoumon, a VKA widely used in Germany, are limited. The RELOADED study aimed to compare effectiveness of factor Xa NOACs and phenprocoumon in NVAF in clinical practice.

METHODS

Patients who started on a factor Xa NOAC or phenprocoumon for NVAF during the study period were enrolled from the Institute for Applied Healthcare Research Berlin. Patients were followed from first prescription until the end of exposure or available data. Primary outcomes were analyzed by Cox proportional hazard regression models and included ischemic stroke and systemic embolism for effectiveness, and intracranial hemorrhage (ICH) for safety. Subgroups of interest were patients with diabetes and patients with renal impairment.

RESULTS

The total study population was 64,920; 36.3% of patients initiated phenprocoumon, 34.4% initiated rivaroxaban, 25.0% apixaban, and 4.4% edoxaban. Treatment with phenprocoumon is associated with a similar risk of ischemic stroke/systemic embolism as treatment with rivaroxaban or apixaban; while rivaroxaban (adjusted hazard ratio [HR] 0.57, 95% confidence interval [CI] 0.43-0.75) and apixaban (adjusted HR 0.43, 95% CI 0.31-0.6) were associated with a lower risk of ICH compared to phenprocoumon in NVAF patients. The use of rivaroxaban and apixaban was associated with a lower risk of developing kidney failure in patients with diabetes or renal impairment in comparison to those treated with phenprocoumon.

CONCLUSION

The factor Xa NOACs rivaroxaban and apixaban demonstrated similar effectiveness and lower rates of ICH compared with phenprocoumon in this study.

Andexanet Alfa: What We Have Learned from Clinical Trials and Real-World Data

Andexanet alfa is a specific reversal agent for factor Xa inhibitors with immediate reversal of their anticoagulant effect. Andexanet alfa is currently approved for use in patients treated with rivaroxaban and apixaban who have life-threatening or uncontrolled bleeding. New data from both controlled clinical trials and real-world experience are continuously being published, providing greater insight into the clinical characteristics of the drug, such as efficacy and safety. It is worth considering that andexanet alfa could be of benefit in a variety of different clinical scenarios where patients receiving treatment with apixaban and rivaroxaban (and endoxaban) have life-threatening conditions. These different clinical scenarios, which range from pre-treatment of urgent surgery, especially neurosurgical interventions, and concomitant use of andexanet alfa and prothrombin complex concentrate to onset of bleeding more than 6 h prior to admission, should be clarified as well as the issue of "low/high" dose of andexanet alfa and the need for baseline anti-Xa inhibitor levels measured by point-of-care testing. Finally, management of patients at high risk of thrombosis or recent arterial/venous thrombotic events needs to be further explored. In this current opinion, we address these urgent questions in the light of recent literature and clinical trial data.

Andexanet Alfa for the Reversal of Factor Xa Inhibitor Activity: Prespecified Subgroup Analysis of the ANNEXA-4 Study in Japan

AIMS

Andexanet alfa, a specific antidote to factor Xa (FXa) inhibitors, has been approved for clinical use in several countries, including Japan, based on the results from the phase 3 trial ANNEXA-4. We aimed to assess the efficacy and safety of andexanet alfa treatment in FXa inhibitor-related acute major bleeding in patients enrolled for ANNEXA-4 in Japan.

METHODS

This prespecified analysis included patients enrolled at Japanese sites in the prospective, open-label, single-arm ANNEXA-4 trial. Eligible patients had major bleeding within 18 hours of oral FXa inhibitor administration. The coprimary efficacy endpoints were percent change in anti-FXa activity and proportion of patients achieving excellent or good hemostatic efficacy 12 hours post-treatment.

RESULTS

A total of 19 patients were enrolled, all of whom had intracranial hemorrhage; 16 patients were evaluable for efficacy. Median percent reduction in anti-FXa activity from baseline to nadir was 95.4% in patients taking apixaban, 96.1% in patients taking rivaroxaban, and 82.2% in patients taking edoxaban. Overall, 14/16 patients (88%) achieved excellent or good hemostasis (apixaban, 5/5; rivaroxaban, 6/7; edoxaban, 3/4). Within 30 days, treatment-related adverse events (AEs) and serious AEs occurred in 2 and 5 patients, respectively. One patient died during follow-up, and 2 patients experienced thrombotic events.

CONCLUSION

Treatment with andexanet alfa rapidly reduced anti-FXa activity with favorable hemostatic efficacy in Japanese patients with acute major bleeding. Serious AEs of thrombotic events during rapid reversal of anti-FXa activity arose as particular safety concerns in this population as with previous studies.

Four-factor prothrombin complex concentrate versus andexanet alfa for the reversal of traumatic brain injuries

BACKGROUND

Andexanet alfa was approved in 2018 for reversal of direct oral anticoagulants but due to issues of cost and access, four-factor prothrombin complex concentrate (4F-PCC) continues to be used for this indication. The objective of this study is to evaluate outcomes of reversal with these agents in patients with isolated traumatic brain injuries (TBI).

METHODS

This is a retrospective review of 35 trauma centres from 2014 to 2021. Patients were included with an Abbreviated Injury Scale (AIS)>2 for head and having received andexanet alfa or 4F-PCC within 24 hours of admission. Patients were excluded if P2Y12 inhibitor use or AIS>2 outside of head. Primary outcome includes rate of mortality/hospice at hospital discharge. Secondary outcomes include a composite of serious hospital complications. A subgroup analysis of severe TBI patients (AIS head 4 or 5) was completed. Multivariable logistic regression was used to account for differences in comorbidities and TBI severity.

RESULTS

4F-PCC was given to 265 patients with another 59 receiving andexanet alfa. Patients in the andexanet alfa group were more likely to have an AIS head score of 5 (47.5% vs 26.1%; p<0.005). After adjusting for severity of TBI and comorbidities with regard to tomortality/hospice, there were 15 (25.4%) patients in the andexanet alfa group and 49 (18.5%) in the 4F-PCC group (OR 1.34; 95% CI 0.67 to 2.71). This remained consistent when looking at severe patients with TBI with 12 (28.6%) andexanet alfa patients and 37 (28.7%) 4F-PCC patients (OR 0.93 (95% CI 0.40 to 2.16)). Severe hospital complications were also similar between groups with 5 (8.5%) andexanet alfa patients as compared with 21 (7.9%) 4F-PCC patients (OR 1.01; 95% CI 0.36 to 2.88).

CONCLUSION

There was no firm conclusion on the treatment effect in mortality/hospice or serious complications among isolated TBI patients reversed with 4F-PCC as compared with andexanet alfa.

Comparative analysis of andexanet alfa and prothrombin complex concentrate in reversing anticoagulation by rivaroxaban ex vivo

BACKGROUND

The comparative effectiveness of the specific antidote andexanet alfa vs the nonspecific therapy four-factor prothrombin complex concentrates (4F-PCCs) as reversal agents for direct factor Xa (FXa) inhibitors in severely bleeding patients is unclear. We hypothesised that specific reversal using andexanet alfa would be more effective than a high dose of PCC (50 IU kg-1) for reversing the FXa inhibitor rivaroxaban.

METHODS

The reversal potential of andexanet alfa, various 4F-PCCs, and activated PCC was investigated ex vivo in human blood anticoagulated with rivaroxaban (37.5, 75, 150, and 300 ng ml-1) using a panel of coagulation parameters, including conventional coagulation assays, thrombin generation, and a newly developed viscoelastometric device. We simulated in vivo conditions of coagulation activation and fibrin formation using flow chamber experiments of thrombogenicity potential under arterial flow conditions.

RESULTS

The 4F-PCCs normalised clotting profiles only at low rivaroxaban concentrations, whereas andexanet alfa and activated PCC significantly shortened clotting time at all rivaroxaban concentrations. Only andexanet alfa restored thrombin generation to baseline. Flow chamber results showed that various 4F-PCCs concentration-dependently restored clot formation.

CONCLUSIONS

In contrast to thrombin generation measurements, haemostatic reversal of rivaroxaban using high-dose 4F-PCCs exhibited similar efficacy as andexanet alfa in flow chamber experiments. The haemostatic effects of 4F-PCCs and andexanet alfa in the context of bleeding patients taking FXa inhibitors requires further study.

Characterization of an andexanet alfa administration protocol guided by drug-specific quantitative anti-Xa assays

Following FDA approval in 2018, consensus guidelines recommend andexanet alfa as first-line therapy for the management of life-threatening or uncontrollable bleeding in patients taking oral factor Xa (FXa) inhibitors. Dosing is based on the specific FXa inhibitor and dose, and the time elapsed since the patient's last administration of the medication. Additionally, at our institution, anti-FXa screens and drug-specific assays are obtained to guide subsequent dosing based on institution protocol. The objective of this study was to evaluate andexanet alfa utilization based on anti-Xa and FXa-inhibitor-specific assays and assess associated outcomes. This was a retrospective, single-center study aimed to describe the use of anti-FXa and specific direct oral anticoagulant assays to guide the utilization and administration of andexanet alfa. Secondary endpoints evaluated included thrombotic events during index hospitalization, hospital length of stay, hospital mortality, and discharge disposition. Overall, most patients were prescribed apixaban for atrial fibrillation and received andexanet alfa for reversal of intracranial hemorrhage in the emergency department. In general, DOAC-specific assays were concordant with last known times; however, there appears to be minimal correlation with DOAC-specific assay levels and survival. There were 9 thrombotic events (8.7%) in 8 patients. In this cohort, collection of an anti-FXa assay screen was a practical strategy to guide reversal with andexanet alfa; however, the addition of DOAC-specific assay levels may not enhance clinical utility.

Real-World Reversal of Factor Xa Inhibition in the Setting of Major Life-Threatening Bleeding or Urgent Surgery

Background: Management of major life-threatening bleeding with factor Xa (FXa) inhibition poses complex challenges involving novel direct reversal agents competing with non-specific preexisting strategies. The recent availability of andexanet alfa (AA) led to a health-system guideline incorporating its use alongside the most commonly used historic agent, four-factor prothrombin complex concentrate (4F-PCC). Objectives: The objective was to characterize the use and efficacy of AA and 4F-PCC for reversal of FXa inhibition after implementation of the health-system guideline. Methods: This multi-hospital, retrospective cohort study included patients aged >18 years administered either AA or 4F-PCC between October 2018 to June 2020 with the indication for urgent reversal of FXa inhibitor-induced coagulopathy. The primary outcome assessed hemostatic efficacy between treatment groups. Secondary outcomes evaluated adjunct blood product administration, incidence of repeat pharmacologic reversal, incidence of thromboembolism, intensive care unit and hospital length of stays, and in-hospital mortality. Results: Eighty-five patients were included; 33 patients received AA and 52 patients received 4F-PCC. Effective hemostasis was achieved at similar rates in both treatment groups (84.8% vs 76.9%; P = .373). Thrombotic events occurring during the observed hospitalization were more frequent among the AA treated group (18% vs 3.8%, P = .027). No differences were observed for other secondary outcomes. Conclusion: Guideline use resulted in similar rates of effective hemostasis with a higher incidence of VTE in patients receiving AA. Further exploration with a larger, prospective study to evaluate these findings is warranted.

The use of andexanet alpha in the Polish setting: An interdisciplinary protocol. Expert consensus statement of the Polish Cardiac Society

Andexanet alfa (AA) is a recombinant inactive analog of human activated factor X (FXa), effectively reversing the effects of its inhibitors - rivaroxaban and apixaban, which are available in Poland. The drug was approved for clinical use registration after the publication of the results of the ANNEXA-4 trial (Andexanet Alfa, a Novel Antidote to the Anticoagulation Effects of FXa Inhibitors 4), in which its efficacy in restoring hemostasis in life-threatening hemorrhages in patients receiving using the aforementioned anticoagulants was demonstrated. Hence, AA is now recommended for patients on apixaban or rivaroxaban therapy with massive and uncontrollable hemorrhages, including hemorrhagic strokes (HS) and gastrointestinal bleeding. Drug-specific chromogenic anti-Xa assays are generally best suited for estimating rivaroxaban and apixaban plasma levels, aside from direct assessment of their concentrations. The absence of anti-Xa activity, determined using these assays, allows us to rule out the presence of clinically relevant plasma concentrations of any FXa inhibitor. On the other hand, the dose of AA should not be modified based on the results of coagulation tests, as it depends solely on the time that elapsed since the last dose of FXa inhibitor and oon the dose and type of FXa inhibitor. AA is administered as an intravenous (i.v.) bolus, followed by an i.v. infusion of the drug. The maximum reversal of anti-Xa activity occurs within two minutes of the end of the bolus treatment, with the continuation of the continuous i.v. infusion allowing the effect to be maintained for up to two hours afterwards. Because anticoagulant activity can reappear after the infusion is completed, it is currently unclear at what point after AA administration FXa inhibitors or heparin should be re-administered. In Poland AA is starting to become available and its urgent need to administer it to patients with severe bleeding on apixaban or rivaroxaban.

Use of Andexanet Alfa for Factor Xa Inhibitor Reversal in US Verified Trauma Centers: A National Survey

Direct oral factor Xa inhibitors are replacing vitamin K-dependent antagonists as anticoagulation treatment in many clinical scenarios. Trauma centers are noting an increase in patients presenting on these medications. The 2018 Food and Drug Administration approval of andexanet alfa provides an alternative anticoagulation reversal. Barriers may limit utilization of new medications including a lack of grade 1A evidence supporting the use of prothrombin complex concentrate (PCC) versus andexanet alfa and cost. To evaluate barriers of andexanet alfa utilization by trauma surgeons, a 15-question survey was conducted. There was a 9% completion rate (n = 89). The results revealed 23.5% would choose andexanet alfa as first-line treatment in children, and 25.8% as first-line treatment in adults. The majority of respondents, 64.7% and 67.4%, would use PCC preferentially in children and adults, respectively. Respondents indicated that cost burden was an overriding factor (76.3%); 42.4% cited lack of high-level efficacy data of andexanet alfa for reversal of factor Xa inhibitors. Additional double-blinded multi-institutional randomized controlled trials comparing 4F-PCC and andexanet alfa for factor Xa inhibitor reversal are needed to support efficacy especially with the increased cost associated.

Dose-Related Effectiveness of Andexanet Alfa for Reversal of Apixaban Anticoagulation in a Porcine Polytrauma Model

BACKGROUND

 Andexanet alfa (andexanet) is a reversal agent for use in patients with life-threatening or uncontrolled bleeding treated with oral factor Xa (FXa) inhibitors. There are limited data on the dose-response relationship of andexanet and FXa inhibitor-related bleeding.

OBJECTIVE

 The aim of this study was to assess the dose-related effectiveness of andexanet in reducing blood loss, improving survival, and reversing apixaban anticoagulation in a porcine polytrauma model.

METHODS

 Apixaban was given orally to 40 male pigs for 3 days at a dose of 20 mg/d. On day 3, following bilateral femur fractures and blunt liver injury, animals (n = 8/group) received andexanet (250-mg bolus, 250-mg bolus + 300-mg 2-hour infusion, 500-mg bolus, or 500-mg bolus + 600-mg 2-hour infusion) or vehicle (control). Total blood loss was the primary endpoint. Coagulation parameters were assessed for 300 minutes or until death. Data were analyzed with a mixed-model analysis of variance.

RESULTS

 Administration of 250-mg bolus + 300-mg infusion, andexanet 500-mg bolus, and 500-mg bolus + 600-mg infusion significantly decreased total blood loss by 37, 58, and 61%, respectively (all p < 0.0001), with 100% survival. Andexanet 250-mg bolus was ineffective in reducing total blood loss (6%) and mortality (63% survival) versus controls. Andexanet 500-mg bolus ± infusion neutralized anti-FXa activity to less than 50 ng/mL. Andexanet neutralization of thrombin generation and thromboelastometry parameters was dose and infusion time dependent.

CONCLUSION

 In a porcine polytrauma model with major bleeding on apixaban, andexanet dose dependently decreased anti-FXa activity. Lower anti-FXa levels (<50 ng/mL) with andexanet 500-mg bolus ± infusion were correlated with 60% less blood loss and 100% survival versus controls.

Decrease of prothrombin level during thrombolysis in acute myocardium infarction

Previously, the direct interactions of Bβ26-42 fibrin residues with prothrombin were demonstrated. It was also shown that forming prothrombin complexes with E- or DDE-fragments causes non-enzymatic prothrombin activation. The direct measuring of the prothrombin level in the blood plasma of patients with acute myocardial infarction (AMI) allowed us to find a situation where such an activation can occur in vivo. Blood coagulation parameters in the blood plasma of patients with AMI were measured at 2 hours, three days, and seven days after the thrombolysis by streptokinase accompanied with intravenous administration of anticoagulants: unfractionated high molecular weight heparin (HMWH) and low-molecular-weight heparin (LMWH). The prothrombin level in the blood plasma of patients with AMI was normal before thrombolytic therapy and substantially decreased after streptokinase administration. This effect was prominent in the case of concomitant anticoagulant therapy with LMWH and was not observed when HMWH was applied. It can be explained by the fact that LMWH preferentially inhibits factor Xa, while the HMWH is an effective inhibitor of both factor Xa and thrombin. This observation suggested that the prothrombin level decrease was caused by the thrombin-like activity and possible autolysis of prothrombin by thrombin. Also, thrombolytic therapy with streptokinase caused the accumulation of fibrin degradation products (FDPs), some of which were able to bind prothrombin. The dramatic decrease of prothrombin level in the blood plasma of patients with AMI during thrombolysis allowed us to conclude the non-enzymatic prothrombin activation with the following autolysis of prothrombin that contributes to the pathology.

Administration of andexanet alfa for traumatic intracranial hemorrhage in the setting of massive apixaban overdose: A case report

PURPOSE

Apixaban is a direct-acting oral anticoagulant that selectively inhibits factor Xa. Reversal strategies utilized to treat factor Xa inhibitor-associated bleeding include andexanet alfa, prothrombin complex -concentrate (PCC), and activated PCC (aPCC). The optimal treatment of traumatic intracranial hemorrhage in the setting of an apixaban overdose is unknown.

SUMMARY

This case report describes a 69-year-old female who initially presented to an emergency department at a community hospital due to a ground-level fall with traumatic intracranial hemorrhage. The patient reportedly ingested apixaban 275 mg, carvedilol 250 mg, atorvastatin 1,200 mg, and unknown amounts of amlodipine and ethanol. Anti-inhibitor coagulant complex, an aPCC, was administered approximately 3 hours after presentation. Initial thromboelastography performed approximately 4 hours after presentation showed a prolonged reaction time of 16.8 minutes. Ongoing imaging and evidence of coagulopathy prompted repeated aPCC administration to a cumulative dose of approximately 100 U/kg. The patient underwent craniotomy with hematoma evacuation. Postoperative imaging showed expansion of the existing intracranial hemorrhage and new areas of hemorrhage. Andexanet alfa was administered approximately 18 hours after presentation, followed by repeat craniotomy with evacuation of the hematoma. No further expansion of the intracranial hemorrhage was observed, and the reaction time on thromboelastography was normalized at 6.3 minutes.

CONCLUSION

This case suggests that andexanet alfa may have a role in the management of traumatic hemorrhage in the setting of an acute massive apixaban overdose. Use of andexanet alfa, PCC, and aPCC in this context requires further research.

Hemostatic efficacy of four factor prothrombin complex concentrate in intracerebral hemorrhage patients receiving warfarin vs. factor Xa inhibitors

INTRODUCTION

4-F PCC is administered for reversal of factor Xa inhibitor-associated coagulopathy despite a lack of quality evidence demonstrating hemostatic efficacy. The aim of this study was to evaluate the hemostatic efficacy of 4-F PCC in intracerebral hemorrhage patients who received factor Xa inhibitors versus warfarin.

MATERIALS AND METHODS

This was a multi-center, retrospective, observational cohort study at a large healthcare system. Patients taking warfarin received 4-F PCC 25-50 units/kg based on the presenting INR, while patients taking a factor Xa inhibitor received 35 units/kg. The primary outcome was the percentage of patients with good or excellent hemostatic efficacy as assessed by modified Sarode scale, with neurologic outcomes assessed as a secondary endpoint. Patients were included in the primary outcome population if they had a repeat CT scan within 24 h.

RESULTS

One hundred fifty-seven patients were included in the primary outcome population; [warfarin (n = 76), factor Xa inhibitors (n = 81)]. Hemostatic efficacy was 83 % in the warfarin group versus 75 % in the factor Xa inhibitor group (p = 0.24). The hemostatic efficacy risk difference between the groups was 7.6 % (95 % CI 5.1 %, 20.2 %). Good neurologic outcome (mRS 0-2) at discharge was 17 % in warfarin patients versus 12 % in the factor Xa inhibitor patients (p = 0.40).

CONCLUSIONS

There was no significant difference in hemostatic efficacy or clinical outcomes between patients taking warfarin or a factor Xa inhibitor following reversal with 4-F PCC. This study provides further support that 4-F PCC can be used for the reversal of factor Xa inhibitor-associated coagulopathy.

Case Report: Extended Duration Andexanet Alfa Infusion in a Surgical Trauma Patient

Background: Andexanet alfa (andexanet) is the only FDA-approved medication for reversal of apixaban and rivaroxaban anticoagulation for life-threatening or uncontrolled bleeding. Infusion modifications may be required in surgical patients undergoing prolonged operative intervention but have not previously been described. Case Report: A 78-year-old woman on rivaroxaban for atrial fibrillation was admitted to the trauma service for a mechanical fall, sustaining a T4 burst fracture with severe canal stenosis and spinal cord edema resulting in loss of strength and sensation in her legs. Clinically relevant rivaroxaban activity was verified with an elevated low molecular weight heparin anti-factor Xa assay, and laboratory confirmed coagulopathy was demonstrated by a prolonged prothrombin time, thromboelastography (TEG) R-time, and activated clotting time (ACT). The patient required urgent surgical intervention for spinal fixation. Given the expected prolonged duration of the procedure, standard dose andexanet was initiated with a prolonged infusion at half the standard rate during the operation. The procedure was successful and intraoperative TEGs demonstrated normalization of R-time and ACT throughout the procedure. The patient did not experience any complications postoperatively and successfully discharged to inpatient rehabilitation. Conclusion: Modifications to the andexanet infusion may be required in surgical patients requiring rivaroxaban reversal for a prolonged procedure. Further data are needed to determine the optimal approach to infusion modification.

Recommendations for the use of andexanet alfa in the management of bleeding in patients on oral factor Xa inhibitors in Switzerland: Guideline from the Working Party Hemostasis of the Swiss Society of Hematology

Anticoagulants are essential in preventing and treating thrombosis. Unfortunately, their use is accompanied by an enhanced risk of bleeding. Since the introduction of direct oral anticoagulants (DOACs), the risk of major bleeding has been reduced but not eliminated. Major bleeding events related to the use of factor Xa inhibitors can be challenging to manage. In recent years, four-factor prothrombin complex concentrates have been used in patients with severe bleeding taking oral direct factor Xa inhibitors (apixaban, edoxaban and rivaroxaban). Andexanet alfa (OndexxyaTM, AstraZeneca AG) is a specially designed recombinant version of human factor Xa that acts as a decoy receptor to reverse the effects of factor Xa inhibitors. Since 2 December 2020, andexanet alfa has been used in Switzerland for adult patients receiving apixaban or rivaroxaban when reversal of anticoagulation is required because of life-threatening or uncontrolled bleeding. However, the use of andexanet alfa remains a challenge owing to its cost, the reported thrombotic complications and the fact that its efficacy mainly relates to intracranial haemorrhage. Moreover, the use of nonspecific reversal agents together with andexanet alfa is controversial. The present recommendations on the use of andexanet alfa in the management of bleeding in patients on factor Xa inhibitors in Switzerland were developed by a group of Swiss experts from the Working Party Hemostasis of the Swiss Society of Hematology. These recommendations aim to provide support to clinicians in their decision-making in the management of patients with major bleeding receiving factor Xa inhibitors.

Thrombin in complex with dabigatran can still interact with PAR-1 via exosite-I and instigate loss of vascular integrity

BACKGROUND

Atrial fibrillation (AF) can lead to the loss of microvascular integrity thereby enhancing AF progression. Mechanistically, the pro-coagulant state that drives the risk of stroke in patients with AF may also play a causal role in microvascular loss. Direct oral anticoagulants (DOACs), the preferred anticoagulants for AF, can target factors upstream (factor Xa [FXa]) or downstream (thrombin) in the coagulation cascade and mediate differential vascular effects through interaction with protease-activated receptors (PARs).

OBJECTIVE

To investigate the potential effect of different DOACs on vascular integrity.

METHODS

To model the impact of DOACs on vascular integrity, we utilized platelet-free plasma in thrombin generation assays and endothelial barrier assays under identical experimental conditions. These multifactorial systems provide all coagulation factors and their respective natural inhibitors in physiological ratios in combination with the pro-coagulant endothelial surface on which coagulation is initiated. Furthermore, the system provides pro- and anti-barrier factors and monitoring both assays simultaneously permits coupling of thrombin kinetics to endothelial barrier dynamics.

RESULTS

We provide evidence that the anti-FXa DOAC rivaroxaban and the anti-thrombin DOAC dabigatran are efficient in blocking their target proteases. However, while rivaroxaban could preserve endothelial barrier function, dabigatran failed to protect endothelial integrity over time, which could be prevented in the presence of a custom-made peptide that blocks thrombin's exosite-I.

CONCLUSIONS

Proteolytically inactive thrombin in complex with dabigatran evokes loss of barrier function that can be prevented by a protease-activated receptor-1 mimicking peptide blocking thrombin's exosite-I.

Availability of Specific Direct Oral Anticoagulant Reversal Agents in US Hospitals

This cross-sectional study assesses the availability of the direct oral anticoagulant reversal agents idarucizumab and andexanet alfa in US hospitals.

Current Evidence for Pharmacologic Reversal Using Direct Oral Anticoagulants: What's New?

Direct oral anticoagulants are increasingly used in clinical practice and have addressed many of the issues related to vitamin K antagonists. However, the lack of reversal in life-threatening situations raises concerns regarding patient safety. Thus, current research is aimed at developing reversal agents that can safely neutralize the effects of anticoagulants. We present the design and mechanisms of action of and the animal models, clinical trials, and current evidence supporting the use of these emerging reversal agents. Idarucizumab is approved in many countries, and andexanet alfa has been approved by the US FDA, whereas others are in clinical trials. In view of the results of clinical studies to date, the problems of safety, price and accessibility remain. Therefore, these antidotes are a significant step towards improving the field of urgent and emergency reversal. From a practical perspective, post-market surveillance will be crucial to monitor the safety and effectiveness of these agents.

Reversal agents for oral anticoagulant-associated major or life-threatening bleeding

Oral anticoagulants (OA) are effective drugs for treating and preventing the formation of blood clots in patients with atrial fibrillation, mechanical heart valves and venous thromboembolism but their therapeutic effect is always counterbalanced by an increased risk of bleeding. Direct oral anticoagulants (DOACs) have brought advantages in the management of many patients, with evidence of a lower risk of intracranial bleeding in comparison to vitamin K antagonists (VKAs). However, due to the increased number of anticoagulated patients worldwide, major and life threatening OA-related bleeding is also increasing, and effective reversal strategies are needed. We reviewed the reversal strategies for both VKAs and DOACs in the light of the latest evidence and recent guidelines, taking into account non-specific methods with fresh frozen plasma (FFP), prothrombin complex concentrate (PCC) or four factor PCC, as well as specific reversal antidotes that are already approved or in approval phase. Most published studies on OA reversal have drawbacks, such as lacking a control arm or data on clinically relevant outcomes, and current guidelines' recommendations are mainly based on panellists' judgment. There is an urgent need for well-designed studies in this field. In the meanwhile, to improve the correct use of available resources and patients' outcomes, we suggest a seven-element bundle for an optimal management of OA-associated major bleeding, including the implementation of fast turnaround time for laboratory tests in emergency, i.e. INR and DOAC plasma levels, and to build up a 'bleeding team' that includes experts of hemostasis, lab, trauma, emergency medicine, endoscopy, radiology, and surgery in every hospital.

[Andexanet alfa: the best antidote for factor Xa inhibitors?]

Andexanet alfa (andexanet) was specifically developed to reverse factor Xa inhibitors. Its effect on patients who are experiencing major bleeding while being treated with an oral Xa inhibitor or low molecular weight heparin was studied in the ANNEXA 4 study. The main outcome of this study was that anti-factor Xa activity decreased during the 2-hour infusion with andexanet, and that 82% of patients had excellent or good haemostatic efficacy after 12 hours according to pre-specified criteria. Although andexanet is the only specific antidote for factor Xa inhibitors available, an alternative treatment may be high-dose prothrombin concentrate (PCC). With the recent approval by the European Medicines Agency (EMA) but unknown Dutch reimbursement status, the role of andexanet for daily clinical practice in the Netherlands remains to be determined. Notably, and importantly, when treating patients with anticoagulant-associated major bleeding, local haemostatic control and-if relevant-adequate fluid resuscitation are at least as important as choosing the optimal anticoagulation antidote.

Full Study Report of Andexanet Alfa for Bleeding Associated with Factor Xa Inhibitors

BACKGROUND

Andexanet alfa is a modified recombinant inactive form of human factor Xa developed for reversal of factor Xa inhibitors.

METHODS

We evaluated 352 patients who had acute major bleeding within 18 hours after administration of a factor Xa inhibitor. The patients received a bolus of andexanet, followed by a 2-hour infusion. The coprimary outcomes were the percent change in anti-factor Xa activity after andexanet treatment and the percentage of patients with excellent or good hemostatic efficacy at 12 hours after the end of the infusion, with hemostatic efficacy adjudicated on the basis of prespecified criteria. Efficacy was assessed in the subgroup of patients with confirmed major bleeding and baseline anti-factor Xa activity of at least 75 ng per milliliter (or ≥0.25 IU per milliliter for those receiving enoxaparin).

RESULTS

Patients had a mean age of 77 years, and most had substantial cardiovascular disease. Bleeding was predominantly intracranial (in 227 patients [64%]) or gastrointestinal (in 90 patients [26%]). In patients who had received apixaban, the median anti-factor Xa activity decreased from 149.7 ng per milliliter at baseline to 11.1 ng per milliliter after the andexanet bolus (92% reduction; 95% confidence interval [CI], 91 to 93); in patients who had received rivaroxaban, the median value decreased from 211.8 ng per milliliter to 14.2 ng per milliliter (92% reduction; 95% CI, 88 to 94). Excellent or good hemostasis occurred in 204 of 249 patients (82%) who could be evaluated. Within 30 days, death occurred in 49 patients (14%) and a thrombotic event in 34 (10%). Reduction in anti-factor Xa activity was not predictive of hemostatic efficacy overall but was modestly predictive in patients with intracranial hemorrhage.

CONCLUSIONS

In patients with acute major bleeding associated with the use of a factor Xa inhibitor, treatment with andexanet markedly reduced anti-factor Xa activity, and 82% of patients had excellent or good hemostatic efficacy at 12 hours, as adjudicated according to prespecified criteria. (Funded by Portola Pharmaceuticals; ANNEXA-4 ClinicalTrials.gov number, NCT02329327.).

A New Option for Reversing the Anticoagulant Effect of Factor Xa Inhibitors: Andexanet Alfa (ANDEXXA)

The use of direct oral anticoagulants over traditional warfarin has increased in the United States over the past 10 years because of advantages such as ease of use, predictable pharmacokinetic response, and safety. In 2015, the U.S. Food and Drug Administration approved idarucizumab (Praxbind) for the reversal of the direct thrombin inhibitor dabigatran, but no reversal agent has been available for oral factor Xa (FXa) inhibitors until recently. Andexanet alfa was approved in May 2018, under the brand name ANDEXXA, for the reversal of 2 of FXa inhibitors, apixaban and rivaroxaban, when life-threatening or uncontrolled bleeding occurs. This accelerated approval was based on change in anti-FXa activity from baseline that indicated a reversal of the anticoagulant effect. Any expanded Food and Drug Administration indication will be contingent on results demonstrating improved hemostasis and efficacy for reversing other FXa inhibitors.

Rendering factor Xa zymogen-like as a therapeutic strategy to treat bleeding

PURPOSE OF REVIEW

New therapies are needed to control bleeding in a range of clinical conditions. This review will discuss the biochemical properties of zymogen-like factor Xa, its preclinical assessment in different model systems, and future development prospects.

RECENT FINDINGS

Underlying many procoagulant therapeutic approaches is the rapid generation of thrombin to promote robust clot formation. Clinically tested prohemostatic agents (e.g., factor VIIa) can provide effective hemostasis to mitigate bleeding in hemophilia and other clinical situations. Over the past decade, we explored the possibility of using zymogen-like factor Xa variants to rapidly improve clot formation for the treatment of bleeding conditions. Compared to the wild-type enzyme, these variants adopt an altered, low activity, conformation which enables them to resist plasma protease inhibitors. However, zymogen-like factor Xa variants are conformationally dynamic and ligands such as its cofactor, factor Va, stabilize the molecule rescuing procoagulant activity. At the site of vascular injury, the variants in the presence of factor Va serve as effective prohemostatic agents. Preclinical data support their use to stop bleeding in a variety of clinical settings. Phase 1 studies suggest that zymogen-like factor Xa is safe and well tolerated, and a phase 1b is ongoing to assess safety in patients with intracerebral hemorrhage.

SUMMARY

Zymogen-like factor Xa is a unique prohemostatic agent for the treatment of a range of bleeding conditions.

Reversal of direct oral anticoagulants: a practical approach

Direct oral anticoagulants (DOACs) have at least noninferior efficacy compared with other oral anticoagulants and have ancillary benefits, including overall better safety profiles, lack of the need for routine monitoring, rapid onset of action, and ease of administration. Reversal of these agents may be indicated in certain situations such as severe bleeding and for perioperative management. DOAC-associated bleeding should be risk stratified: patients with moderate or severe bleeding should have the DOAC discontinued and reversal strategies should be considered. Laboratory testing has limited utility in the acute management of bleeding; thrombin time and activated partial thromboplastin time may be useful for excluding clinically relevant levels of dabigatran. Prothrombin time is potentially useful for rivaroxaban and edoxaban, but calibrated anti-Xa assays are optimal for determining clinically relevant levels of factor Xa inhibitors. Because specific reversal agents are not widely available, supportive care and interventions for local hemostasis remain the cornerstones of therapy in the patient with DOAC-associated bleeding. Nonspecific reversal agents should be considered only in the event of severe bleeding because their efficacy is unknown, and they are associated with risk of thrombosis. Recent results from phase 3/4 studies demonstrate efficacy for an antidote to dabigatran (idarucizumab, a monoclonal antibody fragment with specificity for dabigatran) and an antidote to factor Xa inhibitors (andexanet alfa, a recombinant and inactive form of factor Xa that binds inhibitors). A universal reversal agent (ciraparantag) for many anticoagulants, including the DOACs, shows promise in results from phase 1 and 2 studies.

A comparison of red blood cell transfusion utilization between anti-activated factor X and activated partial thromboplastin monitoring in patients receiving unfractionated heparin

Essentials Anti-activated factor X (Anti-Xa) monitoring is more precise than activated partial thromboplastin (aPTT). 20 804 hospitalized cardiovascular patients monitored with Anti-Xa or aPTT were analyzed. Adjusted transfusion rates were significantly lower for patients monitored with Anti-Xa. Adoption of Anti-Xa protocols could reduce transfusions among cardiovascular patients in the US.

SUMMARY

Background Anticoagulant activated factor X protein (Anti-Xa) has been shown to be a more precise monitoring tool than activated partial thromboplastin time (aPTT) for patients receiving unfractionated heparin (UFH) anticoagulation therapy. Objectives To compare red blood cell (RBC) transfusions between patients receiving UFH who are monitored with Anti-Xa and those monitored with aPTT. Patients/Methods A retrospective cohort study was conducted on patients diagnosed with acute coronary syndrome (ACS) (N = 14 822), diagnosed with ischemic stroke (STK) (N = 1568) or with a principal diagnosis of venous thromboembolism (VTE) (N = 4414) in the MedAssets data from January 2009 to December 2013. Anti-Xa and aPTT groups were identified from hospital billing details, with both brand and generic name as search criteria. Propensity score techniques were used to match Anti-Xa cases to aPTT controls. RBC transfusions were identified from hospital billing data. Multivariable logistic regression was used to identify significant drivers of transfusions. Results Anti-Xa patients had fewer RBC transfusions than aPTT patients in the ACS population (difference 17.5%; 95% confidence interval [CI] 16.4-18.7%), the STK population (difference 8.2%; 95% CI 4.4-11.9%), and the VTE population (difference 4.7%; 95% CI 3.3-6.1%). After controlling for patient age and gender, diagnostic risks (e.g. anemia, renal insufficiency, and trauma), and invasive procedures (e.g. cardiac catheterization, hemodialysis, and coronary artery bypass graft), Anti-Xa patients were less likely to have a transfusion while hospitalized for ACS (odds ratio [OR] 0.16, 95% CI 0.14-0.18), STK (OR 0.41, 95% CI 0.29-0.57), and VTE (OR 0.35, 95% CI 0.26-0.48). Conclusion Anti-Xa monitoring was associated with a significant reduction in RBC transfusions as compared with aPTT monitoring alone.

Preclinical and Clinical Data for Factor Xa and "Universal" Reversal Agents

Oral Factor Xa (FXa) inhibitors, a growing class of direct-acting anticoagulants, are frequently used to prevent stroke and systemic embolism in patients with atrial fibrillation and to prevent and treat venous thromboembolism. These drugs reduce the risk of clotting at the expense of increasing the risk of bleeding, and currently they have no specific reversal agent. However, andexanet alfa, a recombinant modified FXa decoy molecule, is in a late-phase clinical trial in bleeding patients, and ciraparantag, a small molecule that appears to reverse many anticoagulants including the FXa inhibitors, is in development. This review summarizes the published data to date on both drugs, which have the potential to change the management approach to patients with FXa inhibitor-associated major hemorrhage.

Preclinical and clinical data for factor Xa and "universal" reversal agents

Oral Factor Xa (FXa) inhibitors, a growing class of direct-acting anticoagulants, are frequently used to prevent stroke and systemic embolism in patients with atrial fibrillation and to prevent and treat venous thromboembolism. These drugs reduce the risk of clotting at the expense of increasing the risk of bleeding, and currently they have no specific reversal agent. However, andexanet alfa, a recombinant modified FXa decoymolecule, is in a late-phase clinical trial in bleeding patients, and ciraparantag, a small molecule that appears to reverse many anticoagulants including the FXa inhibitors, is in development. This review summarizes the published data to date on both drugs, which have the potential to change the management approach to patients with FXa inhibitoreassociated major hemorrhage.

Andexanet Alfa for Acute Major Bleeding Associated with Factor Xa Inhibitors

BACKGROUND

Andexanet alfa (andexanet) is a recombinant modified human factor Xa decoy protein that has been shown to reverse the inhibition of factor Xa in healthy volunteers.

METHODS

In this multicenter, prospective, open-label, single-group study, we evaluated 67 patients who had acute major bleeding within 18 hours after the administration of a factor Xa inhibitor. The patients all received a bolus of andexanet followed by a 2-hour infusion of the drug. Patients were evaluated for changes in measures of anti-factor Xa activity and were assessed for clinical hemostatic efficacy during a 12-hour period. All the patients were subsequently followed for 30 days. The efficacy population of 47 patients had a baseline value for anti-factor Xa activity of at least 75 ng per milliliter (or ≥0.5 IU per milliliter for those receiving enoxaparin) and had confirmed bleeding severity at adjudication.

RESULTS

The mean age of the patients was 77 years; most of the patients had substantial cardiovascular disease. Bleeding was predominantly gastrointestinal or intracranial. The mean (±SD) time from emergency department presentation to the administration of the andexanet bolus was 4.8±1.8 hours. After the bolus administration, the median anti-factor Xa activity decreased by 89% (95% confidence interval [CI], 58 to 94) from baseline among patients receiving rivaroxaban and by 93% (95% CI, 87 to 94) among patients receiving apixaban. These levels remained similar during the 2-hour infusion. Four hours after the end of the infusion, there was a relative decrease from baseline of 39% in the measure of anti-factor Xa activity among patients receiving rivaroxaban and of 30% among those receiving apixaban. Twelve hours after the andexanet infusion, clinical hemostasis was adjudicated as excellent or good in 37 of 47 patients in the efficacy analysis (79%; 95% CI, 64 to 89). Thrombotic events occurred in 12 of 67 patients (18%) during the 30-day follow-up.

CONCLUSIONS

On the basis of a descriptive preliminary analysis, an initial bolus and subsequent 2-hour infusion of andexanet substantially reduced anti-factor Xa activity in patients with acute major bleeding associated with factor Xa inhibitors, with effective hemostasis occurring in 79%. (Funded by Portola Pharmaceuticals; ANNEXA-4 ClinicalTrials.gov number, NCT02329327 .).

Andexanet Alfa for the Reversal of Factor Xa Inhibitor Activity

BACKGROUND

Bleeding is a complication of treatment with factor Xa inhibitors, but there are no specific agents for the reversal of the effects of these drugs. Andexanet is designed to reverse the anticoagulant effects of factor Xa inhibitors.

METHODS

Healthy older volunteers were given 5 mg of apixaban twice daily or 20 mg of rivaroxaban daily. For each factor Xa inhibitor, a two-part randomized placebo-controlled study was conducted to evaluate andexanet administered as a bolus or as a bolus plus a 2-hour infusion. The primary outcome was the mean percent change in anti-factor Xa activity, which is a measure of factor Xa inhibition by the anticoagulant.

RESULTS

Among the apixaban-treated participants, anti-factor Xa activity was reduced by 94% among those who received an andexanet bolus (24 participants), as compared with 21% among those who received placebo (9 participants) (P<0.001), and unbound apixaban concentration was reduced by 9.3 ng per milliliter versus 1.9 ng per milliliter (P<0.001); thrombin generation was fully restored in 100% versus 11% of the participants (P<0.001) within 2 to 5 minutes. Among the rivaroxaban-treated participants, anti-factor Xa activity was reduced by 92% among those who received an andexanet bolus (27 participants), as compared with 18% among those who received placebo (14 participants) (P<0.001), and unbound rivaroxaban concentration was reduced by 23.4 ng per milliliter versus 4.2 ng per milliliter (P<0.001); thrombin generation was fully restored in 96% versus 7% of the participants (P<0.001). These effects were sustained when andexanet was administered as a bolus plus an infusion. In a subgroup of participants, transient increases in levels of d-dimer and prothrombin fragments 1 and 2 were observed, which resolved within 24 to 72 hours. No serious adverse or thrombotic events were reported.

CONCLUSIONS

Andexanet reversed the anticoagulant activity of apixaban and rivaroxaban in older healthy participants within minutes after administration and for the duration of infusion, without evidence of clinical toxic effects. (Funded by Portola Pharmaceuticals and others; ANNEXA-A and ANNEXA-R ClinicalTrials.gov numbers, NCT02207725 and NCT02220725.).

Rivaroxaban and apixaban in orthopaedics: is there a difference in their plasma concentrations and anticoagulant effects?

The aim of this study was to improve knowledge of what happens in the coagulation of orthopaedic patients under rivaroxaban and apixaban, in order to finalize and cross-validate effective measurement methods and to provide arguments for helping to reference one or the other drug in our central pharmacy. One hundred and two patients undergoing total hip or knee replacement were included. Half of them received rivaroxaban and the other half received apixaban. Blood samples (n = 244 with each drug) were taken at Cmax preoperatively and twice a week, apart from the day of the patient's discharge, when Ctrough concentration was targeted. Routine coagulation parameters, and functional and liquid chromatography tandem mass spectrometry assays for measurement of circulating concentrations were studied. The LC-MS/MS assay and the functional assays carried out in patients under routine conditions were highly correlated, apart from low concentrations (<30 ng/ml), which were affected by the variable individual potential to inhibit the exogenous bovine Xa used in the functional assays. After 1 week of treatment, the drugs differed: Cmax and Ctrough were closer when apixaban was taken twice daily (83 ± 39 and 58 ± 17 ng/ml) than with rivaroxaban taken once a day (113 ± 67 and 13 ± 20 ng/ml). Rivaroxaban had a greater influence on routine coagulation tests and reduced the maximum thrombin concentration more efficiently, as assessed by the thrombin generation test. Although rivaroxaban and apixaban present apparently similar constant rates, they exhibit significant differences in their concentrations and anticoagulant effects when studied ex vivo in orthopedic patients.

PRODIGE: a randomized placebo-controlled trial of dalteparin low-molecular-weight heparin thromboprophylaxis in patients with newly diagnosed malignant glioma

BACKGROUND AND OBJECTIVES

Venous thromboembolism (VTE) occurs in 20-30% of patients with malignant glioma per year of survival. We tested the efficacy of long-term dalteparin low-molecular-weight heparin (LMWH) for prevention of VTE in these patients.

PATIENTS/METHODS

Adults with newly diagnosed malignant glioma were randomized to receive dalteparin 5000 anti-Xa units or placebo, both subcutaneously once daily for 6 months starting within 4 weeks of surgery. Treatment continued for up to 12 months. The primary outcome was the cumulative risk of VTE over 6 months. The target sample size was 512 patients. Events were adjudicated by a committee unaware of treatment.

RESULTS

The trial began in 2002 and closed in May 2006 because of expiration of study medication. Ninety-nine patients were randomized to LMWH and 87 to placebo. Twenty-two patients developed VTE in the first 6 months: nine in the LMWH group and 13 in the placebo group [hazard ratio (HR) = 0.51, 95% confidence interval (CI): 0.19-1.4, P = 0.29]. At 6 months, there were three major bleeds on LMWH and none on placebo; at 12 months, 5 (5.1%) major bleeds on LMWH and 1 (1.2%) on placebo occurred (HR = 4.2, 95% CI: 0.48-36, P = 0.22). All major bleeds were intracranial and occurred while on study medication. The 12-month mortality rates were 47.8% for LMWH and 45.4% for placebo (HR = 1.2, 95% CI: 0.73-2.0, P = 0.48).

CONCLUSIONS

Trends suggesting reduced VTE and increased intracranial bleeding were seen in the LMWH thromboprophylaxis group. The role of long-term anticoagulant thromboprophylaxis in patients with brain tumors remains uncertain.

[Prophylaxis of venous thromboembolism]

Most hospitalized patients present risk factors for venous thromboembolism (VTE). Deep vein thrombosis and pulmonary embolism are relevant causes for morbidity and mortality in the perihospital phase, with a possibly fatal outcome. Surgical as well as nonsurgical patients with acute medical illness are at risk and show comparatively high rates of VTE. Because of this, an effective and safe prophylaxis for hospitalized patients is necessary. Definition of different risk categories and treatment of patients according to the individual risk profile is standard in VTE prophylaxis. For VTE prophylaxis various medical and mechanical options are available.

[New anticoagulants]

This review updates the latest developments concerning new anticoagulants. It describes potential targets in the coagulation pathway: inhibition of the initiation of coagulation, factor Xa and thrombin inhibitors. The focus is laid on substances in late development that already passed the phase II trial for venous thromboembolism (VTE)-prevention as "proof of concept". In the group of factor Xa inhibitors, the indirect inhibitor Fondaparinux has got approval for the indications prevention and therapy of VTE and acute coronary syndromes (OASIS 5 and 6). Rivaroxaban is the first direct factor Xa inhibitor that was admitted for approval in the indication VTE-prevention. The first trial of the program RECORD 1-4 was finished, trials for the indications therapy of VTE (EINSTEIN) and stroke prevention in atrial fibrillation (ROCKET AF) are in phase III. The use in acute coronary symptoms is - like apixaban - evaluated in phase II. The ADOPT trial with apixaban for VTE-prevention, as well as the BOTTICELLI trial for atrial fibrillation, have reached phase III. After the withdrawal of Ximelagatran, Dabigatran is the most developed direct thrombin inhibitor, being extensively studied in the comprehensive phase- III-program REVOLUTION and in approval for the indication VTE-prevention.

Sequential therapy with activated prothrombin complex concentrates and recombinant FVIIa in patients with severe haemophilia and inhibitors: update of our previous experience

Haemophilia patients with inhibitors can develop bleeding episodes, which are refractory to monotherapy with either recombinant factor VIIa (rFVIIa) or activated prothrombin complex concentrates (APCC). Management of such bleeds is often difficult. We previously reported the safety of using a combination of rFVIIa and APCC given in sequential fashion. In this report, we update our experience with sequential therapy. A retrospective review of medical records was conducted including all reports of sequential therapy defined as receiving both rFVIIa and APCC within 6 h. Data extracted included demographic data, treatment prior to and following hospital admission, clinical data including type and location of bleed, response to therapy, physical examination and laboratory data. In addition, for some patients, thromboelastography was performed to document the effect of sequential therapy on clot formation characteristics. Four patients comprising 35 admissions, 209 hospital days and 115 days of sequential therapy were included in the updated dataset. No patient developed thrombosis or overt disseminated intravascular coagulation (DIC) although elevations in the D-dimer above 5 microg mL(-1) were noted in 42% of the courses that lasted >3 days. Efficacy is suggested by the fact that patients had resolution of their bleeds after a median of 3 days of sequential therapy after failing to respond to a median of 3 days of monotherapy. Thromboelastography demonstrated an additive effect. Sequential therapy is a safe, potentially efficacious approach in the management of refractory bleeding episodes in patients with haemophilia and inhibitors.

Sequential therapy with activated prothrombin complex concentrate and recombinant factor VIIa in patients with severe haemophilia and inhibitors

Patients with haemophilia and inhibitors have bleeding episodes that can be refractory to home therapy with either activated prothrombin complex concentrate (APCC) or recombinant factor VIIa (rFVIIa). Sequential therapy with these products has not been widely used because of concern regarding the possibility of thrombosis. This report describes the results of a retrospective chart review of five hospitalized children with severe haemophilia and inhibitors who have been treated with sequential doses of APCC and rFVIIa for refractory bleeding. These patients all had failed home therapy with APCC and rFVIIa alone. A total of 20 admissions were documented covering 170 hospital days, including 91 days of combination therapy. While being closely monitored in the hospital, they received alternating doses of APCC and rFVIIa every 6 h. Anywhere from one to three doses of rFVIIa were given every 2 h between APCC doses. Doses of APCC ranged from 35 to 80 U kg(-1) dose(-1), and doses of rFVIIa ranged from 80 to 225 mcg kg(-1) dose(-1). There was no clinical or laboratory evidence of thrombosis, thrombocytopenia, or disseminated intravascular coagulation (DIC). We found the combination of these factors to be safe and effective for patients with refractory bleeds. However, we recommend this aggressive therapy only in the inpatient setting with careful monitoring of the physical examination and frequent laboratory screening to assess for thrombosis and DIC, and without the concurrent use of antifibrinolytic medications.

A fully recombinant partial prothrombin complex effectively bypasses fVIII in vitro and in vivo

The development of inhibitory antibodies is a serious complication in hemophilic patients, severely compromising therapeutic success. Bleeding episodes in affected patients are controlled by treatment with a plasma-derived prothrombin complex concentrate (PCC), activated PCC (APCC) or recombinant activated factor VII. We hypothesized that a recombinant two-component agent consisting of recombinant prothrombin (rfII) and activated factor X (rfXa) would have substantial fVIII bypassing activity and could be a safe alternative therapeutic option. To test this hypothesis we assembled an agent in vitro solely consisting of rfII and rfXa at a molar ratio of 37,500:1. These factors are believed to be responsible for the activity of APCC preparations. Recombinant fX, used as the source for fXa generation, and rfII were purified from serum-free and protein-free conditioned media of stably transfected CHO and BHK tissue culture cells, respectively. Activation of rfX to rfXa was accomplished by the plant protease ficin, obviating the need for a protease derived from a human or animal source. We found that in vitro the complex reduced the abnormally prolonged activated partial thromboplastin time (APTT) of a high-titer fVIII inhibitor plasma similar to an APCC preparation. Furthermore, addition of increasing amounts of rfII/rfXa to inhibitor plasma resulted in a linear dose-dependent increase in the rate of thrombin generation. In a rabbit fVIII inhibitor model, treatment with rfII/rfXa statistically significantly reduced the intensity of the abnormal cuticle bleeding. In the Wessler test, rfII/rfXa showed no thrombogenicity. These data show that a well-defined, particularly safe and efficacious agent with fVIII bypassing activity can be generated from recombinant fII and fXa.

Prednisone and low-dose activated prothrombin complex concentrates for FVIII inhibitor in nonhaemophilic patients

Eight nonhaemophilic patients with factor VIII (FVIII) inhibitors were reported. There was no difference in sex distribution. Median age at diagnosis was 62 years (ranging from 14 to 73 years). No associated disorders were revealed and all the patients were presented with severe muscular or arthral bleeding. Inhibitor titre was measured by the Bethesda method, which were 6.4, 126.0, 155.0, 4.8, 56.0, 13.5, 35.0 and 150.0 BU mL-1, respectively, at diagnosis. FVIII:C levels were less than 1 U dL-1 in seven patients and less than 2 U dL-1 in one patient. The median vWF:Ag level was 210% (ranging from 80% to 340%). All the patients had good response to activated prothrombin complex concentrates for acute bleeding episodes and prednisone for inhibitor elimination. Inhibitors completely eliminated in seven patients within a follow-up duration over 1 year, and one patient died of intracranial haemorrhage when her inhibitor titre decreased to 4.5 BU mL-1 and FVIII:C increased to 21 U dL-1.

Reversible acylation of factor Xa as a potential therapy for hemophilia

Current therapies for treatment of hemophilia A involve infusion of factor VIII, but are ineffective for patients who develop inhibitory antibodies. We have previously proposed that bypassing the intrinsic pathway (VIIIa/IXa) with reversibly acylated factor Xa offers an improvement on existing therapies as it provides a time-dependent release of procoagulant activity without the addition of factors VIII or IX. The present study was designed to determine the effect of substituted 4-amidinophenyl benzoates on the acylation of factor Xa, as well as the subsequent deacylation rates of the resulting acyl Xa. A subset of this series of acyl Xa's were incorporated into the prothrombinase complex and recovery of catalytic activity was measured by activation of prothrombin to thrombin. Similarly, some acyl Xa's were also evaluated for their capacity to enhance clotting times of human plasma. Our study indicates that by choosing the appropriate acyl Xa, the time course of factor Xa regeneration can be modulated extensively. Animal studies will be required to show that the use of acyl Xa as a procoagulant agent is feasible in an in vivo system.

Effect of human urinary thrombomodulin on endotoxin-induced intravascular coagulation and pulmonary vascular injury in rats

Adult respiratory distress syndrome (ARDS) and disseminated intravascular coagulation (DIC) are serious complications of sepsis. Thrombomodulin, an important endothelial anticoagulant, binds thrombin to generate activated protein C (APC). To determine whether thrombomodulin purified from human urine (urinary thrombomodulin, UTM) is useful for the treatment of DIC and ARDS in sepsis, we examined the effect of UTM on endotoxin (ET)-induced coagulation abnormalities and pulmonary vascular injury in rats. Intravenous administration of UTM prevented the ET-induced pulmonary accumulation of leukocytes and the increase in pulmonary vascular permeability, as well as ET-induced histological changes such as leukocyte infiltration and pulmonary interstitial edema. On the other hand, dansyl-Glu-Gly-Arg-chloromethyl ketone-treated factor Xa (DEGR-Xa), a selective inhibitor of thrombin generation, did not prevent these effects of ET. UTM did not prevent ET-induced pulmonary accumulation of leukocytes and pulmonary vascular injury in rats pretreated with DEGR-Xa. Our findings suggest that UTM attenuates ET-induced coagulation abnormalities and pulmonary vascular injury. Furthermore, the latter effect may be dependent on the capacity of UTM to activate protein C.

A comparative study of prothrombinase and thrombin inhibitors in a novel rabbit model of non-occlusive deep vein thrombosis

A quantitative and non-occlusive deep vein thrombosis model was developed in rabbits. We used this model to test the antithrombotic activity of the prothrombinase complex inhibitors factor rXai and its chemical analog glutamyl-glycyl-arginyl chloromethyl ketone inactivated human factor Xa (EGR-Xai), along with the thrombin inhibitors D-phenylalanyl-prolyl-arginyl chloromethyl ketone (PPACK) and heparin. Dose dependent effects of the inhibitors during constant infusion were monitored. Measurements included thrombus weights, hemostatic parameters and both cuticle and ear bleeding times. In this model, factor rXai and EGR-Xai had comparable in-vivo efficacy, and showed 80%-93% inhibition at plasma levels of 6.5 nM (rXai) and 8 nM (EGR-Xai). Effects on ex-vivo clotting times varied among the inhibitors. At 80-100% thrombus inhibition, factor rXai and EGR-Xai had no statistically significant effect, while PPACK extended thrombin clotting time (TCT) times 2.3-fold, and heparin prolonged both activated partial thromboplastin time (APTT), prothrombin time (PT) and TCT ex-vivo clotting times 6.9-, 1.2-, and 7-fold respectively. At these dosages, cuticle and ear bleeding times were prolonged for all inhibitors and showed increases of 177%-389% (cuticle) and 45%-129% (ear). Our results demonstrate that direct inhibition of prothrombinase complex assembly is effective in arresting venous thrombosis.