Effect of activated prothrombin complex concentrate or recombinant factor VIIa on the bleeding time and thrombus formation during anticoagulation with a direct thrombin inhibitor

Between a rock and a hard place: anticoagulation management for ECMO

Anticoagulation is an essential component of optimal extracorporeal membrane oxygenation (ECMO) management. Unfractionated heparin is still the anticoagulant of choice in most centers due to longstanding familiarity with the agent. Disadvantages include alterations in drug responses due to its capability to bind multiple heparin-binding proteins that compete with antithrombin and the potential for heparin-induced thrombocytopenia. In such cases, direct thrombin inhibitors are the treatment of choice but pose difficulties in monitoring due to the limited experience and target ranges for non-aPTT-guided management (aPTT: activated partial thromboplastin time). The current trend toward low-dose anticoagulation, especially for venovenous ECMO, is supported by data associating bleeding complications with mortality but not thromboembolic events, which include circuit thrombosis. However, only prospective data will provide appropriate answers to how to individualize anticoagulation, transfusions, and bleeding management which is currently only supported by expert opinion. Empiric therapy for ECMO patients based on laboratory coagulation alone should always be critically questioned. In summary, only collaboration and future studies of coagulation management during ECMO will help us to make this life-saving therapy that has become part of daily life of the intensivist even safer and more effective. Until then, a fundamental understanding of coagulation and bleeding management, as well as pearls and pitfalls of monitoring, is essential to optimize anticoagulation during ECMO. This article is freely available.

Updates in Anticoagulation Therapy Monitoring

In the past six decades, heparin and warfarin were the primary anticoagulants prescribed for treatment and prophylaxis of venous thromboembolism worldwide. This has been accompanied by extensive clinical knowledge regarding dosing, monitoring, and reversal of these anticoagulants, and the resources required to do so have largely been readily available at small and large centers alike. However, with the advent of newer oral and parenteral anticoagulants such as low molecular weight heparins, factor Xa inhibitors, and direct thrombin inhibitors in recent years, new corresponding practice guidelines have also emerged. A notable shift in the need for monitoring and reversal agents has evolved as well. While this has perhaps streamlined the process for physicians and is often desirable for patients, it has also left a knowledge and resource gap in clinical scenarios for which urgent reversal and monitoring is necessary. An overview of the currently available anticoagulants with a focus on the guidelines and available tests for anticoagulant monitoring will be discussed in this article.

Reversal of dabigatran-associated bleeding using idarucizumab: review of the current evidence

Major bleeding occurs in about 4% of patients while on treatment with direct oral anticoagulants (DOACs). The case-fatality rate associated with these events is estimated to be about 5%. The specific roles of antidotes, when used with DOACs in reducing the case fatality or improving the overall clinical course of these events, are not thoroughly understood. To this regard, the US Food and Drug Administration as well as European Medicines Agency have recently licensed idarucizumab for the management of patients with life-threatening bleeding or the need for urgent surgery/procedures while on treatment with dabigatran. Specifically, idarucizumab is a humanized monoclonal antibody fragment that rapidly reverses the anticoagulant effect of dabigatran. Two other antidotes, andeXanet and ciraparantag are currently under evaluation for reversal of DOACs. Here, we report on the use of idarucizumab in two patients who experienced life-threatening bleeding while on treatment with dabigatran for atrial fibrillation and provide a review highlighting the need for antidotes use with DOACs.

Reversal of rivaroxaban anticoagulation by haemostatic agents in rats and primates

Rivaroxaban is an oral, direct factor Xa inhibitor for the management of thromboembolic disorders. Despite its short half-life, the ability to reverse rivaroxaban anticoagulation could be beneficial in life-threatening emergencies. The potential of prothrombin complex concentrate (PCC; Beriplex®), activated PCC (aPCC; FEIBA®) or recombinant activated factor VII (rFVIIa; NovoSeven®) to reverse rivaroxaban in rats and baboons was investigated. Anaesthetised rats pre-treated with intravenous rivaroxaban (2 mg/kg) received intravenous rFVIIa (100/400 μg/kg), PCC (25/50 U/kg) or aPCC (50/100 U/kg) after initiation of bleeding. Clotting times and bleeding times (BTs) were recorded. Rivaroxaban was administered as an intravenous 0.6 mg/kg bolus followed by continuous 0.6 mg/kg/hour infusion in baboons. Animals received intravenous aPCC 50 U/kg (2 U/kg/minute) or rFVIIa 210 μg/kg. BT and clotting parameters were measured. In rats pre-treated with high-dose rivaroxaban, PCC 50 U/kg, aPCC 100 U/kg and rFVIIa 400 μg/kg significantly reduced BT vs rivaroxaban alone (5.4 ± 1.4-fold to 1.5 ± 0.4-fold [p<0.05]; 3.0 ± 0.4-fold to 1.4 ± 0.1-fold [p<0.001]; and 3.5 ± 0.7-fold to 1.7 ± 0.2-fold [p<0.01] vs baseline, respectively). In baboons pre-infused with rivaroxaban and then given aPCC, BT increased by 2.0 ± 0.2-fold and aPCC returned BT to baseline for the duration of its infusion. rFVIIa reduced BT from 2.5 ± 0.3-fold over baseline to 1.7 ± 0.3-fold over baseline. Prolongation of prothrombin time was reduced by PCC, aPCC and rFVIIa in both species. Rivaroxaban reduced thrombin-antithrombin levels; application of PCC and aPCC, but not rFVIIa, increased these levels. In conclusion, PCC, aPCC or rFVIIa have the potential to reverse the anticoagulant and anti-haemostatic effects of rivaroxaban.

Reversal of anticoagulant effects of edoxaban, an oral, direct factor Xa inhibitor, with haemostatic agents

Edoxaban, an oral, direct factor Xa inhibitor, has a similar or low incidence of bleeding events compared with other anticoagulants in clinical trials. Therefore, agents to reverse the anticoagulant effects of edoxaban could be desirable in emergency situations. In this study, the reversal effects of haemostatic agents were determined on prothrombin time (PT) prolongation in vitro and bleeding time prolongation in vivo by edoxaban. PT using human plasma was measured in the presence of edoxaban at therapeutic and excess concentrations with the haemostatic agents, prothrombin complex concentrate (PPSB-HT), activated prothrombin complex concentrate (Feiba), and recombinant factor VIIa (rFVIIa). In rats, rFVIIa and Feiba was given during intensive anticoagulation with edoxaban. The haemostatic effect was evaluated in a model of planta template bleeding and a potential prothrombotic effect was evaluated in a venous thrombosis model. PPSB-HT, Feiba, and rFVIIa concentration-dependently shortened PT prolonged by edoxaban. Among these, rFVIIa and Feiba showed potent activities in reversing the PT prolongation by edoxaban. rFVIIa (1 and 3 mg/kg, i.v.) and Feiba (100 U/kg, i.v.) significantly reversed edoxaban (1 mg/kg/h)-induced prolongation of bleeding time in rats. In a rat venous thrombosis model, no potentiation of thrombus formation was observed when the highest dose (3 mg/kg) of rFVIIa was added to edoxaban (0.3 and 1 mg/kg/h) compared with the control. The present study indicated that rFVIIa, Feiba, and PPSB-HT have the potential to be reversal agents for edoxaban.

Tranexamic Acid Failed to Reverse the Anticoagulant Effect and Bleeding by an Oral Direct Factor Xa Inhibitor Edoxaban

BACKGROUND/AIMS

Agents to reverse the anticoagulant effect of edoxaban, an oral direct factor Xa inhibitor, would be desirable in emergency situations. The aim of this study is to determine the effect of tranexamic acid, an antifibrinolytic agent, on the anticoagulant activity and bleeding by edoxaban in rats.

METHODS

A supratherapeutic dose of edoxaban (3 mg/kg) was intravenously administered to rats. Three minutes after dosing, tranexamic acid (100 mg/kg) was given intravenously. Bleeding was induced by making an incision with a blade on the planta 8 min after edoxaban injection and bleeding time was measured. Prothrombin time (PT) and clot lysis were examined.

RESULTS

A supratherapeutic dose of edoxaban significantly prolonged PT and bleeding time. Tranexamic acid did not affect PT or bleeding time prolonged by edoxaban, although tranexamic acid significantly inhibited clot lysis in rat plasma.

CONCLUSION

An antifibrinolytic agent tranexamic acid failed to reverse the anticoagulant effect and bleeding by edoxaban in rats.

Reversal of apixaban anticoagulation by four-factor prothrombin complex concentrates in healthy subjects: a randomized three-period crossover study

Essentials Prothrombin complex concentrates (PCCs) may reverse the effect of factor Xa (FXa) inhibitors. We conducted an open-label, randomized, placebo-controlled, three-period crossover study in 15 subjects. Both PCCs rapidly reversed apixaban-mediated decreases in mean endogenous thrombin potential. Four-factor PCC administration had no effect on apixaban pharmacokinetics or anti-FXa activity.

SUMMARY

Background Currently, there is no approved reversal agent for direct activated factor Xa (FXa) inhibitors; however, several agents are under investigation, including prothrombin complex concentrates (PCCs). Objective This open-label, randomized, placebo-controlled, three-period crossover study assessed the effect of two four-factor PCCs on apixaban pharmacodynamics and pharmacokinetics in 15 healthy subjects. Methods Subjects received apixaban 10 mg twice daily for 3 days. On day 4, 3 h after apixaban, subjects received a 30-min infusion of 50 IU kg-1 Cofact, Beriplex P/N (Beriplex), or saline. Change in endogenous thrombin potential (ETP), measured with a thrombin generation assay (TGA), was the primary endpoint. Secondary endpoints included changes in other TGA parameters, prothrombin time (PT), International Normalized Ratio (INR), activated partial thromboplastin time, anti-FXa activity, apixaban pharmacokinetics, and safety. Results Apixaban-related changes in ETP and several other pharmacodynamic measures occurred following apixaban administration. Both PCCs reversed apixaban's effect on ETP; the differences in adjusted mean change from pre-PCC baseline to end of infusion were 425 nm min (95% confidence interval [CI] 219.8-630.7 nm min; P < 0.001) for Cofact, and 91 nm min (95% CI - 31.3 to 212.4 nm min; P > 0.05) for Beriplex. Both PCCs returned ETP to pre-apixaban baseline levels 4 h after PCC infusion, versus 45 h for placebo. For both PCCs, mean ETP peaked 21 h after PCC initiation, and then slowly decreased over the following 48 h. Both PCCs reversed apixaban's effect on TGA peak height, PT, and INR. Apixaban pharmacokinetic and anti-FXa profiles were consistent across treatments. Conclusions Cofact and Beriplex reversed apixaban's steady-state effects on several coagulation assessments.

Reversal of dabigatran-associated major bleeding with activated prothrombin concentrate: A prospective cohort study

The reversal of dabigatran-associated major bleeding can now be achieved with the antidote idarucizumab. We evaluated activated prothrombin complex concentrate (aPCC) as an alternative for this purpose. Patients treated with dabigatran and suffering a major bleed were treated as per existing hospital protocol with aPCC. They were subsequently recruited for a 30-day follow-up. Effectiveness was evaluated by the treating physician, using an Assessment Guide. Safety outcomes were arterial or venous thromboembolism or death. A comparison was also made with historic cases with dabigatran-associated major bleeds treated with supportive care, by matching 1:2 for type of bleed, age and sex. We aimed at 32 evaluable cases but the study was prematurely discontinued after 14 cases due to the availability of the approved antidote. The effectiveness of aPCC was assessed as Good in 9 (64%), moderate in 5 (36%) and poor in none. There were no thromboembolic events and one death. In the secondary adjudication of effectiveness, using the same criteria and by the same adjudicators as previously done for the historic cases, the outcome was graded for the current cases versus the historic cases as Good, Moderate, or Poor in 10 (71%) versus 16 (57%), 3 (21%) versus 4 (14%), and 1 (7%) versus 8 (29%), respectively. Although supportive care is sufficient to manage many patients with dabigatran-associated bleeding, aPCC might provide an additional benefit to control life-threatening bleeding in selected cases and does not appear to cause an excess of thromboembolic events.

Effects of recombinant human prothrombin on thrombin generation in plasma from patients with hemophilia A and B

BACKGROUND

The present study was carried out to investigate the impact of FII levels, and their increase, on the hemostatic potential in plasma from hemophilia A and B patients with and without inhibitors.

METHOD

Recombinant human factor (F) II (rhFII) was added ex vivo to plasma from 68 patients with hemophilia A and B, with or without inhibitors. The hemostatic potential as measured by thrombin generation (calibrated automated thrombogram [CAT]) was focused on the endogenous thrombin potential (ETP) as it has been shown to correlate with the clinical phenotype of bleeding in hemophilia patients and has also been used to guide bypassing therapy in hemophilia patients with inhibitors before elective surgery. The factor eight inhibitor bypassing agent (FEIBA(®) ) was used as a reference to the clinical situation.

RESULTS

The study shows that rhFII concentration-dependently increased ETP by a similar magnitude in hemophilia A and B, both with and without inhibitors. Compared with FEIBA, rhFII showed a shallower concentration-response curve. In both types of hemophilia 100 mg L(-1) of rhFII roughly doubled the ETP. A corresponding response was obtained by 0.5 U mL(-1) of FEIBA.

CONCLUSION

These data support the theory that FII is one of the major components responsible for the efficacy of FEIBA. The data also indicate that rhFII may be useful, alone or in combination with other coagulation factors, in some of the conditions for which FEIBA is used today, although more data are needed to substantiate this.

Association of bleeding and thrombosis with outcome in extracorporeal life support

OBJECTIVE

Changes in technology and increased reports of successful extracorporeal life support use in patient populations, such as influenza, cardiac arrest, and adults, are leading to expansion of extracorporeal life support. Major limitations to extracorporeal life support expansion remain bleeding and thrombosis. These complications are the most frequent causes of death and morbidity. As a pilot project to provide baseline data for a detailed evaluation of bleeding and thrombosis in the current era, extracorporeal life support patients were analyzed from eight centers in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Collaborative Pediatric Critical Care Research Network.

STUDY DESIGN

Retrospective analysis of patients (< 19 yr) reported to the Extracorporeal Life Support Organization registry from eight Collaborative Pediatric Critical Care Research Network centers between 2005 and 2011.

SETTING

Tertiary children's hospitals within the Collaborative Pediatric Critical Care Research Network.

SUBJECTS

The study cohort consisted of 2,036 patients (13% with congenital diaphragmatic hernia).

INTERVENTIONS

None.

MAIN RESULTS

In the cohort of patients without congenital diaphragmatic hernia (n = 1,773), bleeding occurred in 38% of patients, whereas thrombosis was noted in 31%. Bleeding and thrombosis were associated with a decreased survival by 40% (relative risk, 0.59; 95% CI, 0.53-0.66) and 33% (odds ratio, 0.67; 95% CI, 0.60-0.74). Longer duration of extracorporeal life support and use of venoarterial cannulation were also associated with increased risk of bleeding and/or thrombotic complications and lower survival. The most common bleeding events included surgical site bleeding (17%; n = 306), cannulation site bleeding (14%; n = 256), and intracranial hemorrhage (11%; n = 192). Common thrombotic events were clots in the circuit (15%; n = 274) and the oxygenator (12%; n = 212) and hemolysis (plasma-free hemoglobin > 50 mg/dL) (10%; n = 177). Among patients with congenital diaphragmatic hernia, bleeding and thrombosis occurred in, respectively, 45% (n = 118) and 60% (n = 159), Bleeding events were associated with reduced survival (relative risk, 0.62; 95% CI, 0.46-0.86) although thrombotic events were not (relative risk, 0.92; 95% CI, 0.67-1.26).

CONCLUSIONS

Bleeding and thrombosis remain common complications in patients undergoing extracorporeal life support. Further research to reduce or eliminate bleeding and thrombosis is indicated to help improve patient outcome.

The effect of recombinant and plasma-derived prothrombin on prothrombin time in human plasma

INTRODUCTION

When investigating coagulation assays to measure the effect of infused prothrombin (FII) in in vivo coagulopathy models, we found that addition of FII, plasma-derived human FII (pd-hFII) or recombinant human FII (r-hFII), to normal plasma resulted in a concentration-dependent increase in prothrombin time (PT) initiated with Innovin(®) .

METHODS

The effect on PT by addition to plasma of either pd-hFII or r-hFII, using different commercial PT reagents, was studied both by turbidimetry and viscometry.

RESULT

Addition of FII to plasma resulted in increased PT when initiated with Innovin(®) : PT increased with 20% by doubling the concentration. The prolongation of PT became more pronounced with 2-6000 times diluted Innovin(®) . However, by adjustment of the final free Ca(2+) concentration in the assay with diluted Innovin(®) from 8.3 to 1.3 mmol/L, no FII-dependent increase in PT was found. In contrast, no prolongation of PT was found with other commercial PT reagents. A KM = 3 nmol/L was obtained with pd-hFII, respectively, r-hFII with FII-depleted plasma using Thromborel(®) to initiate PT.

CONCLUSION

At normal plasma concentration of FII, addition of FII should not have an effect on PT. The prolonged PT with Innovin(®) , but not with other PT reagents, at supranormal FII concentration is an artefact.

Comparison of three-factor and four-factor prothrombin complex concentrates regarding reversal of the anticoagulant effects of rivaroxaban in healthy volunteers

BACKGROUND

Four-factor prothrombin complex concentrates (PCCs), which contain factor II, FVII, FIX, and FX, have shown the potential to reverse the anticoagulant effect of rivaroxaban in healthy volunteers. The purpose of this study was to determine whether a three-factor PCC, which contains little FVII, has a similar effect.

METHODS AND RESULTS

We performed an open-label, single-center, parallel-group study comparing the effect of a three-factor PCC (Profilnine SD) with that of a four-factor PCC (Beriplex P/N) on the pharmacodynamics of rivaroxaban in 35 healthy volunteers. After receiving 4 days of rivaroxaban 20 mg twice daily to obtain supratherapeutic steady-state concentrations, volunteers were randomized to receive a single 50 IU kg(-1) bolus dose of four-factor PCC, three-factor PCC or saline 4 h after the morning dose of rivaroxaban on day 5, and the effects of these interventions on prothrombin time and thrombin generation were determined. Within 30 min, four-factor PCC reduced mean prothrombin time by 2.5-3.5 s, whereas three-factor PCC produced only a 0.6-1.0-s reduction. In contrast, three-factor PCC reversed rivaroxaban-induced changes in thrombin generation more than four-factor PCC.

CONCLUSIONS

This study demonstrates the potential of both three-factor and four-factor PCCs to at least partially reverse the anticoagulant effects of rivaroxaban in healthy adults. The discrepant effects of the PCC preparations may reflect differences in the procoagulant components present in each.

Ximelagatran for stroke prevention in atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and the most frequently encountered cause of embolic stroke. Vitamin K antagonists (such as warfarin) have represented the cornerstone of anticoagulation practice for the last 60 years. Although highly effective in preventing thromboembolic events among patients with atrial fibrillation, warfarin therapy is limited by a multitude of potential problems. Hence, warfarin is significantly underused in clinical practice, with only half of warfarin-treated patients actually achieving therapeutic anticoagulation in routine clinical practice. Consequently, there is an overwhelming need for an alternative oral anticoagulant for patients with atrial fibrillation that is safer, more practical and effective. Ximelagatran (Exanta, AstraZeneca) is a novel oral direct thrombin inhibitor that is rapidly converted to the active compound melagatran after oral absorption. It has a low potential for drug interactions, anticoagulation monitoring is not required, and it is administered at a fixed twice-daily dose. The Stroke Prevention using the ORal Thrombin Inhibitor in patients with nonvalvular atrial Fibrillation (SPORTIF) III and V trials have together demonstrated the noninferiority of ximelagatran relative to warfarin for the prevention of stroke and embolic events in atrial fibrillation. Unfortunately, initial optimism has been tempered by serious concerns over its safety data in view of its propensity to cause elevation in liver enzymes.

Current and future antithrombotic agents in children

Thromboembolic complications are increasing in children, and the use of anticoagulation has seen a dramatic increase despite the lack of randomized clinical trials. The most widely used agents in children are heparin and warfarin, however these agents have limitations that are exaggerated in children. This has led to the use of newer agents with improved pharmacologic properties such as low-molecular-weight heparin, however, the use of novel agents such as direct thrombin inhibitors has been limited to case reports. These agents, however, have potential advantages over heparin, low-molecular-weight heparin and warfarin. Current clinical trials are in progress to define the proper dose of two such agents--argatroban (Argatroban, GlaxoSmithKline) and bivalirudin (Angiomax, The Medicines Company). The selective Factor Xa inhibitor fondaparinux (Arixtra, Sanofi-Synthelabo) has not been used in children; however, there are situations in which this agent may be advantageous. This review will discuss the currently available agents, with an emphasis on those that are novel and their potential uses in children.

Anticoagulants: A Review of the Pharmacology, Dosing, and Complications

Anticoagulants remain the primary strategy for the prevention and treatment of thrombosis. Unfractionated heparin, low molecular weight heparin, fondaparinux, and warfarin have been studied and employed extensively with direct thrombin inhibitors typically reserved for patients with complications or those requiring intervention. Novel oral anticoagulants have emerged from clinical development and are expected to replace older agents with their ease of use and more favorable pharmacodynamic profiles. Hemorrhage is the main concerning adverse event with all anticoagulants. With their ubiquitous use, it becomes important for clinicians to have a sound understanding of anticoagulant pharmacology, dosing, and toxicity.

Intracerebral haemorrhage associated with antithrombotic treatment: translational insights from experimental studies

Little is known about the pathophysiology of intracerebral haemorrhage that occurs during anticoagulant treatment. In observational studies, investigators have reported larger haematoma volumes and worse functional outcome in these patients than in those with intracerebral haemorrhage and a normal coagulation status. The need to prevent extensive haematoma enlargement by rapid reversal of the anticoagulation seems intuitive, although no evidence is available from randomised clinical trials. New oral anticoagulants, such as the direct thrombin inhibitor dabigatran and the factor Xa inhibitor rivaroxaban, have been approved recently; however, intracerebral haemorrhage during dabigatran or rivaroxaban anticoagulation has not been characterised, and whether anticoagulation reversal can be beneficial in this scenario is unknown. In a translational approach, new experimental models have been developed to study anticoagulation-associated intracerebral haemorrhage in more detail and to test treatment strategies. Vitamin k antagonists enlarge haematoma volumes and worsen functional outcome in animal models. Rapid reversal of anticoagulation in the experimental setting prevents prolonged haematoma expansion and improves outcome. The new oral anticoagulants increase intracerbral haemorrhage volumes less than does warfarin. Haemostatic approaches that have been used for vitamin k-associated intracerebral haemorrhage also seem to be effective in intracerebral haemorrhage associated with the new anticoagulants. These experimental studies are valuable for filling gaps in knowledge, but the results need careful translation into routine clinical practice.

Pharmacologic tools to reduce bleeding in surgery

Strategies to reduce blood loss and the need for transfusions in surgery include enhancement of coagulation, inhibition of fibrinolysis, and an improved decision algorithm for transfusion based on bedside monitoring of global hemostasis. The synthetic antifibrinolytic drug tranexamic acid has emerged as an effective alternative in this respect for orthopedic and cardiac surgery. Although it seems less effective than aprotinin, it has not been associated with the increased risk of mortality of the latter. Thromboelastography to monitor the global hemostatic capacity and to guide the appropriate use of blood components in cardiac surgery is also effective in reducing the need for transfusion. Patients on antithrombotic drug therapy may need reversal before surgery to avoid excessive blood loss, or intraoperatively in cases of unexpected bleeding. Available options are protamine for unfractionated or low-molecular-weight heparin, recombinant activated factor VII for fondaparinux, prothrombin complex concentrate for vitamin K antagonists and possibly for oral factor Xa inhibitors, dialysis and possibly activated prothrombin complex concentrate for oral thrombin inhibitors, desmopressin for aspirin and possibly for thienopyridines, and platelet transfusions for the latter.

Management of bleeding complications in the anticoagulated patient

As new anticoagulants become available, and the number of anticoagulated patients continues to rise, it is necessary to know how to deal with associated bleeding complications. In this review, reversal strategies for traditional anticoagulants (warfarin and heparin) as well as newer anticoagulants are described. Prothrombin complex concentrates (PPCs) can be used to reverse vitamin K antagonists (VKA), and plasma may be used where they are not available. Recombinant activated factor VII (rFVIIa) may be useful to reverse pentasaccharide anticoagulants. 1-Desamino-8-D-arginine vasopressin (DDAVP), cryoprecipitate, PCCs, and dialysis may help to reverse direct thrombin inhibitors, while rFVIIa seems to be ineffective. The effect of direct factor Xa inhibitors may be reversed by PCCs, FVIIa, or factor Xa concentrates.

How I treat with anticoagulants in 2012: new and old anticoagulants, and when and how to switch

Two novel oral anticoagulants, dabigatran and rivaroxaban, have recently been approved. They differ in many ways from warfarin, including rapid onset of action, shorter half-life, fewer drug-drug interactions, lack of need for monitoring, and no need for titration or dose adjustments. These novel agents represent a landmark shift in anticoagulant care; however, many aspects of their use will be unfamiliar to practicing clinicians, despite the imminent widespread use of these agents in the community. The management of these anticoagulants when transitioning from or back to warfarin, around surgery or in case of major hemorrhage, requires knowledge of their pharmacokinetics and mechanism of action. Unfortunately, there is a limited evidence base to inform decisions around management of these agents. We present our practice in these settings supported, where available, with literature evidence.

Hemostatic Therapy in Experimental Intracerebral Hemorrhage Associated With the Direct Thrombin Inhibitor Dabigatran

Background and Purpose—

Dabigatran-etexilate (DE) recently has been approved for stroke prevention in atrial fibrillation. However, lack of effective antagonists represents a major concern in the event of intracerebral hemorrhage (ICH). The aims of the present study were to establish a murine model of ICH associated with dabigatran, and to test the efficacy of different hemostatic factors in preventing hematoma growth.

Methods—

In C57BL/6 mice receiving DE (4.5 or 9.0 mg/kg), in vivo and in vitro coagulation assays and dabigatran plasma levels were measured repeatedly. Thirty minutes after inducing ICH by striatal collagenase injection, mice received an intravenous injection of saline, prothrombin complex concentrate (PCC; 100 U/kg), murine fresh-frozen plasma (200 μL), or recombinant human factor VIIa (8.0 mg/kg). ICH volume was quantified on brain cryosections 24 hours later.

Results—

DE substantially prolonged tail vein bleeding time and ecarin clotting time for 4 hours corresponding to dabigatran plasma levels. Intracerebral hematoma expansion was observed mainly during the first 3 hours on serial T2* MRI. Anticoagulation with high doses of DE increased the hematoma volume significantly. PCC and, less consistently, fresh-frozen plasma prevented excess hematoma expansion caused by DE, whereas recombinant human factor VIIa was ineffective. Prevention of hematoma growth and reversal of tail vein bleeding time by PCC were dose-dependent.

Conclusions—

The study provides strong evidence that PCC and, less consistently, fresh-frozen plasma prevent excess intracerebral hematoma expansion in a murine ICH model associated with dabigatran. The efficacy and safety of this strategy must be further evaluated in clinical studies.

Practical aspects of the oral new anticoagulants

After years of only oral vitamin K antagonists, there are new many new antithrombotic agents in development and on entering the marketplace. This review will analyze clinical trial results for these new agents-especially dibigatran, rivaroxaban, and apixiban. Also to be discussed are practical aspects of use of these new agents such monitoring, reversal, and use before procedures.

Animal model and clinical evidence indicating low thrombogenic potential of fibrinogen concentrate (Haemocomplettan P)

The objective of this study was to characterize the thrombogenicity of one pasteurized fibrinogen concentrate (Haemocomplettan P) in clinical use for over 20 years. Thrombus formation during venous stasis was assessed in rabbits receiving either 100 or 250 mg/kg Haemocomplettan P. Thrombotic adverse events possibly related to Haemocomplettan P were documented in a long-standing pharmacosurveillance program. A systematic review of thrombotic events in Haemocomplettan P clinical studies was also conducted. There was no evidence of thrombus formation during venous stasis in any Haemocomplettan P-treated animal. The pharmacosurveillance program spanned 22 years, during which a Haemocomplettan P quantity equivalent to more than 250 000 doses of 4 g each was distributed in 21 countries. Nine spontaneous reports of thrombotic adverse events possibly related to Haemocomplettan P were compiled, corresponding to an incidence rate of 3.48 events per 10 treatment episodes (95% confidence interval, 1.59-6.61 events per 10 treatment episodes). In 10 clinical studies involving 298 patients, one patient developed nonfatal venous thrombosis and pulmonary embolism to which fibrinogen concentrate may have contributed. Additionally, four other patients experienced arterial ischemic events that were likely attributable to massive hemorrhage and hypotension rather than fibrinogen replacement. Evidence from an animal model of venous stasis, a comprehensive pharmacosurveillance program, and a systematic review of clinical studies indicates that the thrombogenic potential of fibrinogen concentrate is low.

Emergency reversal of anticoagulation and antiplatelet therapies in neurosurgical patients

Intracranial hemorrhage (ICH) is a common problem encountered by neurosurgeons. Patient outcomes are influenced by hematoma size, growth, location, and the timing of evacuation, when indicated. Patients may have abnormal coagulation due to pharmacological anticoagulation or coagulopathy due to underlying systemic disease or blood transfusions. Strategies to reestablish the integrity of the clotting cascade and platelet function assume a familiarity with these processes. As patients are increasingly treated with anticoagulants and antiplatelet agents, it is essential that the physicians who care for patients with ICH understand these pathways and recognize how they can be manipulated to restore hemostasis.

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

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

Faster onset of effect and greater efficacy of NN1731 compared with rFVIIa, aPCC and FVIII in tail bleeding in hemophilic mice

BACKGROUND

Recombinant factor VIIa (rFVIIa, Novoseven) is currently used to control bleeding in hemophiliacs with inhibitors. A new rFVIIa variant, NN1731, with increased activity on the surface of activated platelets, has demonstrated a more potent and faster onset of reactivity than rFVIIa in various in vitro models. The present study aimed to investigate whether this translates into greater efficacy and faster promotion of hemostasis in vivo.

METHOD AND RESULTS

In a severe tail-bleeding model in hemophilia A mice, NN1731 demonstrated significantly greater efficacy than rFVIIa, plasma-derived activated prothrombin complex concentrate (pd-aPCC, FEIBA or FVIII (Refacto). Assessment of the blood loss over time showed that NN1731 significantly and dose-dependently reduced the blood loss in the first 5-min observation period, whereas the effect of rFVIIa, FVIII and pd-aPCC first became evident 5-10 min after injury.

CONCLUSION

This study shows that NN1731 has a greater efficacy and faster resolution of bleeding in a severe bleeding model in hemophilia A mice compared with any of the other agents tested.

Recombinant human factor VIIa and a factor VIIa-analogue reduces heparin and low molecular weight heparin (LMWH)-induced bleeding in rats

BACKGROUND

Heparin and low molecular weight heparin (LMWH) are widely used for prevention and treatment of thromboemobolic events, but may occasionally cause uncontrollable bleeding. Heparin can readily be antagonized with protamine, but this is less effective against LMWH.

OBJECTIVES

To test the effects of rFVIIa or an analogue of rFVIIa, NN1731, on heparin- and LMWH-induced bleeding in rats.

METHODS

Initially the doses of heparin and tinzaparin (a LMWH) were determined by dose-titration. Following pretreatment with heparin or tinzaparin in rats, tail-transection was performed, and the effect of rFVIIa and NN1731 on the bleeding was observed.

RESULTS

rFVIIa (5, 10 and 20 mg kg(-1)) reduced bleeding time and blood loss caused by heparin- and tinzaparin-induced bleeding, using doses of 200 IU kg(-1) (n = 8) and 500 IU kg(-1) (n = 9), respectively. Similarly, 10 mg kg(-1) NN1731 significantly reduced both heparin- and tinzaparin-induced bleeding to the normal level. Following severe anticoagulation with 1800 IU kg(-1) tinzaparin, 10 mg kg(-1) NN1731 reduced and normalized the bleeding, while the effect of 20 mg kg(-1) rFVIIa failed to reach statistical significance. These data are consistent with the hypothesis that rFVIIa/NN1731 are capable of generating sufficient thrombin locally on the surface of activated platelets to induce hemostasis in the presence of heparin/LMWH.

CONCLUSIONS

This study suggests that rFVIIa and NN1731 may have the potential to control bleedings caused by heparin or LMWH.

Recombinant activated factor VII effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin ex vivo as measured using thromboelastography

Bleeding is the major adverse reaction to anticoagulants, leading to significant morbidity and even mortality. Protamine is a specific antidote for heparin yet is only partially effective for enoxaparin, and the activated factor X inhibitor fondaparinux and the direct thrombin inhibitors argatroban and bivalirudin lack specific antidotes. We evaluated the ability of recombinant activated factor VII (rFVIIa), a general hemostatic agent, to reverse the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, as measured by thromboelastography. Whole-blood samples containing each test anticoagulant, with or without rFVIIa 1.5-4.5 microg/ml, were prepared ex vivo (n >or= 48, each anticoagulant) and analyzed by thromboelastography. The thromboelastography parameters of clot initiation, propagation, rigidity and elasticity were compared for the ex-vivo samples for each anticoagulant. The reversal ability of rFVIIa was also assessed using the standard clinical assay used to monitor each anticoagulant. Thromboelastography was performed on blood from eight stably anticoagulated patients, with and without exogenous rFVIIa. For each anticoagulant, rFVIIa significantly improved and, in some cases, completely normalized all thromboelastography parameters (P < 0.001). rFVIIa significantly (P < 0.01) decreased the activated partial thromboplastin time for argatroban-containing, bivalirudin-containing, or heparin-containing blood yet did not affect the anti-activated factor X levels for enoxaparin-containing or fondaparinux-containing blood. By thromboelastography, rFVIIa exerted generally similar reversal effects on the anticoagulated patient samples as on the ex-vivo samples. In conclusion, rFVIIa effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, and should be considered for patients with excessive bleeding associated with these anticoagulants.

Pharmacology and clinical use of recombinant activated factor seven in neurosciences

Recombinant activated factor VII (rFVIIa, NovoSeven, NovoNordisc, Danemark) has been approved for the treatment of patients with hemophilia with inhibitors, further indications, at least in some countries, include the treatment of factor VII deficiency and Glanzmann thrombasthenia refractory to conventional therapy. Apart from these indications, the agent is increasingly used for the treatment of severe and potentially life-threatening bleeding manifestations, irrespective of the underlying hemostatic abnormality. The agent has successfully been used for the treatment of both inherited and acquired coagulopathies as well as thrombocytopathia or thrombocytopenia, however, most information on off-label use derives from case reports and retrospective studies and therefore publication bias can-not be excluded. In this review, we focus on the use of rFVIIa for the treatment of spontaneous and perioperative intracranial hemorrhage as well as trauma patients. We review the current knowledge regarding the physiology of hemostasis, the pharmacology of rFVIIa, and its clinical use in neurosciences. Further studies are urgently needed to define the efficacy and safety of recombinant activated factor VII in patients without hemophilia, factor VII deficiency, or Glanzmann thrombasthenia. At time, its use can be justified in life-threatening bleeding situations refractory to conventional treatment.

Hemostatic effect of activated factor VII without promotion of thrombus growth in melagatran-anticoagulated primates

INTRODUCTION

Pharmacological enhancement of coagulation using activated prothrombin complex concentrate (APCC) or activated factor VII (FVIIa) might be useful hemostatic approaches to bleeding emergencies during anticoagulant therapy. However, any such intervention should not increase thrombotic risk. We therefore investigated their hemostatic and prothrombotic potential during propagation of large arterial-type thrombin in anticoagulated baboons.

MATERIALS AND METHODS

High dose melagatran, a competitive inhibitor of thrombin (0.6 mg/kg/h), or inactivated FVIIa (FVIIai), a competitive inhibitor of FVIIa (2 mg/kg) were used for anticoagulation. APCC or FVIIa were administered to melagatran-anticoagulated animals only. Primary hemostasis was assessed as template bleeding time (BT). Thrombus formation was quantified as fibrin deposition (FD) and platelet deposition (PLD) in synthetic vascular grafts that were deployed for 40 min into arteriovenous shunts.

RESULTS

Melagatran (n=11) prolonged BT to 279% (95% CI +/-140%; P<0.019), reduced FD to 33% [+/-8%; P<0.001]; and PLD to 39% [+/-11%; P<0.001] of untreated controls. FVIIai (n=3) prolonged BT (222% [+/-51%; P<0.010]) without inhibiting thrombus propagation. APCC (n=10) reduced the antithrombotic effect of melagatran (FD 52% [+/-9%; P<0.002], PLD 61% [+/-17%; P=0.028] versus melagatran alone) at a dose (250 U/kg) that had no effect on the BT (327% [+/-150%; P=0.607]. Meanwhile, FVIIa (n=12) normalized the BT to 115% (+/-32%; P<0.05) at a dose (270 microg/kg) that was not yet prothrombotic (FD 26% [+/-4%; P<0.001], PLD 39% [+/-9%; P=0.970]).

CONCLUSION

Administration of FVIIa during antithrombotic treatment with direct thrombin inhibitors might support hemostasis before promoting the intraluminal expansion of thrombi.