Prothrombin complex concentrate (Beriplex P/N) for control of bleeding after kidney trauma in a rabbit dilutional coagulopathy model

Introduction

Fluid resuscitation after trauma often results in dilutional coagulopathy that may hinder control of bleeding and, once initial hemostasis has been secured, heighten risk of perioperative bleeding when further surgery is required. Since multiple coagulation factor deficiencies typically accompany fluid resuscitation, prothrombin complex concentrate (PCC) containing factors II, VII, IX and X may potentially offer greater hemostatic efficacy than coagulation factor monotherapy.

Materials and methods

Anesthetized normothermic rabbits were hemodiluted 50-60% by phased blood withdrawal and infusion of hydroxyethyl starch and erythrocytes. The animals were randomly assigned to receive saline placebo, 25 IU·kg^- 1 PCC (Beriplex P/N) or 180 μg·kg^- 1 activated recombinant factor VII (rFVIIa; NovoSeven). Immediately thereafter, bleeding was precipitated by a standardized kidney incision.

Results

PCC accelerated hemostasis compared both with saline and rFVIIa (p = 0.002 for both comparisons). The median times to hemostasis in the PCC, saline and rFVIIa groups were 12, 19 and 28 min, respectively. PCC reduced blood loss by a median of 43 mL with a 95% confidence interval (CI) of 8.0-67.5 mL vs. saline and 82 mL (CI, 35.0-110.0 mL) vs. rFVIIa. PCC augmented peak thrombin generation by a median of 104.1 nM (CI, 78.3-142.3 nM) compared with saline and 105.8 nM (CI, 70.7-139.5 nM ) relative to rFVIIa. At the respective 180 μg·kg^- 1 and 25 IU·kg^- 1 doses tested, rFVIIa displayed thrombogenicity in the Wessler stasis model, while PCC did not.

Conclusions

In an animal model of dilutional coagulopathy and kidney trauma, PCC accelerated hemostasis and diminished blood loss compared with rFVIIa monotherapy.     

On the monitoring of dabigatran treatment in “real life” patients with atrial fibrillation

Introduction

The oral direct thrombin inhibitor dabigatran is increasingly used to prevent thromboembolic stroke in patients with atrial fibrillation (AF). Routine laboratory monitoring is currently not recommended, but measurements of dabigatran and/or its effect are desirable in certain situations. We studied dabigatran exposure and compared different tests for monitoring of dabigatran in a real-life cohort of AF patients.

Material and methods

Ninety AF patients (68 ± 9 years, 67% men, mean CHADS₂ score 1.5) were treated with dabigatran 150 (n = 73) or 110 mg BID (n = 17). Trough plasma concentrations of total and free dabigatran by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) were compared to indirect measurements by Hemoclot thrombin inhibitors (HTI) and Ecarin clotting assay (ECA), as well as PT-INR and aPTT.

Results

Total plasma dabigatran varied 20-fold (12–237 ng/mL with 150 mg BID) and correlated well with free dabigatran (r² = 0.93). There were strong correlations between LC-MS/MS and HTI or ECA (p < 0.001) but these assays were less accurate with dabigatran below 50 ng/mL. The aPTT assay was not dependable and PT-INR not useful at all. There were weak correlations between creatinine clearance (Cockcroft-Gault) and LC-MS/MS, HTI and ECA (p < 0.001 for all). A high body weight with normal kidney function was associated with low dabigatran levels.

Conclusions

HTI and ECA reflect the intensity of dabigatran anticoagulation, but LC-MS/MS is required to quantify low levels or infer absence of dabigatran. Most real life patients with a normal creatinine clearance had low dabigatran levels suggesting a low risk of bleeding but possibly limited protection against stroke.     

Ginsenoside Rg1 inhibits platelet activation and arterial thrombosis

Introduction

Derived from the root of Panax ginseng C.A.Mey, Panax notoginsenosides (PNS) is a widely used herbal medicine to treat atherothrombotic diseases in Asian medicine. Ginsenoside Rg1 is one of the main compounds responsible for the pharmaceutical actions of PNS. As platelets play pivotal roles in atherothrombogenesis, we therefore studied the effect of Rg1 on platelet activation and its underlying mechanisms.

Materials and Methods

Human platelets are obtained from healthy subjects. Platelet activation and the inhibition of Rg1 were assessed by Born aggregometer, flow cytmetry, flow chamber and western blot. The in vivo thrombosis model was induced by 10% FeCl₃ on mesenteric arterioles of wild type B57/b6 mice.

Results

Rg1 significantly inhibited platelet aggregation induced by thrombin, ADP, collagen and U46619, e.g., aggregation rate stimulated by 0.1 U mL^- 1 thrombin was decreased 46% by Rg1. Rg1 also reduced thrombin (0.1 U mL^- 1)-enhanced fibrinogen binding and P-selectin expression of single platelet by 81% and 66%, respectively. Rg1 affected αIIbβ3-mediated outside-in signaling as demonstrated by diminished platelet spreading on immobilized fibrinogen. Rg1 also decreased the rate of clot retraction in platelet rich plasma. Furthermore, Rg1 decreased platelet adhesion on collagen surface under a shear rate correlated to the arterial flow (1000 s^- 1) by approximately 70%. Western blot showed that Rg1 potently inhibited ERK phosphrylation. The in vitro findings were further evaluated in the mouse model of in vivo arterial thrombosis, and Rg1 was found to prolong the mesenteric arterial occlusion time (34.9 ± 4.1 min without and 64.3 ± 4.9 min with Rg1; p < 0.01).

Conclusions

Rg1 inhibits platelet activation via the inhibition of ERK pathway, and attenuates arterial thrombus formation in vivo.     

Dabigatran versus enoxaparin for prevention of venous thromboembolism after hip or knee arthroplasty: A pooled analysis of three trials

Background

Three randomized, double-blind trials compared dabigatran, an oral direct thrombin inhibitor, with enoxaparin for the primary prevention of venous thromboembolism (VTE) in patients undergoing elective total hip and knee arthroplasty.

Objectives and Methods

We conducted a pre-specified pooled analysis of these trials. 8,210 patients were randomized, of whom 8,135 were treated (evaluable for safety) with dabigatran 220 mg or 150 mg once-daily, or subcutaneous enoxaparin (40 mg once-daily or 30 mg twice-daily). Efficacy analyses were based on the modified intention-to-treat population of 6,200 patients with an evaluable outcome. The common risk difference (RD) of treatment effect between each dabigatran dose and enoxaparin was estimated using fixed-effects models, and statistical heterogeneity was estimated using the I² statistic.

Results

The composite outcome of major VTE (proximal deep vein thrombosis and/or pulmonary embolism) and VTE-related mortality occurred in 3.3% of the enoxaparin group versus 3.0% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, 95% CI -1.3% to 0.9%, I² = 37%) and 3.8% of the 150 mg group (RD vs. enoxaparin 0.5%, -0.6% to 1.6%, I² = 0%). Major bleeding occurred in 1.4% of the enoxaparin group versus 1.4% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, -0.8% to 0.5%, I² = 40%) and 1.1% of the 150 mg group (RD vs. enoxaparin -0.4%, -1.0% to 0.2%, I² = 0%).

Conclusions

Oral dabigatran was as effective as subcutaneous enoxaparin in reducing the risk of major VTE and VTE-related mortality after hip or knee arthroplasty and has a similar bleeding profile.     

Global Thrombosis Test (GTT) can detect major determinants of haemostasis including platelet reactivity,endogenous fibrinolytic and thrombin generating potential

Background

Detection of both thrombosis and bleeding risk are essential in clinical cardiology. Thrombin generated by activated platelets and from the extrinsic coagulation pathway is the major determinant of thrombogenesis and hemostasis. Although novel oral anticoagulants further increase the bleeding risk of antiplatelet drugs, platelet function tests do not reliably predict hemorrhagic complications. It seems that in addition to platelet aggregation, true assessment of bleeding risks requires the measurement of both platelet and plasma derived thrombin activity.

Objective

To adapt a novel, near-patient test for the assessment of both antithrombotic and anticoagulant effects of oral thrombin inhibitors.

Methods

The point-of-care Global Thrombosis Test (GTT), which measures platelet reactivity to shear-activation in native blood, was used. Thrombin, generated from activated platelets (procoagulant activity) plays a pivotal role in GTT measurement. In order to assess endogenous thrombin potential, in a separate blood sample thrombin generation was induced by microparticles formed during hypotonic hemolysis. Thus two blood samples were tested to measure simultaneously platelet reactivity (occlusion time, OT) and hemolysis (microparticles)-induced endogenous thrombin potential (OT-H).

Results

In healthy subjects (n = 32), OT measured in native blood was reduced in hemolysed blood (100% vs. 43 ± 4%; OT vs. OT-H respectively). Shortening of OT in hemolysed blood (OT-H) was dose-dependently inhibited by the in vitro added thrombin inhibitor argatroban. In patients receiving dabigatran (n = 27), OT and, to a lesser extent, OT-H was prolonged, compared to healthy volunteers. Intra-assay variation of OT-H was low (4.5%), but interindividual variation was great, both in healthy subjects (61%) and in patients on dabigatran (65%). Thrombin inhibitors argatroban, heparin (in vitro) and dabigatran (in vivo) all prolonged both OT and OT-H. There was no correlation between the measured OT and OT-H data.

Conclusions

Microparticles shed from erythrocytes during hypotonic lysis of native blood considerably shortened OT. In a direct proportion to the applied concentrations, various thrombin inhibitors prolonged both OT (antithrombotic effect) and to a lesser extent, OT-H (anticoagulant effect). Further large studies are required to evaluate the usefulness of this technique in a clinical setting, in assessing the anticoagulant and antithrombotic effects of medication and relating GTT results with observed thrombotic and bleeding events.     

Antithrombotic effects of PAR1 and PAR4 antagonists evaluated under flow and static conditions

Introduction

Thrombin-mediated activation of human platelets involves the G-protein-coupled protease-activated receptors PAR1 and PAR4. Inhibition of PAR1 and/or PAR4 is thought to modulate platelet activation and subsequent procoagulant reactions. However, the antithrombotic effects of PAR1 and PAR4 antagonism have not been fully elucidated, particularly under flow conditions.

Materials and Methods

A microchip-based flow chamber system was used to evaluate the influence of SCH79797 (PAR1 antagonist) and YD-3 (PAR4 antagonist) on thrombus formation mediated by collagen and tissue thromboplastin at shear rates simulating those experienced in small- to medium-sized arteries (600 s^- 1) and large arteries and small veins (240 s^- 1).

Results

At a shear rate of 600 s^- 1, SCH79797 (10 μM) efficiently reduced fibrin-rich platelet thrombi and significantly delayed occlusion of the flow chamber capillary (1.44 fold of control; P < 0.001). The inhibitory activity of SCH79797 was diminished at 240 s^- 1. YD-3 (20 μM) had no significant effect at either shear rate. The antithrombotic effects of SCH79797 were significantly augmented when combined with aspirin and AR-C66096 (P2Y₁₂ antagonist), but not with YD-3. In contrast, no significant inhibition of tissue factor-induced clot formation under static conditions was observed in blood treated with SCH79797 and YD-3, although thrombin generation in platelet-rich plasma was weakly delayed by these antagonists.

Conclusions

Our results suggest that the antithrombotic activities of PAR1 and/or PAR4 antagonism is influenced by shear conditions as well as by combined platelet inhibition with aspirin and a P2Y₁₂-antagonist.     

Indirect treatment comparison of new oral anticoagulants for the treatment of acute venous thromboembolism

Background

Numerous new oral anticoagulants (NOACs) have been compared to a parenteral anticoagulant/oral vitamin K antagonist (VKA) for the treatment of acute venous thromboembolism (VTE). We aimed to conduct a systematic review and adjusted indirect comparison meta-analysis to compare the efficacy and safety of NOACs for this indication.

Methods

We conducted a systematic literature search through November 2013 for randomized trials that evaluated treatment of acute VTE with a NOAC including rivaroxaban, apixaban, dabigatran and edoxaban. Trials had to report at least one of the following outcomes of interest: mortality, recurrent VTE, recurrent pulmonary embolism (PE), recurrent deep vein thrombosis (DVT), or major bleeding. Included trials were evaluated for quality using the Cochrane Risk of Bias tool. We performed an adjusted indirect comparison meta-analysis to evaluate the comparative efficacy and safety of NOACs, reporting relative risks (RRs) and 95% confidence intervals for each outcome.

Results

Six trials (n = 27,069) met inclusion criteria, one each evaluating apixaban and edoxaban and two trials each evaluating rivaroxaban and dabigatran. Risk of bias was low for all trials. NOACS did not differ significantly in the risk of mortality, recurrent VTE, recurrent PE or recurrent DVT. Dabigatran increased major bleeding risk compared to apixaban [RR 2.69 (1.19 to 6.07)] as did edoxaban compared to apixaban [RR 2.74 (1.40 to 5.39)].

Conclusion

Although NOACs do not appear to differ in the efficacy of treating acute VTE, data suggests apixaban to be the safer than some of its competitors.     

High Shear Dependent von Willebrand Factor Self-assembly Fostered by Platelet Interaction and Controlled by ADAMTS13

Introduction

The paradigm of activation induced platelet aggregation has recently been refuted under blood flow conditions with shear rates exceeding 20,000 s^- 1. These lead to reversible rolling platelet aggregates, which were dependent on the presence of immobilized and soluble von Willebrand factor.

Material and Methods

In vitro experiments using direct fluorescence video-microscopy were performed in wall parallel and stagnation point flow chambers with shear rates raised from 20,000 to 50,000 s^- 1. Washed blood cell suspension containing recombinant von Willebrand factor (rVWF) was perfused over rVWF or collagen coated surfaces.

Results

Here we show for the first time with the visualization of rVWF that not only colloid and polymer, i.e. platelets and VWF, form a composite, but that VWF itself is capable of entirely reversible self-assembly. On a collagen surface the platelet-VWF-conglomerates did not roll but VWF nets bound permanently to the collagen fibers and captured and immobilized platelets from the flow. Lowering the shear rate below the threshold of 20,000 s^- 1 no longer dissolved these deposits. Ultralarge multimer containing rVWF was most effective compared to normal sized rVWF. The presence of ADAMTS13 limited rolling aggregate and platelet-VWF-conglomerate formation to a time window of 7-8 minutes. Changing wall parallel flow to stagnation point flow halved the required shear rate threshold.

Conclusion

We conclude that flow dynamics can trigger reversible von Willebrand factor self-assembly and platelet-VWF-conglomerate accrual, which are regulated by ADAMTS13 to a time span needed by coagulation to stabilize it, e.g. in case of vessel injury.     

Reversal of rivaroxaban-induced anticoagulation with prothrombin complex concentrate,activated prothrombin complex concentrate and recombinant activated factor VII in vitro

Introduction

Anticoagulation therapies carry a risk of bleeding; reversal agents may be beneficial in cases of severe bleeding even for anticoagulants with a relatively short half-life, such as the oral factor Xa inhibitor rivaroxaban.

Materials and Methods

We investigated the in vitro reversal effect of prothrombin complex concentrate (PCC; 0.2-1.0 U/mL), activated PCC (aPCC; 0.2–1.0 U/mL) and recombinant activated factor VII (rFVIIa; 5–50 μg/mL) on rivaroxaban-induced (200–1000 ng/mL) changes in prothrombin time (PT) and thrombin generation (TG) in plasma, and in thromboelastometry (clotting time [CT]) in whole blood from healthy subjects.

Results

All three agents were partially effective in reversing rivaroxaban-induced anticoagulation but showed different profiles. rFVIIa and aPCC were more effective than PCC in reversing prolongations of PT, CT and TG lag time; rFVIIa was more effective than aPCC. However, the reversal effect reached a plateau with a maximal effect of approximately 50%. Inhibition of maximum thrombin concentration was slightly reversed by these agents; aPCC was the most effective. In contrast, inhibition of endogenous thrombin potential (ETP) was strongly reversed by aPCC, with significant increases over baseline at low rivaroxaban concentrations. Compared with aPCC, PCC showed a similar but less effective reversal profile. rFVIIa reversed ETP inhibition by approximately 50%.

Conclusions

The extent of reversal by aPCC, PCC and rFVIIa was dependent on the parameter measured in rivaroxaban-anticoagulated plasma or blood. ETP measurements may have predictive power for assessing the reversal potential of PCC or aPCC and may be used to indicate an increased prothrombotic risk.     

Preclinical efficacy and safety of rVIII-SingleChain (CSL627), a novel recombinant single-chain factor VIII

Introduction

The preclinical efficacy and safety of rVIII-SingleChain (CSL627), a novel recombinant single-chain factor VIII, was assessed in a series of animal studies.

Materials and Methods

In the tail-clip bleeding model, hemophilia A mice were injected with escalating doses (1–150 IU/kg) of rVIII-SingleChain, B-domain deleted (BDD) rFVIII (ReFacto AF^®), or full-length rFVIII products (Advate^®, Helixate^®). Total blood loss and the percentage of animals in which hemostasis occurred were assessed in this observer-blinded, randomized study. In a second non-randomized study in hemophilia A mice, thromboelastographic analysis, thrombin generation, and activated partial thromboplastin time assays were performed. General safety and toxicity were assessed in three animal species, including determination of the prothrombotic potential of rVIII-SingleChain in a rabbit venous thrombosis model.

Results

Under acute bleeding conditions, the effect of rVIII-SingleChain on total blood loss and hemostasis was indistinguishable from BDD and full-length rFVIII. rVIII-SingleChain and full-length rFVIII (both 20 IU/kg) corrected thromboelastographic parameters, activated partial thromboplastin time, and thrombin generation to a similar degree in hemophilia A mice. In a thrombosis model, the effect of rVIII-SingleChain on thrombus incidence was non-significant and comparable to BDD rFVIII at doses up to 500 IU/kg. Treatment with rVIII-SingleChain did not cause anaphylactic reaction or local intolerance in safety and toxicity studies, and demonstrated an excellent overall safety profile.

Conclusions

rVIII-SingleChain showed convincing hemostatic efficacy and excellent tolerability in animal studies, warranting continued investigation in human Phase I/III trials (AFFINITY).     

Cost-effectiveness of dabigatran etexilate for the prevention of stroke and systemic embolism in atrial fibrillation in Taiwan

Background

Economic evaluation of dabigatran, a new anti-antithrombotic agent, is done mostly in Western countries. It remains to be seen whether dabigatran will be cost effective in a practice environment where warfarin is significantly underused and the costs of both warfarin and international normalized ration INR monitoring are cheap.

Methods

We performed a cost-effectiveness analysis with a Markov model to evaluate the value of dabigatran to prevent stroke and systemic embolism in patients with atrial fibrillation (AF) in Taiwan. Dabigatran was given through sequential dosing, where patients < 80 years old received 150 mg of dabigatran twice a day and the dosage was reduced to 110 mgs for patients ≥ 80 years old. Dabigatran was compared with warfarin under two scenarios: the “real-world adjusted-dose warfarin” assuming all AF patients eligible for warfarin were given the medication and maintained at the INR observed in routine clinical practice in Taiwan, and the “real-world prescribing behaviour” similar to the treatment with antithrombotics in real-world practice in Taiwan, where eligible patients could receive warfarin, aspirin, or no treatment.

Results

The percentage of AF patients who received warfarin, aspirin or no treatment in Taiwan was 16%, 62% and 22%, respectively. The event rates of ischemic stroke per 100 patient-years were 4.5, 8.0, and 6.0 for sequential dabigatran, real-world prescribing behaviour and real-world warfarin use, respectively. The incremental cost-effectiveness ratio was $280 US per quality-adjusted-year (QALY) in the real-world prescribing scenario and $10,551 US/QALY in real-word warfarin use.

Conclusions

Dabigatran was highly cost-effective in a clinical practice setting where warfarin has been significantly underused.     

Thromboembolic safety and efficacy of prothrombin complex concentrates in the emergency reversal of warfarin coagulopathy

Background

There is uncertainty regarding the efficacy and incidence of thromboembolic events in patients treated with prothrombin complex concentrates (PCC) for the emergency reversal of warfarin effect.

Methods

During 2002 to 2010 we prospectively included 160 patients treated with PCC for emergency reversal of warfarin either for bleeding or because of the need of emergency surgery. A possible relationship to PCC was considered if objectively verified thromboembolism occurred within 7 days of PCC administration. Efficacy was adjudicated as good if the bleeding was controlled promptly or if the surgeon did not report excessive perioperative bleeding.

Results

We included 160 patients; 72% received PCC for bleeding. The median international normalized ratio (INR) before and after treatment with PCC was 3.5 (interquartile range [IQR] 2.6-5.4) and 1.4 (IQR 1.2-1.6). The mean dose of PCC was 1800 IU (IQR 1200-2000). In addition to PCC, 74% of the patients received vitamin K and 34% received plasma. Six patients (3.8%; 95% confidence interval [CI], 1.4-8.0%) developed thromboembolic events (3 strokes, 1 myocardial infarction, 1 deep vein thrombosis, 1 splenic infarction), possibly related to PCC. The clinical efficacy was good in 146 (91%), moderate in 6 (4%), poor in 4 (2.5%) and non-evaluable in 4 patients.

Conclusion

The administration of PCC for the emergency reversal of warfarin may be associated with a low risk of thromboembolism. The contribution of an unmasked thrombotic process by cessation of anticoagulation or of activation of coagulation by the hemorrhagic event should also be considered.     

Emergency reversal of anticoagulation: The real use of prothrombin complex concentrates: A prospective multicenter two year French study from 2006 to 2008

Introduction

Prothrombin complex concentrate (PCC) for reversal of vitamin K antagonist (VKA) is the main therapeutic option in cases of life-threatening bleeding. Clinical use of PCC is poorly documented.

Methods

We prospectively assessed PCC use in four French emergency departments during a two year period 2006-2008 before publication of French Guidelines. An appropriate treatment was defined when PCC was recommended, with a dose of PCC above or equal to 20 UI/kg, with vitamin K and with an assessment of international normalized ratio (INR) after PCC. Time of diagnosis and PCC administration were collected, as INR values, thromboembolic events within seven days, hospital mortality.

Results

256 patients received PCC for reversal of OAT. PCC was mainly prescribed for major intracerebral (ICH) or gastrointestinal hemorrhage. An appropriate treatment was observed in 26% of patients. Intra-hospital mortality for major bleeding was 33% for ICH and 26% for non-ICH major bleeding. A PCC dose > 20 UI/kg was able to reach an INR < 1.5 in 65% of patients. For major hemorrhages (70%), time between patient arrival and treatment delivery exceeded three hours in half of cases. Control of INR was omitted in 20% of patients. No patients presented a thromboembolic event.

Conclusion

A suitable treatment was administered in 26% of patients. A PCC dose of 20-30 IU/kg seems adequate in most cases to reverse VKA activity, but both higher and lower doses achieve similar effects. Considerable progress is required to improve PCC administration and control of treatment efficacy, and to shorten time to diagnosis.     

Safety and Efficacy of Edoxaban,an Oral Factor Xa Inhibitor,Versus Enoxaparin for Thromboprophylaxis After Total Knee Arthroplasty: The STARS E-3 Trial

Introduction

This phase 3 trial compared the safety and efficacy of edoxaban, an oral direct factor Xa inhibitor, with enoxaparin sodium (enoxaparin) for thromboprophylaxis after total knee arthroplasty (TKA) in patients in Japan and Taiwan.

Materials and methods

In this randomized, double-blind, double-dummy study, patients received oral edoxaban 30 mg once daily beginning 6 to 24 hours postsurgery or enoxaparin 2000 IU (equivalent to 20 mg) subcutaneously twice daily beginning 24 to 36 hours postsurgery for 11 to 14 days. The primary efficacy endpoint was the composite of symptomatic pulmonary embolism and symptomatic and asymptomatic deep vein thrombosis. Safety endpoints included the incidence of major bleeding, clinically relevant non-major (CRNM) bleeding, major bleeding or CRNM bleeding, all bleeding events, adverse events, and adverse drug reactions.

Results

Of 716 patients enrolled, 360 and 356 were randomized to receive edoxaban or enoxaparin, respectively. The primary efficacy outcome occurred in 22/299 (7.4%) and 41/295 (13.9%) patients in the edoxaban and enoxaparin groups, respectively (relative risk reduction = 46.8%), indicating non-inferiority (P < 0.001) and superiority (P = 0.010) of edoxaban versus enoxaparin. In the edoxaban and enoxaparin groups, major bleeding occurred in 4/354 (1.1%) versus 1/349 (0.3%) patients (P = 0.373); major or CRNM bleeding occurred in 22/354 (6.2%) versus 13/349 (3.7%) patients (P = 0.129), respectively.

Conclusions

Edoxaban 30 mg once daily was more effective for thromboprophylaxis than subcutaneous enoxaparin 2000 IU twice daily following TKA and demonstrated a similar incidence of bleeding events.     

Safety and efficacy of edoxaban in patients undergoing hip fracture surgery

Introduction

Edoxaban is an oral, direct, once-daily factor Xa inhibitor. This study evaluated the safety and efficacy of edoxaban compared to subcutaneous enoxaparin in Japanese patients undergoing hip fracture surgery.

Materials and methods

In this multicenter, randomized, open-label, active-comparator, phase 3 trial, 92 patients were randomized 2:1 to receive edoxaban 30 mg once daily (n = 62) or enoxaparin sodium (enoxaparin) 2000 IU (equivalent to 20 mg) twice daily (n = 30) for 11 to 14 days. The primary endpoints were the incidence of major or clinically relevant non-major (CRNM) bleeding and incidence of any bleeding events (major, CRNM, or minor bleeding). Secondary efficacy endpoints included the incidence of thromboembolic events, venous thromboembolism-related deaths, and all-cause deaths. Additional adverse events were recorded throughout the study.

Results

In the edoxaban and enoxaparin treatment groups, the incidence of major or CRNM bleeding was 3.4% and 6.9%, respectively, while any bleeding event occurred in 25.4% and 17.2% of patients, respectively. The incidence of thromboembolic events was 6.5% in the edoxaban group and 3.7% in the enoxaparin group. All events were asymptomatic deep vein thrombosis. The incidence of adverse events was 72.9% and 82.8% in the edoxaban and enoxaparin groups, respectively.

Conclusions

Compared to subcutaneous enoxaparin 2000 IU twice daily, oral edoxaban 30 mg once daily demonstrated similar safety and efficacy in the prevention of thromboembolic events in Japanese patients undergoing hip fracture surgery.Clinical trials registration number: NCT01181141.     

Nonadherence with INR Monitoring and Anticoagulant Complications

Introduction

This study tests the hypothesis that nonadherence with INR monitoring is associated with an increased risk for warfarin-related bleeding and thrombosis and describes patient characteristics associated with INR monitoring nonadherence.

Materials and Methods

This was a retrospective, longitudinal, matched cohort study wherein patients were categorized into adherent and nonadherent cohorts; adherent patients were matched 2:1 to nonadherent patients. The primary study endpoint was the first occurrence of bleeding or thromboembolism. Multivariate logistic regression modeling identified patient characteristics associated with INR monitoring adherence or nonadherence.

Results

A total of 4995 and 2544 patients contributed 10729 and 5385 patient-years of warfarin therapy in the adherent and nonadherent groups, respectively. The rate of thromboembolic events during follow up was higher in the nonadherent group than in the adherent group (0.95% vs. 0.62% per patient-year, respectively; p = 0.019) and nonadherence to INR monitoring was associated with a moderately higher risk of thromboembolism (adjusted Hazard Ratio = 1.51; 95% confidence interval = 1.04 – 2.20). The difference in bleeding between the two groups was not statistically significant.

Conclusions

Repeatedly missing INR tests is an easily identified clinical parameter that is associated with moderately increased risk for thromboembolism in patients taking chronic warfarin therapy. Clinicians should carefully consider the underlying thromboembolic risk and extent of nonadherence when weighing the benefits of continued warfarin therapy for a given patient.     

Identification of novel small molecule inhibitors of activated protein C

Introduction

Activated protein C (APC) is the central enzyme of the anticoagulant protein C pathway. Low concentrations of APC circulate in plasma and are believed to contribute to the maintenance of a normal haemostatic balance.

Materials and Methods

We have used a structure-based virtual screening approach to discover small drug-like molecules that inhibit the interaction between APC and its substrate FVa through inhibition of a predominant APC exosite, known to be involved in FVa substrate binding. We have combined in silico selection with functional screening and direct binding analysis to identify novel molecules and to ascertain and characterize the inhibition of the interaction between APC and FVa.

Results

We have identified a number of novel molecules that bind to APC and protein C with Kd values in the range of 10^- 3– 10^- 5 M. Inhibition by these molecules is incomplete, which most likely reflects the extended surface that is involved in the interaction between APC and its substrates. Direct binding of hit molecules to variant APC molecules that were mutated in the targeted binding site revealed that several of the molecules presented a 100–500 fold lower affinity for the variant molecule, suggesting that these molecules indeed bind the exosite of APC.

Conclusions

The protein-protein interaction inhibitors discovered here, could function as starting molecules for further development of small molecules with anti-APC properties. Such molecules may be of clinical interest, in particular in individuals where thrombin formation is compromised and the haemostatic balance is tipped towards bleeding tendencies, such as in haemophilia A.     

Recombinant fusion protein linking factor VIIa with albumin (rVIIa­FP): Tissue distribution in rats

Introduction

A novel fusion protein linking coagulation factor VIIa with albumin (rVIIa-FP) is currently undergoing clinical investigations.

Objective

This study was conducted to examine the biodistribution of rVIIa-FP in comparison to recombinant factor VIIa (rFVIIa).

Materials and Methods

[³H]-rVIIa-FP (10 mg kg^− 1) or [³H]-rFVIIa (1.6 mg kg^− 1) were administered intravenously to rats, followed by quantitative whole-body and knee joint autoradiography for 24 ([³H]-rFVIIa) or 240 ([³H]-rVIIa-FP) hours post-dose. Pharmacokinetic and excretion balance analyses were performed.

Results

In contrast to [³H]-albumin, the tissue distributions of [³H]-rVIIa-FP and [³H]-rFVIIa were similar. Within the knee, both were rapidly present within synovial and mineralized regions. Importantly, rVIIa-FP- and albumin-derived radioactivity were detectable up to 72–120 hours, whereas [³H]-rFVIIa signals were already close to detection limits at 24 hours. The longest rVIIa-FP retention times were observed in bone marrow and endosteum, in which the retention times were up to 5 times longer for rVIIa-FP compared with rFVIIa. Up to 8 hours post-dose, 100% of radioactivity was assigned to unchanged [³H]-rVIIa-FP. Elimination of both proteins occurred primarily via the urine.

Conclusions

The data suggest that the FVIIa moiety is directing rVIIa-FP’s tissue distribution while the albumin moiety is responsible for the prolonged tissue retention. Importantly, rVIIa-FP is highly concentrated and retained over a long period in the growth plate of the knee joint − a vulnerable site in haemophilia patients. Overall, these improved tissue distribution characteristics of rVIIa-FP may enhance compliance and allow a more convenient dosing frequency.     

Dose escalation of low molecular weight heparin in patients with recurrent cancer-associated thrombosis

Introduction

Patients with cancer-associated thrombosis are at a high risk of developing recurrent events despite anticoagulant therapy. Escalation of the dose of low molecular weight heparin (LMWH) has been suggested as a potential treatment option to manage these patients. We sought to confirm the benefit and risk of this management strategy in patients with recurrent cancer-associated thrombosis.

Material and Methods

A retrospective cohort study of consecutive cancer outpatients seen for management of a symptomatic recurrent cancer-associated thrombosis while on anticoagulation was undertaken. Objectively confirmed episodes of recurrent thrombosis were treated with either dose escalation of LMWH or initiation of therapeutic dose of LMWH in patients already anticoagulated with LMWH or vitamin K antagonist (VKA) respectively. Included patients were followed for a minimum of 3 months after the index recurrent event.

Results

Fifty-five cancer patients with a recurrent venous thromboembolism (VTE) despite anticoagulation were included. At the time of the recurrence, 89% of patients were on LMWH. The median time between the initial cancer-associated thrombosis to the index recurrent event was 2.3 months (range 0.1 to 30.4 months). Four patients (7.3%; 95% CI: 2.0 to 17.6%) had a second recurrent VTE during the 3-month follow-up period. Three patients (5.5%; 95% CI 1.1 to 15.1%) had major bleeding complications after dose escalation of LMWH. There were no recurrent fatal VTE or major bleeding episodes.

Conclusion

Escalating the dose of LMWH seems effective and safe for managing patients with recurrent cancer-associated thrombosis despite anticoagulant therapy.     

Coronary thrombi neovascularization in patients with ST-elevation myocardial infarction - clinical and angiographic implications

Introduction

Coronary artery thrombosis in ST-elevation myocardial infarction (STEMI) is a dynamic process often preceded by episodes of silent plaque rupture and subocclusive thrombosis. Thrombus organization is achieved by ingrowth of endothelial and smooth muscle cells. Clinical significance and impact of thrombus neovascularization on primary percutaneous coronary intervention (pPCI) outcome remain unclear. Therefore we investigated composition and neovascularization of thrombi aspirated during pPCI and their association with clinical and angiographic parameters of STEMI patients.

Methods

Aspirated thrombi retrieved from 84 STEMI patients were classified as fresh (< 1 day), lytic (1-5 days) or organized (> 5 days). Thrombus neovascularization was evaluated immunohistochemically using CD34, CD31 and VEGF antibodies. CD34 and CD31 immunopositive (CD34/CD31 +) cells were organized as single, clusters and microvessels. VEGF positivity was graded as low or high, based on thrombus surface immunopositive area.

Results

CD34/CD31 + cells were present in 67% of all aspirated thrombi. Thrombus CD34/CD31 positivity was associated with previous history of angina pectoris (χ² = 6.142, p = 0.013) and lower myocardial blush grade (MBG < 3, χ² = 12.602, p < 0.001). Organization of CD34/CD31 + cells showed inverse association with the extent of VEGF positivity (χ² = 10.607, p = 0.005). Fresh thrombi were associated with shorter ischemic time (U = 237.5, p = 0.002) and MBG 3 (χ² = 6.379, p = 0.012).

Conclusions

Older thrombus age and neovascularization are associated with suboptimal myocardial perfusion in STEMI patients. Thrombus VEGF expression is inversely associated with degree of CD34 + cell organization. Therefore, neovascularization of aspirated thrombi may indicate the duration of thrombosis, coronary microcirculation status and outcome in STEMI patients.