Effects of rivaroxaban, acetylsalicylic acid and clopidogrel as monotherapy and in combination in a porcine model of stent thrombosis

Switching from Dual Antiplatelet Therapy with Aspirin Plus a P2Y12 Inhibitor to Dual Pathway Inhibition with Aspirin Plus Vascular-Dose Rivaroxaban: The Switching Anti-Platelet and Anti-Coagulant Therapy (SWAP-AC) Study

BACKGROUND

 To date, there are no data on switching to dual pathway inhibition (DPI) patients who have completed a guideline-recommended dual antiplatelet therapy (DAPT) regimen.

OBJECTIVES

 To assess the feasibility of switching from DAPT to DPI and to compare the pharmacodynamic (PD) profiles of these treatments.

METHODS

 This was a prospective, randomized, PD study conducted in 90 patients with chronic coronary syndrome (CCS) on DAPT with aspirin (81 mg/qd) plus a P2Y12 inhibitor (clopidogrel [75 mg/qd; n = 30], ticagrelor [90 mg/bid; n = 30], or prasugrel [10 mg/qd; n = 30]). Patients in each cohort were randomized to maintain DAPT or switch to DPI (aspirin 81 mg/qd plus rivaroxaban 2.5 mg/bid). PD assessments included: VerifyNow P2Y12 reaction units; light transmittance aggregometry following stimuli with adenosine diphosphate (ADP), tissue factor (TF), and a combination of collagen, ADP, and TF (maximum platelet aggregation %); thrombin generation (TG). Assays were performed at baseline and 30 days postrandomization.

RESULTS

 Switching from DAPT to DPI occurred without major side effects. DAPT was associated with enhanced P2Y12 inhibition, while DPI with reduced TG. Platelet-mediated global thrombogenicity (primary endpoint) showed no differences between DAPT and DPI in the ticagrelor (14.5% [0.0-63.0] vs. 20.0% [0.0-70.0]; p = 0.477) and prasugrel (20.0% [0.0-66.0] vs. 4.0% [0.0-70.0]; p = 0.482), but not clopidogrel (27.0% [0.0-68.0] vs. 53.0% [0.0-81.0]; p = 0.011), cohorts.

CONCLUSION

 In patients with CCS, switching from different DAPT regimens to DPI was feasible, showing enhanced P2Y12 inhibition with DAPT and reduced TG with DPI, with no differences in platelet-mediated global thrombogenicity between DPI and ticagrelor- and prasugrel-, but not clopidogrel-, based DAPT.

CLINICAL TRIAL REGISTRATION

 http://www.

CLINICALTRIALS

gov Unique Identifier: NCT04006288.

Comparison between canine and porcine models of chronic deep venous thrombosis

OBJECTIVE

To first induce chronic deep venous thrombosis in the left iliac veins of canines and porcines and then compare these two models to validate endovascular treatment devices.

METHODS

Thrombin and fibrinogen were used to produce a solid thrombus in the left iliac veins of a stenosis model. The researchers used venous angiography and histological staining to investigate the progression of thrombosis.

RESULTS

A left iliac vein thrombus was successfully formed in all experimental animals, including six Labrador dogs and three Bama miniature pigs, and there was minimal surgical bleeding. All dogs survived until 90 days, and three pigs died on Days 29, 33, and 58.

CONCLUSION

The researchers first established the models and then observed the progression of chronic deep venous thrombosis of the iliac vein in large animals for up to 90 days. Dogs are better suited for chronic deep venous thrombosis models due to their uncomplicated anatomy, excellent obedience, and proneness to physical activity compared with pigs.

Synergistic inhibitory effects of clopidogrel and rivaroxaban on platelet function and platelet-dependent thrombin generation in cats

BACKGROUND

Dual antithrombotic treatment (DAT) with clopidogrel and rivaroxaban sometimes is prescribed to cats with hypertrophic cardiomyopathy at risk of thromboembolism. To date, no studies have evaluated their combined effects on platelet function.

OBJECTIVES/HYPOTHESIS

Evaluate the safety of DAT in healthy cats and compare, ex vivo, platelet-dependent thrombin generation and agonist-induced platelet activation and aggregation in cats treated with clopidogrel, rivaroxaban, or DAT. We hypothesized that DAT would safely modulate agonist-induced platelet activation and aggregation more effectively than single agent treatment.

ANIMALS

Nine apparently healthy 1-year-old cats selected from a research colony.

METHODS

Unblinded, nonrandomized ex vivo cross-over study. All cats received 7 days of rivaroxaban (0.6 ± 0.1 mg/kg PO), clopidogrel (4.7 ± 0.8 mg/kg PO), or DAT with defined washout periods between treatments. Before and after each treatment, adenosine diphosphate (ADP)- and thrombin-induced platelet P-selectin expression was evaluated using flow cytometry to assess platelet activation. Platelet-dependent thrombin generation was measured by fluorescence assay. Platelet aggregation was assessed using whole blood impedance platelet aggregometry.

RESULTS

No cats exhibited adverse effects. Of the 3 treatments, only DAT significantly decreased the number of activated platelets (P = .002), modulated platelet activation in response to thrombin (P = .01), dampened thrombin generation potential (P = .01), and delayed maximum reaction velocity (P = .004) in thrombin generation. Like clopidogrel, DAT inhibited ADP-mediated platelet aggregation. However, rivaroxaban alone resulted in increased aggregation and activation in response to ADP.

CONCLUSION AND CLINICAL IMPORTANCE

Treatment combining clopidogrel and rivaroxaban (DAT) safely decreases platelet activation, platelet response to agonists, and thrombin generation in feline platelets more effectively than monotherapy with either clopidogrel or rivaroxaban.

Thrombosis Models: An Overview of Common In Vivo and In Vitro Models of Thrombosis

Occlusions in the blood vessels caused by blood clots, referred to as thrombosis, and the subsequent outcomes are leading causes of morbidity and mortality worldwide. In vitro and in vivo models of thrombosis have advanced our understanding of the complex pathways involved in its development and allowed the evaluation of different therapeutic approaches for its management. This review summarizes different commonly used approaches to induce thrombosis in vivo and in vitro, without detailing the protocols for each technique or the mechanism of thrombus development. For ease of flow, a schematic illustration of the models mentioned in the review is shown below. Considering the number of available approaches, we emphasize the importance of standardizing thrombosis models in research per study aim and application, as different pathophysiological mechanisms are involved in each model, and they exert varying responses to the same carried tests. For the time being, the selection of the appropriate model depends on several factors, including the available settings and research facilities, the aim of the research and its application, and the researchers' experience and ability to perform surgical interventions if needed.

Antiplatelet therapy after percutaneous coronary intervention

Antiplatelet therapy is key to reducing local thrombotic complications and systemic ischaemic events among patients undergoing percutaneous coronary interventions (PCI), but it is inevitably associated with increased bleeding. The continuous refinement in stent technologies, together with the high incidence of ischaemic recurrences after PCI and the understanding of prognostic implications associated with bleeding, have led to a substantial evolution in antiplatelet treatment regimens over the past decades. Numerous investigations have been conducted to better stratify patients undergoing PCI according to their ischaemic and bleeding risks and to implement antithrombotic regimens accordingly. Evidence from these investigations have resulted in a number of antithrombotic treatment options as recommended by recent guidelines. In this State-of-the-Art review we provide the rationale, summarise the evidence, and discuss current and future directions of antiplatelet treatment regimens after PCI.

Prevalence of VOYAGER PAD trial exclusion criteria in unselected patients undergoing lower limb revascularisation

BACKGROUND

The VOYAGER PAD trial investigated data on dual pathway inhibition after lower limb revascularisation for peripheral arterial disease (PAD). Multiple exclusion criteria were applied. However, neither data on the prevalence of exclusion criteria nor on the total number of patients screened for inclusion was discussed.

METHODS

We performed a single-center prospective observational study in unselected PAD patients undergoing lower limb revascularisation. Demographic and disease-specific data was collected.

RESULTS

150 patients were included with only 29 patients (19.3%) as potential candidates for the VOYAGER PAD study medication. Poorly controlled diabetes or severe uncontrolled hypertension (33.3%), major tissue loss (18.7%), acute limb ischaemia within prior 2 weeks (17.3%) and a history of intracranial haemorrhage, stroke or TIA (16%) were amongst the exclusion criteria most frequently met. Compared to VOYAGER PAD study patients, significant differences regarding sex (36.7% female vs. 25.8%), renal insufficiency (29.0% vs. 20.1%), previous myocardial infarction (16.7% vs. 11.1%) and known carotid artery disease (18.7% vs. 8.6%) revealed. Patients presented significantly more frequently with critical limb ischemia (56.7% vs. 30.4%) and a history of previous peripheral revascularisation (72.0% vs. 35.9%). Fewer endovascular interventions (52% vs. 65.5%) and more surgeries (58% vs. 34.5%) were performed.

CONCLUSIONS

In unselected patients undergoing revascularisation for peripheral arterial disease, the majority presents with characteristics that, at present, preclude prescription of rivaroxaban in addition to aspirin. This patient cohort represents a population with higher rates of comorbidities and more complex vascular interventions, but might also benefit from dual pathway inhibition strategy.

Efficacy and safety of next-generation tick transcriptome-derived direct thrombin inhibitors

Despite their limitations, unfractionated heparin (UFH) and bivalirudin remain standard-of-care parenteral anticoagulants for percutaneous coronary intervention (PCI). We discovered novel direct thrombin inhibitors (DTIs) from tick salivary transcriptomes and optimised their pharmacologic activity. The most potent, ultravariegin, inhibits thrombin with a K_i of 4.0 pM, 445-fold better than bivalirudin. Unexpectedly, despite their greater antithrombotic effect, variegin/ultravariegin demonstrated less bleeding, achieving a 3-to-7-fold wider therapeutic index in rodent thrombosis and bleeding models. When used in combination with aspirin and ticagrelor in a porcine model, variegin/ultravariegin reduced stent thrombosis compared with antiplatelet therapy alone but achieved a 5-to-7-fold lower bleeding time than UFH/bivalirudin. Moreover, two antibodies screened from a naïve human antibody library effectively reversed the anticoagulant activity of ultravariegin, demonstrating proof-of-principle for antidote reversal. Variegin and ultravariegin are promising translational candidates for next-generation DTIs that may reduce peri-PCI bleeding in the presence of antiplatelet therapy.

Dual Pathway of Inhibition and Vascular Protection in Patients with Atherosclerotic Disease

Несмотря на широкое внедрение в клиническую практику современной антитромботической стратегии (моно- или двойной антитромбоцитарной терапии), резидуальный риск неблагоприятных сердечно-сосудистых событий у пациентов с ишемической болезнью сердца (ИБС) и заболеваниями периферических артерий (ЗПА) по-прежнему остается высоким. До настоящего времени двойная антитромбоцитарная терапия является «золотым стандартом» вторичной профилактики при остром коронарном синдроме (ОКС), а монотерапия рекомендована пациентам с симптоматическим течением ЗПА, стабильной ИБС и цереброваскулярной болезнью. Вместе с тем разрыв атеросклеротической бляшки приводит не только к активации тромбоцитов, но также, вследствие экспозиции тканевого фактора, потенцирует образование тромбина. Поэтому терапевтическая стратегия, направленная на одновременное подавление генерации тромбина и активации тромбоцитов и называемая «двойной путь ингибирования», представляется более эффективной, чем известные варианты лечения, связанные с торможением только одного из двух путей. Как показали результаты исследования COMPASS, комбинация 2,5 мг ривароксабана дважды в сутки со 100 мг/сутки аспирина оказалась более эффективной по сравнению с монотерапией 100 мг/сутки аспирина в части снижения риска серьезных сердечно-сосудистых событий, незапланированных госпитализаций и летальности без увеличения количества фатальных и интракраниальных геморрагических осложнений. Преимущества режима двойного ингибирования, апробированного в исследовании COMPASS, были продемонстрированы в популяции пациентов с недавним ОКС, стабильной ИБС и ЗПА, а также после реваскуляризации нижних конечностей. На сегодняшний день ривароксабан является единственным антикоагулянтом, подтвердившим безусловные преимущества в сочетании с антитромбоцитарной терапией в указанных группах пациентов. Комбинированная терапия низкими дозами ривароксабана (2,5 мг/дважды/сутки) и аспирином (100 мг/сутки) уже включена в последние международные рекомендации как вариант вторичной профилактики у пациентов с патологией коронарных и периферических артерий.

Patients with cardiovascular (CV) disease are at high residual risk of CV events (including peripheral ischemic events), even when they receive the current antithrombotic strategies (single/dual antiplatelet therapy). Until now, dual antiplatelet therapy is the standard of care for the secondary prevention in patients with acute coronary syndrome (ACS), whereas the single antiplatelet therapy, generally with aspirin, is the standard of care for the secondary prevention in stable patients with coronary artery disease (CAD), peripheral artery disease (PAD), or cerebrovascular disease. Meanwhile, atherosclerotic plaque disruption not only induces the platelet activation, but also results in thrombin generation because of tissue factor exposure. Therefore, interrupting both pathways by combining antiplatelet therapy with an anticoagulant (dual pathway inhibition [DPI]), has the potential to be more effective than inhibiting either pathway alone. The COMPASS trial showed that in comparison with aspirin 100 mg, rivaroxaban 2.5 mg twice a day plus aspirin 100 mg reduced the risk of major cardiac events, CV hospitalization, and mortality, without the increase of intracranial or fatal bleedings. The benefit of DPI using the COMPASS regimen was demonstrated in patients with the recent ACS, in chronic CAD and PAD patients, and after the lower extremity revascularization. So far, rivaroxaban is the only anticoagulant, which is effective in combination with antiplatelet therapies in the mentioned groups. The combination of low-dose rivaroxaban (2.5 mg twice daily) and aspirin (100 mg once daily) has been included recently into the latest international recommendations for the secondary prevention in patients with coronary or peripheral artery disease.

Effect of Rivaroxaban and Clopidogrel Combination Therapy on In-Stent Responses After Everolimus-Eluting Stent Implantation in a Porcine Coronary Model

Aim: According to recent clinical trials, a combination of direct oral anticoagulants with antiplatelet drugs is often recommended for atrial fibrillation patients who receive drug-eluting stents (DESs). Although the optimal combination comprises direct factor Xa inhibitors and a P2Y ₁₂ receptor antagonist (or aspirin), their influence on vascular responses to DESs remains unclear.

Methods: Pigs were given either aspirin and clopidogrel (dual antiplatelet therapy [DAPT] group), aspirin and rivaroxaban (AR group), or clopidogrel and rivaroxaban (CR group), followed by everolimus-eluting stent (Promus Element) implantation into the coronary artery. Stented coronary arteries were evaluated via intravascular optical coherence tomography (OCT) and histological analysis at 1 and 3 months.

Results: OCT revealed lower neointimal thickness in the DAPT group and comparable thickness among all groups at 1 and 3 months, respectively. Histological analyses revealed comparable neointimal area among all groups and the smallest neointimal area in the CR group at 1 and 3 months, respectively. In the DAPT and AR groups, the neointima continued to grow from 1 to 3 months. A shortened time course for neointima growth was observed in the CR group, with rapid growth within a month (maintained for 3 months). A higher incidence of in-stent thrombi was observed in the AR group at 1 month; no thrombi were found in either group at 3 months. More smooth muscle cells with contractile features were found in the CR group at both 1 and 3 months.

Conclusions: Our results proved the noninferiority of the combination of rivaroxaban with an antiplatelet drug, particularly the dual therapy using rivaroxaban and clopidogrel, compared to DAPT after DES implantation.

Dual Pathway Inhibition for Vascular Protection in Patients with Atherosclerotic Disease: Rationale and Review of the Evidence

Despite advances in secondary prevention strategies in patients with cardiovascular disease, the residual risk of recurrent atherothrombotic events remains high. Dual-antiplatelet therapy is the standard of care for secondary prevention in patients with acute coronary syndrome (ACS), whereas single antiplatelet therapy, generally with aspirin, is the standard of care for secondary prevention in stable patients with coronary artery disease (CAD), peripheral artery disease (PAD), or cerebrovascular disease. However, atherosclerotic plaque disruption not only triggers platelet activation but also results in thrombin generation because of tissue factor exposure. Therefore, blocking both pathways by combining antiplatelet therapy with an anticoagulant, or dual pathway inhibition (DPI), has the potential to be more effective than inhibiting either pathway alone. The benefit of DPI has been demonstrated in the ATLAS ACS 2-TIMI 51, COMPASS, and VOYAGER PAD trials, where the combination of rivaroxaban vascular dose (2.5 mg twice daily) plus aspirin significantly reduced the risk of atherothrombotic events compared with aspirin across a broad range of patients, including those with recent ACS, those with chronic CAD and/or PAD, and patients with PAD who have undergone peripheral revascularization. This article provides the rationale for this regimen in more detail, including why the DPI regimen with the rivaroxaban vascular dose was developed for vascular protection in a broad spectrum of patients with atherosclerotic disease.

Dual-pathway inhibition for secondary and tertiary antithrombotic prevention in cardiovascular disease

Advances in antiplatelet therapies for patients with cardiovascular disease have improved patient outcomes over time, but the challenge of balancing the risks of ischaemia and bleeding remains substantial. Moreover, many patients with cardiovascular disease have a residual risk of ischaemic events despite receiving antiplatelet therapy. Therefore, novel strategies are needed to prevent clinical events through mechanisms beyond platelet inhibition and with an acceptable associated risk of bleeding. The advent of non-vitamin K antagonist oral anticoagulants, which attenuate fibrin formation by selective inhibition of factor Xa or thrombin, has renewed the interest in dual-pathway inhibition strategies that combine an antiplatelet agent with an anticoagulant drug. In this Review, we highlight the emerging pharmacological rationale and clinical development of dual-pathway inhibition strategies for the prevention of atherothrombotic events in patients with different manifestations of cardiovascular disease, such as coronary artery disease, cerebrovascular disease and peripheral artery disease.

Clinically significant bleeding with low-dose rivaroxaban versus aspirin, in addition to P2Y12 inhibition, in acute coronary syndromes (GEMINI-ACS-1): a double-blind, multicentre, randomised trial

BACKGROUND

Dual antiplatelet therapy (DAPT), aspirin plus a P2Y12 inhibitor, is the standard antithrombotic treatment following acute coronary syndromes. The factor Xa inhibitor rivaroxaban reduced mortality and ischaemic events when added to DAPT, but caused increased bleeding. The safety of a dual pathway antithrombotic therapy approach combining low-dose rivaroxaban (in place of aspirin) with a P2Y12 inhibitor has not been assesssed in acute coronary syndromes. We aimed to assess rivaroxaban 2·5 mg twice daily versus aspirin 100 mg daily, in addition to clopidogrel or ticagrelor (chosen at investigator discretion before randomisation), for patients with acute coronary syndromes started within 10 days after presentation and continued for 6-12 months.

METHODS

In this double-blind, multicentre, randomised trial (GEMINI-ACS-1) done at 371 clinical centres in 21 countries, eligible patients were older than 18 years with unstable angina, non-ST segment elevation myocardial infarction (NSTEMI) or ST segment elevation myocardial infarction (STEMI), with positive cardiac biomarkers and either ischaemic electrocardiographic changes or an atherosclerotic culprit lesion identified during angiography. Participants were randomly assigned (1:1) within 10 days after admission for the index acute coronary syndromes event to either aspirin or rivaroxaban based on a computer-generated randomisation schedule. Randomisation was balanced by using randomly permuted blocks with size of four and was stratified based on the background P2Y12 inhibitor (clopidogrel or ticagrelor) intended to be used at the time of randomisation. Investigators and patients were masked to treatment assignment. Patients received a minimum of 180 days of double-blind treatment with rivaroxaban 2·5 mg twice daily or aspirin 100 mg daily. The choice of clopidogrel or ticagrelor during trial conduct was not randomised and was based on investigator preference. The primary endpoint was thrombolysis in myocardial infarction (TIMI) clinically significant bleeding not related to coronary artery bypass grafting (CABG; major, minor, or requiring medical attention) up to day 390. Primary analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT02293395.

FINDINGS

Between April 22, 2015, and Oct 14, 2016, 3037 patients with acute coronary syndromes were randomly assigned; 1518 to receive aspirin and 1519 to receive rivaroxaban. 1704 patients (56%) were in the ticagrelor and 1333 (44%) in the clopidogrel strata. Median duration of treatment was 291 days (IQR 239-354). TIMI non-CABG clinically significant bleeding was similar with rivaroxaban versus aspirin therapy (total 154 patients [5%]; 80 participants [5%] of 1519 vs 74 participants [5%] of 1518; HR 1·09 [95% CI 0·80-1·50]; p=0·5840).

INTERPRETATION

A dual pathway antithrombotic therapy approach combining low-dose rivaroxaban with a P2Y12 inhibitor for the treatment of patients with acute coronary syndromes had similar risk of clinically significant bleeding as aspirin and a P2Y12 inhibitor. A larger, adequately powered trial would be required to definitively assess the efficacy and safety of this approach.

FUNDING

Janssen Research & Development and Bayer AG.

Differential inhibitory action of apixaban on platelet and fibrin components of forming thrombi: Studies with circulating blood and in a platelet-based model of thrombin generation

Introduction

Mechanisms of action of direct oral anticoagulants (DOAC) suggest a potential therapeutic use in the prevention of thrombotic complications in arterial territories. However, effects of DOACs on platelet activation and aggregation have not been explored in detail. We have investigated the effects of apixaban on platelet and fibrin components of thrombus formation under static and flow conditions.

Methods

We assessed the effects of apixaban (10, 40 and 160 ng/mL) on: 1) platelet deposition and fibrin formation onto a thrombogenic surface, with blood circulating at arterial shear-rates; 2) viscoelastic properties of forming clots, and 3) thrombin generation in a cell-model of coagulation primed by platelets.

Results

In studies with flowing blood, only the highest concentration of apixaban, equivalent to the therapeutic C_max, was capable to significantly reduce thrombus formation, fibrin association and platelet-aggregate formation. Apixaban significantly prolonged thromboelastometry parameters, but did not affect clot firmness. Interestingly, results in a platelet-based model of thrombin generation under more static conditions, revealed a dose dependent persistent inhibitory action by apixaban, with concentrations 4 to 16 times below the therapeutic C_max significantly prolonging kinetic parameters and reducing the total amount of thrombin generated.

Conclusions

Our studies demonstrate the critical impact of rheological conditions on the antithrombotic effects of apixaban. Studies under flow conditions combined with modified thrombin generation assays could help discriminating concentrations of apixaban that prevent excessive platelet accumulation, from those that deeply impair fibrin formation and may unnecessarily compromise hemostasis.

Direct oral anticoagulant use and stent thrombosis following an acute coronary syndrome: A potential new pharmacological option?

With the evolution of techniques and pharmacological strategies in percutaneous coronary intervention, significant advances have been made towards reducing the risk of in-stent restenosis and improving patient outcomes. However, in spite of these advances, stent thrombosis remains a deadly complication of stent implantation. The fundamental challenge in implementing a combined anticoagulant and antiplatelet strategy is balancing the risk of bleeding with the enhanced efficacy of therapy on both pathways. Results from the ATLAS ACS 2-TIMI 51 trial suggest that the addition of rivaroxaban 2.5mg twice daily to standard antiplatelet therapy may achieve this desired balance alongside careful patient selection. This review considers the clinical burden and pathology of stent thrombosis, oral antithrombotic strategies to reduce stent thrombosis, and what findings from recent trials could mean for the long-term management of patients with an acute coronary syndrome.

Combination of factor Xa inhibition and antiplatelet therapy after stenting in patients with iliofemoral post-thrombotic venous obstruction

OBJECTIVES

Studies addressing optimal postprocedural pharmacological management after endovascular stenting of iliofemoral post-thrombotic venous obstruction are lacking. We report our early clinical experience with a combination of rivaroxaban and clopidogrel in patients after iliofemoral post-thrombotic venous obstruction stenting.

METHODS

Demographic, procedural, and follow-up data of nine patients (seven women; mean age of 32 ± 11 years) undergoing 10 procedures for iliofemoral post-thrombotic venous obstruction performed between August 2012 and January 2014 were retrospectively reviewed. After endovascular intervention, all patients were administered 20 mg rivaroxaban once daily (s.i.d.) and 75 mg clopidogrel s.i.d. or every second day depending on the individual drug responsiveness for at least six months. The adenosine diphosphate-induced platelet aggregation (platelet aggregation, in aggregation units × min) was assessed on a Multiplate analyzer. Patency was verified venographically at procedure end and was evaluated with duplex ultrasound in regular follow-ups.

RESULTS

Iliofemoral venous flow was successfully re-established by percutaneous endovascular angioplasty and stent implantation in nine left-sided and one bilateral iliofemoral post-thrombotic venous obstruction. Under dual treatment strategy of rivaroxaban and clopidogrel with platelet aggregation control (median (range): 285 aggregation units × min (192; 402)), none of the patients experienced restenosis or stent thrombosis, respectively. After a median follow-up of 14 months (range: 6-26 months), the primary patency rate was 100% and no in-stent restenosis, stent occlusion or relevant minor or major bleeding occurred.

CONCLUSION

Combined factor Xa inhibition and tailored antiplatelet therapy after stenting of iliofemoral post-thrombotic venous obstruction were safe and performed favorably in terms of vessel patency.

Rivaroxaban: a review of its use in acute coronary syndromes

Rivaroxaban (Xarelto(®)) is an orally administered highly selective direct inhibitor of factor Xa that has been approved in many countries to reduce the risk of stroke in patients with atrial fibrillation and for the treatment and prevention of venous thromboembolism. More recently, rivaroxaban at a low dosage of 2.5 mg twice daily, co-administered with aspirin alone or aspirin plus either clopidogrel or ticlopidine, was approved for use in the EU for patients with a recent acute coronary syndrome (ACS). The approval of rivaroxaban in ACS was primarily based on findings of the phase III ATLAS ACS 2-TIMI 51 trial, which showed that after a median of 13.1 months of treatment with rivaroxaban 2.5 mg twice daily (combined with aspirin or aspirin plus either clopidogrel or ticlopidine) there was a statistically significant reduction in the rate of the primary composite endpoint, which was death from cardiovascular causes, myocardial infarction or stroke, compared with placebo. Rivaroxaban 2.5 mg twice daily was also associated with a reduction in all-cause and cardiovascular mortality. There was an increase in the risk of major bleeding and intracranial haemorrhage with rivaroxaban 2.5 mg twice daily compared with placebo; however, there was no increase in the risk of fatal bleeding. Aspirin plus either ticagrelor or prasugrel was not evaluated as background dual antiplatelet therapy in ATLAS ACS 2-TIMI 51 and the safety implications of rivaroxaban used in combination with such therapy are unknown. In conclusion, results of the ATLAS ACS 2-TIMI 51 trial suggest a potentially important role for rivaroxaban 2.5 mg twice daily co-administered with aspirin alone or aspirin plus either clopidogrel or ticlopidine in patients with a recent ACS.

Effects of Rivaroxaban on Platelet Activation and Platelet-Coagulation Pathway Interaction: In Vitro and In Vivo Studies

Introduction:

Activation of coagulation and platelets is closely linked, and arterial thrombosis involves coagulation activation as well as platelet activation and aggregation. In these studies, we investigated the possible synergistic effects of rivaroxaban in combination with antiplatelet agents on thrombin generation and platelet aggregation in vitro and on arterial thrombosis and hemostasis in rat models.

Materials and Methods:

Thrombin generation was measured by the Calibrated Automated Thrombogram method (0.5 pmol/L tissue factor) using human platelet-rich plasma (PRP) spiked with rivaroxaban (15, 30, or 60 ng/mL), ticagrelor (1.0 µg/mL), and acetylsalicylic acid (ASA; 100 µg/mL). Tissue factor-induced platelet aggregation was measured in PRP spiked with rivaroxaban (15 or 30 ng/mL), ticagrelor (1 or 3 µg/mL), or a combination of these. An arteriovenous (AV) shunt model in rats was used to determine the effects of rivaroxaban (0.01, 0.03, or 0.1 mg/kg), clopidogrel (1 mg/kg), ASA (3 mg/kg), and combinations on arterial thrombosis.

Results:

Rivaroxaban inhibited thrombin generation in a concentration-dependent manner and the effect was enhanced with ticagrelor and ticagrelor plus ASA. Rivaroxaban and ticagrelor also concentration-dependently inhibited tissue factor-induced platelet aggregation, and their combination increased the inhibition synergistically. In the AV shunt model, rivaroxaban dose-dependently reduced thrombus formation. Combining subefficacious or weakly efficacious doses of rivaroxaban with ASA or ASA plus clopidogrel increased the antithrombotic effect.

Conclusion:

These data indicate that the combination of rivaroxaban with single or dual antiplatelet agents works synergistically to reduce platelet activation, which may in turn lead to the delayed/reduced formation of coagulation complexes and vice versa, thereby enhancing antithrombotic potency.

Comparative evaluation of direct thrombin and factor Xa inhibitors with antiplatelet agents under flow and static conditions: an in vitro flow chamber model

Dabigatran and rivaroxaban are novel oral anticoagulants that specifically inhibit thrombin and factor Xa, respectively. The aim of this study is to elucidate antithrombotic properties of these anticoagulant agents under arterial and venous shear conditions. Whole blood samples treated with dabigatran or rivaroxaban at 250, 500, and 1000 nM, with/without aspirin and AR-C66096, a P2Y12 antagonist, were perfused over a microchip coated with collagen and tissue thromboplastin at shear rates of 240 and 600 s(-1). Fibrin-rich platelet thrombus formation was quantified by monitoring flow pressure changes. Dabigatran at higher concentrations (500 and 1000 nM) potently inhibited thrombus formation at both shear rates, whereas 1000 nM of rivaroxaban delayed, but did not completely inhibit, thrombus formation. Dual antiplatelet agents weakly suppressed thrombus formation at both shear rates, but intensified the anticoagulant effects of dabigatran and rivaroxaban. The anticoagulant effects of dabigatran and rivaroxaban were also evaluated under static conditions using thrombin generation (TG) assay. In platelet-poor plasma, dabigatran at 250 and 500 nM efficiently prolonged the lag time (LT) and moderately reduce peak height (PH) of TG, whereas rivaroxaban at 250 nM efficiently prolonged LT and reduced PH of TG. In platelet-rich plasma, however, both anticoagulants efficiently delayed LT and reduced PH of TG. Our results suggest that dabigatran and rivaroxaban may exert distinct antithrombotic effects under flow conditions, particularly in combination with dual antiplatelet therapy.