A Comparative Study of Molecular Structure, pKa, Lipophilicity, Solubility, Absorption and Polar Surface Area of Some Antiplatelet Drugs

Theoretical chemistry methods have been used to study the molecular properties of antiplatelet agents (ticlopidine, clopidogrel, prasugrel, elinogrel, ticagrelor and cangrelor) and several thiol-containing active metabolites. The geometries and energies of most stable conformers of these drugs have been computed at the Becke3LYP/6-311++G(d,p) level of density functional theory. Computed dissociation constants show that the active metabolites of prodrugs (ticlopidine, clopidogrel and prasugrel) and drugs elinogrel and cangrelor are completely ionized at pH 7.4. Both ticagrelor and its active metabolite are present at pH = 7.4 in neutral undissociated form. The thienopyridine prodrugs ticlopidine, clopidogrel and prasugrel are lipophilic and insoluble in water. Their lipophilicity is very high (about 2.5–3.5 logP values). The polar surface area, with regard to the structurally-heterogeneous character of these antiplatelet drugs, is from very large interval of values of 3–255 Ų. Thienopyridine prodrugs, like ticlopidine, clopidogrel and prasugrel, with the lowest polar surface area (PSA) values, exhibit the largest absorption. A high value of polar surface area (PSA) of cangrelor (255 Ų) results in substantial worsening of the absorption in comparison with thienopyridine drugs.

Acetylsalicylic Acid Daily vs Acetylsalicylic Acid Every 3 Days in Healthy Volunteers: Effect on Platelet Aggregation, Gastric Mucosa, and Prostaglandin E2 Synthesis

Substantial platelet inhibition was observed 3 days after a single administration of acetylsalicylic acid 81 mg to healthy volunteers. Here we investigate prostaglandin E2 (PGE2 ) antrum concentrations and gastrointestinal symptoms in two treatment groups: one receiving losartan and acetylsalicylic acid every day and the other receiving losartan every day and acetylsalicylic acid every 3 days. Twenty-eight healthy volunteers from both sexes received either 50 mg losartan and acetylsalicylic acid 81 mg daily or 50 mg losartan and acetylsalicylic acid 81 every 3 days with placebo on the other days. Therapy was delivered for 30 days for both groups. Gastric endoscopy was performed before and after treatment period. Biopsies were collected for PGE2 quantification. Platelet function tests were carried out before and during treatment and TXB2 release on platelet rich plasma was measured. The every 3 day low-dose acetylsalicylic acid regimen produced complete inhibition of platelet aggregation compared to the daily treatment. Thromboxane B2 release was substantially abolished for both groups during treatment. There was no significant difference on the endoscopic score of both treatment groups after the 30-day treatment (P = .215). There was over 50% suppression of antrum PGE2 content on volunteers receiving acetylsalicylic acid daily (P = .0016), while for the every 3 day dose regimen there was no significant difference between pre and post-treatment antrum PGE2 dosages (P = .4193). Since PGE2 is involved in gastric healing, we understand that this new approach could be safer and as efficient as the standard daily therapy on a long-term basis.

Prediction models for intracranial hemorrhage or major bleeding in patients on antiplatelet therapy: a systematic review and external validation study

ESSENTIALS: Prediction models may help to identify patients at high risk of bleeding on antiplatelet therapy. We identified existing prediction models for bleeding and validated them in patients with cerebral ischemia. Five prediction models were identified, all of which had some methodological shortcomings. Performance in patients with cerebral ischemia was poor.

SUMMARY

Background Antiplatelet therapy is widely used in secondary prevention after a transient ischemic attack (TIA) or ischemic stroke. Bleeding is the main adverse effect of antiplatelet therapy and is potentially life threatening. Identification of patients at increased risk of bleeding may help target antiplatelet therapy.

OBJECTIVE

This study sought to identify existing prediction models for intracranial hemorrhage or major bleeding in patients on antiplatelet therapy and evaluate their performance in patients with cerebral ischemia.

METHODS

We systematically searched PubMed and Embase for existing prediction models up to December 2014. The methodological quality of the included studies was assessed with the CHARMS checklist. Prediction models were externally validated in the European Stroke Prevention Study 2, comprising 6602 patients with a TIA or ischemic stroke. We assessed discrimination and calibration of included prediction models.

RESULTS

Five prediction models were identified, of which two were developed in patients with previous cerebral ischemia. Three studies assessed major bleeding, one studied intracerebral hemorrhage and one gastrointestinal bleeding. None of the studies met all criteria of good quality. External validation showed poor discriminative performance, with c-statistics ranging from 0.53 to 0.64 and poor calibration.

CONCLUSION

A limited number of prediction models is available that predict intracranial hemorrhage or major bleeding in patients on antiplatelet therapy. The methodological quality of the models varied, but was generally low. Predictive performance in patients with cerebral ischemia was poor. In order to reliably predict the risk of bleeding in patients with cerebral ischemia, development of a prediction model according to current methodological standards is needed.

[EXPERIENCE WITH THE USE OF EPTIFIBATIDE IN ACUTE CORONARY SYNDROME DURING CORONARY INTERVENTION IN PATIENTS OLDER AGE GROUP]

Acute coronary syndrome is the leading cause of death in patients older age group. Primary PCI is nearly uncontested revascularization method because of its efficacy in reperfusion achievement and less hemorrhagic complications compared to systemic thrombolytic therapy. Nevertheless, the age of the patients is a significant bleeding risk factor, sophisticating the choice and dosing antiplatelet and anticoagulant therapy during coronary angioplasty and stenting. Blocker 2b/3a receptor eptifibatide are used to avoids the development of ischemic complications and improves myocardial perfusion, but accompanied with bleeding risk during common infusion (12-18 hours). Combined intracoronary and intravenous infusion eptifibatide during only coronary intervention enhance procedure safety.

Medication management of cardiac allograft vasculopathy after heart transplantation

Cardiac allograft vasculopathy (CAV) is a common complication following heart transplantation (HT), resulting in diminished graft survival. The preferred strategy for preventing CAV is optimal medical management; however, for patients who develop CAV, delaying disease progression through effective medication management is equally important. A review of the literature regarding medication management of CAV was conducted via a search of the MEDLINE database. Studies were included if they were published in English, conducted in humans ≥ 18 years of age or older, and used noninvestigational medications. Immunosuppressive medications such as the antiproliferative mycophenolate, the calcineurin inhibitor tacrolimus, and the proliferation signal inhibitors sirolimus and everolimus have been shown to prevent the development of CAV. Certain cardiovascular medications, such as HMG-CoA reductase inhibitors (statins), gemfibrozil, calcium channel blockers, and angiotensin-converting enzyme inhibitors, have also demonstrated efficacy in preventing this disease process. Prevention of CAV has also been observed with prophylaxis against cytomegalovirus infection and antioxidant medications. Despite being commonly used in HT patients, neither antiplatelet agents nor glycemic control have proved effective at preventing CAV. Only sirolimus has been shown to arrest the progress of existing CAV.

Antiplatelet Treatment Reduces All-Cause Mortality in COPD Patients: A Systematic Review and Meta-Analysis

Previous studies clearly showed that patients with chronic obstructive pulmonary disease (COPD) are at high risk for cardiovascular events. Platelet activation is significantly heightened in these patients, probably because of a chronic inflammatory status. Nevertheless, it is unclear whether antiplatelet treatment may contribute to reduce all-cause mortality in COPD patients. To clarify this issue, we performed a systematic review and meta-analysis including patients with COPD (outpatients or admitted to hospital for acute exacerbation). The primary endpoint was all-cause mortality. We considered studies stratifying the study population according the administration or not of antiplatelet therapy and reporting its relationship with the primary endpoint. Overall, 5 studies including 11117 COPD patients were considered (of those 3069 patients were with acute exacerbation of COPD). IHD was present in 33% of COPD patients [95%CI 31%-35%). Antiplatelet therapy administration was common (47%, 95%CI 46%-48%), ranging from 26% to 61%. Of note, IHD was considered as confounding factor at multivariable analysis in all studies. All-cause mortality was significantly lower in COPD patients receiving antiplatelet treatment (OR 0.81; 95%CI 0.75-0.88). The data was consistent both in outpatients and in those with acute exacerbation of COPD. The pooled studies analysis showed a very low heterogeneity (I(2) : 8%). Additional analyses (meta-regression) showed that antiplatelet therapy administration was effective independently (to potential confounding factors as IHD, cardiovascular drugs and cardiovascular risk factors. In conclusion, our meta-analysis suggested that antiplatelet therapy might significantly contribute to reduce all-cause mortality in COPD patients.

Platelet P2Y12 Inhibitors Reduce Systemic Inflammation and Its Prothrombotic Effects in an Experimental Human Model

OBJECTIVE

Clinical studies suggest that platelet P2Y12 inhibitors reduce mortality from sepsis, although the underlying mechanisms have not been clearly defined in vivo. We hypothesized that P2Y12 inhibitors may improve survival from sepsis by suppressing systemic inflammation and its prothrombotic effects. We therefore determined whether clopidogrel and the novel, more potent P2Y12 inhibitor, ticagrelor, modify these responses in an experimental human model.

APPROACH AND RESULTS

We randomized 30 healthy volunteers to ticagrelor (n=10), clopidogrel (n=10), or no antiplatelet medication (controls; n=10). We examined the effect of P2Y12 inhibition on systemic inflammation, which was induced by intravenous injection of Escherichia coli endotoxin. Both P2Y12 inhibitors significantly reduced platelet-monocyte aggregate formation and peak levels of major proinflammatory cytokines, including tumor necrosis factor α, interleukin-6, and chemokine (C-C motif) ligand 2. In contrast to clopidogrel, ticagrelor also significantly reduced peak levels of IL-8 and growth colony-stimulating factor and increased peak levels of the anti-inflammatory cytokine IL-10. In addition, ticagrelor altered leukocyte trafficking. Both P2Y12 inhibitors suppressed D-dimer generation and scanning electron microscopy revealed that ticagrelor also suppressed prothrombotic changes in fibrin clot ultrastructure.

CONCLUSIONS

Potent inhibition of multiple inflammatory and prothrombotic mechanisms by P2Y12 inhibitors demonstrates critical importance of platelets as central orchestrators of systemic inflammation induced by bacterial endotoxin. This provides novel mechanistic insight into the lower mortality associated with P2Y12 inhibitors in patients with sepsis in clinical studies.

Management of Antithrombotic Agents in Oral Surgery Maria Martinez and Dimitrios A. Tsakiris

Systemic anticoagulation with intravenous or oral anticoagulants and antiplatelet agents is an efficient treatment against thromboembolic or cardiovascular disease. Invasive dental procedures or oral surgery might be associated with bleeding complications if carried out under anticoagulants. Patients on vitamin K antagonists, new direct anticoagulants or antiplatelet agents having dental interventions with low-risk for bleeding do not need interruption of anticoagulation. In case of bleeding complications local hemostatic measures, such as local surgical sutures, fibrin glue, local antifibrinolytic treatment with tranexamic acid, or e-aminocaproic acid suffice to stop bleeding. In patients with high risk of bleeding an individual assessment of the benefit/risk ratio of interrupting anticoagulation should be carried out. Bridging the long-term anticoagulation with short-term anticoagulants should be planned according to national or international guidelines. The introduction of the newer direct oral anticoagulants having more flexible pharmacokinetic properties has facilitated bridging, allowing short-term interruption without increasing the risk of relapsing thrombotic or cardiovascular events.

Prevention of cardiovascular events with antiplatelet treatment: does time of intake matter for aspirin and ADP receptor blockers?

Long-term evidence supports a clustering of cardiovascular events in the early morning. Several studies have shown that platelet hyper-reactivity to various stimuli is also present at this period of the day. However, the idea of treatment strategies reflecting the circadian variation in platelet reactivity has been largely neglected so far, and this is true despite the huge number of patients being treated with these drugs. Some pharmacodynamic data suggest that early-morning platelet hyper-reactivity may be overcome by shifting aspirin intake to the bedtime. However, there is lack of evidence whether shifting the time of intake or splitting the daily dose of P2Y12-inhibitors with a regular QD dosing (clopidogrel or prasugrel) to the evening would be effective to overcome platelet hyper-reactivity or to suppress the excess of cardiovascular events observed during morning hours. Further research is warranted to clarify whether such a simple and costless effort like dose shifting or splitting may be beneficial to prevent cardiovascular events.

Risk factors for small bowel bleeding in chronic nonsteroidal anti-inflammatory drug users

OBJECTIVE

The incidence of nonsteroidal anti-inflammatory drugs (NSAIDs)-induced enteropathy is currently increasing. However, the predictors of small bowel bleeding (SBB) associated with NSAIDs are unknown. This study aimed to assess the risk factors of SBB in chronic NSAIDs users.

METHODS

We retrospectively compared the medical records of 147 patients receiving NSAIDs in a tertiary-care setting (31 with SBB and 116 without previous bleeding events) and analyzed the predictors of SBB.

RESULTS

In total, 31 patients underwent video capsule endoscopy to detect SBB, 74.2% of whom showed the evidence of SBB. Non-invasive treatment was performed in 90.3% of the patients. Multivariate logistic regression analysis revealed that the presence of coronary artery disease [adjusted odds ratio (aOR) 12.43, 95% confidence interval (CI) 1.19-130.34, P = 0.04], use of thienopyridine (aOR 16.93, 95% CI 3.78-75.72, P < 0.001) and prior use of rebamipide (aOR 0.31, 95% CI 0.12-0.82, P = 0.02) were independently associated with SBB in NSAIDs users.

CONCLUSIONS

Coronary artery disease and co-use of thienopyridine were associated with SBB in NSAIDs users. The patients with coronary artery disease co-using thienopyridine need to be monitored for the occurrence of SBB when they were prescribed with NSAIDs.

Exploration of efficacy and bleeding with combined phosphoinositide 3-kinase β inhibition and aspirin in man

BACKGROUND

Based on animal and human data, phosphoinositide 3-kinase (PI3K)β is a promising antithrombotic target. However, the relation between efficacy and bleeding when combined with current antiplatelet therapies is unclear.

OBJECTIVE

To strengthen the PI3Kβ target validation using the short-acting inhibitor AZD6482 alone and in different combinations with P2Y12 and cyclooxygenase (COX)-1 inhibition in vitro (human platelets), in vivo (dog), and in healthy subjects.

METHODS AND RESULTS

Evaluation of complete target inhibition of PI3Kβ (by AZD6482), P2Y12 (by ticagrelor), and COX-1 (by aspirin) alone and in the different combinations vs. concentration responses for a panel of platelet agonists in vitro (adenosine diphosphate, collagen, thrombin receptor activating peptide) indicates that the rank order of antiplatelet efficacy is P2Y12  > PI3Kβ > COX-1 as monotherapy and P2Y12 plus PI3Kβ > P2Y12 plus COX-1 > PI3Kβ plus COX-1 as dual therapy, with little additional effect with triple therapy. Use of a conscious dog model to assess ex vivo antiplatelet effect in parallel with bleeding time prolongation (standard incision in the ear) confirms the wide separation of efficacy vs. bleeding for PI3Kβ inhibition and that this separation is reduced when combined with aspirin and more reduced when combined with clopidogrel. In healthy subjects, AZD6482, in combination with aspirin, shows a potential for greater antiplatelet potency but less bleeding potential compared with clopidogrel plus aspirin.

CONCLUSIONS

PI3Kβ inhibition, in comparison with P2Y12 and COX-1, delivers medium antiplatelet effect but with minimal bleeding. PI3Kβ inhibition, in combination with aspirin, in healthy subjects, provides a potential for greater overall antiplatelet effect compared with clopidogrel plus aspirin, but with significantly less bleeding potential.

The pharmacogenetic control of antiplatelet response: candidate genes and CYP2C19

INTRODUCTION

Aspirin, clopidogrel, prasugrel and ticagrelor are antiplatelet agents for the prevention of ischemic events in patients with acute coronary syndromes (ACS), percutaneous coronary intervention (PCI) and other indications. Variability in response is observed to different degrees with these agents, which can translate to increased risks for adverse cardiovascular events. As such, potential pharmacogenetic determinants of antiplatelet pharmacokinetics, pharmacodynamics and clinical outcomes have been actively studied.

AREAS COVERED

This article provides an overview of the available antiplatelet pharmacogenetics literature. Evidence supporting the significance of candidate genes and their potential influence on antiplatelet response and clinical outcomes are summarized and evaluated. Additional focus is directed at CYP2C19 and clopidogrel response, including the availability of clinical testing and genotype-directed antiplatelet therapy.

EXPERT OPINION

The reported aspirin response candidate genes have not been adequately replicated and few candidate genes have thus far been implicated in prasugrel or ticagrelor response. However, abundant data support the clinical validity of CYP2C19 and clopidogrel response variability among ACS/PCI patients. Although limited prospective trial data are available to support the utility of routine CYP2C19 testing, the increased risks for reduced clopidogrel efficacy among ACS/PCI patients that carry CYP2C19 loss-of-function alleles should be considered when genotype results are available.

Design, green synthesis and pharmacological evaluation of novel 5,6-diaryl-1,2,4-triazines bearing 3-morpholinoethylamine moiety as potential antithrombotic agents (.)

The aim of this research work was to investigate a series of novel 5,6-diaryl-1,2,4-triazines (3a-3q) containing 3-morpholinoethylamine side chain, and to address their antiplatelet activity by in vitro, ex vivo and in vivo methods. All compounds were synthesized by environment benign route and their structures were unambiguously confirmed by spectral data. Compounds (3l) and (3m) were confirmed by their single crystal X-ray structures. Out of all the synthesized compounds, 10 were found to be more potent in vitro than aspirin; six of them were found to be prominent in ex vivo assays and one compound (3d) was found to have the most promising antithrombotic profile in vivo. Moreover, compound (3d) demonstrated less ulcerogenicity in rats as compared to aspirin. The selectivity of the most promising compound (3d) for COX-1 and COX-2 enzymes was determined with the help of molecular docking studies and the results were correlated with the biological activity.

Association of spontaneous bleeding and myocardial infarction with long-term mortality after percutaneous coronary intervention

BACKGROUND

Platelet inhibition after percutaneous coronary intervention (PCI) reduces the risk of myocardial infarction (MI) but increases the risk of bleeding. MIs and bleeds during the index hospitalization for PCI are known to negatively affect long-term outcomes. The impact of spontaneous bleeding occurring after discharge on long-term mortality is unknown.

OBJECTIVES

This study sought to examine, in a real-world cohort, the association between spontaneous major bleeding or MI after PCI and long-term mortality.

METHODS

We conducted a retrospective cohort study of patients ≥30 years of age who underwent a PCI between 1996 and 2008 in an integrated healthcare delivery system. We used extended Cox regression to examine the associations of spontaneous bleeding and MI with all-cause mortality, after adjustment for time-updated demographics, comorbidities, periprocedural events, and longitudinal medication exposure.

RESULTS

Among 32,906 patients who had a PCI and survived the index hospitalization, 530 had bleeds and 991 had MIs between 7 and 365 days post-discharge. There were 4,048 deaths over a mean follow-up of 4.42 years. The crude annual death rate after a spontaneous bleed (9.5%) or MI (7.6%) was higher than among patients who experienced neither event (2.6%). Bleeding was associated with an increased rate of death (adjusted hazard ratio [HR]: 1.61, 95% confidence interval [CI]: 1.30 to 2.00), similar to that after an MI (HR: 1.91; 95% CI: 1.62 to 2.25). The association of bleeding with death remained significant after additional adjustment for the longitudinal use of antiplatelet agents.

CONCLUSIONS

Spontaneous bleeding after a PCI was independently associated with higher long-term mortality, and conveyed a risk comparable to that of an MI during follow-up. This tradeoff between efficacy and safety bolsters the argument for personalizing antiplatelet therapy after PCI on the basis of the patient's long-term risk of both thrombotic and bleeding events.

High on-treatment platelet reactivity with ticagrelor versus prasugrel: a systematic review and meta-analysis

BACKGROUND

Ticagrelor and prasugrel have shown superiority over clopidogrel. However, it remains unclear if one is superior to another regarding on-treatment platelet reactivity.

OBJECTIVES

To compare the impact of ticagrelor and prasugrel on high on-treatment platelet reactivity (HTPR).

METHODS

The PubMed and Cochrane databases were searched for eligible studies in December 2014. Studies were eligible if they compared ticagrelor and prasugrel regarding high on-treatment platelet reactivity (HTPR). Pooled estimates were calculated by using a random-effects model with 95% confidence intervals.

RESULTS

We included 14 studies and 1822 patients: 805 and 1017 in the ticagrelor and prasugrel groups, respectively. The rate of HTPR was significantly lower in the ticagrelor group: 1.5% vs. 9.8% (RR = 0.27 [0.14-0.50]). The pre-specified analysis focusing on randomized trials (n = 10) showed consistent results (RR = 0.27 [0.12-0.60]).

CONCLUSION

Our results suggest that ticagrelor allows a higher platelet reactivity inhibition as compared with prasugrel and leads to a further decrease in the rate of HTPR.

Role of sodium tungstate as a potential antiplatelet agent

Purpose

Platelet inhibition is a key strategy in the management of atherothrombosis. However, the large variability in response to current strategies leads to the search for alternative inhibitors. The antiplatelet effect of the inorganic salt sodium tungstate (Na₂O₄W), a protein tyrosine phosphatase 1B (PTP1B) inhibitor, has been investigated in this study.

Methods

Wild-type (WT) and PTP1B knockout (PTP1B^−/−) mice were treated for 1 week with Na₂O₄W to study platelet function with the platelet function analyzer PFA-100, a cone-and-plate analyzer, a flat perfusion chamber, and thrombus formation in vivo. Human blood aliquots were incubated with Na₂O₄W for 1 hour to measure platelet function using the PFA-100 and the annular perfusion chamber. Aggregometry and thromboelastometry were also performed.

Results

In WT mice, Na₂O₄W treatment prolonged closure times in the PFA-100 and decreased the surface covered (%SC) by platelets on collagen. Thrombi formed in a thrombosis mice model were smaller in animals treated with Na₂O₄W (4.6±0.7 mg vs 8.9±0.7 mg; P<0.001). Results with Na₂O₄W were similar to those in untreated PTP1B⁻/⁻ mice (5.0±0.3 mg). Treatment of the PTP1B⁻/⁻ mice with Na₂O₄W modified only slightly this response. In human blood, a dose-dependent effect was observed. At 200 μM, closure times in the PFA-100 were prolonged. On denuded vessels, %SC and thrombi formation (%T) decreased with Na₂O₄W. Neither the aggregating response nor the viscoelastic clot properties were affected.

Conclusion

Na₂O₄W decreases consistently the hemostatic capacity of platelets, inhibiting their adhesive and cohesive properties under flow conditions in mice and in human blood, resulting in smaller thrombi. Although Na₂O₄W may be acting on platelet PTP1B, other potential targets should not be disregarded.

Aspirin and P2Y12 Inhibitors in platelet-mediated activation of neutrophils and monocytes

Platelets are key players in haemostasis and represent a pivotal link between inflammation, immunity and atherogenesis. Depending on the (patho)physiological environment platelets modulate various leukocyte functions via release of inflammatory mediators and direct cell-cell interactions. Elevated levels of circulating platelet-leukocyte aggregates are found in patients suffering from several thrombotic or inflammatory conditions. Platelet-monocyte and platelet-neutrophil interaction can trigger pro- and anti-inflammatory responses and modulate effector functions of all leukocyte subpopulations. These platelet-mediated immune responses have implications for the progression of cardiovascular diseases and also play a crucial role during infections, cancer, transplantations and other inflammatory diseases of several organs. Antiplatelet therapy including the COX inhibitor aspirin and/or ADP receptor P2Y12 inhibitors such as clopidogrel, prasugrel and ticagrelor are the therapy of choice for various cardiovascular complications. Both aspirin and P2Y12 inhibitors attenuate platelet-leukocyte interactions, thereby also modulating immune responses. This may have beneficial effects in some pathological conditions, while it might be detrimental in others. This review aims to summarise the current knowledge on platelet-leukocyte interactions and the impact of aspirin and P2Y12 inhibition on platelet-mediated immune responses and to give an overview on the effects of antiplatelet therapy on platelet-leukocyte interplay in various diseases.

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.

Outcome in patients previously on antithrombotic therapy in the SAMMPRIS trial: subgroup analysis

BACKGROUND AND PURPOSE

Stenting has been used as a rescue therapy in patients with intracranial arterial stenosis and a transient ischemic attack or stroke when on antithrombotic therapy (AT). We determined whether the stenting versus aggressive medical therapy for intracranial arterial stenosis (SAMMPRIS) trial supported this approach by comparing the treatments within subgroups of patients whose qualifying event (QE) occurred on versus off of AT.

METHODS

The primary outcome, 30-day stroke and death and later strokes in the territory of the qualifying artery, was compared between (1) percutaneous transluminal angioplasty and stenting plus aggressive medical therapy (PTAS) versus aggressive medical management therapy alone (AMM) for patients whose QE occurred on versus off AT and between (2) patients whose QE occurred on versus off AT separately for the treatment groups.

RESULTS

Among the 284/451 (63%) patients who had their QE on AT, the 2-year primary end point rates were 15.6% for those randomized to AMM (n=140) and 21.6% for PTAS (n=144; P=0.043, log-rank test). In the 167 patients not on AT, the 2-year primary end point rates were 11.6% for AMM (n=87) and 18.8% for PTAS (n=80; P=0.31, log-rank test). Within both treatment groups, there was no difference in the time to the primary end point between patients who were on or off AT (AMM, P=0.96; PTAS, P=0.52; log-rank test).

CONCLUSIONS

SAMMPRIS results indicate that the benefit of AMM over PTAS is similar in patients on versus off AT at the QE and that failure of AT is not a predictor of increased risk of a primary end point.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT00576693.

Characterization of a novel function-blocking antibody targeted against the platelet P2Y1 receptor

OBJECTIVE

Platelet hyperactivity is associated with vascular disease and contributes to the genesis of thrombotic disorders. ADP plays an important role in platelet activation and activates platelets through 2 G-protein-coupled receptors, the Gq-coupled P2Y1 receptor (P2Y1R), and the Gi-coupled P2Y12 receptor. Although the involvement of the P2Y1R in thrombogenesis is well established, there are no antagonists that are currently available for clinical use.

APPROACH AND RESULTS

Our goal is to determine whether a novel antibody targeting the ligand-binding domain, ie, second extracellular loop (EL2) of the P2Y1R (EL2Ab) could inhibit platelet function and protect against thrombogenesis. Our results revealed that the EL2Ab does indeed inhibit ADP-induced platelet aggregation, in a dose-dependent manner. Furthermore, EL2Ab was found to inhibit integrin GPIIb-IIIa activation, dense and α granule secretion, and phosphatidylserine exposure. These inhibitory effects translated into protection against thrombus formation, as evident by a prolonged time for occlusion in a FeCl3-induced thrombosis model, but this was accompanied by a prolonged tail bleeding time. We also observed a dose-dependent displacement of the radiolabeled P2Y1R antagonist [(3)H]MRS2500 from its ligand-binding site by EL2Ab.

CONCLUSIONS

Collectively, our findings demonstrate that EL2Ab binds to and exhibits P2Y1R-dependent function-blocking activity in the context of platelets. These results add further evidence for a role of the P2Y1R in thrombosis and validate the concept that targeting it is a relevant alternative or complement to current antiplatelet strategies.

Patterns of Antiplatelet Therapy in Patients Who Have Experienced an Acute Coronary Event: A Descriptive Study in UK Primary Care

BACKGROUND

Antiplatelet (AP) therapy is well established for the secondary prevention of acute coronary events. However, patients may discontinue treatment, often owing to gastrointestinal (GI) complications, leaving them at elevated risk of recurrent cardiovascular events.

OBJECTIVES

This descriptive retrospective study assessed trends in prescription of AP agents and coprescription of gastroprotective therapy, after an acute coronary event. Discontinuation of AP therapy within 2 years of an event and factors predicting discontinuation were investigated.

METHODS

The study was conducted in a UK primary care setting from 2000 to 2008; a total of 27, 351 patients aged 50 to 84 years were included in the analysis. Main outcome measures were exposures to low-dose acetylsalicylic acid (ASA), clopidogrel, and proton pump inhibitors (PPIs).

RESULTS

At 90 days after an acute coronary event, 85.9% of patients had been prescribed some form of AP therapy and 33.6% of patients who were issued at least 1 ASA prescription in this period were also issued a PPI prescription. The use of dual antiplatelet therapy (DAT) 90 days after an event increased from 2% in 2000 to over 50% in 2008. An estimated 15.1% of patients on ASA monotherapy and 37.5% on DAT discontinued treatment within 1 year. A bleeding event during follow-up, including upper GI bleeding or hemorrhagic stroke, was the strongest predictor of discontinuation.

CONCLUSION

Although most patients were prescribed AP therapy in the 90 days following an acute coronary event, a substantial proportion discontinued DAT or ASA monotherapy within 1 year. It is essential that physicians consider strategies to reduce the risk of discontinuation of AP therapy.

Updates in antiplatelet agents used in cardiovascular diseases

BACKGROUND

Antiplatelet therapy is a cornerstone in coronary artery disease management. However, patients with acute coronary syndrome still remain at risk of recurrent cardiovascular events despite the advance of medical therapy.

OBJECTIVE

This article provides a review of antiplatelet agents used in cardiovascular diseases and focus on updates in the past 5 years.

METHOD

Peer-reviewed clinical trials and relevant treatment guidelines were identified from MEDLINE and Current Content database (from 1966 to April 15, 2013) using search terms aspirin, clopidogrel, prasugrel, ticagrelor, glycoprotein IIb/IIIa inhibitors, antiplatelet agents, coronary artery disease, acute coronary syndrome, pharmacology, pharmacokinetics, and pharmacodynamics. Citations from the available articles were also reviewed for additional references.

RESULTS

In unstable angina and non-ST-segment elevation myocardial infarction (MI), dual antiplatelet therapy (aspirin and clopidogrel) demonstrated a reduction in death from cardiovascular causes, nonfatal MI, or stroke (relative risk 0.80; 95% confidence interval [CI], 0.72-0.90). In ST-segment elevation MI, dual antiplatelet therapy reduced the rate of occluded infarct-related artery/death or recurrent MI (95% CI, 24%-47%). Newer agents such as prasugrel, when compared to clopidogrel, reduced death from vascular causes, MI, or stroke in patients undergoing percutaneous coronary intervention (PCI; hazard ratio [HR], 0.81; 95% CI 0.73-0.90) but not in those receiving medical management only. When compared to clopidogrel, ticagrelor reduces death from vascular causes, MI, or stroke (HR: 0.84; 95% CI, 0.77-0.92) in patients undergoing PCI or receiving medical management only. Both the agents, however, increase the risk of bleeding in certain patient population.

CONCLUSIONS

In the last 5 years, newer antiplatelet agents, including prasugrel and ticagrelor, have been demonstrated to reduce recurrent cardiovascular events compared to standard therapy and, however, also caused increase bleeding in selected patient populations. Newer agents including shorter acting P2Y12 inhibitor or antiplatelets that target other receptors are being evaluated to improve/maintain therapeutic efficacy yet minimize the risk of bleeding.