Rapid detection of platelet inhibition and dysfunction in traumatic brain injury: A prospective observational study

BACKGROUND

Rapid platelet function testing is frequently used to determine platelet function in patients with traumatic intracranial hemorrhage (tICH). Accuracy and clinical significance of decreased platelet response detected by these tests is not well understood. We sought to determine whether VerifyNow and whole blood aggregometry (WBA) can detect poor platelet response and to elucidate its clinical significance for tICH patients.

METHODS

We prospectively enrolled patients with isolated tICH between 2018 and 2020. Demographics, medical history, injury characteristics, and patient outcomes were recorded. Platelet function was determined by VerifyNow and WBA testing at the time of arrival to the trauma bay and 6 hours later.

RESULTS

A total of 221 patients were enrolled, including 111 patients on no antiplatelet medication, 78 on aspirin, 6 on clopidogrel, and 26 on aspirin and clopidogrel. In the trauma bay, 29.7% and 67.7% of patients on no antiplatelet medication had poor platelet response on VerifyNow and WBA, respectively. Among patients on aspirin, 72.2% and 82.2% had platelet dysfunction on VerifyNow and WBA. Among patients on clopidogrel, 67.9% and 88.9% had platelet dysfunction on VerifyNow and WBA. Patients with nonresponsive platelets had similar in-hospital mortality (3 [3.0%] vs. 6 [6.3%], p = 0.324), tICH progression (26 [27.1%] vs. 24 [26.1%], p = 0.877), intensive care unit admission rates (34 [34.3%] vs. 38 [40.0%), p = 0.415), and length of stay (3 [interquartile range, 2-8] vs. 3.2 [interquartile range, 2-7], p = 0.818) to those with responsive platelets. Platelet transfusion did not improve platelet response or patient outcomes.

CONCLUSION

Rapid platelet function testing detects a highly prevalent poor platelet response among patients with tICH, irrespective of antiplatelet medication use. VerifyNow correlated fairly with whole blood aggregometry among patients with tICH and platelet responsiveness detectable by these tests did not correlate with clinical outcomes. In addition, our results suggest that platelet transfusion may not improve clinical outcomes in patients with tICH.

LEVEL OF EVIDENCE

Diagnostic tests, level II.

Relationship Between Platelet Reactivity and Periprocedural Myonecrosis in Patients Undergoing Percutaneous Coronary Intervention

BACKGROUND

The impact of platelet reactivity on periprocedural myonecrosis (PMN) in East Asian patients with stable ischemic heart disease or non-ST elevation acute coronary syndrome undergoing percutaneous coronary intervention (PCI) is unclear.

METHODS

We enrolled 256 patients with normal high-sensitivity troponin I levels who underwent PCI for stable ischemic heart disease or non-ST elevation acute coronary syndrome. Residual platelet reactivity was assessed by VerifyNow point-of-care P2Y12 assay before PCI and at 18-24 hours following PCI. High platelet reactivity (HPR) was defined using three cut-off scores for platelet reactivity units (PRUs). PMN was defined as a high-sensitivity troponin I elevation of >5x the 99th percentile upper reference limit (URL) in patients with normal baseline values (<99th percentile URL).

RESULTS

The rate of PMN was 55.9% (n = 143) and was significantly higher for pre-PCI and post-PCI PRU values in the fourth quartile compared with those in the first quartile (15% vs 37% [P<.001] and 20% vs 36% [P<.001], respectively). The rate of PMN was higher in patients with HPR, regardless of the criteria used (PRU >208, PRU >235, and PRU >272) and time point. Multivariable analysis revealed that pre-PCI HPR (PRU >208) was an independent predictor of increased risk of PMN (odds ratio, 3.39; 95% confidence interval, 1.87-6.17; P<.001).

CONCLUSION

Pre-PCI HPR (PRU >208) was associated with an increased risk of PMN in East Asian patients with stable ischemic heart disease or non-ST elevation acute coronary syndrome undergoing PCI. Achievement of optimal platelet reactivity may decrease the risk of PMN.

Antiplatelet agents for preventing vaso-occlusive events in people with sickle cell disease: a systematic review

BACKGROUND

Sickle cell disease (SCD) is the most common hemoglobinopathy, occurring worldwide, and vaso-occlusive events (VOEs) are its paramount, hallmark clinical manifestation. Evidence exists that platelets play an important role in generating VOEs.

OBJECTIVE

To assess the clinical benefits and harms of antiplatelet agents for preventing VOEs in patients with SCD.

METHODS

We conducted searches of the Cochrane Central Register of Controlled Trials (CENTRAL; up to 2018, issue 3 of 12), PubMed/MEDLINE (up to April 20, 2018), and the Excerpta Medica database (EMBASE; from 1980 to week 16 of 2018). We also searched the Latin American and Caribbean Health Sciences Literature (LILACS) database, the US Food and Drug Administration (FDA) website, the European Medicines Agency (EMA) website, the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP), and www.ClinicalTrials.gov. We checked the bibliographies of included studies and any relevant systematic reviews. Our systematic review included randomized clinical trials (RCTs) conducted in people who had SCD without VOEs at trial entry. Eligible trials compared a single or combination treatment regimen (with each treatment classified as a conventional or nonconventional antiplatelet agent) with conventional care, placebo, or another regimen. No restrictions were placed on the route of administration, dose, frequency, or duration of treatment. We selected RCTs, assessed the risk for bias, and extracted data in a duplicate and independent fashion. We estimated risk ratios for dichotomous outcomes and mean differences for continuous outcomes. We also subjected our analyses to a random-effects model, and Trial Sequential Analysis (TSA) was used. We used the grading of recommendations, assessment, development, and evaluation (GRADE) approach to assess the overall quality of data for each individual outcome.

RESULTS

We identified 5 RCTs (N=747) that met our criteria. Of these, 4 trials were multicenter and multinational. The trials included patients of all ages and assessed prasugrel, ticagrelor, crizanlizumab, and aspirin vs either placebo or no intervention. The most frequent route of administration was oral. The trials were small and carried a high risk for bias, given that pharmaceutical companies sponsored 4 of them. None of the trials reported information on quality of life. No meta-analysis was performed owing to heterogeneity in the ages of the participants and in the interventions. No single trial showed evidence of certainty regarding all-cause mortality. One trial showed uncertainty in comparing prasugrel vs placebo for preventing VOEs in patients younger than 18 years (relative risk [RR], 0.92; 95% CI, 0.80 to 1.06; low quality of evidence). TSA for this outcome suggested that a new trial should be conducted. One trial found a difference in the size effect of uncomplicated VOEs, favoring high-dose crizanlizumab vs placebo (mean difference, -1.50; 95% CI, -2.61 to -0.39; very low quality of evidence). No difference in VOEs was found in studies that compared either ticagrelor in children or prasugrel in adults vs placebo. The overall incidence of harms in any intervention did not differ from that in the control.

CONCLUSIONS

The current evidence does not support or reject the use of any antiplatelet agent for preventing VOEs in people with SCD. This conclusion was based on small RCTs that carried a high risk for bias. No conclusive evidence exists regarding relevant clinical outcomes because the evidence is limited and of very low quality.

Optical Coherence Tomography for Guiding Plaque Stabilization in a Patient With Myocardial Infarction and Massive Coronary Thrombosis

An OCT-guided watchful-waiting strategy is used to avoid the invasive treatment of the LMCA in a very young patient with massive coronary thrombosis.

Efficacy and safety of dual antiplatelet therapy after coronary stenting in patients with chronic kidney disease

BACKGROUND

We compared efficacy and safety of short- (3 or 6 months) versus long-term (≥12 months) dual antiplatelet therapy (DAPT) after drug-eluting stent (DES) implantation, according to the presence of chronic kidney disease (CKD).

METHODS

Patient-level pooled analysis was performed with 7242 patients (87.2% with 2nd generation DES) from 5 randomized controlled trials.

RESULTS

In both CKD (1273 patients) and non-CKD (5969 patients) population, the rates of patient-oriented composite outcomes at 1-year (POCO, all-cause death, any myocardial infarction [MI], stroke and TIMI major bleeding) were not different between the short- and long-term DAPT (hazard ratio [HR] 1.19, 95% confidence interval [CI] 0.76-1.86, P=.449 in CKD population; HR 1.14, 95% CI 0.83-1.56, P=.434 in non-CKD population). The rates of coronary thrombotic events (any MI and definite/probable stent thrombosis) also did not differ between short- and long-term DAPT in either CKD or non-CKD population. As for bleeding events, long-term DAPT increased the TIMI major bleeding (HR 2.91, 95% CI 1.31-6.48, P=.009) in non-CKD population. The similar trend was observed with long-term DAPT in CKD population. But it did not reach statistical significance (HR 3.15, 95% CI 0.64-15.63, P=.160).

CONCLUSIONS

The rates of POCO and coronary thrombotic events were significantly higher in patients with CKD compared with those without CKD, which were not affected by short- or long-term DAPT. Higher bleeding incidence by long-term DAPT was only observed in non-CKD patients but not in CKD patients. Further large scale studies are warranted to confirm our findings.

Almanac 2013: Acute coronary syndromes

Unstable coronary artery plaque is the most common underlying cause of acute coronary syndromes (ACS) and can manifest as unstable angina, non-ST segment elevation infarction (NSTE-ACS), and ST elevation myocardial infarction (STEMI), but can also manifest as sudden cardiac arrest due to ischaemia induced tachyarrhythmias. ACS mortality ha decreased significantly over the last few years, especially from the more extreme manifestations of ACS, STEMI, and cardiac arrest. This trend is likely to continue based on recent therapeutic progress which includes novel antiplatelet agents such as prasugrel, ticagrelor, and cangrelor.

[The effect of anticoagulation and anti-aggregation treatment on the extent, development and prognosis of acute craniocerebral injury]

PURPOSE OF THE STUDY

A retrospective analysis of the effect of anticoagulation and anti-aggregation treatments on the post-injury clinical status, frequency of necessary surgical interventions including re-operations, course of intracranial haemorrhage dynamics and treatment outcome in patients with acute traumatic intracranial haematoma.

MATERIAL AND METHODS

The group consisted of 328 patients with acute post-traumatic intracranial haemorrhage treated at the author's institution from 2008 to 2012. Fifteen patients with anticoagulation therapy (warfarin; 8 females, 7 males; median age, 72.0 years) and 46 patients with anti-aggregation treatment (21 females, 25 males; median age, 75.5 years ; 37 with acetylsalicylic acid, 5 with thienopyridines, 2 with new antithrombotics and 2 taking dual anti-aggregation therapy), all older than 55 years, were included in statistical analysis. The post-injury clinical condition (Glasgow Coma Scale), incidence of haemorrhagic contusions, intracranial haematoma progression, particularly when surgery was indicated, incidence of re-operations and treatment outcome (Glasgow Outcome Scale - GOS) were the study parameters. The control group included 77 patients with post-traumatic intracranial haematoma with normal coagulation who were older than 55 years (27 females, 50 males; median age, 67 years). Patients younger than 55 years and those with normal coagulation were not included in the statistical analysis. The treatment of all patients with anti-aggregation or anticoagulation therapy was consulted with the haematology specialist.

RESULTS

The median age and initial status evaluated by the Glasgow Coma Scale were similar in the groups of anti-aggregated and anticoagulated patients and the control group. The number of good treatment outcomes, as evaluated by the GOS, was significantly higher in the anti-aggregated patients than in those on warfarin. A comparison of anti-aggregated, anticoagulated and normal coagulation patients did not show any statistically significant differences in the incidence of patients operated on, in the incidence of haemorrhagic contusions requiring surgery as a marker of the severity of brain parenchyma injury, intracranial haemorrhage progression with time, particularly when requiring surgery, and the rate of re-operations. However, when comparing the group of anti-aggregated patients with the control group, the higher incidence of haemorrhagic contusions and the lower number of patients requiring surgery were found to be close to the level of statistical significance.

DISCUSSION

The positive effect of anti-aggregation and anticoagulation treatment on the morbidity and mortality from cardiovascular diseases should be regarded in relation to a higher risk of haemorrhagic complications. If a bleeding complication occurs, the possibility of neutralising this treatment should be considered, but this is particularly difficult in new agents. The relationship between anti-aggregation or anticoagulation treatment and the treatment results in the patients with head injury is particularly important from the neurosurgical point of view, because the relevant literature data are ambiguous.

CONCLUSIONS

The results did not confirm any statistically significant adverse effects of anticoagulation or anti-aggregation treatment on the severity of post-injury status and risk of intracranial bleeding progression. The incidence of poor outcomes is higher in anticoagulated patients than in anti-aggregated patients. Although not reaching the level of statistical significance, the results also indicate higher risk of significant haemorrhagic brain contusions in anti-aggregated patients.

[Antiplatelet therapy in atherosclerosis of various localizations: acute and stable States]

We present in this review current data on specificities of efficacy and safety of antiplatelet therapy in patients with atherosclerosis of various localizations. Reduced priority of aspirin monotherapy in several clinical situations is shown. Controversial issues of the use of dual antiplatelet therapy including its application in patients with acute coronary syndrome are discussed. Novel groups of antiplatelet agents as well as individual new drugs are also presented.

[Possibilities of primary prevention of stroke: elaboration of a population level strategy]

This review is devoted to principles of primary prevention of cerebral stroke. Prevalence of stroke and its contribution to development of complications and lethal outcomes is analyzed in detail. Main principles of prevention of stroke are delineated and contemporary international guidelines on correction risk factors (arterial hypertension, smoking, disorders of lipid metabolism, diabetes mellitus, atrial fibrillation) are reviewed. Special attention is given to the significance of asymptomatic stenoses of carotid arteries as predictors of stroke and to modern methods of diagnosis and treatment of such stenoses. Expediency of the use of hormonal replacement therapy with the aim of stroke prevention in postmenopausal women is considered. It is noted that antiaggregant therapy and specifically acetyl salicylic acid should be administered only in the presence of high risk of cardiovascular complications. The authors believe that overall success of stroke prevention depends on realization of complex long term national programs.

[The differences between the guidelines of the European Society of Cardiology and the American College of Cardiology/ American Heart Association for oral P2Y12 inhibitor therapy in the management of patients with acute coronary syndromes]

The analysis of the evidence that formed the basis for the current guidelines of the European Society of Cardiology (ESC) on oral therapy by antithrombotic drugs for acute coronary syndromes (ACS), and a comparison with the U.S. guidelines. The ESC guidelines, published during 2011-2012, declared the superiority of prasugrel and ticagrelor over clopidogrel in patients with ACS without ST elevation and myocardial infarction (MI) with ST elevation. These guidelines are based in each case on a subgroup analysis of a single study using either prasugrel (TRITON), or ticagrelor (PLATO). In contrast, the American College of Cardiology (ACC) and the American Heart Association (AHA) guidelines, published in 2012-2013, are more balanced, conservative and present evidence-based outlook, suggesting no proven extra benefit of one P2Y12 antagonist over the other(s). The ESC guidelines regarding the findings of the superiority of prasugrel or ticagrelor over clopidogrel are overly optimistic and not always evidence-based. A small frequency of clinical use of prasugrel and ticagrelor in the world in general and Europe in particular, suggests a discrepancy between the traditionally appointed treatment and published ESC guidelines.

[Novel agents in antiplatelet therapy]

Antiplatelet therapy is the cornerstone of management of acute coronary syndromes. Currently used antiplatelet drugs present several limitations that provoke new searches. These limitations include resistance, delay in the onset of action, risk for bleeding, variations in the individual response, and interaction with other medications (i.e. proton pump inhibitors, calcium channel blockers). New concepts and medications have emerged for the effective inhibition of platelets. Prasugrel, AZD6140 (ticagrelor), cangrelor, and SCH 530348 (thrombin receptor antagonist) are among some of the novel agents that survived randomized trials. In this review, we aimed to summarize novel concepts and agents in antiplatelet therapy.

Antiplatelet agents

The introduction of aspirin as an anti-thrombotic agent some 50 years ago has changed the therapeutic approach in cardiovascular medicine. Since platelets play a key role in the development of arterial thrombosis, antiplatelet drugs serve as a cornerstone in the prevention and the treatment of these conditions. After many years of a "monopoly" of aspirin, ADP receptor P2Y12 inhibitors were introduced with a significant improvement in clinical outcome. Nowadays dual antiplatelet therapy is the common practice for both acute events and secondary prevention in selected groups of patients. Another revolution was the development of potent inhibitors of the platelet integrin GPIIbIIIa, which significantly improved the outcome of percutaneous interventions (PCI), in cardiology. The improved efficacy of multiple-drug therapy is associated with an increased risk of bleeding, which raises the issue of the dosing of these drugs. Recently, numerous studies have reported a variable laboratory response to aspirin and clopidogrel, which correlates with clinical outcome. Several mechanisms have been proposed to cause this variable response, including genetic variability, disease burden and others. A major obstacle in this field is the lack of a standardized method for testing these responses, and thus some studies cannot be compared to others. Ongoing studies are currently investigating the potential translation of these observations into clinical practice. Such studies may lead to a change in the paradigm of antiplatelet therapy, where individual dose adjustment may improve efficacy and safety. Finally, a variety of new drugs are currently in different stages of development, including new P2Y12 receptor inhibitors, thromboxane receptor blockers, direct thrombin inhibitors and other signaling pathway inhibitors including oral GPIIbIIIa inhibitors. Thus, antiplatelet therapy is currently under intensive development toward multiple-drug therapy and personal-dose adjustment, which may improve clinical outcome.

The patient taking antiplatelet drugs: a review with dental management considerations

Antiplatelet drugs are used in clinical practice to prevent the adverse sequelae of thromboses in atherosclerotic arteries of the heart, brain, and limbs and in the veins and heart chambers. They have diverse mechanisms of action, half-lives, and pharmacodynamic effects. A major concern among dental health care providers is the potential for excessive bleeding after invasive dental procedures. This article reviews the current antiplatelet agents used for managing cardiovascular and cerebrovascular diseases and suggests how patients taking these agents may be managed when invasive dental procedures are planned.

[Association of antiagregants: when and how]

Aterothrombotic disease (coronary, cerebrovascular and peripheral artery disease) is the most common cause of mortality and disability in the world, antiaggregants representing one of its therapeutic and preventive pillars. We have drugs at present that act at different levels of platelet aggregation (COX inhibitors as well as inhibitors of phosphodiesterase, ADP P2Y12 receptor and IIb/IIIa receptor). We review here the efficacy and safety of the association of antiaggregants in most relevant clinical scenarios, including current clinical recommendations and an analysis of supportive evidence.

The pharmacogenetics of antiplatelet drugs

Platelets play a pivotal role in coronary heart disease and atherothrombotic events, and thus antiplatelet therapy is commonly used to treat cardiovascular disease. Unfortunately, the benefits of this approach are limited, and a large proportion of treated patients will suffer a new thrombotic event, either within the first few weeks following stent implantation or in the follow-up period after myocardial infarction. This lack of clinical benefit may be related to a heterogeneous response to antiplatelet drugs among individuals. Recently, the field of pharmacogenetics has tried to identify gene variants in order to explain tile observed heterogeneity in patient responses to drugs. This review explores the genetic influences on antiplatelet drug efficacy by analyzing the modulating role of different genetic polymorphisms on individual responses to antiplatelet therapy.

Isolation and cloning of a metalloproteinase from king cobra snake venom

A 50 kDa fibrinogenolytic protease, ohagin, from the venom of Ophiophagus hannah was isolated by a combination of gel filtration, ion-exchange and heparin affinity chromatography. Ohagin specifically degraded the alpha-chain of human fibrinogen and the proteolytic activity was completely abolished by EDTA, but not by PMSF, suggesting it is a metalloproteinase. It dose-dependently inhibited platelet aggregation induced by ADP, TMVA and stejnulxin. The full sequence of ohagin was deduced by cDNA cloning and confirmed by protein sequencing and peptide mass fingerprinting. The full-length cDNA sequence of ohagin encodes an open reading frame of 611 amino acids that includes signal peptide, proprotein and mature protein comprising metalloproteinase, disintegrin-like and cysteine-rich domains, suggesting it belongs to P-III class metalloproteinase. In addition, P-III class metalloproteinases from the venom glands of Naja atra, Bungarus multicinctus and Bungarus fasciatus were also cloned in this study. Sequence analysis and phylogenetic analysis indicated that metalloproteinases from elapid snake venoms form a new subgroup of P-III SVMPs.

[Snake venom disintegrins: classification and therapeutic potential]

Biochemistry and pharmacology of snake venoms reveal structural and functional polymorphisms of proteins they contain. These lead their effects by their enzymatic activities (proteases, phospholipases A2, L-amino acid oxydases...) or by binding to membrane receptors. Disintegrin from snake venoms play a role as antagonists of cell adhesion and migration by binding integrins and blocking their function. Characterization of integrin antagonists from snake venom allows us understanding the function of some integrins providing new information to develop new therapeutic agents. In this review, we report classification and therapeutic implications of disintegrins. In particular the structural and the functional characteristics of lebestatin; a short disintegrin isolated from Tunisian Macrovipera lebetina snake venom.

The antiplatelet drug target in atherosclerotic diseases

The aim of this review is (1) to give a rationale for anti-platelet therapy based on mechanisms of platelet rich arterial thrombosis, (2) to point out the pitfalls involved in monitoring therapy with platelet function tests and (3) to outline the potential clinical applications of such therapy based on the various modes of action of anti-platelet drugs. The primary event in arterial thrombosis is platelet-mediated, either due to increased shear or exposed collagen, followed by fibrin-rich thrombosis. Anti-platelet therapy needs to be monitored but most platelet function tests, now in use, do not reflect in vivo function; the anticoagulant used for blood samples removes extra-cellular calcium ions, platelets are often separated before the test, or very high doses of agonist are used: all of these can give misleading results. We review means whereby platelet function can be monitored in whole blood samples anticoagulated with the pure thrombin inhibitor, hirudin. We review the available methods of modifying platelet activity and are particularly interested in agents that do not cause bleeding. Present therapy causes bleeding by interference with COX1, the P2Y(12) receptor or the platelet fibrinogen receptor complex, all of which can be associated with bleeding complications. In contrast, serotonin does not influence formation of haemostatic layers although it is implicated in shear-induced aggregation and thrombus propagation by positive feedback from the large amount of intraplatelet serotonin. We suggest that further investigation of selective serotonin 5HT(2) antagonism would allow effective management of intravascular thrombosis without bleeding complications. This would be safer both as prophylaxis and would also allow cardioprotection of vascular patients undergoing surgical operations.

[Anticoagulation for secondary prevention: which drug in which situation?]

Thromboembolic events are a major complication of cardiovascular diseases. Secondary prevention of thromboembolic complications can be achieved by anticoagulation with heparin or vitamin-K-antagonists. A new class of direct thrombin inhibitors has been recently introduced into clinical medicine. Clinical studies have demonstrated theses agents to be comparable in efficacy for prophylaxis of venous thromboembolism. However, the results of ongoing trials are awaited in helping to define the place of direct thrombin inhibitors in secondary prevention. Antiplatelet therapy constitutes the cornerstone in the management of patients with acute coronary syndromes and generally high-risk patients with atherothrombosis. Until recently, long-term antiplatelet therapy for the treatment and prevention of atherothrombotic disease was traditionally limited to aspirin. The availability of the thienopyridines and glycoprotein IIb/IIIa inhibitors represents an important addition to the physician's armamentarium. Due to the increased risk of major bleeding, for each patient the decision of anticoagulation and antiplatelet therapy must be tightly correlated to the individual benefit-risk ratio.

Cost-effectiveness of antiplatelet agents in secondary stroke prevention: the limits of certainty

Which of the available antiplatelet therapies should be preferred for secondary prevention of recurrent ischemic stroke has been contentious.

OBJECTIVE

We applied the Duke Stroke Policy Model (DSPM) to reconsider this issue, paying particular attention to the degree of uncertainty in the estimates of their efficacy. The DSPM is a continuous-time simulation model of stroke development and outcome.

METHODS

We modified the inputs to reflect the cost of the drugs aspirin (ASA), extended release dipyridamole/aspirin (DP/A) and clopidogrel (CLO), as well as their relative risk in preventing subsequent ischemic stroke in comparison with placebo (PBO). These relative risks were derived from published reports from the second European Stroke Prevention Study (ESPS-2) and Clopidogrel Versus Aspiring in Patients at Risk of Ischemic Events studies. Precision was addressed by applying bootstrapping to the above estimates of relative risk. The target population was 70-year-old men with nondisabling stroke. The outcome measures were quality-adjusted life-years (QALYs), costs, and costs per QALY.

RESULTS

Results of Base Case Analysis: In large part because of its modest drug cost, ASA was cost-effective in comparison with PBO. DP/A tended to have improved outcomes, but at increased costs. CLO was dominated in the base case.

RESULTS OF SENSITIVITY ANALYSIS

ASA and DP/A cannot be differentiated on a statistical basis alone. In probabilistic sensitivity analysis, CLO was rarely preferred.

CONCLUSIONS

Either DP/A or ASA appear to be a good value in comparison with no treatment, but there is no clear winner between the two. In the absence of a definitive randomized trial, simulation modeling can help clarify the trade-offs between the various antiplatelet agents, but not beyond the constraints imposed by the imprecision in the estimates that can be obtained from the current evidence base.

[Anticoagulants and antiplatelet agents in pregnancy]

Anticoagulants and antiplatelet agents are currently used during pregnancy as treatment or prophylaxis for thromboembolic disease. Main adverse events of these agents are bleeding episodes, which put the pregnancy at risk. Unfractionated and low molecular weight heparins are first-line treatment or prophylaxis for thromboembolism. If an antiplatelet agent is needed, aspirin alone or in combination with heparins can be safely administered. Coumarine derivatives are still contraindicated during pregnancy because of teratogenicity and/or bleeding. No adequate data are yet available on the safety profile of the new antiplatelet agents or the direct thrombin inhibitors. Special considerations are discussed on the risks of regional anesthesia, as well as on nursing during anticoagulation.

Antiplatelet Agents: Current Drugs and Future Trends

Antiplatelet drugs in clinical use are discussed in terms of their mechanisms of action and the relevancy of that to the physiology of platelets and the pathophysiology of arterial thrombosis. Current clinical usage is outlined in detail for each drug. Experimental antiplatelet drugs also are discussed.

New Approaches for Antithrombotic Antiplatelet Therapies

Cardiovascular diseases are one of the major causes of mortality in the western world. As platelet dependent thrombosis is of central importance in their pathophysiology, several successful strategies, targeting a specific platelet function or interaction, have been developed to prevent or treat these disorders. However, as the current antiplatelet strategies are limited in efficacy and safety, and often influence normal haemostatic functions, new compounds are being developed with improved characteristics. This review deals with the development of novel antiplatelet compounds for which evidence is available on their antithrombotic action in vivo. In a first part, these compounds, their targets and their potential applicability are discussed. The second part of this review focuses on BT tests and bleeding models and their usefulness for determination and/or prediction of the safety of novel antiplatelet compounds.

[Platelet inhibitors: old and new]

Platelet inhibiting drugs are mainly used to prevent arterial thrombosis complicating atherosclerosis. Numerous clinical trials have delineated their clinical indications and precise guidelines are internationally available. The mechanism of action of aspirin is well understood: inhibition of platelet synthesis of thromboxane, and there is a pretty good relationship between pharmacology at the molecular and cellular levels and clinical results. The recently available drugs are the following. Clopidogrel is a thienopyridine, which irreversibly inhibits platelet activation by ADP interacting with the recently cloned P2Y12 receptor. There are also inhibitors of the fibrinogen binding to its platelet receptor, the glycoprotein IIb/IIIa complex, which is the key mechanism of platelet aggregation. These new drugs are widely used in patients with active coronary artery disease, on top of aspirin.

Is platelet aggregation a more important contributor than platelet adhesion to the overall platelet-related primary haemostasis measured by PFA-100?

BACKGROUND

Platelet-related primary haemostasis (PRPH), measured in PFA-100 as a closure time (CT), reflects platelets' combined ability to adhere and aggregate under higher shear stress. The inputs of platelet aggregation and platelet adhesion into the real values of CT remain unknown, and this poor discrimination results in the complexity of the PFA-100 measurement.

OBJECTIVE

To estimate the particular contributions of two physiological phenomena, platelet aggregation and adhesion, and the importance of various membrane receptors underlying platelets' capability of the plug formation in PFA-100 cartridges.

MATERIALS AND METHODS

Effects of various blockers antagonizing ligands binding to platelet surface membrane receptors (antagonists of GPIIb-IIIa complex, collagen receptors and purinoreceptors), and aurintricarboxylic acid (ATA), the antagonist of GPIb-von Willebrand factor (vWF) interaction, were monitored in 47 healthy donors with the use of PFA-100 and whole blood electrical aggregometry (WBEA).

RESULTS

PFA-100 collagen/ADP CT was the most sensitive in probing the effect of platelet membrane receptor antagonists acting via the blockade of GPIIb-IIIa complex and those antagonizing GPIb-vWF interaction (GR144053F, Integrilin, ATA), whereas the other blockers, acting on collagen receptors or purinoreceptors, remained much less efficient. For the examined GPIIb-IIIa and GPIb antagonists, the overall variability in WBEA explained a very significant part (30-60%) of the overall variability in PFA-100 CT.

CONCLUSIONS

GPIIb-IIIa-mediated platelet aggregation and von Willebrand factor interactions with GPIb and/or GPIIb-IIIa seem to be the major determinants of PFA-100 CT. On the contrary, other platelet receptors participating in platelet aggregation and/or platelet adhesion are of secondary importance and minor significance in blood flow at higher shear stress monitored in PFA-100.

[Platelet aggregation inhibitor in general practice. Every 3rd infarct prevented--reinfarction rate cut in half]

Depending on their mode of action, pharmaceuticals with an antithrombocytic effect are divided into five groups. In the doctor's office, acetylsalicylic acid (ASA) and the thienopyridines, such a ticlopidine and clopidogrel predominate. Acetylsalicylic acid should be considered for primary prevention in patients over 50 with a marked cardiovascular risk profile. In the secondary prophylaxis of myocardial infarction, life-long ASA treatment continues to be the treatment of choice. As an alternative, however, clopidogrel may be applied. A combination of acetylsalicylic acid and clopidogrel is recommended for patients who have been implanted with a stent. In patients with acute coronary syndrome, this regimen is superior to monotherapy with acetylsalicylic acid. In comparison with ticlopidine, clopidogrel has a more rapid onset of action, and has fewer side effects. In patients with an acute coronary syndrome and an elevated risk glycoprotein IIb/IIIa antagonists have proved highly effective.

Comparison of the effect of different platelet GPIIb/IIa antagonists on the dynamics of platelet/fibrin-mediated clot strength induced using thromboelastography

The effect of various platelet glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists on the dynamics of platelet-fibrin clot formation and strength induced by various stimuli was measured by thromboelastography (TEG). GPIIb/IIIa antagonists with high affinity for resting and activated platelets and with slow rates of dissociation from GPIIb/IIIa (Class I antagonists) demonstrated potent and comparable inhibition of platelet aggregation and tissue factor (TF), lipopolysaccharide (LPS), Factor Xa, and thrombin-induced clot strength, in contrast to antagonists that dissociate rapidly from GPIIb/IIIa (Class II antagonists). For example, the Class I antagonist XV459 (the free acid form of roxifiban) inhibited TF, endotoxin, Factor Xa, and thrombin-induced maximal clot strength and platelet aggregation with an IC(50)=30-70 nM, whereas the IC(50) of the Class II antagonist YZ211 (the free acid form of sibrafiban) for altering clot formation and strength was 0.3-4.7 microM. Moreover, the IC(50)'s of sibrafiban, and another Class II antagonist, orbofiban, for inhibiting platelet-fibrin clot formation and strength were substantially greater than their clinically achievable concentrations. Further, although aspirin treatment improved the efficacy of all GPIIb/IIIa antagonists, it did not alter the differences between Classes I and II antagonists. Thus, these data indicate that there are differences in the efficacy of various GPIIb/IIIa antagonists in inhibiting platelet-fibrin clot formation and strength. They also suggest that inhibiting platelet aggregation may not be the sole determinant for the in vivo efficacy of various GPIIb/IIIa antagonists.

Paeonilide, a novel anti-PAF-active monoterpenoid-derived metabolite from Paeonia delavayi

A novel monoterpenoid-derived metabolite, paeonilide, was isolated from the roots of Paeonia delavayi. Its structure was established by a combination of spectroscopic and X-ray crystallographic analyses. It showed an anti-PAF effect with an IC50 value of ca. 8 microg/ml.

Antiplatelet therapy

Within the last few years antiplatelet therapy has developed exponentially, with new agents being tested in an increasing number of clinical scenarios. The mechanism of action of these newer agents and evidence of benefit is prevented in this review.

New adjunctive therapy for ischemic syndromes

Because anticoagulant and GP IIb/IIIa inhibitors reduce mortality, myocardial ischemia, AMI, and reintervention, these agents are now becoming the standard of care for patients with USA and NQWMI. Unanswered questions remain about the best treatment regimen, appropriate dosing, long-term benefit, and cost-effectiveness of these agents, however, and many additional trials are ongoing or planned. As nurses administer these drugs, assess the patients' responses to therapy, and educate patients and families about these agents, they contribute to recent advances in preventing ischemic heart disease.

An overview of commonly used antiplatelet agents

Several agents inhibiting platelet function are commonly used in clinical practice, each having a unique mechanism of action. The complex cascade of events ultimately resulting in thrombus formation has several areas that pharmacologic agents can affect. The resultant effects range from being relatively non-specific with aspirin, ticlopidine, and clopidogrel to being specific with the glycoprotein IIb/IIIa receptor antagonists such that platelet aggregation will be inhibited irregardless of the metabolic pathway responsible for initiating aggregation. The clinical indications for these agents are vast, as platelet aggregation has been widely implicated in cardiovascular events. The degree of platelet inhibition is related to the frequency of bleeding. Aspirin is a relatively weak inhibitor of platelet function, ticlopidine has been said to have moderate activity, while the glycoprotein IIb/IIIa receptor antagonists are the most potent inhibitors of platelet aggregation. As our knowledge of the mechanisms of platelet aggregation expands, so will our treatment regimens. Clearly, we will await the results of future clinical trials to further define the role of antiplatelet agents.

Antiplatelet agents isolated from medicinal plants

Platelet-vessel wall interaction is an important process in physiological hemostasis and pathological thrombosis. In oriental countries, some medicinal plants have been claimed for uses to improve circulation, induce fibrinolysis or prevent thrombosis. In cooperation with chemists using bioassay-based step-by-step purification, some antiplatelet agents were isolated from plant sources. According to their effects on platelet aggregation, release reaction and signal transductions involved, these antiplatelet agents can be classified into eight groups: 1. platelet-activating factor (PAF) antagonists, 2. collagen-receptor antagonists, 3. thromboxane-receptor antagonists, 4. ADP-receptor agonists, 5. inhibitors of phosphoinositide breakdown, 6. inhibitors of thromboxane formation, 7. agents increasing cyclic nucleotides, and 8. protein kinase C activators. These new pharmacological agents derived from medicinal plant sources may be useful as leads to develop as effective cardiovascular drugs.

Association between ligand-induced conformational changes of integrin IIbbeta3 and IIbbeta3-mediated intracellular Ca2+ signaling

Platelet IIbbeta3 is a prototypic integrin and plays a critical role in platelet aggregation. Occupancy of IIbbeta3 with multivalent RGD ligands, such as fibrinogen, induces both expression of ligand-induced binding sites (LIBS) and IIbbeta3 clustering, which are thought to be necessary for outside-in signaling. However, the association between LIBS expression and outside-in signaling remains elusive. In this study, we used various IIbbeta3-specific peptidomimetic compounds as a monovalent ligand instead of fibrinogen and examined the association between LIBS expression and outside-in signaling such as IIbbeta3-mediated intracellular Ca2+ signaling. Using a set of monoclonal antibodies (MoAbs) against LIBS, we showed that antagonists can be divided into two groups. In group I, antagonists can induce LIBS on both IIb and beta3 subunits. In group II, antagonists can induce LIBS on the IIb subunit, but not on the beta3 subunit. Inhibition studies suggested that group I and group II antagonists interact with distinct but mutually exclusive sites on IIbbeta3. Neither group I nor group II antagonist increased intracellular Ca2+ concentrations ([Ca2+]i) in nonactivated platelets. All antagonists at nanomolar concentrations abolished the increase in [Ca2+]i in 0.03 U/mL thrombin-stimulated platelets, which is dependent on both fibrinogen-binding to IIbbeta3 and platelet-aggregation. However, only group I antagonists at higher concentrations dose-dependently augmented the [Ca2+]i increase, which is due to aggregation-independent thromboxane A2 production. This increase in [Ca2+]i was not observed in thrombasthenic platelets, which express no detectable IIbbeta3. Thus, only the group I antagonists, albeit a monovalent ligand, can initiate IIbbeta3-mediated intracellular Ca2+ signaling in the presence of thrombin stimulation. Our findings strongly suggest the association between beta3 LIBS expression and IIbbeta3-mediated intracellular Ca2+ signaling in platelets.

Acute coronary syndromes: 2. Antiplatelet agents

Therapies with novel antiplatelet agents and anticoagulants are the focus of current research. When used separately or in combination, these agents prevent generation of thrombin by activated platelets. The new therapies, in conjunction with judicious use of fibrinolytic drugs and mechanical interventions, are revolutionizing the management of patients with acute coronary syndromes.

[Anticoagulants and platelet aggregation inhibitors in urology]

Anticoagulants are widely used in the prevention of thromboembolic disease (particularly during the postoperative period) and in the curative treatment of deep vein thromboses. Two classes of anticoagulants are currently available: heparins (standard heparin, low molecular weight heparin) and coumarin anticoagulants. The choice of anticoagulant must take into account the clinical context (preventive or curative treatment), as well as the pharmacological and pharmacokinetic properties of the anticoagulant. This treatment requires laboratory monitoring adopted to the anticoagulant selected.

Anti-platelet drugs: do they affect megakaryocytes?

Anti-platelet drugs are used in clinical medicine to prevent thromboembolic complications of cardiovascular diseases. Among anti-platelet drugs, very little is known of their possible effects on megakaryocytes. ASA is the only compound for which it has clearly been demonstrated that its mechanism of action involves acetylation of the Ser 529 residue in cyclo-oxygenase in platelets and megakaryocytes. Because megakaryocytes possess membrane receptors for ADP, the thienopyridine metabolites of ticlopidine and clopidogrel may modify these receptors as in platelets and hence prevent ADP binding and further activation. Megakaryocytes also have GPIIb-IIIa receptors for the adhesive protein fibrinogen and may be accessible in vivo to GPIIb-IIIa antagonists such as the monoclonal antibody abciximab. Drugs such as heparin or the phosphodiesterase inhibitor anagrelide can either inhibit or stimulate megakaryocytopoiesis and platelet production, while cytokines such as thrombopoietin affect megakaryocytopoiesis, platelet production and platelet function by potentiating the activation of platelets by other agonists.

[New antithrombotic agents in coronary disease]

Aspirin is effective in, treating patients with unstable angina or myocardial infarction. However, questions remain about the optimal dose of aspirin and aspirin-resistance in subgroups of patients. Heparin also has beneficial effects mostly during the acute phase of unstable angina, but thrombolytics are effective only in acute myocardial infarction and not in unstable angina. Recently, low molecular weight heparins have proved to be as effective (FRIC trial) or more effective (ESSENCE trial) than unfractionated heparin in unstable angina. Ongoing studies (TIMI 11B) are evaluating the efficacy of a prolonged administration of low molecular weight heparin to alter the chronic process of unstable angina. The new antiplatelet drugs directed against GP IIb/IIIa receptors are now available to improve the acute results of high risk percutaneous transluminal angioplasty (PTCA). This new drug (c7E3) binds rapidly to GP IIb/IIIa and prevents fibrinogen binding to the receptor. This very potent and irreversible effect prevents platelet aggregation and decreases the incidence of acute occlusions following PTCA. especially in patients with unstable angina. The counterpart is an increased risk of hemorrhage, knowing that patients receive simultaneously aspirin and heparin. The first results of the EPILOG study also demonstrate a better outcome in elective angioplasty without significant increase of serious bleeding, thanks to a low dose heparin regimen. In contrast to thrombolytics, the GP IIb/IIIa antagonist does not increase the risk of intracranial bleeding. The results of the CAPTURE trial also confirm the clinical benefit obtained with this drug in refractory unstable angina. The reduction of death and myocardial infarction is very consistent throughout the studies performed with c7E3. The Kaplan-Meier curves of freedom of death and myocardial infarction diverge immediately after start of study medication. The acute benefits are preserved at 3 years in the EPIC trial. Similar trends were present during the acute phase with other compounds (tirofiban, integrelin), meaning that a class effect may exist but the long term results are disappointing. The results with new direct antithrombins such as hirudin, or hirulog in acute myocardial infarction or in PTCA for unstable angina are negative. The development of new potent oral antiplatelet drugs might change the treatment of acute coronary syndromes in the future. The current progress made with antithrombotic drugs should improve the prognosis of acute coronary syndromes.

[New therapeutic prospects in acute coronary thrombosis]

The principal new clinical approaches to the treatment of acute coronary thrombosis are reviewed. They include fibrinogen platelet receptor antagonists (anti GP IIb-IIIa) and direct thrombin inhibitors. The anti GP IIb-IIIa have been shown to be effective in unstable angina and in the prevention of acute coronary occlusion after transluminal angioplasty. Thrombin inhibitors, the leader being hirudine, also give promising results. The real clinical benefits of these agents and the risk of haemorrhage that they incur in monotherapy or in association, will only become clear when the results of large scale trials which are under way at present, become available. Other antiplatelet agents (clopidogrel, thromboxane inhibitors) are also discussed.

Supercooperativity in platelet aggregation: substituted pyridyl isoxazoles, a new class of supercooperative platelet aggregation inhibitors

The phenomenon of supercooperativity in platelet aggregation is manifested by the occurrence of clear-cut thresholds in dose-response relationships; in such cases the Hill coefficient has unusually high values. Approximation, by the Hill equation, of the relationship of the rate of arachidonate-induced platelet aggregation to the concentrations of either the inducer or inhibitors such as substituted pyridyl isoxazoles (synthesized by us), indomethacin, and pinane thromboxane A2, demonstrated that the Hill coefficients ranged from 30 to 100. 3-(3-Pyridyl)-5-phenylisoxazole, which exhibited maximal anti-aggregatory activity among the synthesized compounds, inhibited neither cyclooxygenase nor thromboxane synthase. The compounds affected the signal transduction pathway at/or posterior to the stage of thromboxane A2 reception.