Effect of a high loading dose of clopidogrel on platelet function in patients undergoing coronary stent placement

Historical lessons in translational medicine: cyclooxygenase inhibition and P2Y12 antagonism

The development of drugs that inhibit platelets has been driven by a combination of clinical insights, fundamental science, and sheer luck. The process has evolved as the days of stumbling on therapeutic gems, such as aspirin, have long passed and have been replaced by an arduous process in which a drug is designed to target a specific protein implicated in a well-characterized pathophysiological process, or so we would like to believe. The development of antiplatelet therapy illustrates the importance of understanding the mechanisms of disease and the pharmacology of the compounds we develop, coupled with careful clinical experimentation and observation and, yes, still, a fair bit of luck.

High on-treatment platelet reactivity and P2Y12 antagonists in clinical trials

Dual antiplatelet therapy with aspirin and clopidogrel in patients undergoing percutaneous coronary intervention (PCI) and in patients with acute coronary syndromes (ACS) has substantially decreased the rate of cardiovascular events. Within the past decade, the variability in pharmacodynamic response as well as the moderate antiplatelet efficacy of clopidogrel has raised major concerns, since high on-clopidogrel platelet reactivity has consistently been associated with increased risk for ischaemic events in PCI patients. The variability in response could be linked to genetic polymorphisms impacting on activity of cytochrome P450 enzymes as well as clinical and demographic variables, but, taken together, factors identified so far can explain only up to approximately 12% of this variability in adenosine diphosphate-induced platelet aggregation on clopidogrel. Regulatory agencies as well as major cardiac societies suggest the use of other anti-platelet medications or alternative dosing strategies for clopidogrel in patients with reduced effectiveness of clopidogrel. This review will focus on the current status of alternate strategies for more sufficient suppression of high platelet reactivity.

Aspirin and platelet adenosine diphosphate receptor antagonists in acute coronary syndromes and percutaneous coronary intervention: role in therapy and strategies to overcome resistance

Platelet activation and aggregation are key components in the cascade of events causing thrombosis following plaque rupture. Antiplatelet therapy is essential in the treatment of patients with acute coronary syndromes (ACS) and for those requiring percutaneous coronary intervention (PCI). Aspirin (acetylsalicylic acid) is a well established antiplatelet therapy and is mandated for secondary prevention of cardiovascular events following ACS. In patients with ACS, the addition of clopidogrel to aspirin is more effective than aspirin alone. For patients undergoing PCI, dual antiplatelet therapy with aspirin and clopidogrel is warranted. Aspirin should be continued indefinitely after PCI. Pretreatment of patients with clopidogrel prior to PCI lowers the incidence of cardiovascular events, yet the optimum timing of drug administration and dose are still being investigated, as is the duration of therapy following PCI. Late-stent thrombosis with drug-eluting stents has pushed the recommendation for duration of clopidogrel therapy up to 1 year and perhaps beyond, in patients without risks for bleeding. The concepts of aspirin and clopidogrel resistance are important clinical questions. No uniform definition exists for aspirin or clopidogrel resistance. Measurements of resistance are often highly variable and do not necessarily correlate with clinical resistance. Noncompliance remains the most prominent mode of resistance. Screening of selected patient populations for resistance or pharmacologic intervention of those patients termed 'resistant' warrants further study.

Impaired bioavailability and antiplatelet effect of high-dose clopidogrel in patients after cardiopulmonary resuscitation (CPR)

PURPOSE

Bioavailability of clopidogrel in the form of crushed tablets administered via nasogastric tube (NGT) has not been established in patients after cardiopulmonary resuscitation. Therefore, we performed a study comparing pharmacokinetic and pharmacodynamic response to high loading dose of clopidogrel in critically ill patients after cardiopulmonary resuscitation (CPR) with patients scheduled for elective coronary angiography with stent implantation.

METHODS

In the NGT group (nine patients, after cardiopulmonary resuscitation, mechanically ventilated, therapeutic hypothermia), clopidogrel was administered in the form of crushed tablets via NGT. Ten patients undergoing elective coronary artery stenting took clopidogrel per os (po) in the form of intact tablets. Pharmacokinetics of clopidogrel was measured with high-performance liquid chromatography (HPLC) before and at 0.5, 1, 6, 12, 24 h after administration of a loading dose of 600 mg. In five patients in each group, antiplatelet effect was measured with thrombelastography (TEG; Platelet Mapping) before and 24 h after administration.

RESULTS

The carboxylic acid metabolite of clopidogrel was detected in all patients in the po group. In eight patients, the maximum concentration was measured in the range of 0.5-1 h after the initial dose. In four patients in the of NGT group, the carboxylic acid metabolite of clopidogrel was undetectable and in the remaining patients was significantly delayed (peak values at 12 h). All patients in the po group reached clinically relevant (>50 %) inhibition of thrombocyte adenosine diphosphate (ADP) receptor after 24 h compared with only two in the NGT group (p = 0.012). There was a close correlation between peak of inactive clopidogrel metabolite plasmatic concentration and inhibition of the ADP receptor (r = 0.79; p < 0.001).

CONCLUSION

The bioavailability of clopidogrel in critically ill patients after cardiopulmonary resuscitation is significantly impaired compared with stable patients. Therefore, other drugs, preferentially administered intravenously, should be considered.

Latest evidence in personalized antiplatelet therapy in patients with acute coronary syndromes undergoing percutaneous coronary intervention

In patients with acute coronary syndromes undergoing percutaneous coronary intervention, the combination of aspirin and clopidogrel, a P2Y12 adenosine diphosphate (ADP) receptor antagonist, is the gold standard of antiplatelet therapy. Two more potent P2Y12 ADP receptor antagonists are now available. Pharmacodynamic studies have revealed a large interindividual variability in the biological response to clopidogrel that is primarily related to variable active metabolite generation, depending on clinical factors, drug-drug interactions, and genetic polymorphisms. Several assays to measure platelet function are available and have revealed a high prevalence of high on-treatment platelet reactivity (HTPR). Patients exhibiting HTPR after a clopidogrel loading dose have a higher risk of thrombotic recurrence after percutaneous coronary intervention. A recent consensus has defined HTPR for the main platelet assays available (using receiver operating characteristic curve analysis) to define the optimal cutoff value for each assay in order to predict thrombotic recurrences. In this article, we present several lines of evidence that suggest a therapeutic window of platelet reactivity inhibition with P2Y12 ADP receptor antagonists. Such a paradigm shift is supported by the results of the Platelet Inhibition and Patient Outcomes (PLATO) trial and the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in Myocardial Infarction (TRITON-TIMI) 38, which showed the superiority of ticagrelor and prasugrel on thrombotic events compared with clopidogrel; however, these 2 medications had an increased bleeding rate. With the results of these trials, in addition to the evidence of a therapeutic window with P2Y12 ADP receptor antagonists, we summarize the potential of platelet reactivity monitoring and pharmacogenomics to tailor therapy.

Perioperative management of antithrombotic therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

This guideline addresses the management of patients who are receiving anticoagulant or antiplatelet therapy and require an elective surgery or procedure.

METHODS

The methods herein follow those discussed in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines. Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines article of this supplement.

RESULTS

In patients requiring vitamin K antagonist (VKA) interruption before surgery, we recommend stopping VKAs 5 days before surgery instead of a shorter time before surgery (Grade 1B). In patients with a mechanical heart valve, atrial fibrillation, or VTE at high risk for thromboembolism, we suggest bridging anticoagulation instead of no bridging during VKA interruption (Grade 2C); in patients at low risk, we suggest no bridging instead of bridging (Grade 2C). In patients who require a dental procedure, we suggest continuing VKAs with an oral prohemostatic agent or stopping VKAs 2 to 3 days before the procedure instead of alternative strategies (Grade 2C). In moderate- to high-risk patients who are receiving acetylsalicylic acid (ASA) and require noncardiac surgery, we suggest continuing ASA around the time of surgery instead of stopping ASA 7 to 10 days before surgery (Grade 2C). In patients with a coronary stent who require surgery, we recommend deferring surgery > 6 weeks after bare-metal stent placement and > 6 months after drug-eluting stent placement instead of undertaking surgery within these time periods (Grade 1C); in patients requiring surgery within 6 weeks of bare-metal stent placement or within 6 months of drug-eluting stent placement, we suggest continuing antiplatelet therapy perioperatively instead of stopping therapy 7 to 10 days before surgery (Grade 2C).

CONCLUSIONS

Perioperative antithrombotic management is based on risk assessment for thromboembolism and bleeding, and recommended approaches aim to simplify patient management and minimize adverse clinical outcomes.

A risk-benefit assessment of prasugrel, clopidogrel, and genotype-guided therapy in patients undergoing percutaneous coronary intervention

The objective of this study was to quantitatively evaluate the clinical benefits and harms of prasugrel, clopidogrel, and a CYP2C19 genotype-guided drug selection strategy for patients with acute coronary syndrome (ACS) and planned percutaneous coronary intervention (PCI). We used decision-analytic techniques to model the risks and benefits of alternative antiplatelet strategies. Sensitivity and scenario analyses were conducted to assess the uncertainty of the results. Prasugrel demonstrated little difference in net benefit as compared with clopidogrel (+0.02 quality-adjusted life-years (QALYs); 95% confidence range (CR), -0.23 to 0.21). The genotype-guided strategy had a 93% probability of greater net benefit as compared with clopidogrel (+0.05 QALYs; 95% CR, -0.02 to 0.11), and 66% probability of greater net benefit as compared with prasugrel (+0.03 QALYs; 95% CR, -0.13 to 0.24). Prasugrel and clopidogrel differ in their risk-benefit profiles but appear to offer similar net benefit on average. Use of patient-specific factors such as CYP2C19 genotype offers promise for developing a personalized medicine approach to antiplatelet treatment regimens.

[Periinterventional antiplatelet therapy: from bench to bedside]

The recruitment and activation of blood platelets initiate ischemic events in patients with coronary artery diseases (myocardial infarction). Moreover, platelet activation and aggregation are key events triggering early and late thrombotic complications (stent thromboses) in patients successfully treated with coronary stent implantation. Hence, the inhibition of the thromboxane A2 synthesis by aspirin and the ADP-receptor pathway by clopidogrel have drastically reduced the risk of ischemic complications following coronary stenting. However, clopidogrel has several inherent limitations, including the high incidence of non- or low-responders and the increased risk of bleeding due to the prolonged persistence of its anti-platelet effect. The latter is of particular concern in patients who require non-deferrable surgery. In recent years, novel anti-platelet substances have been clinically evaluated and are now approved for use in patients. These substances offer several potential advantages over the previous strategies and could pave the way for more individualized anti-platelet regimens. In this review, we give an overview on the available clinical data evaluating the benefits of these novel anti-platelet substances.

The pattern of platelet response to clopidogrel in Iranian patients after percutaneous coronary intervention

Despite certain clinical benefit in using clopidogrel in patients undergoing percutaneous coronary intervention (PCI), some patients do not attain adequate antiplatelet effects. In this study, the authors investigated the response to clopidogrel in Iranian patients after PCI. Patients who were candidates for elective PCI were enrolled in this study. All patients had received aspirin 80 to 325 mg daily for ≥1 week before PCI. Blood samples were taken from patients at baseline, 2 hours after taking a 600-mg loading dose of clopidogrel, and 24 hours and 30 days after stenting. Platelet aggregation was measured by light transmittance aggregometry with adenosine diphosphate (5 and 20 μM) and arachidonic acid (500 and 5000 μg/mL). One hundred twelve patients were included (79 men, 33 women). Maximal and minimal clopidogrel nonresponsiveness occurred at 2 hours (26%) and 48 hours (13%) after taking 600 mg clopidogrel, respectively. Pretreatment platelet reactivity had no effects on posttreatment platelet reactivity. Moreover, clopidogrel responsiveness did not correlate with pretreatment reactivity. Patients' demographic and procedural characteristics had no significant effect on clopidogrel responsiveness. The frequency of clopidogrel nonresponsiveness in this study was similar to other studies. However, clopidogrel required more than 2 hours for induction of its maximal antiplatelet effect in this study.

Thienopyridines and other ADP-receptor antagonists

Platelet P2Y12 receptor inhibition plays a pivotal role in preventing thrombotic vascular events in patients with ACS and in patients undergoing percutaneous coronary intervention (PCI). Among the P2Y12 receptor inhibitors, the group of thienopyridines include ticlopidine, clopidogrel and prasugrel, all of which are orally administered prodrugs leading to irreversible P2Y12 receptor inhibition. Non-thienopyridine derivatives including ticagrelor, cangrelor and elinogrel do not require metabolic activation and lead to a reversible P2Y12 receptor inhibition in contrast to thienopyridines. The extend of platelet inhibition is subject to the administered antiplatelet agent and influenced by individual genetic and clinical factors. Insufficient platelet inhibition, termed high platelet reactivity (HPR) is associated with an increased risk for ischemic events after PCI whereas exceeding platelet inhibition results in an increased bleeding risk. Pharmacologic properties and clinical outcome data differ substantially between the existing P2Y12 receptor inhibitors. Whether individualized antiplatelet treatment incorporating different P2Y12 receptor inhibitors improves patients' clinical outcomes warrants further investigation.

Stent-Assisted Coiling of Wide-Necked Aneurysms in the Setting of Acute Subarachnoid Hemorrhage

BACKGROUND:

Stent-assisted coiling in the setting of subarachnoid hemorrhage remains controversial. Currently, there is a paucity of data regarding the utility of this procedure and the risks of hemorrhagic and ischemic complications.

OBJECTIVE:

To assess the utility of stent-assisted coil embolization and pretreatment with antiplatelet agents in the management of ruptured wide-necked aneurysms.

METHODS:

A retrospective study of 65 patients with ruptured wide-necked aneurysms treated with stent-assisted coiling. Patients with hydrocephalus or a Hunt and Hess grade ≥ III received a ventriculostomy before endovascular intervention. Patients were treated intraoperatively with 600 mg of clopidogrel and maintained on daily doses of 75 mg of clopidogrel and 81 mg of aspirin. The Glasgow outcome scale (GOS) score was recorded at the time of discharge. We identified major bleeding complications secondary to antiplatelet therapy and cases of in-stent thrombosis that required periprocedural thrombolysis.

RESULTS:

Of the aneurysms, 66.2% arose within the anterior circulation; 69.2% of patients presented with hydrocephalus or a Hunt and Hess grade ≥ III and required a ventriculostomy. A good outcome (GOS of 4 or 5) was achieved in 63.1% of patients, and the overall mortality rate was 16.9%. There were 10 (15.38%) major complications associated with bleeding secondary to antiplatelet therapy (5 patients, 7.7%) or intraoperative in-stent thrombosis (5 patients, 7.7%). Three (4.6%) patients had a fatal hemorrhage.

CONCLUSION:

Our findings suggest that stent-assisted coiling and routine treatment with antiplatelet agents is a viable option in the management of ruptured wide-necked aneurysms.

Intracoronary bolus-only compared with intravenous bolus plus infusion of tirofiban application in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention

OBJECTIVES

The aim of this pilot study was to compare intracoronary bolus-only with standard intravenous bolus plus maintenance infusion of tirofiban with respect to improvement in myocardial reperfusion after primary percutaneous coronary intervention (p-PCI).

BACKGROUND

Changes in clinical practice may obviate the need for a maintenance infusion of small molecule glycoprotein IIb/IIIa inhibitors in current practice.

METHODS

Forty-nine patients undergoing p-PCI were randomized to either intracoronary bolus-only (n = 25) or intravenous bolus plus infusion (n = 24) of tirofiban. The primary end point was coronary hemodynamic indices of microvascular perfusion measured 4-5 days after p-PCI. The secondary end points were ST segment resolution at 90 min, the corrected TIMI frame count and myocardial blush grade. At 6 months, echocardiography and technetium-99m single-photon-emission computed tomography were performed.

RESULTS

Microvascular perfusion did not differ significantly between the two treatment groups: index of microvascular resistance (27 ± 13 vs. 35 ± 15 U, P = 0.08) and coronary flow reserve (2.2 ± 0.7 vs. 1.9 ± 0.6, P = 0.25). The corrected TIMI frame counts assessed in the first (P = 0.13) and the second (P = 0.09) catheterization or the myocardial blush grades evaluated immediately (P = 0.23) and 4-5 days after MI (P = 1.00) were not significantly different between the two groups. At 6 months, there was no difference between the two groups in infarct size, left ventricular volumes, or ejection fraction.

CONCLUSIONS

The standard intravenous bolus plus maintenance infusion of tirofiban in p-PCI is not superior to intracoronary bolus-only administration with respect to microvascular perfusion. Further, adequately powered randomized trials are warranted to evaluate the clinical outcomes associated with this strategy.

The onset of inhibition of platelet aggregation with prasugrel compared with clopidogrel loading doses using gatekeeping analysis of integrated clinical pharmacology data

The purpose of this analysis was to determine the time by which a prasugrel 60-mg loading dose (LD) achieved significantly greater inhibition of platelet aggregation (IPA) than the peak IPA after a clopidogrel 300-mg LD or 600-mg LD. Data were pooled from nine studies representing 587 individuals: 274 healthy subjects and 313 patients with stable coronary artery disease. The primary pharmacodynamic measure was IPA using 20 [mu]M adenosine-5'-diphosphate as the agonist. Gatekeeping analysis compared the peak IPA at 4, 6, and 24 hours after a clopidogrel 300-mg or 600-mg LD with IPA at various prior time points backwards after a prasugrel LD until a statistically nonsignificant difference was reached. Prasugrel 60-mg LD produced greater IPA by 30 minutes than the peak IPA after a clopidogrel 300-mg LD (P < 0.0001). Significantly greater IPA was achieved at 1 hour after prasugrel 60-mg LD compared with the peak IPA after 600-mg clopidogrel LD (P < 0.0001), regardless of sex, body weight, or age and as early as 30 minutes in the diabetic subgroup. A prasugrel 60-mg LD produces significantly faster onset and greater IPA compared with a clopidogrel 300-mg LD or 600-mg LD.

Clopidogrel "resistance": where are we now?

Antiplatelet therapy with aspirin and clopidogrel in PCI patients, though effective, is still associated with thrombotic complications. These are multifactorial in origin, but partially attributable to "clopidogrel resistance." However, how best to identify and manage "clopidogrel resistance" remains unclear. Targeting therapeutic changes specifically at those individuals with poor response to clopidogrel is likely to be a solution. A "one size fits all" approach to clopidogrel dosing is probably flawed. This review will explore (1) the definition and mechanisms of clopidogrel resistance, (2) assessment of clopidogrel resistance by (i) platelet function testing and (ii) genetic testing, (3) the management of "clopidogrel resistance," and (4) newer antiplatelet agents, and evolving stent technology. A pubmed literature review was performed using the keywords "clopidogrel", "resistance", "poor response", "adverse events", "platelet function tests", and "genetic tests". In looking at new agents, keywords "prasugrel", "cangrelor", "ticagrelor""Elinogrel", and "P2Y12 receptor antagonists" were used. Third, a search was performed looking at "stent design", "IVUS", "bioabsorbable stents", and "stent apposition". Whilst new P2Y12 receptor antagonists and improved stent technology may reduce thrombotic events in the future, there is still a need for clopidogrel. There is good evidence that poor response to clopidogrel is associated with adverse outcome. Platelet function tests probably provide more clinically useful data than genetic tests, but the question of how best to identify and manage variability in response to clopidogrel demands further research.

Efficacy and safety of abciximab in diabetic patients who underwent percutaneous coronary intervention with thienopyridines loading: a meta-analysis

BACKGROUND

It has been controversial whether abciximab offered additional benefits for diabetic patients who underwent percutaneous coronary intervention (PCI) with thienopyridines loading.

METHODS

MEDLINE, EMBASE, the Cochrane library clinical trials registry, ISI Science Citation Index, ISI Web of Knowledge and China National Knowledge Infrastructure (CNKI) were searched, supplemented with manual-screening for relevant publications. Quantitative meta-analyses were performed to assess differences between abciximab groups and controls with respect to post-PCI risk of major cardiac events (MACEs), angiographic restenosis and bleeding complications.

RESULTS

9 trials were identified, involving 2,607 diabetic patients receiving PCI for coronary artery diseases. Among those patients who underwent elective PCI or primary PCI, pooling results showed that abciximab did not significantly reduce risks of MACEs (for elective-PCI patients: RR(1-month): 0.93, 95% CI: 0.60-1.44; RR(1-year): 0.95, 95% CI: 0.81-1.11; for primary-PCI patients: RR(1-month): 1.05, 95% CI: 0.70-1.57; RR(1-year): 0.98, 95% CI: 0.80-1.21), nor all-cause mortality, re-infarction and angiographic restenosis in either group. The only beneficial effect by abciximab appeared to be a decrease 1-year TLR (target lesion revascularization) risk in elective-PCI patients (RR1-year: 0.83, 95% CI: 0.70-0.99). Moreover, occurrence of minor bleeding complications increased in elective-PCI patients treated with abciximab (RR: 2.94, 95% CI: 1.68-5.13, P<0.001), whereas major bleedings rate was similar (RR: 0.83, 95% CI: 0.27-2.57).

CONCLUSIONS

Concomitant dosing of abciximab and thienopyridines provides no additional benefit among diabetic patients who underwent PCI; this conclusion, though, needs further confirmation in larger studies.

Antiplatelet therapy and vascular disease: an update

Atherosclerosis is a diffuse, systemic disorder of the large and medium-sized arterial vessels, affecting the coronary, cerebral and peripheral circulation. Chronic inflammatory processes are the central pathophysiological mechanism largely driven by lipid accumulation, and provide the substrate for occlusive thrombus formation. The clinical sequelae of acute arterial thrombosis, heart attack and stroke, are the most common causes of morbidity and mortality in the industrialized world. Such acute events are characterized by rupture or erosion of the atherosclerotic plaque leading to acute thrombosis. The atherosclerotic process and associated thrombotic complications are collectively termed atherothrombosis. The platelet is a pivotal mediator of various endothelial, immune, thrombotic and inflammatory responses and therefore a key player in the initiation and progression of atherothrombosis. A robust evidence base supports the clear clinical benefits of antiplatelet agents in the primary and secondary therapy of atherothrombotic disorders. Percutaneous coronary and peripheral interventions have an established central role in the management of atherothrombotic disease and demand a greater understanding of platelet biology. In this article, we provide a clinically orientated overview of the pathophysiology of arterial thrombosis and the evidence supporting the use of the various established antiplatelet therapies, and discuss new and future agents.

Optimizing antiplatelet therapy in acute coronary syndrome and percutaneous coronary intervention

Dual antiplatelet therapy with aspirin and clopidogrel is the standard of care for patients with acute coronary syndrome (ACS) and those undergoing percutaneous coronary intervention (PCI). It is well established that inhibition of platelet aggregation reduces the risk of recurrent thrombotic events and stent thrombosis. However, some patients show a reduced antiplatelet response to standard clopidogrel loading (300 mg) and maintenance (75 mg day(-1)) doses, which has been associated with poorer patient outcomes. Pharmacodynamic and pharmacokinetic studies show that higher-than-standard clopidogrel dosing strategies facilitate more rapid platelet inhibition of a greater intensity as a result of greater plasma concentrations of the clopidogrel active metabolite. Recently completed studies suggest that in patients with ACS undergoing PCI, higher-than-standard clopidogrel dosing regimens provide greater inhibition of platelet function and improved clinical outcomes with a small but significant increase in major bleeding. Newer, more potent antiplatelet agents such as prasugrel and ticagrelor are other alternative strategies that result in more rapid, greater inhibition of platelet function and better outcomes than standard-dose clopidogrel. Whether platelet reactivity-guided therapy or genotyping for cytochrome P450 polymorphisms is useful in managing patients needs to be further defined. Most importantly, early and effective antiplatelet therapy results in the best short- and long-term outcomes for patients with ACS or those undergoing PCI.

Pharmacogenomics of clopidogrel: evidence and perspectives

Clopidogrel has become the mainstay oral antiplatelet regimen to prevent recurrent ischemic events after acute coronary syndromes or stent placement. However, there is marked interindividual variability in the antiplatelet effects of clopidogrel, and a reduced response to this drug may be a risk factor for ischemic complications. Pharmacogenomic analyses, including candidate-gene and genome-wide association studies, have confirmed that genetic polymorphisms in the hepatic cytochrome P450 (CYP) 2C19 dominantly affect the antiplatelet effects of clopidogrel. CYP2C19 reduced-function alleles have been associated with a significant decrease in clopidogrel responsiveness and a higher risk of adverse cardiac events including stent thrombosis, myocardial infarction, and death in several prospective studies, although these effects were not reproduced in a recent large randomized study that included a randomized control group. The US Food and Drug Administration addressed this issue by adding a boxed warning to the clopidogrel label and suggesting that adjusting the clopidogrel dose or using alternative antiplatelet agents should be potentially implemented for high-risk individuals who are identified based on the CYP2C19 genotype. Although it is promising that CYP2C19 genotyping could be used to guide personalized antiplatelet clopidogrel therapy, currently there is insufficient evidence to recommend routine genetic testing. Prospective randomized clinical trials are necessary to validate this pharmacogenomic approach to clopidogrel therapy. In the most recent trial, paraoxonase-1 (PON1) was identified as a crucial new enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite and the clinical activity of clopidogrel. Further studies are needed to investigate the comprehensive influence of a number of different polymorphisms of CYP2C19 and PON1 variant alleles or other genetic variants on clopidogrel in various ethnic populations.

No association of paraoxonase-1 Q192R genotypes with platelet response to clopidogrel and risk of stent thrombosis after coronary stenting

AIMS

In clopidogrel-treated patients undergoing coronary stenting, high on-treatment platelet reactivity was linked to a higher risk of stent thrombosis (ST). Platelet response to clopidogrel is significantly influenced by genetic factors. Recently published findings showed a highly significant impact of a common polymorphism (Q192R) within the paraoxonase-1 (PON1) gene on clopidogrel treatment efficacy but no influence of the CYP2C19*2 genetic variant as previously demonstrated. The aim of this study was to assess the impact of the PON1 Q192R genotype in parallel to that of CYP2C19*2 on the antiplatelet effect of clopidogrel and the risk of ST in clopidogrel-treated patients.

METHODS AND RESULTS

In 1524 patients undergoing percutaneous coronary intervention, ADP-induced platelet aggregation was assessed in relation to PON1 Q192R and CYP2C19*2 genotypes. The clinical impact of genetic variants was investigated by comparing genotype frequencies of both genetic variants in a registry of 127 cases with early ST vs. an early ST-free control cohort (n = 1439). For PON1 Q192R genotypes, platelet aggregation values were similar across all genotype groups (P = 0.65). For CYP2C19*2 genotypes, significantly higher aggregation values were found in CYP2C19 wt/*2 and *2/*2 patients when compared with wt/wt allele carriers (P < 0.0001). Comparing genotype frequencies between ST cases and controls, no differences were observed for PON1 Q192R genotype distributions (P = 0.23), whereas the genotype distribution differed for CYP2C19*2 genotypes (P = 0.019).

CONCLUSION

The PON1 Q192R genotype did not influence platelet response to clopidogrel or the risk of ST in clopidogrel-treated patients, whereas the CYP2C19*2 genotype impacted on both antiplatelet effect of clopidogrel and risk of coronary ST.

Antiplatelet therapy in elderly patients

With remarkable advances of medical care, the aging population is growing rapidly. Cardiovascular disease remains the leading cause of morbidity and mortality in elderly people and therefore antiplatelet therapy has been a mainstay of cardiovascular medicines for reducing and preventing cardiovascular risk in these populations. The benefits of several antiplatelet drugs in the elderly are well documented. However, there are limited data regarding the optimal use of antiplatelet agents considering the risk:benefit ratio in elderly patients, who are more vulnerable to safety issues owing to different pharmacokinetics and pharmacodynamics as compared with young patients. In this article, we review currently available evidence regarding the efficacy and safety of antiplatelet therapy (i.e., aspirin, old and new P2Y12 inhibitors and glycoprotein IIb/IIIa inhibitors) in the elderly for primary and secondary prevention strategies in cardiovascular care.

Ticagrelor: from concept to clinical evaluation

Dual antiplatelet therapy with aspirin and a platelet adenosine diphosphate P2Y12 receptor blocker reduces the risk of major adverse cardiovascular events following percutaneous coronary intervention or an acute coronary syndrome. Clopidogrel is the most widely used P2Y12 receptor blocker, but has suboptimal speed of onset of action and maximal platelet inhibition, as well as variability in the inhibition of platelet aggregation achieved. Therefore, novel P2Y12 receptor blockers have been developed to address these limitations, including prasugrel and ticagrelor. This article describes the pharmacokinetic and pharmacodynamic evaluation of ticagrelor, which has been demonstrated to have significantly faster onset, faster offset, greater maximal inhibition of platelet aggregation and less variability in response compared with clopidogrel. These detailed Phase II data helped guide the design of the large landmark clinical trial Platelet Inhibition and Patient Outcomes (PLATO; n = 18,624 patients with acute coronary syndrome) in which ticagrelor was associated with a 16% relative risk reduction in the primary composite end point of cardiovascular death, myocardial infarction or stroke at 12 months (9.8 vs 11.7%; hazard ratio: 0.84; 95% CI: 0.77–0.92; p < 0.001). Ongoing trials are evaluating the clinical value of individualizing therapy according to on-treatment residual platelet activity, genetic polymorphism (loss-of-function allele status) and by improved safety/efficacy risk stratification.

Low responsiveness to clopidogrel increases risk among CKD patients undergoing coronary intervention

Patients with CKD are at higher risk for major events after percutaneous coronary intervention (PCI) compared with subjects with normal renal function. The aims of this study were to evaluate responsiveness to clopidogrel in patients with CKD and to examine the effect of antiplatelet drug response on post-PCI outcome. We retrospectively evaluated a consecutive cohort of 1567 patients with symptomatic coronary artery disease undergoing PCI, 648 (41%) of whom had stage 3 to 5 CKD. We assessed responsiveness to clopidogrel by ADP-induced platelet aggregation after oral administration of a 600-mg clopidogrel loading dose and 100 mg of aspirin. In a multivariate survival analysis that included 1335 (85%) of the cohort, stage 3 to 5 CKD and low response to clopidogrel were independent predictors of the primary end point (composite of myocardial infarction, ischemic stroke, and death within 1 year). In summary, a low response to clopidogrel might be an additional risk factor for the poorer outcomes in patients with stage 3 to 5 CKD compared with patients with better renal function.

Humanized mouse model of thrombosis is predictive of the clinical efficacy of antiplatelet agents

BACKGROUND

In vivo testing of novel antiplatelet agents requires informative biomarkers. By genetically modifying mouse von Willebrand factor (VWF(R1326H)), we have developed a small animal model that supports human but not mouse platelet-mediated thrombosis. Here, we evaluate the use of this biological platform as a pharmacodynamic biomarker for antithrombotic therapies.

METHODS AND RESULTS

The antithrombotic effects of several αIIbβ3 inhibitors were determined in VWF(R1326H) mutant mice infused with human platelets. Administration of abciximab, eptifibatide, or tirofiban at doses recommended for percutaneous coronary intervention (per 1 kg of body weight) significantly reduced human platelet-mediated thrombus formation in laser-injured arterioles by > 75% (P < 0.001). In contrast, clot size in wild-type control animals remained essentially unchanged (P > 0.05), results consistent with observed species differences in IC₅₀ values obtained by aggregometry. To further demonstrate that our biological platform is unique among standard mouse models, we evaluated the thrombogenic potential of platelets from healthy volunteers before and after clopidogrel therapy. Consistent with the antithrombotic effect of this agent, platelets postdrug administration formed smaller thrombi than cells before therapy and were less responsive to ADP-induced aggregation (P < 0.001).

CONCLUSIONS

The ability of αIIbβ3 and P2Y₁₂ inhibitors to limit human platelet clot formation at doses recommended by the American College of Cardiology/American Heart Association suggests that VWF(R1326H) mutant mice can serve as both a pharmacodynamic and a functional response biomarker, attributes essential for not only expediting drug development but also designing clinical studies.

Comparison of 600 versus 300-mg Clopidogrel loading dose in patients with ST-segment elevation myocardial infarction undergoing primary coronary angioplasty

The aim of the present study was to compare 600- and 300-mg clopidogrel loading doses in patients with ST-segment elevation myocardial infarctions who underwent primary percutaneous coronary intervention (PCI). Two hundred fifty-five consecutive patients presenting with ST-segment elevation myocardial infarctions who underwent primary PCI were enrolled. Patients were divided into 2 groups on the basis of the loading dose of clopidogrel received before the procedure (600 vs 300 mg). Procedural angiographic end points and 1-year major adverse cardiac events were compared between the 2 groups. Major adverse cardiac events were defined as death, nonfatal myocardial infarction, and target vessel revascularization. There were no significant differences in baseline clinical and angiographic features between the 2 groups: 157 (62%) in the clopidogrel 600 mg group and 98 (38%) in the 300 mg group. Patients receiving 600-mg loading dose of clopidogrel showed a significantly lower incidence of post-PCI myocardial blush grade 0 or 1 (odds ratio 0.64, 95% confidence interval 0.43 to 0.96, p = 0.03) and significantly less common no-reflow phenomenon (odds ratio 0.38, 95% confidence interval 0.15 to 0.98, p = 0.04) compared to those in the 300-mg group. Propensity-adjusted Cox analysis showed significantly higher survival free of major adverse cardiac events in patients receiving 600-mg loading dose of clopidogrel compared to those receiving the lower dose (hazard ratio 0.57, 95% confidence interval 0.33 to 0.98, p = 0.04). In conclusion, a 600-mg loading dose of clopidogrel is associated with improvements in procedural angiographic end points and 1-year clinical outcomes in patients with ST-segment elevation myocardial infarction who undergo primary PCI compared to a 300-mg dose.

A review of the use of common antiplatelet agents in orthopaedic practice

Antiplatelet agents are widely prescribed for the primary and secondary prevention of cardiovascular events. A common clinical problem facing orthopaedic and trauma surgeons is how to manage patients receiving these agents who require surgery, either electively or following trauma. The dilemma is to balance the risk of increased blood loss if the antiplatelet agents are continued peri-operatively against the risk of coronary artery/stent thrombosis and/or other vascular event if the drugs are stopped. The traditional approach of stopping these medications up to two weeks before surgery appears to pose significant danger to patients and may require review. This paper covers the important aspects regarding the two most commonly prescribed antiplatelet agents, aspirin and clopidogrel.

Double-dose versus standard-dose clopidogrel and high-dose versus low-dose aspirin in individuals undergoing percutaneous coronary intervention for acute coronary syndromes (CURRENT-OASIS 7): a randomised factorial trial

BACKGROUND

Clopidogrel and aspirin are the most commonly used antiplatelet therapies for percutaneous coronary intervention (PCI). We assessed the effect of various clopidogrel and aspirin regimens in prevention of major cardiovascular events and stent thrombosis in patients undergoing PCI.

METHODS

The CURRENT-OASIS 7 trial was undertaken in 597 centres in 39 countries. 25,086 individuals with acute coronary syndromes and intended early PCI were randomly assigned to double-dose (600 mg on day 1, 150 mg on days 2-7, then 75 mg daily) versus standard-dose (300 mg on day 1 then 75 mg daily) clopidogrel, and high-dose (300-325 mg daily) versus low-dose (75-100 mg daily) aspirin. Randomisation was done with a 24 h computerised central automated voice response system. The clopidogrel dose comparison was double-blind and the aspirin dose comparison was open label with blinded assessment of outcomes. This prespecified analysis is of the 17,263 individuals who underwent PCI. The primary outcome was cardiovascular death, myocardial infarction, or stroke at 30 days. Analyses were by intention to treat, adjusted for propensity to undergo PCI. This trial is registered with ClinicalTrials.gov, number NCT00335452.

FINDINGS

8560 patients were assigned to double-dose and 8703 to standard-dose clopidogrel (8558 and 8702 completed 30-day follow-up, respectively), and 8624 to high-dose and 8639 to low-dose aspirin (8622 and 8638 completed 30-day follow-up, respectively). Compared with the standard dose, double-dose clopidogrel reduced the rate of the primary outcome (330 events [3·9%] vs 392 events [4·5%]; adjusted hazard ratio 0·86, 95% CI 0·74-0·99, p=0·039) and definite stent thrombosis (58 [0·7%] vs 111 [1·3%]; 0·54 [0·39-0·74], p=0·0001). High-dose and low-dose aspirin did not differ for the primary outcome (356 [4·1%] vs 366 [4·2%]; 0·98, 0·84-1·13, p=0·76). Major bleeding was more common with double-dose than with standard-dose clopidogrel (139 [1·6%] vs 99 [1·1%]; 1·41, 1·09-1·83, p=0·009) and did not differ between high-dose and low-dose aspirin (128 [1·5%] vs 110 [1·3%]; 1·18, 0·92-1·53, p=0·20).

INTERPRETATION

In patients undergoing PCI for acute coronary syndromes, a 7-day double-dose clopidogrel regimen was associated with a reduction in cardiovascular events and stent thrombosis compared with the standard dose. Efficacy and safety did not differ between high-dose and low-dose aspirin. A double-dose clopidogrel regimen can be considered for all patients with acute coronary syndromes treated with an early invasive strategy and intended early PCI.

FUNDING

Sanofi-Aventis and Bristol-Myers Squibb.

Prasugrel as antiplatelet therapy in patients with acute coronary syndromes or undergoing percutaneous coronary intervention

The authors provide information on prasugrel, compare and contrast it with clopidogrel, and review the use of prasugrel in patients who require an antiplatelet agent.

Effectiveness of in-laboratory high-dose clopidogrel loading versus routine pre-load in patients undergoing percutaneous coronary intervention: results of the ARMYDA-5 PRELOAD (Antiplatelet therapy for Reduction of MYocardial Damage during Angioplasty) randomized trial

OBJECTIVES

This study sought to evaluate safety and effectiveness of in-laboratory (in-lab) 600-mg clopidogrel loading pre-percutaneous coronary intervention (PCI) versus routine 6-h pre-load.

BACKGROUND

Clopidogrel pre-treatment significantly improves outcome in patients undergoing PCI; however, efficacy of an in-lab loading strategy before PCI after coronary angiography versus routine pre-load has not been fully characterized.

METHODS

A total of 409 patients (39% with acute coronary syndrome) were randomized to receive a 600-mg clopidogrel loading dose 4 to 8 h before PCI (pre-load group, n = 204) or a 600-mg loading dose given in the catheterization lab after coronary angiography, but prior to PCI (in-lab group, n = 205). Primary end point was 30-day incidence of major adverse cardiac events: cardiac death, myocardial infarction (MI), or unplanned target vessel revascularization.

RESULTS

There was no significant difference in primary end point between the 2 randomization arms (8.8% in-lab vs. 10.3% pre-load; p = 0.72); this was mainly driven by periprocedural MI (8.8% vs. 9.3%, p = 0.99). No increased risk of bleeding or vascular complications was observed in the pre-load arm (5.4% vs. 7.8%; p = 0.42). As determined by the VerifyNow assay (Accumetrics, San Diego, California), patients in the in-lab group showed higher platelet reactivity during PCI and 2 h after intervention versus those in the pre-load arm (p < or = 0.043).

CONCLUSIONS

ARMYDA-5 PRELOAD (Antiplatelet therapy for Reduction of MYocardial Damage during Angioplasty) trial indicates that a strategy of 600-mg in-lab clopidogrel load pre-PCI may have similar clinical outcomes as routine 4- to 8-h pre-load. Thus, when indicated, in-lab clopidogrel administration can be a safe alternative to routine pre-treatment given before knowing patients' coronary anatomy.

Dose comparisons of clopidogrel and aspirin in acute coronary syndromes

BACKGROUND

Clopidogrel and aspirin are widely used for patients with acute coronary syndromes and those undergoing percutaneous coronary intervention (PCI). However, evidence-based guidelines for dosing have not been established for either agent.

METHODS

We randomly assigned, in a 2-by-2 factorial design, 25,086 patients with an acute coronary syndrome who were referred for an invasive strategy to either double-dose clopidogrel (a 600-mg loading dose on day 1, followed by 150 mg daily for 6 days and 75 mg daily thereafter) or standard-dose clopidogrel (a 300-mg loading dose and 75 mg daily thereafter) and either higher-dose aspirin (300 to 325 mg daily) or lower-dose aspirin (75 to 100 mg daily). The primary outcome was cardiovascular death, myocardial infarction, or stroke at 30 days.

RESULTS

The primary outcome occurred in 4.2% of patients assigned to double-dose clopidogrel as compared with 4.4% assigned to standard-dose clopidogrel (hazard ratio, 0.94; 95% confidence interval [CI], 0.83 to 1.06; P=0.30). Major bleeding occurred in 2.5% of patients in the double-dose group and in 2.0% in the standard-dose group (hazard ratio, 1.24; 95% CI, 1.05 to 1.46; P=0.01). Double-dose clopidogrel was associated with a significant reduction in the secondary outcome of stent thrombosis among the 17,263 patients who underwent PCI (1.6% vs. 2.3%; hazard ratio, 0.68; 95% CI, 0.55 to 0.85; P=0.001). There was no significant difference between higher-dose and lower-dose aspirin with respect to the primary outcome (4.2% vs. 4.4%; hazard ratio, 0.97; 95% CI, 0.86 to 1.09; P=0.61) or major bleeding (2.3% vs. 2.3%; hazard ratio, 0.99; 95% CI, 0.84 to 1.17; P=0.90).

CONCLUSIONS

In patients with an acute coronary syndrome who were referred for an invasive strategy, there was no significant difference between a 7-day, double-dose clopidogrel regimen and the standard-dose regimen, or between higher-dose aspirin and lower-dose aspirin, with respect to the primary outcome of cardiovascular death, myocardial infarction, or stroke. (Funded by Sanofi-Aventis and Bristol-Myers Squibb; ClinicalTrials.gov number, NCT00335452.)

ISAR--a story of trials with impact on practice

Since its inception approximately 15 years ago, the ISAResearch group has completed more than 40 randomized controlled trials (RCT) in the field of interventional cardiology, including more than 40,000 patients. Three main principles have characterized the ISAR trials: first, simplicity: 1 question 1 answer; second, a focus on issues that are relevant for practice at the given moment and third, a strong spirit of performing industry-independent studies. The seamless integration of clinical trials into everyday practice and a stringent study discipline allowed inclusion of more than 90% of the patients in 1 of the device or drug trials, the prerequisite for fast recruitment and evaluation of an all-comers population. Moreover, the early setup and maintenance of a comprehensive database with routine follow-up of all patients undergoing percutaneous coronary intervention made it possible to build up a large registry to answer questions beyond clinical trials. Finally, the close collaboration with basic research working groups within the department has triggered new innovations and facilitated translational research from bench to bedside.

Oral antiplatelet therapy after acute coronary syndrome and percutaneous coronary intervention: balancing efficacy and bleeding risk

PURPOSE

The benefits and risk of bleeding associated with oral antiplatelet agents used for acute coronary syndrome (ACS) or in patients who have undergone percutaneous coronary intervention (PCI) are discussed.

SUMMARY

Over the past decade, significant advances have been made with the use of oral antiplatelet agents in ACS patients and in those undergoing PCI and stenting. Dual antiplatelet therapy with clopidogrel and aspirin has been considered the gold standard for reducing cardiovascular events in these patients. However, use of clopidogrel has limitations, including variable patient response. These limitations can affect patient outcomes achieved with clopidogrel, leading to concerns regarding its use. Subsequently, more potent oral antiplatelet agents have been developed, including prasugrel and ticagrelor. Prasugrel is an oral thienopyridine with greater potency and less antiplatelet variability than clopidogrel. Ticagrelor, another oral antiplatelet agent that has shown greater platelet inhibition than clopidogrel, is currently under investigation. Although a greater reduction in ischemic events has been observed with dual antiplatelet therapy and the use of newer oral antiplatelet agents, there is also a progressive increase in the risk of major bleeding. Treatment decisions should be based on current practice guidelines, as well as individualized patient risk and benefit analyses.

CONCLUSION

Knowledge of the benefits and bleeding risks associated with oral antiplatelet agents, as well as guideline recommendations, can help health care providers make informed decisions regarding the most appropriate therapy for patients after ACS and PCI.

Platelet response to clopidogrel and restenosis in patients treated predominantly with drug-eluting stents

BACKGROUND

Preclinical studies suggest a relationship between early thrombotic response after vascular injury and later development of restenosis. The aim of this study was to assess the impact of platelet response to clopidogrel on the risk of restenosis after drug-eluting stenting (DES).

METHODS

A total of 1,608 consecutive patients were previously enrolled in a study on the relation between platelet reactivity and outcomes after DES. All patients received a loading dose of 600 mg clopidogrel. Blood samples for the assessment of adenosine diphosphate-induced platelet aggregation with multiple electrode platelet aggregometry were drawn directly before percutaneous coronary intervention. Clopidogrel low response was defined as upper quintile of multiple electrode platelet aggregometry measurements. Accordingly, 323 patients (20%) were considered as low and 1,285 (80%) as normal responders. Primary end point of the present study was target lesion revascularization at 1 year. Secondary end points included binary angiographic restenosis and late lumen loss at 6- to 8-month angiography.

RESULTS

Target lesion revascularization rates were comparable in both groups (10.9% vs 9.5%, hazard rate [HR] 1.2, 95% CI 0.8-1.7, P = .441). Follow-up angiography revealed no difference in binary angiographic restenosis (13.9% vs 15.9%, P = .445) and late lumen loss (0.32 +/- 0.64 vs 0.35 +/- 0.63 mm, P = .477). Low responders had significantly more stent thromboses (2.5% vs 0.5%, HR 5.4, 95% CI 1.9-15.6, P = .002), Q wave myocardial infarctions (2.5% vs 0.6%, HR 4.0, 95% CI 1.5-10.7, P = .005), and ischemic strokes (1.3% vs 0.2%, HR 5.4, 95% CI 1.2-24.0, P = .028) at 1 year.

CONCLUSION

Low platelet responsiveness to clopidogrel, a known predictor of thrombotic complications, does not have a significant impact on restenosis after DES.