Frequency of nonresponse antiplatelet activity of clopidogrel during pretreatment for cardiac catheterization

Trends in Dual Antiplatelet Therapy Use for Neurointerventional Procedures for the Management of Intracranial Aneurysms

The use of periprocedural dual antiplatelet therapy (DAPT) has significantly evolved along with innovations in the endovascular management of intracranial aneurysms. Historically, aspirin and clopidogrel have been the most commonly employed regimen due to its safety and efficacy. However, recent studies highlight the importance of tailoring DAPT regimens to individual patient characteristics which may affect clopidogrel metabolism, such as genetic polymorphisms. In the present report, a systematic review of the literature was performed to determine optimal antiplatelet use with flow diverting stents, intracranial stents, intrasaccular devices, and stent-assisted coiling. Studies were analyzed for the number of aneurysms treated, DAPT regimen, and any thromboembolic complications. Based on inclusion criteria, 368 studies were selected, which revealed the increasing popularity of alternative DAPT regimens with the aforementioned devices. Thromboembolic or hemorrhagic complications associated with antiplatelet medications were similar across all medications. DAPT with ticagrelor, tirofiban, or prasugrel are effective and safe alternatives to clopidogrel and do not require enzymatic activation. Further clinical trials are needed to evaluate different antiplatelet regimens with various devices to establish highest-level evidence-based guidelines and recommendations.

Novel use of cangrelor in pediatrics: A pilot cohort study demonstrating use in ventricular assist devices

Thromboembolic events and bleeding are major sources of morbidity among pediatric patients supported on a ventricular assist device (VAD). Pharmacokinetics and pharmacodynamics of enteral antiplatelet agents are affected and variable due to erratic enteral absorption in end-stage heart failure and VAD circulation. Additionally, 20%-40% of the population are poor metabolizers of clopidogrel, a prodrug, making cangrelor an alternative when antiplatelet therapy is crucial. Cangrelor has been used effectively and safely for short durations in adults during percutaneous coronary interventions, but the use of cangrelor is still under investigation in pediatrics. This case series utilized cangrelor, a novel short-acting, reversible, intravenous P2Y₁₂ platelet inhibitor in managing pediatric patients supported with a VAD. We performed a retrospective, single-center review of patients admitted to a tertiary medical center with end-stage heart failure requiring mechanical circulatory support and concomitant cangrelor administration between January 2019 and March 2020. Platelet function testing, cangrelor dose, bleeding complications, thromboembolic events, and frequency of circuit interventions during the use of cangrelor were recorded. Optimal platelet reactivity, defined as P2Y₁₂ < 180 platelet reaction units (PRU), was measured with serial point-of-care testing (VerifyNow). Seven patients, median age of 4.9 years, met the above criteria. Three patients had a diagnosis of complex congenital heart disease. Four patients had dilated or restrictive cardiomyopathy. All patients were on continuous flow VADs. The median VAD duration was 84.5 days (IQR 61.5-103). The median duration on cangrelor was 43 days (IQR 8-70). The median cangrelor dose to reach the therapeutic threshold was 0.75 μg/kg/min with the mean P2Y₁₂ , while on cangrelor of 164.75 PRU. Bleeding complications included mild gastrointestinal bleeding and hematuria. There was one patient with pump thrombosis requiring intervention. There were no cerebrovascular events while on cangrelor. We report the first successful long-term use of cangrelor in pediatric patients. The reversibility and short half-life of cangrelor make it a feasible antiplatelet agent in selected patients. This data supports the use of cangrelor in children as a viable antiplatelet option; with minimal bleeding complications and no cerebrovascular events demonstrated in this cohort.

Prevalence of poor biological response to clopidogrel

The existence of poor biological response to clopidogrel has been shown in some patients. Despite the increasing number of studies, this phenomenon remains difficult to quantify. We performed a systematic review to estimate the prevalence of poor biological response to clopidogrel and investigate the factors known to modulate this. An exhaustive search was performed. Altogether 171 publications were identified, providing data for a total of 45,664 subjects. The estimated prevalence of poor biological response to clopidogrel ranged from 15.9% to 49.5% according to the platelet function assay employed. The assays most frequently used were light transmittance aggregometry (LTA), the vasodilator-stimulated phosphoprotein (VASP) assay and the Verify -now® assay. For all these assays, higher cut-off values were associated with a lower prevalence of poor biological response to clopidogrel. However, when choosing a fixed cut-off point for each assay, the prevalence of poor biological response to clopidogrel was highly variable suggesting that other factors could modulate poor biological response to clopidogrel. Finally, none of the studied factors could apparently explain the variability of poor biological response to clopidogrel. This meta-analysis shows that the prevalence of poor biological response depends on the assay employed, the cut-off value and on various unidentified additional factors.

Comparison of current platelet functional tests for the assessment of aspirin and clopidogrel response

The two most widely used antiplatelet drugs in the world are aspirin and clopidogrel. However, some patients on aspirin and/or clopidogrel therapy do not respond appropriately to either aspirin or clopidogrel. This phenomenon is usually called “aspirin/clopidogrel resistance”. Several platelet function tests have been used in various studies for the assessment of aspirin and clopidogrel resistance in healthy individuals and patients admitted in cardiology departments. An accurate assessment of platelet response to aspirin/clopidogrel could benefit patients by proposing tailored-antiplatelet therapy based on test results. However, there is a clear lack of standardisation of such techniques and their analytical variability may induce misinterpretation. After a quick report of the mechanisms responsible for aspirin/clopidogrel resistance, we describe the pre-analytical aspects and the analytical performances of current platelet function tests (Light-transmission aggregometry, whole-blood aggregometry, VerifyNow®, Platelet Function Analyzer®, thromboelastography, VASP assay) that are used for the assessment of aspirin/clopidogrel resistance in clinical studies. Considering the different variables that have to be taken into account with each of the platelet function tests, a particular attention should be paid when interpreting results.

Feline Cardiogenic Arterial Thromboembolism: Prevention and Therapy

Feline cardiogenic arterial thromboembolism (CATE) is a devastating disease whereby 33% of cats survive their initial event, although approximately 50% of mortality is from euthanasia. Short-term management focuses on inducing a hypocoagulable state, improving blood flow, and providing supportive care. Ideally, all cats should be given 72 hours of treatment to determine the acute clinical course. Preventive protocols include antiplatelet and/or anticoagulant drugs, with the only prospective clinical trial demonstrating that clopidogrel is superior to aspirin with a lower CATE recurrence rate and longer time to recurrent CATE. Newer anticoagulant drugs hold great promise in the future of managing this disease.

[Prevalence and prognosis of aspirin resistance in critical limb ischemia patients]

OBJECTIVES

To assess the prevalence and the association between aspirin resistance in critical limb ischemia patients using the VerifyNow^® bed-side platelet test, and occurrence of cardiovascular morbidity and/or death at one year.

MATERIALS AND METHODS

National multicenter prospective observational study related to COPART II centers. From 2010 through 2014, 64 subjects hospitalized for critical limb ischemia and already treated by aspirin before the VerifyNow^® test were included. A VerifyNow^® test>550 ARU was defined as aspirin resistance. Critical limb ischemia was defined according to the TASC I criteria. The primary outcome was a composite including death, acute coronary syndrome, stroke and major amputation during the one-year follow-up period.

RESULTS

In all, 9/64 patients were aspirin resistant, the status was confirmed in one case. The prevalence of aspirin resistance was 14.06%. There was no significant difference between aspirin resistant and aspirin non-resistant groups in terms of cardiovascular history and glycemia status. Neither was there significant difference between the two groups in terms of survival.

CONCLUSION

Aspirin resistance was not predictive of poorer survival in critical limb ischemia patients. However, our population was limited. Considering that a clear definition of aspirin resistance and standardized diagnostic tests are lacking, complementary studies might be useful.

Oral antiplatelet therapy and platelet inhibition: An experience from a tertiary care center

AIMS AND OBJECTIVES

Although clopidogrel combined with aspirin is the most commonly used dual drug combination to avert thrombotic events in patients with coronary artery disease, the poor responsiveness to clopidogrel remains a concern. The objective of the current study is to assess the extent of resistance to clopidogrel, prasugrel, and ticagrelor in a real life set of patients with coronary artery disease who underwent percutaneous coronary intervention (PCI).

MATERIALS AND METHODS

A total of 539 patients, who underwent PCI and were on aspirin and on any of the three drugs, namely, clopidogrel, prasugrel and ticagrelor, were followed up regularly in the outpatient department. After 24h of initiation of antiplatelet medication, response to the treatment in all the patients was assessed using thrombelastography. The average percentage platelet inhibition was assessed along with the resistance and sensitivity to the drug in each patient. Sensitivity and resistance to the specific drug was defined as >50% and <50% of mean platelet inhibition, respectively.

RESULTS

About 99.15% of the patients treated with ticagrelor were sensitive to the drug and the difference between ticagrelor, clopidogrel, and prasugrel groups for sensitivity was significant with a p value of 0.00001, in favor of ticagrelor. It was also found that ticagrelor was significantly (p value of 0.001) associated with least resistance as compared with the other drugs assessed in the study.

CONCLUSIONS

Use of ticagrelor as dual therapy along with aspirin in patients with coronary artery disease (CAD) and undergoing PCI was associated with a significantly higher mean percentage platelet inhibition, higher sensitivity, and lower resistance as compared with the usage of clopidogrel or prasugrel.

Point-of-Care Platelet Function Testing

Cardiopulmonary bypass has unpredictably deleterious effects on platelet function. Patients with cardiovascular disease have treatments aimed at reducing platelet aggregation and are at risk of excessive bleeding during surgery. Transfusion of blood products, particularly platelets, probably causes increased morbidity and mortality. Conversely, patients with excessive platelet aggregation are at risk of thrombotic complications—undesirable outcomes in the context of myocardial revascularization and prevention of stroke. Platelet function is difficult to monitor. Laboratory tests take time, and the results are not immediately available. Point-of-care (POC) testing of platelet function should facilitate the clinical management of bleeding patients by rationalizing platelet transfusion and avoiding unnecessary transfusion. Furthermore, POC platelet function could alert the clinician to risks of excessive platelet activation and measure the efficacy of antiplatelet therapy. This article outlines some of the POC platelet function monitors available as well as their potential applications.

Clopidogrel Resistance: Myth or Reality?

Platelets have a central role in the development of arterial thrombosis and subsequent cardiovascular events. An appreciation of this complex process has made antiplatelet therapy the cornerstone of cardiovascular disease management. Dual antiplatelet therapy with aspirin and clopidogrel has been approved for the secondary prevention of cardiovascular events and is currently part of the postpercutaneous coronary intervention treatment regimen. However, subacute stent thrombosis continues to occur in 1% to 2% of patients despite dual antiplatelet therapy. Studies have shown interindividual variations in response to clopidogrel, where a cohort of patients seems to be resistant to the antithrombotic effects of clopidogrel. Furthermore, there is an apparent link between clopidogrel resistance and clinical outcomes. Currently, there is neither a universally accepted definition of clopidogrel resistance nor an agreement on the phenomenon's mechanism. This review highlights the origins of clopidogrel resistance, the current problems that exist with its definition, and discusses the future implications and relevant challenges it poses for the clinician.

Successful Prasugrel Therapy for Recurrent Left Main Stent Thrombosis in a Clopidogrel Hyporesponder

Stent thrombosis is a life-threatening sequela of drug-eluting stent implantation. Dual antiplatelet therapy with aspirin and thienopyridine is typically used to prevent this catastrophic event. In terms of stent thrombosis, the major concern is the variable response of patients to clopidogrel, and this has raised interest in new antiplatelet agents. We present the case of a 64-year-old woman whom we successfully treated with prasugrel after she had repeated episodes of stent thrombosis caused by a poor response to clopidogrel. This case highlights the potential role of new antiplatelet agents for patients who are undergoing drug-eluting stent implantation.

Dual antiplatelet therapy tailored on platelet function test after coronary stent implantation: a real-world experience

Patients' response to dual antiplatelet therapy (DAPT) is subject to variations and its monitoring allows to individualize this therapy. In this study, we evaluated if a strategy of tailored DAPT after platelet function testing could reduce high on-treatment platelet reactivity (HPR) and improve outcome of patients treated with stent implantation. In 257 patients undergoing percutaneous angioplasty, platelet function was measured by light transmittance aggregometry (LTA) using 10 µM/L adenosine-diphosphate (ADP) and 1 mM arachidonic acid (AA) as agonists. Patients with HPR by ADP (≥70%) were switched to double-dose clopidogrel, ticlopidine, prasugrel or ticagrelor; in patients with HPR by AA (≥20%) acetylsalicylic acid dose was increased if not contraindicated. Platelet function analysis was repeated 48 hours after therapy variation. At 20-month follow-up major adverse cardiovascular events (MACE) and bleedings were assessed. HPR was detected in 97/257 (37.7%) patients: 69/257 (26.8%) had HPR by ADP and 71/257 (27.6%) had HPR by AA. In patients with HPR by ADP or by AA, tailored DAPT determined a significant reduction in residual platelet reactivity. No significant difference in MACE or bleeding occurrence was documented in HPR patients treated with tailored DAPT vs. those without HPR. HPR patients treated with tailored DAPT had significant lower follow-up MACE and deaths vs. 139 HPR patients not switched, even after propensity score analysis. These results suggest that a DAPT tailored on platelet testing can improve antiplatelet response in HPR patients, possibly reducing their thrombotic events to a level similar to non-HPR patients, without increasing the risk of bleeding.

Effects of cytochrome P450 2C19 and paraoxonase 1 polymorphisms on antiplatelet response to clopidogrel therapy in patients with coronary artery disease

Clopidogrel is an antiplatelet prodrug that is recommended to reduce the risk of recurrent thrombosis in coronary artery disease (CAD) patients. Paraoxonase 1 (PON1) is suggested to be a rate-limiting enzyme in the conversion of 2-oxo-clopidogrel to active thiol metabolite with inconsistent results. Here, we sought to determine the associations of CYP2C19 and PON1 gene polymorphisms with clopidogrel response and their role in ADP-induced platelet aggregation. Clopidogrel response and platelet aggregation were determined using Multiplate aggregometer in 211 patients with established CAD who received 75 mg clopidogrel and 75–325 mg aspirin daily for at least 14 days. Polymorphisms in CYP2C19 and PON1 were genotyped and tested for association with clopidogrel resistance. Linkage disequilibrium (LD) and their epistatic interaction effects on ADP-induced platelet aggregation were analysed. The prevalence of clopidogrel resistance in this population was approximately 33.2% (n = 70). The frequencies of CYP2C19*2 and *3 were significantly higher in non-responder than those in responders. After adjusting for established risk factors, CYP2C19*2 and *3 alleles independently increased the risk of clopidogrel resistance with adjusted ORs 2.94 (95%CI, 1.65–5.26; p<0.001) and 11.26 (95%CI, 2.47–51.41; p = 0.002, respectively). Patients with *2 or *3 allele and combined with smoking, diabetes and increased platelet count had markedly increased risk of clopidogrel resistance. No association was observed between PON1 Q192R and clopidogrel resistance (adjusted OR = 1.13, 95%CI, 0.70–1.82; p = 0.622). Significantly higher platelet aggregation values were found in CYP2C19*2 and *3 patients when compared with *1/*1 allele carriers (p = 1.98×10⁻⁶). For PON1 Q192R genotypes, aggregation values were similar across all genotype groups (p = 0.359). There was no evidence of gene-gene interaction or LD between CYP2C19 and PON1 polymorphisms on ADP-induced platelet aggregation. Our findings indicated that only CYP2C19*2 and *3 alleles had an influence on clopidogrel resistance. The risk of clopidogrel resistance increased further with smoking, diabetes, and increased platelet count.

Gene polymorphism of cytochrome P450 2C19*2 and clopidogrel resistance reflected by platelet function assays: a meta-analysis

BACKGROUND

The relationship between CYP2C19*2 gene polymorphism and clopidogrel resistance reflected by platelet function assays has been studied extensively in the past several years, while no clear conclusion can be drawn from the previous studies. To explore a more precise estimation of the relationship, a meta-analysis was conducted in the present study.

METHODS

The relevant studies were identified by searching PubMed, EMBASE, the Web of Science, Cochrane Collaboration Database, Chinese National Knowledge Infrastructure (CNKI), Wanfang Database, and China Biological Medicine (CBM) up to February, 2014. The meta-analysis was performed by the STATA 11.

RESULTS

Eight studies with a total of 2,331 subjects, including 1,066 patients with clopidogrel resistance and 1,265 patients without clopidogrel resistance were included. The pooled analysis showed that CYP2C19*2 gene polymorphism was probably associated with clopidogrel resistance (OR (95% CI): GA vs. GG: 2.10 (1.74-2.53); AA vs. GG: 3.05 (2.10-4.45); dominant model: 2.22 (1.85-2.65); recessive model: 2.33 (1.62-3.36)). No statistically significant difference was found in the analysis of the three subgroups. The statistical stability and reliability was also demonstrated by the sensitivity analysis and publication bias outcomes.

CONCLUSION

The meta-analysis suggests that CYP2C19*2 gene polymorphism may be associated with clopidogrel resistance.

Prevalence of CYP2C19 variant alleles and pharmacodynamic variability of aspirin and clopidogrel in Native Americans

BACKGROUND

The prevalence of variant alleles of the CYP2C19 gene has been determined for most population groups, but not Native Americans. Furthermore, the overall effectiveness of clopidogrel and aspirin has not been well studied in Native Americans, although this group has high mortality rates for cardiovascular disease and diabetes.

METHODS

We recruited 50 volunteers from the Oglala Sioux Tribe with coronary artery disease taking aspirin and clopidogrel. Whole blood was collected for analysis using the VerifyNow P2Y12 and aspirin tests. Samples from the coronary artery disease patients and 50 additional tribal volunteers (n = 100 total) were genotyped for CYP2C19 variants *2, *3, and *17.

RESULTS

The allele frequencies for CYP2C19*2 and CYP2C19*17 in the population group were 11% (95% CI 7%-16%) and 9% (95% CI 5%-13%), respectively. No subjects carried the CYP2C19*3 allele. The median PRU (P2Y12 reaction units) in the population group was 194 with wide variability (range 29-400). There was no significant effect of genotype on platelet aggregation as measured by the VerifyNow P2Y12 test (P = .77). The median ARU (aspirin reaction units) for the group was 437 (range 350-659), and 73% had aspirin reaction unit values <550.

CONCLUSIONS

The prevalence of variant CYP2C19 alleles is low in Native Americans of the Oglala Sioux Tribe compared with certain HapMap populations. The variable response to aspirin and clopidogrel in the Oglala Sioux Tribe is consistent with reported values for other groups as measured by the VerifyNow assay (Accumetrics, San Diego, CA).

A comparison of INNOVANCE® PFA P2Y and VerifyNow P2Y12 assay for the assessment of clopidogrel resistance in patients undergoing percutaneous coronary intervention

INTRODUCTION

VerifyNow P2Y12 is commonly used to measure responsiveness to clopidogrel. We sought to compare the results obtained from novel INNOVANCE® PFA P2Y and VerifyNow P2Y12 assay to assess the clopidogrel resistance in patients undergoing percutaneous coronary intervention.

METHODS

A total of 255 patients undergoing percutaneous coronary intervention, preliminarily treated with 100 mg/day of aspirin followed by coadministration of clopidogrel (loading dose, 600 mg; maintenance dose, 75 mg/day), were enrolled in this study. Platelet aggregation was measured by INNOVANCE® PFA P2Y and VerifyNow P2Y12.

RESULTS

INNOVANCE® PFA P2Y and VerifyNow P2Y12 assay showed moderate correlations with INNOVANCE® PFA P2Y vs. VerifyNow%inhibition: r = 0.412, P < 0.0001; INNOVANCE® PFA P2Yvs.VerifyNow P2Y12 reaction units (PRU): r = -0.402, P < 0.0001. The agreement between INNOVANCE® PFA P2Y and VerifyNow%inhibition was 85% and that of INNOVANCE® PFA P2Y and VerifyNow PRU was 79%. The k statistics between INNOVANCE® PFA P2Y and VerifyNow%inhibition and PRU were 0.52 and 0.44, respectively.

CONCLUSIONS

The sensitivity of INNOVANCE® PFA P2Y in detecting clopidogrel resistance is comparable to that of VerifyNow P2Y12 assay. As the PFA-100® system is already widely used, the new test cartilage may be a useful tool for the assessment of clopidogrel effects. Additional clinical correlation studies are required to validate the effectiveness of INNOVANCE® PFA P2Y in predicting long-term clinical outcomes.

Efficacy and safety of triple antiplatelet therapy in obese patients undergoing stent implantation

We evaluated the impact of triple antiplatelet therapy on platelet reactivity, reducing cardiovascular events and the safety in obese patients undergoing coronary stenting. Obese patients (n = 428) undergoing coronary stenting were randomly assigned to 2 groups: standard dual group (clopidogrel plus aspirin, n = 215) and triple group (n = 213); adjunctive cilostazol was added to the dual group treatment. Platelet reactivity was assessed at baseline and at 1-year follow-up by conventional aggregometry. Major adverse cardiovascular events, stent thrombosis, target lesion revascularization (TLR), target vessel revascularization, and bleeding events were analyzed after 1-year follow-up. At 1-year follow-up after stenting, major adverse cardiac events including death, myocardial infarction, and ischemic-driven TLR were lower in the triple group than the dual group. Major bleeding was similar in both the groups. In obese patients undergoing percutaneous coronary intervention, triple antiplatelet therapy was superior to dual antiplatelet therapy in decreasing thrombotic events in 12-month cardiac events, mainly driven by a decrease in the incidence of clopidogrel resistance.

Clinical, pharmacokinetic, and pharmacogenetic determinants of clopidogrel resistance in Korean patients with acute coronary syndrome

BACKGROUND

Clopidogrel has been widely used to prevent recurrent ischemia in patients with acute coronary syndrome (ACS). However, inter-individual variability in response to clopidogrel has been a problem in the clinical setting. The aim of the present study was to investigate the frequency of clopidogrel resistance and to determine the clinical, pharmacokinetic, and pharmacogenetic factors for clopidogrel resistance in Korean patients with ACS.

METHODS

Clinical information, such as the underlying diseases and concurrent medications, of 114 patients with ACS who received clopidogrel therapy was studied. The degree of inhibition of platelets was assessed using the VerifyNow assay (Accumetrics, USA). The patients who showed less than 20% inhibition of platelets were defined as non-responders to clopidogrel treatment. Steady state plasma concentrations of clopidogrel were measured using HPLC/tandem mass spectrometry. CYP2C19 genotyping was also performed.

RESULTS

A wide inter-individual variability was observed in platelet inhibition (0-76%); 56 patients (49%) showed less than 20% inhibition. There were no differences between the patients' history of diabetes mellitus and concurrent medications as well as the plasma concentrations of clopidogrel of the responders and non-responders. CYP2C19 variants, including CYP2C19*2 and CYP2C19*3, were more commonly observed in the non-responders than in the responders (P value < 0.0001).

CONCLUSIONS

The response to clopidogrel was highly variable in Korean patients with ACS. The results of the present study confirmed that the genetic polymorphism of CYP2C19 could be important in clopidogrel response. However, further studies are required to investigate other likely factors involved in clopidogrel resistance.

Clopidogrel resistance and the effect of combination cilostazol in patients with ischemic stroke or carotid artery stenting using the VerifyNow P2Y12 Assay

OBJECTIVE

The inhibitory response to clopidogrel considerably varies among individuals and clopidogrel resistance is a risk factor for thrombotic events in patients with cardiovascular disease. Based on the platelet aggregation evaluated by the VerifyNow P2Y12 Assay, the present study investigated clopidogrel resistance and the effect of cilostazol addition.

METHODS

We measured the ability of 20 µM ADP to aggregate platelets using the VerifyNow P2Y12 Assay. Clopidogrel resistance was defined as % inhibition of <20% in this assay.

PATIENTS

We examined 77 patients (53 men and 24 women, aged 65.8 ± 9.9 years) with ischemic stroke or carotid artery stenting who received clopidogrel (75 mg) for >7 days at our hospital between October 2009 and March 2010. For 62 patients (42 men and 20 women, aged 65.3 ± 9.9 years) 75 mg clopidogrel alone was administered (clopidogrel only group); the other 15 patients (11 men and 4 women, aged 67.9 ± 9.9 years) received 75 mg of clopidogrel plus 100 or 200 mg of cilostazol (cilostazol combination group).

RESULTS

Clopidogrel resistance was identified in 18 (29%) of the 62 patients in the clopidogrel only group. The percent inhibition was significantly higher in the cilostazol combination group than in the clopidogrel only group (41.7 ± 28.0% vs. 64.9 ± 22.7%, p=0.005). None of the patients in the cilostazol combination group had % inhibition of <20%.

CONCLUSION

Clopidogrel resistance developed in 29% of patients given clopidogrel alone. The addition of cilostazol to clopidogrel may have intensified platelet inhibition.

Clopidogrel resistance

Clopidogrel resistance is an emerging clinical scenario, as antiplatelet therapy has become the cornerstone of modern cardiovascular treatment. This leads to an increase in stent thromboses and recurrent ischemic events which add to the health care costs, and increased periprocedural morbidity and mortality. Management of clopidogrel resistance is challenging as there are no standardized guidelines. The arrival of newer antiplatelet drugs and the detection of genetic polymorphisms in susceptible populations may have an impact on the management. Further trials are needed regarding the target population who should be screened for clopidogrel resistance, a standardized diagnostic test to detect clopidogrel resistance, the role of pharmacogenetics, and the need for tailored therapeutic options for a patient with clopidogrel resistance.

Beyond Genetics-Stratified and Personalised Medicines Using Multiple Parameters

Prescribers have been practicing stratified medicine for many years. Patient characteristics, usually non-genetic, including age, comorbidities and concomitant medications are taken into account when deciding which drug to prescribe. In addition, the majority of drugs require dose adjustments across patient subgroups, usually determined by non-genetic differences between the subgroups. Whilst pharmacogenetics hold promise for enhancing treatment stratification and even treatment individualisation, non-genetic factors will continue to be very important. Both non-genetic and genetic factors must be considered to improve understanding and quantification of the variability in treatment outcomes and to guide stratification and targeting of patient subgroups to the right drug and also to the right range of doses within that subgroup. Development of stratified medicines must consider non-genetic as well as genetic factors and, where appropriate, include stratification through optimising the dose for each patient or subgroup as well as by choosing the drug most likely to deliver efficacy to that patient or group.

Bioequivalence of two tablet formulations of clopidogrel in healthy Argentinian volunteers: a single-dose, randomized-sequence, open-label crossover study

BACKGROUND

Platelet activation is a major component in the pathogenesis of coronary thrombosis and myocardial infarction. Thienopyridines, particularly clopidogrel, are highly effective in reducing in-stent thrombosis and functional inhibition of adenosine diphosphate-induced platelet activation.

OBJECTIVE

The aim of this study was to evaluate the bioequivalence of a new generic formulation of clopidogrel 75-mg tablets (test) and the available branded formulation (reference) to meet regulatory criteria for marketing the test product in Argentina.

METHODS

This was a randomized-sequence, open-label, 2-period crossover study conducted in healthy white volunteers in the fasted state. A single oral dose of the test or reference formulation was followed by a 7-day washout period, after which subjects received the alternative formulation. Blood samples were collected at baseline and at 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 4, 6, 8, and 12 hours after dosing. Clopidogrel concentrations were determined using an LC-MS/MS method. The formulations were considered bioequivalent if the 90% CI of the geometric mean ratios (test:reference) for C(max) and AUC(0-last) were within the range from 80% to 125%. Adverse events were monitored throughout the study based on clinical parameters and patient reports.

RESULTS

Twenty-four volunteers (13 male, 11 female; mean [SD] age, 33.7 [5.2] years [range, 21-42 years]; weight, 72.4 [6.83] kg [range, 59-82 kg]) were enrolled in and completed the study. The geometric mean C(max) for the test and reference formulations was 877.76 and 913.49 pg/mL, respectively. The geometric mean AUC(0-t) was 1911.53 and 2053.09 pg . h/mL, and the geometric mean AUC(0-infinity)) was 2021.33 and 2188.25 pg . h/mL. The geometric mean ratios (test:reference) for C(max), AUC(0-t), and AUC(0-infinity)) were 96.09% (90% CI, 90.71-101.78), 93.10% (90% CI, 85.57-101.3), and 92.37% (90% CI, 85.06-100.31), respectively. There were no significant differences in pharmacokinetic parameters between groups. No adverse events were reported.

CONCLUSION

In this single-dose study in healthy fasted volunteers, the test formulation of clopidogrel tablets met the US and Argentinian regulatory criterion for bioequivalence to the reference formulation.

Clinical implications of clopidogrel non-response in cardiovascular patients: a systematic review and meta-analysis

BSUMMARY BACKGROUND: Previous studies have shown an important risk of cardiovascular events in patients with clopidogrel biological non-response, and data have shown considerable, unexplored heterogeneity.

OBJECTIVES

To evaluate the magnitude of cardiovascular risk associated with clopidogrel non-response and to explore heterogeneity.

METHODS

This was a systematic review and meta-analysis of prospective studies of patients treated with clopidogrel for symptomatic atherothrombosis, evaluated by light transmission aggregometry with ADP and monitored prospectively for clinical ischemic events.

RESULTS

Fifteen studies were included, totaling 3960 patients, of whom 25% were considered to be clopidogrel non-responders. The global relative risk (RR) for recurrent ischemic events in clopidogrel non-responders was 3.5 [95% confidence interval (CI) 2.4-5.2, P < 0.0001]. The results of the different studies were heterogeneous (Cochran P = 0.01 and I(2) = 52%). The most recent studies yielded lower RRs [global RR = 2.9 (95% CI 2.3-3.8) after 2007, and global RR = 6.6 (95% CI 3.7-11.9) before 2007, P = 0.01]. Heterogeneity was present in the group of studies in which more than 10% of patients took glycoprotein (GP)IIb-IIIa inhibitors [Cochran P = 0.003 and I(2) = 70%; RR = 3.8 (95% CI 2.9-5.1)] and was absent in the other studies [Cochran P = 0.88 and I(2) = 0; RR = 2.5 (95% CI 1.7-3.6)]. The RR was significantly higher in studies using higher ADP maximal aggregation cut-offs (> 65%) for clopidogrel non-response than in studies using lower cut-offs [RR = 5.8 (95% CI 3.2-10.3) and RR = 2.9 (95% CI 2.2-3.7), respectively, P = 0.03].

CONCLUSIONS

The risk of ischemic events associated with clopidogrel non-response is now more precisely defined. The risk is heterogeneous across studies, possibly because of an interaction with GPIIb-IIIa inhibitors and the use of different cut-offs to identify non-responders.

Antiplatelet therapy in percutaneous coronary intervention: a critical review of the 2007 AHA/ACC/SCAI guidelines and beyond

Antiplatelet therapy is a mainstay in the treatment of patients who have undergone percutaneous coronary intervention (PCI). Although the 2007 PCI treatment guidelines were published by the American College of Cardiology, the American Heart Association, and the Society for Cardiovascular Angiography and Interventions, new clinical evidence has emerged, expanding our understanding of antiplatelet use and potentially affecting the treatment guidelines. For example, clinical trial results prompted a Science Advisory to recommend that dual therapy with aspirin and clopidogrel be used for longer periods-up to 1 year in patients who receive bare metal stents and at least 1 year in patients receiving drug-eluting stents. New trial results have also emerged regarding the use of glycoprotein IIb/IIIa antagonists such as abciximab, eptifibatide, and tirofiban. This article reviews the current recommendations for antiplatelet therapy in PCI patients, recent trial results, newly developed agents, ongoing clinical trials, and the future direction of antiplatelet therapy in patients who undergo PCI.

Antiplatelet Resistance—Does it Exist and how to Measure it?

Aspirin and clopidogrel are the most commonly used antiplatelet agents in patients with coronary artery disease. The existence of resistance to these agents has been a controversial issue and new drugs are being developed to overcome this problem. Laboratory tests, which can identify resistance and correlate this with clinical outcome, are being studied in order to identify patients at risk of future thrombotic events. We discuss the evidence for the existence of antiplatelet resistance—both in the laboratory and in the clinical setting. So far, platelet aggregometry has been considered the gold standard test, but is very operator dependant, time consuming, and has shown little correlation with other available tests of antiplatelet resistance. We discuss the available tests of platelet function, their limitations, and evidence for their use. A simple, rapid, near-patient test, which is affordable and useful in the clinical (not just laboratory) setting, could allow risk stratification of patients and individualization of antiplatelet medication to improve outcome.

Hypercoagulability and platelet inhibition after OPCAB. Randomized intervention with clopidogrel

OBJECTIVE

Data on graft patency after Off-Pump Coronary Artery Bypass (OPCAB) suggest that the incidence of early graft closure is not increased compared to conventional coronary artery bypass surgery. However, hypercoagulability following OPCAB is still of concern, and acetylsalicylic acid as thromboembolic prophylaxis might be insufficient in the first weeks following OPCAB surgery.

DESIGN

Twenty nine patients were randomly assigned to+/- 75 mg of clopidogrel until 30 days after OPCAB surgery. The follow-up time was 2 months including standard blood samples and thrombelastography (TEG) with a specific platelet inhibition assay, which was evaluated as a part of the study.

RESULTS

In both groups a significant increase in TEG maximum amplitude was found 5 days after surgery. Platelet inhibition showed great variations but was significantly increased in the clopidogrel group (34.1%) vs. control group (11.0%) after 1 month.

CONCLUSION

Hypercoagulability was seen 5 days after OPCAB and could not be demonstrated after 1 month. No clinical effects of the hypercoagulability were observed, and further research is needed to determine if clopidogrel should be recommended after OPCAB.

Clopidogrel anti-platelet effect: An evaluation by optical aggregometry, impedance aggregometry, and the Platelet Function Analyzer (PFA-100™)

Platelet aggregation inhibition by clopidogrel may be suboptimal in 4-30% of patients. Traditionally, optical aggregometry is used to assess clopidogrel's anti-platelet effects by inhibition of ADP-induced aggregation in platelet rich plasma. Red blood cells are an important source of ADP and, thus, are known to modulate platelet function. Because the whole blood aggregation by impedance method assesses platelet function in a physiological milieu, we compared clopidogrel response by this method with the optical method in platelet rich plasma (PRP) and the Platelet Function Analyzer (PFA-100). Platelet function studies were performed in 17 healthy subjects at baseline and after 10 days of clopidogrel intake (75 mg/day). Optical and impedance aggregometry were performed after addition of ADP (10 and 20 microM) and collagen (1 and 2 microg/mL). For PFA-100 analysis, whole blood closure time was measured in collagen-coated cartridges with ADP and epinephrine. All subjects except one showed a decrease in ADP-induced aggregation using both aggregation methods. However, ADP-induced platelet aggregation was significantly inhibited when assessed in whole blood as compared to the optical method (71+/- 34% vs. 34.2+/- 23%, p = 0.0002); this suggests that whole blood aggregometry is more sensitive in the detection of clopidogrel effect in the presence of red cells, which are known to modulate platelet function. The PFA-100 ADP closure time was slightly prolonged above the reference interval in only 5/17 (29%) subjects, suggesting that this instrument is not able to detect clopidogrel effect. We conclude that whole blood aggregation appears to be more sensitive in detecting clopidogrel effect compared with the platelet rich plasma method; the PFA-100 was unable to detect clopidogrel effect in the majority of the subjects.

Relation of genetic polymorphisms in the cytochrome P450 gene with clopidogrel resistance after drug-eluting stent implantation in Koreans

Clopidogrel is a prodrug that has to be converted to an active metabolite by hepatic cytochrome P450 (CYP) isoenzymes to inhibit platelet aggregation. Individual variability of platelet inhibition by clopidogrel suggests a possibility for genetic factors having a significant influence on clopidogrel responsiveness. In this study, we sought to determine the relation of genetic polymorphisms of CYP genes to clopidogrel resistance in Koreans. Four hundred fifty patients who underwent successful percutaneous coronary intervention with drug-eluting stents were randomly assigned to treatment with dual antiplatelet regimen (aspirin plus clopidogrel) or triple antiplatelet regimen (aspirin plus clopidogrel plus cilostazol). Clopidogrel resistance using VerifyNow P2Y12 assay and genetic analysis were performed in 387 patients. Clopidogrel resistance was found in 112 patients (28.9%). In the clopidogrel-responsive group, there was a significantly higher proportion of cilostazol use. Because cilostazol showed a significant influence on clopidogrel resistance, we examined the association of single-nucleotide polymorphisms and clopidogrel resistance in the dual and triple antiplatelet therapy groups, respectively. In all subjects, the CYP2C19*3A allele was significantly more prevalent in the clopidogrel-resistant group compared with the clopidogrel-responsive group. Multiple logistic regression analysis demonstrated that CYP2C19*3 is an independent predictor of clopidogrel resistance. In conclusion, CYP2C19*3 single-nucleotide polymorphisms is an independent risk factor of clopidogrel resistance in Korean subjects with coronary artery disease.

Point-of-care assessment of antiplatelet agents in the perioperative period: a review

The aim of this paper was to review the strengths and limitations of current 'point-of-care' techniques for the detection of antiplatelet drug effects. The review was based on a Medline search for articles with key words related to "platelet function tests", "point-of-care", and "anaesthesia", published in English between January 1996 and September 2008. It was found that global assessments of 'haemostasis', such as the standard thrombelastograph, Sonoclot, Clot Signature Analyser and Hemodyne, are not specific for platelet function and are essentially insensitive to cyclooxygenase inhibitors (aspirin, non-steroidal anti-inflammatory drugs) and P2Y12 antagonists (ticlopidine, clopidogrel). Global assessments of 'platelet function', such as the PFA-100 and PlateletWorks, are more specific for platelet function, but also have limited sensitivity for cyclooxygenase inhibitors and P2Y12 antagonists. The newer devices developed specifically for the assessment of antiplatelet drugs, such as Platelet Mapping, the Impact Cone and Platelet Analyser and the VerifyNow, are more promising, but are not as sensitive as laboratory platelet aggregometry. All three categories of devices detect G(p)II(b)/III(a) antagonists (abciximab, tirofiban, eptifibatide) activity, but not all provide quantitative assessments for monitoring therapy. The limitations appeared to be related to the complexity of platelet function, the multiple pathways of platelet activation, the wide interpatient variability in platelet responses and the interdependence between platelets and other aspects of coagulation. The strengths and limitations of point-of-care devices should be appreciated before they are used to assist clinical decision-making in the perioperative period.

Variability in platelet response to the antiplatelet agents aspirin and clopidogrel: mechanisms, measurement, and clinical relevance

Platelet reactivity (eg, platelet adhesion, activation, aggregation) is the underlying pathology for atherothrombotic processes and subsequent ischemic complications. Antiplatelet drugs, including aspirin, dipyridamole, thienopyridines (clopidogrel and ticlopidine), and glycoprotein IIb/IIIa antagonists, have proven efficacy in atherothrombotic event prevention. However, variability of platelet response measured in the laboratory has been reported and is a subject of keen interest.It is unclear to what extent variability of platelet response to antiplatelet agents is associated with clinical outcomes. A better understanding of this issue requires a general consensus for a standard, preferably point-of-care, ex vivo or in vitro assay to determine the effects of antiplatelet agents on key platelet functions. Currently, results using various methods have not yielded an obvious answer. Small-scale studies have examined the correlation between ex vivo inhibition of platelet aggregation or residual platelet activity and clinical endpoints, and although evidence shows that such correlations may exist, results have not been consistent or definitive. Data from large-scale prospective trials are needed to expand our current understanding of the benefits and limitations of utilizing platelet function tests to effectively manage the balance between protection and risks associated with the antiplatelet therapies, aspirin, and clopidogrel.

Prasugrel: A New Thienopyridine Inhibitor

The objective of this review is to report the pharmacologic and pharmacokinetic properties of prasugrel, the potential advantages and disadvantages over the other agent in its class, clopidogrel, and the clinical data establishing its efficacy in the management of patients with acute coronary syndromes receiving stent implantation. A MEDLINE (1966 to May 2008) search using the key word prasugrel was performed to identify pertinent literature. Additional references were selected from the bibliographies of the articles cited. Searches were not limited by time or human subject. Preclinical studies evaluating the pharmacologic and pharmacokinetic properties of prasugrel in humans were selected for review. Clinical trials assessing the efficacy of prasugrel for the treatment of patients with acute coronary syndromes receiving percutaneous coronary intervention were included as long as they were randomized, blinded, and controlled. The authors concluded that prasugrel is a thienopyridine antiplatelet agent with a faster onset of action and increased potency, in terms of inhibiting platelet aggregation, than clopidogrel. It has been shown in one major clinical trial that this enhanced pharmacological effect of prasugrel reduces the combined incidence of cardiovascular death, nonfatal myocardial infarction, and nonfatal stroke when compared with clopidogrel. However, this enhanced effect of prasugrel did result in an increased risk of bleeding.

Evaluation of the platelet count drop method for assessment of platelet function in comparison with "gold standard" light transmission aggregometry

INTRODUCTION

Hyporesponsiveness to antiplatelet agents has been linked to an increased risk of major adverse cardiovascular events. However, light transmission aggregometry (LTA), the gold standard methodology for assessing platelet function, requires expertise and is labour-intensive, which render its use in clinical settings impractical. We assessed whether platelet count drop (PCD), a technique widely available in any haematology laboratory, could replace LTA in testing for inhibition of platelet aggregation induced by antiplatelet agents.

MATERIALS AND METHODS

One hundred and sixty-one coronary artery disease patients taking aspirin alone and 91 patients taking a combination of aspirin and clopidogrel were enrolled. Platelet aggregation was measured by LTA and PCD stimulated with 1.6 mM of arachidonic acid (AA) for aspirin and 5 and 20 microM of adenosine diphosphate (ADP) for clopidogrel.

RESULTS

Correlation between AA-induced LTA and PCD was nonexistent (r=-0.043, p=0.587), while correlation between ADP-induced LTA and PCD was low (r=0.374, p<0.0001 for ADP 5 microM and r=0.402, p<0001 for ADP 20 microM ). PCD, whether stimulated with AA or ADP, overestimated platelet aggregation as assessed by LTA, by 13-18%. The wide 95% limits of agreement suggest that the assays can disagree significantly in individual patients.

CONCLUSIONS

Although the PCD method is widely available in non-specialized laboratories, our results demonstrate that there is poor correlation with the current gold standard, i.e. LTA. Thus, PCD should not be used in replacement of LTA to assess antiplatelet responsiveness.

Clopidogrel and coronary stents: risks and benefits

Clopidogrel has become increasingly important in the management of patients with coronary stents. Clopidogrel is an oral agent that acts on the adeno-sine diphosphate receptor to irreversibly inhibit platelet aggregation. Along with aspirin, clopidogrel has a significant role in the treatment of atherothrombotic diseases. Recent concerns about late stent thrombosis highlight the need for long-term therapy with clopidogrel in addition to aspirin in these populations. This article reviews the role of clopidogrel in the treatment of atherothrombotic diseases and after coronary intervention, as well as the current approach in the prevention of stent thrombosis. It also discusses experimental and upcoming drugs that may be superior to clopidogrel.