Drug Insight: clopidogrel nonresponsiveness

Interindividual variability in platelet reactivity among individuals with or without antiplatelet therapy: results from a large tertiary care hospital

Antiplatelet therapy is crucial for reducing thrombotic events in patients with atherosclerotic disease, but the response vary widely among individuals. The identification of patients at high (HPR), optimal (OPR) or low platelet reactivity (LPR) is dependent on high interlaboratory variability. We report results of a large dataset of patients to assess the gold standard light transmission aggregometry (LTA). A total of 11,913 patients who sequentially underwent LTA assessment using several stimuli (ADP-2µM, collagen-2 µg/ml, arachidonic acid 0.5 mM, epinephrine 10µM) with a standardized methodology between 2004 and 2022 were screened. After application of inclusion-exclusion criteria, 5,901 patients were included and divided into five groups: healthy-volunteers (HV; N = 534); controls (CTR; N = 1073); aspirin-treated patients (ASA; 75-150 mg/die; N = 3280); clopidogrel-treated patients (CLOP; 75 mg/die; N = 495) and patients treated with dual antiplatelet therapy, ASA plus CLOP (DAPT; N = 519). The mean PA% in response to ADP 2 μm was 72.4 ± 33.3 in the CTR population, 40.6 ± 29.9 in the ASA group, 25.1 ± 35.1 in the CLOP group and 10.2 ± 18.5 in the DAPT group. The mean PA% in response to collagen 2 ug/ml was 90.7 ± 10.5 in the CTR population, 40.8 ± 26.3 in the ASA group, 79.4 ± 21.8 in the CLOP group and 17.9 ± 19.9 in the DAPT group. The percentage of patients at OPR following ADP stimuli was 66%, 25%, and 26%, in the ASA, CLOP, and DAPT group, respectively. The percentage of patients at OPR following collagen stimuli was 56%, 22%, and 41%, in the ASA, CLOP, and DAPT group, respectively. LTA was significantly increased in response to ADP (72.4 ± 33.3vs62.7 ± 37.1; p < 0.001) and AA (90.7 ± 15.6vs87.6 ± 20.5; p < 0.001) in CTR compared to HV. Our findings support the concept that a significant proportion of individuals present a hyper- or hypo-reactive platelet phenotype potentially affecting the safety and efficacy of antiplatelet therapy. The variability in response to antiplatelet therapy was particularly evident in patients undergoing single as opposed to dual antiplatelet therapy regimens. These data support ongoing strategies of guided selection of antiplatelet therapy in patients with cardiovascular disease.

Convolutional neuronal network for identifying single-cell-platelet-platelet-aggregates in human whole blood using imaging flow cytometry

Imaging flow cytometry is an attractive method to investigate individual cells by optical properties. However, imaging flow cytometry applications with clinical relevance are scarce so far. Platelet aggregation naturally occurs during blood coagulation to form a clot. However, aberrant platelet aggregation is associated with cardiovascular disease under steady-state conditions in the blood. Several types of so-called antiplatelet drugs are frequently described to reduce the risk of stroke or cardiovascular diseases. However, an efficient monitoring method is missing to identify the presence and frequency of platelet-platelet aggregates in whole blood on a single cell level. In this work, we employed imaging flow cytometry to identify fluorescently labeled platelets in whole blood with a conditional gating strategy. Images were post-processed and aligned. A convolutional neural network was designed to identify platelet-platelet aggregates of two, three, and more than three platelets, and results were validated against various data set properties. In addition, the neural network excluded erythrocyte-platelet aggregates from the results. Based on the results, a parameter for detecting platelet-platelet aggregates, the weighted platelet aggregation, was developed. If employed on a broad scale with proband and patient samples, our method could aid in building a future diagnostic marker for cardiovascular disease and monitoring parameters to optimize drug prescriptions in such patient groups.

Dual Antiplatelet Therapy with Parenteral P2Y12 Inhibitors: Rationale, Evidence, and Future Directions

Dual antiplatelet therapy (DAPT), consisting of the combination of aspirin and an inhibitor of the platelet P2Y₁₂ receptor for ADP, remains among the most investigated treatments in cardiovascular medicine. While a substantial amount of research initially stemmed from the observations of late and very late stent thrombosis events in the first-generation drug-eluting stent (DES) era, DAPT has been recently transitioning from a purely stent-related to a more systemic secondary prevention strategy. Oral and parenteral platelet P2Y₁₂ inhibitors are currently available for clinical use. The latter have been shown to be extremely suitable in drug-naïve patients with acute coronary syndrome (ACS), mainly because oral P2Y₁₂ inhibitors are associated with delayed efficacy in patients with STEMI and because pre-treatment with P2Y₁₂ inhibitors is discouraged in NSTE-ACS, and in patients with recent DES implantation and in need of urgent cardiac and non-cardiac surgery. More definitive evidence is needed, however, about optimal switching strategies between parenteral and oral P2Y₁₂ inhibitors and about newer potent subcutaneous agents that are being developed for the pre-hospital setting.

Pharmacogenetics of Antiplatelet Therapy

Antiplatelet therapy is used in the treatment of patients with acute coronary syndromes, stroke, and those undergoing percutaneous coronary intervention. Clopidogrel is the most widely used antiplatelet P2Y12 inhibitor in clinical practice. Genetic variation in CYP2C19 may influence its enzymatic activity, resulting in individuals who are carriers of loss-of-function CYP2C19 alleles and thus have reduced active clopidogrel metabolites, high on-treatment platelet reactivity, and increased ischemic risk. Prospective studies have examined the utility of CYP2C19 genetic testing to guide antiplatelet therapy, and more recently published meta-analyses suggest that pharmacogenetics represents a key treatment strategy to individualize antiplatelet therapy. Rapid genetic tests, including bedside genotyping platforms that are validated and have high reproducibility, are available to guide selection of P2Y12 inhibitors in clinical practice. The aim of this review is to provide an overview of the background and rationale for the role of a guided antiplatelet approach to enhance patient care.

Pharmacokinetics and Pharmacodynamics of Approved and Investigational P2Y12 Receptor Antagonists

Coronary artery disease remains the major cause of mortality worldwide. Antiplatelet drugs such as acetylsalicylic acid and P2Y12 receptor antagonists are cornerstone treatments for the prevention of thrombotic events in patients with coronary artery disease. Clopidogrel has long been the gold standard but has major pharmacological limitations such as a slow onset and long duration of effect, as well as weak platelet inhibition with high inter-individual pharmacokinetic and pharmacodynamic variability. There has been a strong need to develop potent P2Y12 receptor antagonists with more favorable pharmacological properties. Prasugrel and ticagrelor are more potent and have a faster onset of action; however, they have shown an increased bleeding risk compared with clopidogrel. Cangrelor is highly potent and has a very rapid onset and offset of effect; however, its indication is limited to P2Y12 antagonist-naïve patients undergoing percutaneous coronary intervention. Two novel P2Y12 receptor antagonists are currently in clinical development, namely vicagrel and selatogrel. Vicagrel is an analog of clopidogrel with enhanced and more efficient formation of its active metabolite. Selatogrel is characterized by a rapid onset of action following subcutaneous administration and developed for early treatment of a suspected acute myocardial infarction. This review article describes the clinical pharmacology profile of marketed P2Y12 receptor antagonists and those under development focusing on pharmacokinetic, pharmacodynamic, and drug-drug interaction liability.

Risk of stroke in CYP2C19 LoF polymorphism carrier coronary artery disease patients undergoing clopidogrel therapy: An ethnicity-based updated meta-analysis

BACKGROUND

Antiplatelet agent clopidogrel has been widely used for stroke management for many years, although resistance to clopidogrel may increase the chance of stroke recurrence. CYP2C19 loss-of-function (LoF) polymorphism is assumed to be responsible for the poor metabolism of clopidogrel that ultimately turns to resistance. Previous publications could not provide firm evidence due to highly conflicting and heterogeneous outcomes.

AIM

To get clear evidence from an updated meta-analysis on CYP2C19 LoF polymorphism association with stroke risk in clopidogrel treated patients, this study has been performed.

METHODS

We conducted a meta-analysis with 72 selected studies from authentic databases, including 40,035 coronary artery disease patients treated with clopidogrel.

RESULTS

This analysis showed that the worldwide carrier of one or more CYP2C19 LoF alleles had a significantly higher risk of stroke and composite events than the non-LoF carriers (RR=1.78, 95% CI=1.52-2.07, p<0.00001 and RR=1.39, 95% CI=1.26-1.54, p<0.00001, respectively). Besides, subgroup analysis showed that Asian CYP2C19 LoF carriers had a significantly increased risk of stroke (RR=1.91, 95% CI=1.60-2.28, p<0.00001) while the risk of composite events was significantly higher in all ethnic populations (Asian: RR=1.58, 95% CI=1.32-1.89, p<0.00001; Caucasian: RR=1.27, 95% CI=1.08-1.50, p=0.003; Hispanic and others: RR=1.21, 95% CI=1.09-1.34, p=0.0003).

CONCLUSION

Our meta-analysis confirmed that the presence of CYP2C19 LoF alleles increases the risk of stroke and composite events recurrence in the worldwide population, especially in Asians undergoing clopidogrel treatment. Alternative antiplatelet therapy should be investigated thoroughly for the intermediate and poor metabolizers.

Effectiveness of Platelet Function Analysis-Guided Aspirin and/or Clopidogrel Therapy in Preventing Secondary Stroke: A Systematic Review and Meta-Analysis

Background: Antiplatelet medications such as aspirin and clopidogrel are used following thrombotic stroke or transient ischemic attack (TIA) to prevent a recurrent stroke. However, the antiplatelet treatments fail frequently, and patients experience recurrent stroke. One approach to lower the rates of recurrence may be the individualized antiplatelet therapies (antiplatelet therapy modification (ATM)) based on the results of platelet function analysis (PFA). This review was undertaken to gather and analyze the evidence about the effectiveness of such approaches. Methods: We searched Medline, CINAHL, Embase, Web of Science, and Cochrane databases up to 7 January 2020. Results: Two observational studies involving 1136 patients were included. The overall effects of PFA-based ATM on recurrent strokes (odds ratio (OR) 1.05; 95% confidence interval (CI) 0.69 to 1.58), any bleeding risk (OR 1.39; 95% CI 0.92 to 2.10) or death hazard from any cause (OR 1.19; 95% CI 0.62 to 2.29) were not significantly different from the standard antiplatelet therapy without ATM. Conclusions: The two studies showed opposite effects of PFA-guided ATM on the recurrent strokes in aspirin non-responders, leading to an insignificant difference in the subgroup meta-analysis (OR 1.59; 95% CI 0.07 to 33.77), while the rates of any bleeding events (OR 1.04; 95% CI 0.49 to 2.17) or death from any cause (OR 1.17; 95% CI 0.41 to 3.35) were not significantly different between aspirin non-responders with ATM and those without ATM. There is a need for large, randomized controlled trials which account for potential confounders such as ischemic stroke subtypes, technical variations in the testing protocols, patient adherence to therapy and pharmacogenetic differences.

CHADS2 and CHA2DS2-VASc scores as predictors of platelet reactivity in acute coronary syndrome

BACKGROUND

Platelet function testing (PFT) in patients treated with P2Y₁₂ inhibitors has been widely evaluated for the prediction of stent thrombosis, myocardial infarction, and bleeding events following percutaneous coronary intervention (PCI) in acute coronary syndrome (ACS). Thus, PFT-guided treatment could positively affect patient outcomes. Data regarding clinical parameters for predicting platelet reactivity in ACS patients are limited. Therefore, our study aims to evaluate CHADS2 and CHA2DS2-VASc scores as predictors for platelet reactivity in ACS patients.

METHODS

Two hundred and ninety-one consecutive patients who underwent PCI and were treated with aspirin and clopidogrel due to ACS were tested for their CHADS2, CHA2DS2-VASc scores and platelet reactivity using adenosine diphosphate (ADP)-induced aggregation (conventional aggregometry). Patients were classified into groups according to their CHADS2 and CHA2DS2-VASc scores. Low-risk group (0-1 score) for CHADS2 and CHA2DS2-VASc scores and high-risk group (2-6, 2-9) for CHADS2 and CHA2DS2-VASc scores, respectively. Furthermore, platelet reactivity in each group were compared (low CHADS2 group vs high CHADS2 group, and low CHA2DS2-VASc vs high CHA2DS2-VASc). Platelet reactivity was defined as low platelet reactivity (<19 U), optimal platelet reactivity [(OPR); 19-46 U], and high on-treatment platelet reactivity [(HPR); >46 U]. Thereafter receiver operating characteristic curve analysis was conducted to verify whether CHADS2 and CHA2DS2-VASc scores could predict platelet reactivity.

RESULTS

Low CHADS2 and CHA2DS2-VASc scores were significantly correlated with lower mean platelet ADP-induced aggregation as compared with high CHADS2 and CHA2DS2-VASc scores [45.5 U (± 16) vs. 54.8 U (±15) and 44.2 U (±16) vs. 51.0 U (±17), respectively, p = 0.01 for both].

CONCLUSION

In ACS patients treated with clopidogrel following PCI, high CHADS2 and CHA2DS2-VASc scores correlated with HPR and lower scores correlated with OPR. Further studies are needed to evaluate our findings' clinical implications.

Prasugrel-based de-escalation of dual antiplatelet therapy after percutaneous coronary intervention in patients with acute coronary syndrome (HOST-REDUCE-POLYTECH-ACS): an open-label, multicentre, non-inferiority randomised trial

BACKGROUND

A potent P2Y12 inhibitor-based dual antiplatelet therapy is recommended for up to 1 year in patients with acute coronary syndrome receiving percutaneous coronary intervention (PCI). The greatest benefit of the potent agent is during the early phase, whereas the risk of excess bleeding continues in the chronic maintenance phase. Therefore, de-escalation of antiplatelet therapy might achieve an optimal balance between ischaemia and bleeding. We aimed to investigate the safety and efficacy of a prasugrel-based dose de-escalation therapy.

METHODS

HOST-REDUCE-POLYTECH-ACS is a randomised, open-label, multicentre, non-inferiority trial done at 35 hospitals in South Korea. We enrolled patients with acute coronary syndrome receiving PCI. Patients meeting the core indication for prasugrel were randomly assigned (1:1) to the de-escalation group or conventional group using a web-based randomisation system. The assessors were masked to the treatment allocation. After 1 month of treatment with 10 mg prasugrel plus 100 mg aspirin daily, the de-escalation group received 5 mg prasugrel, while the conventional group continued to receive 10 mg. The primary endpoint was net adverse clinical events (all-cause death, non-fatal myocardial infarction, stent thrombosis, repeat revascularisation, stroke, and bleeding events of grade 2 or higher according to Bleeding Academic Research Consortium [BARC] criteria) at 1 year. The absolute non-inferiority margin for the primary endpoint was 2·5%. The key secondary endpoints were efficacy outcomes (cardiovascular death, myocardial infarction, stent thrombosis, and ischaemic stroke) and safety outcomes (bleeding events of BARC grade ≥2). The primary analysis was in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, NCT02193971.

RESULTS

From Sept 30, 2014, to Dec 18, 2018, 3429 patients were screened, of whom 1075 patients did not meet the core indication for prasugrel and 16 were excluded due to randomisation error. 2338 patients were randomly assigned to the de-escalation group (n=1170) or the conventional group (n=1168). The primary endpoint occurred in 82 patients (Kaplan-Meier estimate 7·2%) in the de-escalation group and 116 patients (10·1%) in the conventional group (absolute risk difference -2·9%, p_{non-inferiority}<0·0001; hazard ratio 0·70 [95% CI 0·52-0·92], p_equivalence=0·012). There was no increase in ischaemic risk in the de-escalation group compared with the conventional group (0·76 [0·40-1·45]; p=0·40), and the risk of bleeding events was significantly decreased (0·48 [0·32-0·73]; p=0·0007).

INTERPRETATION

In east Asian patients with acute coronary syndrome patients receiving PCI, a prasugrel-based dose de-escalation strategy from 1 month after PCI reduced the risk of net clinical outcomes up to 1 year, mainly driven by a reduction in bleeding without an increase in ischaemia.

FUNDING

Daiichi Sankyo, Boston Scientific, Terumo, Biotronik, Qualitech Korea, and Dio.

An Observational Study of the Relationship Between Outcome and Platelet Reactivity in Chinese Patients Undergoing PCI Loading with 600 mg Clopidogrel

Objectives: We sought to determine whether high posttreatment platelet reactivity (HPPR) to a 600 mg loading dose of clopidogrel affects outcomes in Chinese patients with acute coronary syndrome (ACS) following percutaneous coronary intervention (PCI) and to investigate whether there is a relationship between the number of platelet reactivity units (PRUs) and the characteristics of the patients.Background: Although impaired platelet response to clopidogrel is a strong predictor of unfavorable outcome after PCI, the impact of HPPR to a 600 mg loading dose of clopidogrel in Chinese patients with ACS undergoing PCI is still unknown.Methods: We performed observational research on 134 unselected patients with ACS undergoing urgent or planned PCI with a 600 mg loading dose of clopidogrel. Platelet activation was expressed as the PRU value measured by the VerifyNow assay.Results: Among the 134 patients (mean age 60.62 years [standard deviation 9.13 years], 60.4% male), there were 46 patients with HPPR (34.3%) and 88 patients without HPPR (65.7%). At a mean follow-up of 6 months (standard deviation 1 month), the rates of cardiac death, unstable angina, and rehospitalization for target lesion revascularization were higher in the HPPR group (19.6% vs. 6.8%, P=0.029). Multivariate analysis identified hemoglobin level and sex as independent predictors of the PRU value (y=456.355−1.736x1−31.880x2, P<0.05). On receiver operating characteristic curve analysis, PRU values could significantly discriminate between patients with and patients without cardiac death, unstable angina, and rehospitalization for target lesion revascularization (area under the curve 0.758, 95% confidence interval 0.62‐0.85, P=0.001, P<0.05).Conclusion: In patients with ACS, HPPR to a 600 mg loading dose of clopidogrel is associated with worse outcomes after PCI. There is some relationship between the PRU value and the hemoglobin level and sex. PRU values can predict the prognosis.

Cangrelor in clinical use

Inadequate antiplatelet effects can result in substantial morbidity and mortality in patients with acute coronary syndrome and percutaneous coronary intervention (PCI). Cangrelor is a rapid onset and potent intravenous P2Y12 inhibitor that has been shown in large randomized controlled trials to reduce periprocedural complications for PCI compared with clopidogrel, the most commonly used P2Y12 inhibitor. Cangrelor should be considered in the setting of PCI to reduce the risk of periprocedural complications such as myocardial infarction, repeat coronary revascularization and stent thrombosis in patients not yet treated with another P2Y12 inhibitor or glycoprotein IIb/IIIa inhibitor. In this review, the importance of adequate P2Y12 inhibition, cangrelor's pharmacology and clinical profiles, and future directions for the cangrelor are discussed.

Stratified Approaches to Antiplatelet Therapies Based on Platelet Reactivity Testing

Antiplatelet therapy with P2Y₁₂ receptor inhibitors (clopidogrel, prasugrel, ticagrelor, cangrelor) is a cornerstone of medical therapy after percutaneous coronary interventions. Significant prevalence of high on-treatment platelet reactivity (HTPR) on clopidogrel treatment led to introduction of more potent P2Y₁₂ inhibitors: prasugrel (a third generation thienopyridine), ticagrelor, and cangrelor (cyclopentyl-triazolo-pyrimidines). Nevertheless, more potent platelet inhibition and resulting low on-treatment platelet reactivity (LTPR) has led to increased risk of major bleeding events. These limitations resulted in a need for an individualized antiplatelet therapy approach. This review discusses the current role and future perspectives of diagnostic tools such as platelet function testing to optimize antiplatelet therapy with a focus on deescalating therapies to reduce bleeding risks.

Pharmacogenomic Impact of CYP2C19 Variation on Clopidogrel Therapy in Precision Cardiovascular Medicine

Variability in response to antiplatelet therapy can be explained in part by pharmacogenomics, particularly of the CYP450 enzyme encoded by CYP2C19. Loss-of-function and gain-of-function variants help explain these interindividual differences. Individuals may carry multiple variants, with linkage disequilibrium noted among some alleles. In the current pharmacogenomics era, genomic variation in CYP2C19 has led to the definition of pharmacokinetic phenotypes for response to antiplatelet therapy, in particular, clopidogrel. Individuals may be classified as poor, intermediate, extensive, or ultrarapid metabolizers, based on whether they carry wild type or polymorphic CYP2C19 alleles. Variant alleles differentially impact platelet reactivity, concentration of plasma clopidogrel metabolites, and clinical outcomes. Interestingly, response to clopidogrel appears to be modulated by additional factors, such as sociodemographic characteristics, risk factors for ischemic heart disease, and drug-drug interactions. Furthermore, systems medicine studies suggest that a broader approach may be required to adequately assess, predict, preempt, and manage variation in antiplatelet response. Transcriptomics, epigenomics, exposomics, miRNAomics, proteomics, metabolomics, microbiomics, and mathematical, computational, and molecular modeling should be integrated with pharmacogenomics for enhanced prediction and individualized care. In this review of pharmacogenomic variation of CYP450, a systems medicine approach is described for tailoring antiplatelet therapy in clinical practice of precision cardiovascular medicine.

The genetic basis of platelet responsiveness to clopidogrel

Clopidogrel reduces ischaemic complications in a wide range of patients with coronary artery disease. However, there is much inter-individual variation in clopidogrel-induced platelet inhibition, and a substantial proportion of patients will exhibit non-responsiveness to clopidogrel. Multiple studies have demonstrated an association between the presence of genetic polymorphisms associated with suboptimal clopidogrel-active metabolite generation, decreased platelet responsiveness, and adverse clinical outcomes. However, it is not clear to what extent the genetic polymorphisms account for the observed variability in response to clopidogrel. In this review we provide a critical summary of the available evidence linking genetic factors with response to clopidogrel, and discuss the clinical implications of this association.

The Personalization of Clopidogrel Antiplatelet Therapy: The Role of Integrative Pharmacogenetics and Pharmacometabolomics

Dual antiplatelet therapy of aspirin and clopidogrel is pivotal for patients undergoing percutaneous coronary intervention. However, the variable platelets reactivity response to clopidogrel may lead to outcome failure and recurrence of cardiovascular events. Although many genetic and nongenetic factors are known, great portion of clopidogrel variable platelets reactivity remain unexplained which challenges the personalization of clopidogrel therapy. Current methods for clopidogrel personalization include CYP2C19 genotyping, pharmacokinetics, and platelets function testing. However, these methods lack precise prediction of clopidogrel outcome, often leading to insufficient prediction. Pharmacometabolomics which is an approach to identify novel biomarkers of drug response or toxicity in biofluids has been investigated to predict drug response. The advantage of pharmacometabolomics is that it does not only predict the response but also provide extensive information on the metabolic pathways implicated with the response. Integrating pharmacogenetics with pharmacometabolomics can give insight on unknown genetic and nongenetic factors associated with the response. This review aimed to review the literature on factors associated with the variable platelets reactivity response to clopidogrel, as well as appraising current methods for the personalization of clopidogrel therapy. We also aimed to review the literature on using pharmacometabolomics approach to predict drug response, as well as discussing the plausibility of using it to predict clopidogrel outcome.

Stirred, shaken, or stagnant: What goes on at the blood-biomaterial interface

There is a widely recognized need to improve the performance of vascular implants and external medical devices that come into contact with blood by reducing adverse reactions they cause, such as thrombosis and inflammation. These reactions lead to major adverse cardiovascular events such as heart attacks and strokes. Currently, they are managed therapeutically. This need remains unmet by the biomaterials research community. Recognized stagnation of the blood-biomaterial interface research translates into waning interest from clinicians, funding agencies, and practitioners of adjacent fields. The purpose of this contribution is to stir things up. It follows the 2014 BloodSurf meeting (74th International IUVSTA Workshop on Blood-Biomaterial Interactions), offers reflections on the situation in the field, and a three-pronged strategy integrating different perspectives on the biological mechanisms underlying blood-biomaterial interactions. The success of this strategy depends on reengaging clinicians and on the renewed cooperation of the funding agencies to support long-term efforts.

P2Y12 receptor blockade synergizes strongly with nitric oxide and prostacyclin to inhibit platelet activation

AIMS

In vivo platelet function is a product of intrinsic platelet reactivity, modifiable by dual antiplatelet therapy (DAPT), and the extrinsic inhibitory endothelial mediators, nitric oxide (NO) and prostacyclin (PGI2 ), that are powerfully potentiated by P2Y12 receptor blockade. This implies that for individual patients endothelial mediator production is an important determinant of DAPT effectiveness. Here, we have investigated this idea using platelets taken from healthy volunteers treated with anti-platelet drugs.

METHODS

Three groups of male volunteers (n = 8) received either prasugrel (10 mg), aspirin (75 mg) or DAPT (prasugrel + aspirin) once daily for 7 days. Platelet reactivity in the presence of diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NONOate) and PGI2 was studied before and following treatment.

RESULTS

Ex vivo, PGI2 and/or DEA/NONOate had little inhibitory effect on TRAP-6-induced platelet reactivity in control conditions. However, in the presence of DAPT, combination of DEA/NONOate + PGI2 reduced platelet aggregation (74 ± 3% to 19 ± 6%, P < 0.05). In vitro studies showed even partial (25%) P2Y12 receptor blockade produced a significant (67 ± 2% to 39 ± 10%, P < 0.05) inhibition when DEA/NONOate + PGI2 was present.

CONCLUSIONS

We have demonstrated that PGI2 and NO synergize with P2Y12 receptor antagonists to produce powerful platelet inhibition. Furthermore, even with submaximal P2Y12 blockade the presence of PGI2 and NO greatly enhances platelet inhibition. Our findings highlight the importance of endothelial mediator in vivo modulation of P2Y12 inhibition and introduces the concept of refining ex vivo platelet function testing by incorporating an assessment of endothelial function to predict thrombotic outcomes better and adjust therapy to prevent adverse outcomes in individual patients.

On-treatment platelet reactivity: State of the art and perspectives

High on-clopidogrel platelet reactivity (HcPR) during dual-antiplatelet therapy is a marker of vascular risk, in particular stent thrombosis, in patients with acute coronary syndromes (ACS). Genetic determinants (CYP2C19*2 polymorphism), advanced age, female gender, diabetes and reduced ventricular function are related to a higher risk to develop HcPR. In addition, inflammation and increased platelet turnover, as revealed by the elevated percentage of reticulated platelets in patients' blood, that characterize the acute phase of acute coronary syndromes, are associated with HcPR. To overcome the limitation of clopidogrel, new antiplatelet agents (prasugrel and ticagrelor) were developed and the demonstration of their superiority over clopidogrel was obtained in the two randomized trials, TRITON TIMI 38 and PLATO. Emerging evidence is accumulating on the role of high-on aspirin platelet reactivity (HaPR), especially in the clinical context of diabetes. Finally, the presence of new, potent antiplatelet drugs has shifted the focus from thrombotic to bleeding risk. Recent data document that low on-treatment platelet reactivity (LPR) is associated with a significantly higher bleeding risk. Due to the current possibility to choose between multiple antiplatelet strategies, the future perspective is to include in the management of ACS, in addition to clinical data and classical risk factors, the definition of platelet function during treatment in order to set a tailored therapy.

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.

Determination of genotypes using a fully automated molecular detection system

CONTEXT

Although the value of pharmacogenomics to improve patient outcomes has become increasingly clear, adoption in medical practice has been slow, which can be attributed to several factors, including complicated and expensive testing procedures and required equipment, lack of training by private practice physicians, and reluctance of both private and commercial payers to reimburse for such testing.

OBJECTIVES

To evaluate a fully automated molecular detection system for human genotyping assays, starting with anticoagulated whole blood samples, and to perform all sample preparation, assay, and analysis steps automatically with actionable results reported by the system's software.

DESIGN

The genotypes of 254 random individuals were determined by performing bidirectional DNA sequencing, and that information was used to statistically train the imaging software of the automated molecular detection system to distinguish the 3 possible genotypes (ie, homozygous wild type, heterozygous, and homozygous mutant) at each of 3 different loci (CYP2C9*2, CYP2C9*3, and VKORC1).

RESULTS

The resulting software algorithm was able to correctly identify the genotypes of all 254 individuals (100%) evaluated without any further user analysis.

CONCLUSIONS

The EncompassMDx workstation (Rheonix, Inc, Ithaca, New York) is a molecular detection system that can automatically determine the genotypes of individuals in an unattended manner. Considerably less technical expertise was required to achieve results identical to those obtained using more complex, time-consuming, and expensive bidirectional DNA sequencing. This optimized system may dramatically simplify and reduce the costs of pharmacogenomics testing, thus leading to more-widespread use.

New approaches to inhibiting platelets and coagulation

Ischemic heart disease and stroke are major causes of death and morbidity worldwide. Coronary and cerebrovascular events are a consequence of thrombus formation caused by atherosclerotic plaque rupture or embolism, both of which result from platelet activation and aggregation and thrombin-mediated fibrin generation via the coagulation cascade. Current and emerging antiplatelet and anticoagulant agents are evolving rapidly. The use of aspirin for primary prevention continues to be controversial, as are the doses appropriate for secondary prevention. Development of new oral and intravenous adenosine diphosphate P2Y12 inhibitors and novel antiplatelet agents continues to transform the landscape of antiplatelet therapy. Oral anticoagulation has advanced with the use of direct thrombin and factor Xa inhibitors that do not require therapeutic monitoring. In this review, we discuss the pharmacology and growing clinical evidence for traditional and new antiplatelet and anticoagulant therapies.

Individualised dual antiplatelet therapy in a patient with short bowel syndrome after acute myocardial infarction with coronary artery stenting

Short bowel syndrome after extensive surgical resection of the intestine is characterised by inadequate digestion and absorption of nutrients. Additional clinical problems include impaired absorption and metabolism of diverse drugs requiring individualised medical therapy or alternative treatments. We report a case of individualised dual antiplatelet therapy in a patient who underwent an extensive intestinal resection complicated by acute myocardial infarction requiring percutaneous coronary intervention and stent implantation. Genetic testing of CYP2C19 gene polymorphisms and platelet aggregation testing were used to assess responses to aspirin, clopidogrel, prasugrel and ticagrelor. Given its unique pharmacokinetics with good absorption and without need of metabolism to an active substance, ticagrelor appears to be the best for patients with short bowel syndrome who require dual antiplatelet therapy after coronary stent implantation.

Monitoring Residual Platelet Activity Among Patients With Acute Coronary Syndrome Post-PCI by Modified Impedance Whole Blood Platelet Aggregation and Release Method

Antiplatelet medicines have been one of the cornerstones in the treatment of patients with acute coronary syndrome (ACS). However, adverse cardiovascular events still occur in some patients on standard antiplatelet therapy. Therefore, a reliable laboratory test to monitor the residual platelet activity (RPA) is urgent. We aim to modify the impedance whole blood platelet aggregation (WBA) assay associated with release assay to monitor RPA, despite antiplatelet therapy and assess their relationship with clinical ischemic events. In this study, RPA was tested in 133 patients with ACS postpercutaneous coronary intervention between 24 and 36 hours after a 300-mg clopidogrel loading dose by modified assay. Then, these patients were followed up for 3 months for clinical ischemic events. Meanwhile, platelet activity of 58 healthy volunteers was also tested by modified assay. Results showed that in modified assay the point of platelet magnified activation time (MAT) and maximal platelet adenosine triphosphate release values (RV) have significant differences between healthy volunteers and patients ([90.86 ± 27.60 seconds] vs [206.44 ± 58.97 seconds] and [2.07 ± 0.64 nmol] vs [0.98 ± 0.49 nmol];P< .001 andP< .001, respectively). During follow-up, 5 patients present ischemic events. Receiver-operator characteristic curve showed that the cutoff values for MAT and RV were 156.5 seconds and 1.05 nmol, respectively, with the sensitivity and specificity of 60.00% and 83.30% and 80.00% and 67.50%, respectively; when MAT combined with RV, the sensitivity can be increased to 100%. Therefore, modified impedance WBA and release assay may be a potentially recommended reliable laboratory assays for monitoring the RPA.

Cangrelor versus clopidogrel in percutaneous coronary intervention: a systematic review and meta-analysis

AIMS

Cangrelor is a new antiplatelet agent that has been used in percutaneous coronary intervention (PCI) with mixed results. We aimed to review the evidence on the efficacy of cangrelor in comparison to clopidogrel in reducing ischaemic endpoints at 48 hours in patients undergoing PCI in large randomised trials.

METHODS AND RESULTS

In three large clinical trials involving 25,107 participants, the risk of the primary composite efficacy endpoint of death, MI and ischaemia-driven revascularisation at 48 hours, (pooled OR 0.94; 95% CI: 0.77-1.14, p=0.51, I2=68%), death from all cause (pooled OR 0.72, 95% CI: 0.36-1.43, p=0.34, I2=52%), myocardial infarction (pooled OR 0.94, 95% CI: 0.77-1.14, p=0.51, I2=68%) was not significantly different between cangrelor and clopidogrel. Likewise, severe or life-threatening bleeding was similar between cangrelor and clopidogrel (pooled OR 1.21, 95% CI: 0.70-2.12, p=0.50, I2=0%). The risk of stent thrombosis (pooled OR 0.59, 95% CI: 0.43-0.81, p=0.001, I2=0%), Q-wave myocardial infarction (pooled OR 0.53, 95% CI: 0.30-0.92, p=0.02, I2=0%) and ischaemia-driven revascularisation (pooled OR 0.71, 95% CI: 0.52-0.98, p=0.04, I2=0%) was lower in the cangrelor group.

CONCLUSIONS

Based on this meta-analysis, we did not find any difference in the risk of the primary composite efficacy endpoint of all-cause death, ischaemia-driven revascularisation, and myocardial infarction at 48hours between cangrelor and clopidogrel use. Given that cangrelor was associated with a lower risk of stent thrombosis, ischaemia-driven revascularisation and Q-wave myocardial infarction compared to clopidogrel, cangrelor can be considered as a suitable alternative during PCI.

Comparison of new adenosine diphosphate receptor antagonists with clopidogrel in patients with coronary artery disease: a meta-analysis

Recent data suggest the superiority of new adenosine diphosphate (ADP) receptor antagonists compared with clopidogrel in acute coronary syndrome patients. We aimed to assess the risks and benefits of new ADP receptor antagonists in patients with coronary artery disease (CAD). Relevant studies published through February 28, 2014 were searched and identified in the MEDLINE, EMBASE, and Cochrane databases. Summary estimates were obtained using a random-effects model. All nine published randomized controlled studies comparing new ADP receptor antagonists with clopidogrel in CAD were included. The database consisted of 66,900 patients; 33,782 on novel agents, and 33,118 on clopidogrel. New ADP receptor antagonists reduced the composite incidence of all-cause mortality, myocardial infarction or stroke (odds ratio [OR] 0.89, 95 % confidence interval [CI] 0.81-0.97, p = 0.01) but increased the incidence of non-coronary artery bypass grafting-related major bleeding (OR 1.24, 95 % CI 1.08-1.42, p = 0.003). The composite end point of the net rate of adverse clinical events, which was the combination of the primary efficacy end point and the primary safety end point, was significantly lower in the new agent group compared to the clopidogrel group (9.7 versus 10.6 %, OR 0.92, 95 % CI 0.85-1.00). Use of recently introduced new ADP receptor antagonists results in a reduction in adverse clinical outcomes but a substantial increase in bleeding. New agents revealed an improved combined efficacy and safety outcome compared to that of clopidogrel in patients with CAD.

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.

P2Y12-receptor-inhibiting antiplatelet strategies in acute coronary syndromes

Antiplatelet therapy in acute coronary syndromes is essential for preventing stent thrombosis and for reducing major adverse cardiovascular events. Treatment strategy has changed over the last years by frequent use of more active agents inhibiting the ADP mediated activation of platelets instead of clopidogrel, such as prasugrel and ticagrelor. Compared to clopidogrel these modern antiplatelet drugs showed a significant reduction of efficacy endpoints as well as an acceptable safety profile in large multicenter randomized trials (TRITON TIMI 38, PLATO). Going in with higher efficacy a generally higher bleeding risk of prasugrel could be reduced by optimizing the maintenance dose in elderly and underweight patients (TRILOGY-ACS). However even prasugrel and ticagrelor have shown a delayed onset of action in special patient populations (e.g. STEMI) suggesting that the optimal ADP inhibitor has not been found yet. Results of the CHAMPION PHOENIX trial indicate that cangrelor, an intravenous agent, might fulfill these high expectations of an ideal platelet inhibitor in the first hours of an ACS in special patient cohorts. This review summarizes the results of most important clinical studies investigating the novel P2Y12 receptor inhibiting antiplatelet drugs.

Pharmacogenomics of anti-platelet and anti-coagulation therapy

Arterial thrombosis is a major component of vascular disease, especially myocardial infarction (MI) and stroke. Current anti-thrombotic therapies such as warfarin and clopidogrel are effective in inhibiting cardiovascular events; however, there is great inter-individual variability in response to these medications. In recent years, it has been recognized that genetic factors play a significant role in drug response, and, subsequently, common variants in genes responsible for metabolism and drug action have been identified. These discoveries along with new diagnostic targets and therapeutic strategies hold promise for more effective individualized anti-coagulation and anti-platelet therapy.

Oral antiplatelet therapy in acute coronary syndromes: update 2012

Dual antiplatelet therapy (DAPT), usually consisting of clopidogrel and acetylsalicylic acid (ASA), has come into discussion in recent years due to an increasing number of major adverse cardiac events based on insufficient ADP-mediated platelet inhibition with clopidogrel, mainly explained by drug interactions or genetic variants slowing or hindering the bioactivation of the prodrug clopidgrel into an active metabolite. Accordingly, new antiplatelet agents like prasugrel and ticagrelor were investigated in large prospective randomized clinical trials in patients with different entities of acute coronary syndromes (ACS). Based on their beneficial results in comparison to clopidogrel, these agents have found their way into the recent international guidelines for treatment of patients with acute coronary syndromes. Both antiplatelet agents demonstrated superiority with respect to the primary composite endpoint (cardiovascular death/non-lethal myocardial infarction/stroke). Ticagrelor even exhibited a mortality benefit over the comparator, but both compounds also increased the risk of spontaneous major bleedings to a significant extent. However, the efficacy/safety ratio of prasugrel and ticagrelor compared to clopidogrel is better. This article widens the insight into the recent changes in antiplatelet therapy in ACS by discussing the clinically most important data derived from the TRITON-TIMI 38 trial and the PLATO trial, including also the retrospective and pre-defined subgroup analyses. This article also gives information about the recommended duration of DAPT and the situation when patients who need permanent anticoagulation (e.g. in case of non-valvular atrial fibrillation) deserve also DAPT after coronary stenting ('triple therapy').

Influence of genetic variations on levels of inflammatory markers of healthy subjects at baseline and one week after clopidogrel therapy; results of a preliminary study

We aimed to assess the association between the most common polymorphisms of cytochrome P450 (CYP) epoxygenases on the plasma levels of inflammatory markers in a population of healthy subjects. We also sought to determine whether CYP2C19*2 polymorphism is associated with the anti-inflammatory response to clopidogrel. In a population of 49 healthy young males, the baseline plasma levels of inflammatory markers including C-reactive protein, haptoglobin, orosomucoid acid, CD-40 were compared in carriers vs. non-carriers of the most frequent CYP epoxygenase polymorphisms: CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C8*2 and CYP2J2*7. Also, the variation of inflammatory markers from baseline to 7 days after administration of 75 mg per day of clopidogrel were compared in carriers vs. non-carriers of CYP2C19* allele and also in responders vs. hypo-responders to clopidogrel, determined by platelet reactivity tests. There was no significant association between epoxygenase polymorphisms and the baseline levels of inflammatory markers. Likewise, CYP2C19* allele was not associated with anti-inflammatory response to clopidogrel. Our findings did not support the notion that the genetic variations of CYP epoxygenases are associated with the level of inflammatory markers. Moreover, our results did not support the hypothesis that CYP2C19*2 polymorphism is associated with the variability in response to the anti-inflammatory properties of clopidogrel.

Pharmacogenomics of anti-platelet therapy: how much evidence is enough for clinical implementation?

Pharmacogenomics, the study of the genomics of drug response and adverse effects, holds great promise for more effective individualized (personalized) medicine. Recent evidence supports a role of loss-of-function (LOF) variants in the cytochrome P450 enzyme CYP2C19 as a determinant of clopidogrel response. Patients given clopidogrel after percutaneous coronary intervention who carry LOF variants do not metabolize clopidogrel, a prodrug, into its active form resulting in decreased inhibition of platelet function and a higher likelihood of recurrent cardiovascular events. Despite a large body of evidence supporting clinical utility, adoption of anti-platelet pharmacogenetics into clinical practice has been slow. In this review, we summarize the pharmacokinetic, pharmacodynamic and clinical evidence, identify gaps in knowledge and other barriers that appear to be slowing adoption, and describe CYP2C19 pharmacogenetics implementation projects currently underway. Only when we surmount these barriers will clinicians be able to use pharmacogenetic information in conjunction with the history, physical examination and other medical tests and information to choose the most efficacious anti-platelet therapy for each individual patient.

Successful prasugrel rescue therapy in clopidogrel resistant patients who had recurrent stent thrombosis of drug-eluting-stent: the role of prasugrel in clopidogrel nonresponders

Stent thrombosis is a very serious problem after drug-eluting stent (DES) implantation even though its incidence is about or less than 1%. As the clopidogrel resistance is expected to play an important role in the occurrence of stent thrombosis, new anti-platelet agents overcoming this issue can give us another choice. We experienced a case of a 58-year-old male with successful prasugrel rescue therapy in a patient with clopidogrel resistance who had recurrent stent thrombosis following DES implantation.

Antiplatelets in acute coronary syndrome: personal perspectives

High platelet reactivity (HPR) during dual-antiplatelet therapy is a marker of vascular risk, in particular stent thrombosis, in patients with acute coronary syndromes. Genetic determinants (CYP2C19*2 polymorphism), advanced age, female gender, diabetes and reduced ventricular function are related to a higher risk to develop HPR. In addition, inflammation and increased platelet turnover, as revealed by the elevated percentage of reticulate platelets in patients' blood, that characterize the acute phase of acute coronary syndrome are associated with HPR. To overcome the limitation of clopidogrel, new antiplatelet agents (prasugrel and ticagrelor) were developed and the demonstration of their superiority over clopidogrel was obtained in the two randomized trials, TRITON TIMI 38 and PLATO. Due to the current possibility not a choice between multiple antiplatelet strategies, the future prospect is to include, in addition to clinical data and classical risk factors, the definition of platelet function during treatment in order to set a tailored therapy.

High platelet reactivity on clopidogrel therapy correlates with increased coronary atherosclerosis and calcification: a volumetric intravascular ultrasound study

OBJECTIVES

This study sought to evaluate the relationship between platelet reactivity and atherosclerotic burden in patients undergoing percutaneous coronary intervention (PCI) with pre-intervention volumetric intravascular ultrasound (IVUS) imaging.

BACKGROUND

Atherosclerosis progresses by the pathologic sequence of subclinical plaque rupture, thrombosis, and healing. In this setting, increased platelet reactivity may lead to more extensive arterial thrombosis at the time of plaque rupture, leading to a more rapid progression of the disease. Alternatively, abnormal vessel wall biology with advanced atherosclerosis is known to enhance platelet reactivity. Therefore, it is possible that by either mechanism, increased platelet reactivity may be associated with greater atherosclerotic burden.

METHODS

This study included patients who underwent PCI with pre-intervention IVUS imaging and platelet reactivity functional assay (P2Y(12) reaction units) performed >16 h after PCI, after the stabilization of clopidogrel therapy (administered before PCI). Platelet reactivity >230 P2Y(12) reaction units defined high on-treatment platelet reactivity (HPR).

RESULTS

Among 335 patients (mean age 65.0 years, 71% men), there were 109 patients with HPR (32.5%) and 226 without HPR (67.5%), with HPR being associated with diabetes and chronic renal insufficiency. By IVUS analysis, patients with HPR had significantly greater target lesion calcium lengths, calcium arcs, and calcium indexes. Furthermore, patients with HPR tended to have longer lesions and greater volumetric dimensions, indicating higher plaque volume, larger total vessel volume, and also greater luminal volume, despite similar plaque burden. By multivariate analysis controlling for baseline clinical variables, HPR was the single consistent predictor of all IVUS parameters examined, including plaque volume, calcium length, and calcium arc.

CONCLUSIONS

Increased platelet reactivity on clopidogrel treatment, defined as >230 P2Y(12) reaction units, is associated with greater coronary artery atherosclerotic disease burden and plaque calcification.

Clinical utility of pharmacogenetic biomarkers in cardiovascular therapeutics: a challenge for clinical implementation

In the past decade, significant strides have been made in the area of cardiovascular pharmacogenomic research, with the discovery of associations between certain genotypes and drug-response phenotypes. While the motivations for personalized and predictive medicine are promising for patient care and support a model of health system efficiency, the implementation of pharmacogenomics for cardiovascular therapeutics on a population scale faces substantial challenges. The greatest obstacle to clinical implementation of cardiovascular pharmacogenetics may be the lack of both reproducibility and agreement about the validity and utility of the findings. In this review, we present the scientific evidence in the literature for diagnostic variants for the US FDA-labeled cardiovascular therapies, namely CYP2C19 and clopidogrel, CYP2C9/VKORC1 and warfarin, and CYP2D6/ADRB1 and β-blockers. We also discuss the effect of HMGCR/LDLR in decreasing the effectiveness of low-density lipoprotein cholesterol with statin therapy, the SLCO1B1 genotype and simvastatin myotoxicity, and ADRB1/ADD1 for antihypertensive response.

Change of Platelet Reactivity to Antiplatelet Therapy after Stenting Procedure for Cerebral Artery Stenosis: VerifyNow Antiplatelet Assay before and after Stenting

Purpose

VerifyNow antiplatelet assays were performed before and after stenting for various cerebral artery stenoses to determine the effect of the procedure itself to the function of dual antiplatelets given.

Materials and Methods

A total of 30 consecutive patients underwent cerebral arterial stenting procedure were enrolled. The antiplatelet pretreatment regimen was aspirin (100 mg daily) and clopidogrel (300 mg of loading dose followed by 75mg daily). VerifyNow antiplatelet assay performed before and right after stenting. The two test results were compared in terms of aspirin-reaction unit (ARU), P2Y12 reaction units (PRU), baseline (BASE), and percentage inhibition. We evaluated occurrence of any intra-procedural in-stent thrombosis or immediate thromboembolic complication, and ischemic events in 1-month follow-up.

Results

The median Pre-ARU was 418 (range, 350-586). For clopidogrel the medians of the pre-BASE, PRU, and percent inhibition were 338 (279-454), 256 (56-325), and 27% (0-57%). The medians of the post-ARU, BASE, PRU, and percent inhibition after stenting were 469 (range, 389-573), 378 (288-453), 274 (81-370), and 26% (0-79%). There was a significant increase of ARU (p=0.045), BASE (p=0.026), and PRU (p=0.018) before and after stenting. One immediate thromboembolic event was observed in poor-response group after stenting. There was no in-stent thrombosis and ischemic event in 1-month follow-up.

Conclusion

We observed a significant increase of platelet reactivity to dual antiplatelet therapy right after stenting procedure for various cerebral arterial stenoses.

Personalized antiplatelet therapy: review of the latest clinical evidence

P2Y12-ADP receptor antagonist use has been critical in the development of percutaneous coronary intervention, dramatically reducing the rate of early stent thrombosis. However, it recently was observed that a significant proportion of patients do not achieve optimal platelet reactivity inhibition after clopidogrel loading dose. The large interindividual variability in clopidogrel responsiveness is related to several factors, including the genetic polymorphism of hepatic cytochrome P450 2C19 (CYP2C19*2), which recently has been highlighted by a warning from the U.S. Food and Drug Administration. Of importance, patients exhibiting reduced clopidogrel metabolism and/or low clopidogrel responsiveness (ie, high on-treatment platelet reactivity) have an increased rate of thrombotic events after percutaneous coronary intervention. This review summarizes the current knowledge on this important clinical issue. While the future of genetic testing remains undetermined, several trials are underway to demonstrate the potential utility of platelet reactivity testing with P2Y12-ADP receptor antagonists.

Role of newly formed platelets in thrombus formation in rat after clopidogrel treatment: comparison to the reversible binding P2Y₁₂ antagonist ticagrelor

Platelet P2Y₁₂ receptors play an important role in arterial thrombosis by stimulating thrombus growth. Both irreversibly (clopidogrel) and reversibly binding (ticagrelor, AZD6140) P2Y₁₂ antagonists are clinically used for restricted periods, but possible differences in platelet function recovery after drug cessation have not been investigated. We treated WKY rats with a single, high dose of 200 mg/kg clopidogrel or 40 mg/kg ticagrelor. Blood was collected at different time points after treatment. Flow cytometry confirmed full platelet protection against ADP-induced αIIbβ₃ activation shortly after clopidogrel or ticagrelor treatment. At later time points after clopidogrel treatment, a subpopulation of juvenile platelets appeared that was fully responsive to ADP. Addition of ticagrelor to clopidogrel-treated blood reduced αIIbβ₃ activation of the unprotected platelets. In contrast, at later time points after ticagrelor treatment, all platelets gradually lost their protection against ADP activation. Perfusion experiments showed abolishment of thrombus formation shortly after clopidogrel or ticagrelor treatment. Thrombus formation on collagen was determined under high shear flow conditions. At later time points, large thrombi formed in the clopidogrel but not in the ticagrelor group, and unprotected, juvenile platelets preferentially incorporated into the formed thrombi. However, platelets from both groups were still similarly reduced in assays of whole blood aggregation. Conclusively, recovery of rat platelet function after ticagrelor differs mechanistically from that after clopidogrel. This difference is masked by conventional platelet aggregation methods, but is revealed by thrombus formation measurement under flow. Juvenile platelets formed at later time points after clopidogrel treatment promoted thrombus formation.