Clopidogrel loading dose adjustment according to platelet reactivity monitoring in patients carrying the 2C19*2 loss of function polymorphism

High on-treatment platelet reactivity in peripheral arterial disease: A systematic review

OBJECTIVES

To highlight current evidence pertaining to the measurement methods and prevalence of high on-treatment platelet reactivity (HTPR) in patients with PAD, as well as to evaluate the relationship between HTPR and recurrent adverse cardiovascular and limb events in PAD patients.

METHODS

A systematic review of English-language literature on HTPR in patients with PAD. An electronic literature search of PubMed and Medline was performed in May 2021.

RESULTS

A total of 29 studies with a total number of 11,201 patients with PAD were identified. HTPR during clopidogrel treatment ranges from 9.8 to 77%, and during aspirin treatment ranges from 4.1 to 50% of PAD patients. HTPR was associated with adverse clinical outcomes. The need for limb revascularisation was higher in patients with HTPR during clopidogrel use. Similarly, HTPR during aspirin use in the PAD population was predictive of adverse cardiovascular events (HR 3.73; 95% CI, 1.43-9.81; p = .007). A wide range of techniques were applied to measure platelet resistance, without consensus on cut-off values. Furthermore, differing patient populations, a variety of antiplatelet regimens, and differing clinical endpoints highlight the high degree of heterogeneity in the studies included in this review.

CONCLUSION

No consensus on technique or cut-off values for HTPR testing has been reached. Patients with HTPR are potentially at a greater risk of adverse limb-related and cardiovascular events than patients sensitive to antiplatelet therapy illustrating the need for clinical implementation of HTPR testing. Future research must aim for consistent methodology. Adaptation of antiplatelet therapy based on HTPR results requires further exploration.

Pharmacokinetics and bioequivalence evaluation of omeprazole and sodium bicarbonate dry suspensions in healthy Chinese volunteers

Omeprazole and sodium bicarbonate dry suspension are effective treatments for acid-related disorders. This study compared the bioequivalence and safety of the two formulations of omeprazole and sodium bicarbonate powder and assessed how CYP2C19 gene polymorphisms affect pharmacokinetics (PK). A single-center, randomized, single-dose, 2-sequence and 2-period crossover method was performed in forty healthy Chinese subjects. Blood samples were collected after a single dose for PK (AUC0-∞, AUC0-t, and Cmax) analysis. The concentrations of Omeprazole in human plasma were determined by HPLC-MS/MS. Besides, the gene polymorphisms of CYP2C19 were assessed by Sanger sequencing. The geometric mean ratios (90% confidence interval) [GMR (95% CI)] of Test/Reference preparation for Cmax: 95.2% (88.48%, 102.43%), AUC0-t: 97.47% (94.4%, 101.02%), AUC0-∞: 97.68% (94.27%, 101.21%) were within the range of 80.00-125.00%. The non-parametric test showed no statistical difference in Tmax between the two groups (p > 0.05). All drugs were well tolerated, no severe adverse reactions occurred, and no significant differences in adverse events between the two drugs. For CYP2C19 gene polymorphisms, the results showed that of 40 subjects, 12 subjects were extensive metabolizers, 24 were intermediate metabolizers, and 4 were poor metabolizers, the frequency of metabolic genotypes were 30%, 60%, and 10%. And the allele distributions for CYP2C19 were *1, *2, and *3 at 60%, 38.75%, and 1.25%. Both the CYP2C19 alleles and metabolic genotypes were consistent with other studies in Chinese. The results of PK parameters showed that different genotypes of CYP2C19 lead to significant differences in t1/2, AUC0-t, AUC0-∞ and Cmax, but no significant differences in Tmax in each group. At the same time, we confirmed that the PK parameters of the test and reference had no differences between the males and females. This study has shown that the pharmacokinetic parameters of the two formulations are not significantly different, which showed bioequivalence and exemplary safety. CYP2C19 gene polymorphism significantly differed in the PK parameters of omeprazole sodium bicarbonate powder.

Co-prescription of Dual-Antiplatelet Therapy and Proton Pump Inhibitors: Current Guidelines

Dual-antiplatelet therapy (DAPT) prevents thrombotic complications associated with coronary artery disease, acute coronary syndrome, and stent thrombosis following the percutaneous coronary intervention or coronary artery bypass grafting. When initiating DAPT, the risk of thrombosis must be balanced with the increased risk of upper gastrointestinal bleed (UGIB). Proton-pump inhibitors (PPIs) are concurrently prescribed with DAPT to reduce bleeding risk.

In this review, we discuss the benefits and potential complications of DAPT/PPI co-prescription. The only large international randomized control trial (RCT), Clopidogrel and the Optimization of Gastrointestinal Events Trial (COGENT), shows robust evidence that PPIs are a safe and effective method to reduce the risk of bleeding in patients on DAPT. However, more large-scale RCTs are needed to study potential long-term effects and draw a stronger conclusion on this topic.

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.

Should CYP2C19 Genotyping Be Recommended as a Straight Forward Approach to Optimize Clopidogrel Utilization in Patients with Ischemic Stroke Complicated by Type 2 Diabetes Mellitus?

BACKGROUND

There have been few studies on CYP2C19 genotypes and clopidogrel response associated with ischemic stroke (IS), especially IS complicated by type 2 diabetes mellitus (T2DM). This study aimed to investigate the possible association between CYP2C19 polymorphisms and high on-treatment platelet reactivity (HTPR) in IS patients with T2DM in China.

PATIENTS AND METHODS

A total of 426 consecutive IS patients with T2DM were enrolled in this case-control study and they were divided into HTPR group and non-HTPR group according to the ADP-induced platelet inhibition (PIADP) assessed by thromboelastography (TEG). Genotypes were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Various clinical and demographic data were also recorded. The association between CYP2C19 genetic variants and platelet function was assessed.

RESULTS

Carriers of CYP2C19*2 heterozygous and mutant homozygous genotypes showed significantly lower PIADP than non-carriers (27.2% vs 38.3%, p < 0.001; 27.41% vs 38.3%, p = 0.012, respectively). Compared with the control group, the CYP2C19*2 A allele was more frequent in the HTPR group (34.51% vs 25.82%, p = 0.002). The carriage of CYP2C19*2 mutant allele was significantly associated with increased risk of HTPR (odds ratio (OR) = 1.94, 95% confidence interval (CI) = 1.32-2.85). There was no significant correlation between CYP2C19*3 or *17 genotypes and HTPR risk.

CONCLUSION

CYP2C19*2 mutant allele was associated with attenuated platelet response to clopidogrel and increased risk of HTPR in IS patients with T2DM, suggesting that CYP2C19*2 polymorphism might be an important predictor of HTPR in this high-risk population.

The ABCB1, CYP2C19, CYP3A5 and CYP4F2 genetic polymorphisms and platelet reactivity in the early phases of acute coronary syndromes

Background

The aim was to study seven polymorphic markers of genes encoding proteins involved in the absorption, metabolism and pharmacokinetics of clopidogrel among patients with an acute coronary syndrome (ACS), who have undergone percutaneous coronary intervention (PCI).

Methods

Eighty-one ACS and PCI patients older than 18 years and treated with dual antiplatelet therapy were enrolled in the study. Platelet function testing and ABCB1, CYP2C19, CYP3A5 and CYP4F2 genotyping were performed. The predictive role of categorical variables, such as genotypes (carriers and non-carriers of polymorphism), on platelet reactivity (platelet reactivity units [PRU] platelet inhibition [PI]) was assessed by logistic regression (for categorical outcomes) and linear regression (for continuous outcomes) analysis. A p-value<0.05 was considered significant. The allele frequencies were estimated by gene counting, and Hardy-Weinberg equilibrium was tested using the chi-square test.

Results

Regarding clopidogrel response, 62 patients (76.5%) were clopidogrel responders and 19 were non-responders (23.5%). Mean PRU value and the percentage of platelet inhibition were 170.0±50.9 PRU and 28.6±19.9%, respectively. The effects of the CYP2C19*2 polymorphisms on PRU (166.0±50.8 vs. 190.7±48.2, p<0.038) and PI (30.6±20.0 vs. 18.1±16.3, p<0.013) were observed, and the rates of high platelet reactivity (HPR) were lower in CYP2C19*1/*1 than those in CYP2C19*1/*2+CYP2C19*2/*2 (16.2% vs. 53.8% p<0.0067). In comparison, no significant difference in PRU value and PI was observed at <5 days between the rest of polymorphisms (p>0.05). Based on the logistic regression analysis, CYP2C19*2 (OR: 4.365, CI: 1.25–17.67, p=0.022) was an independent predictor of HPR at <5 days, as was the stent diameter (OR: 0.219, CI: 0.002–0.229, p=0.049). The remaining polymorphisms had no influence.

Conclusions

The reactivity of the on-clopidogrel platelet in the early phase of ACS is influenced primarily by the CYP2C19 polymorphisms. We believe that the findings of the present study could supply additional evidence regarding the clinical appropriateness of the CYP2C19 genetic testing for designing suitable antiplatelet therapy in the early phase of ACS.

Pharmacogenetic testing by polymorphic markers 681G>A and 636G>A CYP2C19 gene in patients with acute coronary syndrome and gastric ulcer in the Republic of Sakha (Yakutia)

BACKGROUND

The focus of the study is to determine the prevalence of CYP2C19 alleles, associated with the risk of changes in the pharmacological response to clopidogrel and proton pump inhibitors in patients with acute coronary syndrome (ACS) and gastric ulcer from Russian and Yakut ethnic groups.

METHODS

The research included 411 patients with ACS (143 Russians and 268 Yakuts) and 204 patients with histologically confirmed gastric ulcer (63 Russians and 141 Yakuts). Genotyping of 681G>A and 636G>A polymorphisms was performed by using polymerase real-time chain reaction.

RESULTS

In both ethnic groups, Hardy-Weinberg equilibrium was followed in a distribution of alleles and genotypes in the population (p>0.05). The 681A allele frequency in the Yakut ethnic group was higher than in the Russian group: 17.53% vs. 8.39% (p=0.001). No statistically significant difference was found in the frequency of 636A in Yakuts and Russians with ACS: 3.92% vs. 3.50% (p=0.840). While comparing the frequency distribution of alleles 681A (13.49% vs. 14.54%, p=0.878) and 636A (7.94% vs. 7.80%, p=1) in patients with a gastric ulcer from Russian and Yakut ethnic groups, no significant difference was found in carrier frequency.

CONCLUSIONS

The results of the present study may be helpful for developing guidelines for CYPC19 genotype-directed antiplatelet therapy for Yakut and Russian patients.

Dabigatran versus vitamin k antagonist: an observational across-cohort comparison in acute coronary syndrome patients with atrial fibrillation

Essentials Acute coronary syndrome (ACS) with atrial fibrillation (AF) is a therapeutic challenge. Dual and triple antithrombotic therapy showed a similar thrombotic risk in ACS patients with AF. The omission of aspirin during the first month did not increase the rate of ischemic events. Replacement of vitamin K antagonist by dabigatran leads to an increased thrombotic risk.

SUMMARY

Background Dual antithrombotic therapy comprising a vitamin K antagonist (VKA) plus clopidogrel reduces the incidence of major bleeding compared with triple therapy (VKA + clopidogrel + aspirin) in acute coronary syndrome (ACS) patients with atrial fibrillation (AF), with a similar thrombotic risk. The oral thrombin inhibitor dabigatran (150 mg twice a day) showed superiority over VKA in non-valvular AF, but data supporting its use in AF patients presenting with ACS are limited. Objective We sought to evaluate the efficacy of dabigatran vs. VKA in the management of AF patients undergoing percutaneous coronary intervention for an ACS. Methods In this open-label study, 133 consecutive patients received dabigatran plus clopidogrel. Another cohort of 133 patients treated with VKA plus clopidogrel was used as the control group. Results After propensity score adjustment, the cumulative incidence of major adverse cardiovascular events over 24 months was higher with dabigatran vs. VKA (adjusted hazard ratio, 2.28; 95% confidence interval, 1.46-3.56). Similar rates of major bleeding were found (adjusted hazard ratio, 1.17; 95% confidence interval, 0.46-2.96). Conclusions In AF patients presenting with ACS, replacement of VKA by dabigatran concurrently with clopidogrel is associated with an increased thrombotic risk, without a reduction in major bleeding.

Genetic variability in response to clopidogrel therapy and its clinical implications

This article concentrates on individual genetic differences responsible for variations of action of clopidogrel, which have been found to be partially responsible for increased cardiovascular events in patients with coronary artery disease under dual antiplatelet therapy. According to these results, genotyping for the relevant gene polymorphisms, especially for the CYP2C19 loss-of-function alleles, has been discussed to be an effective method of individualising and optimising clopidogrel treatment. However, due to the facts that 1) there are no prospective studies demonstrating a clinical benefit of personalising antiplatelet therapy based on genotyping; 2) CYP2C19 polymorphisms account for only approximately 12% of variability in clopidogrel platelet response; 3) the positive predictive value of CYP2C19 loss-of-function polymorphisms for cardiovascular events in patients with acute coronary syndrome undergoing percutaneous coronary intervention is only approximately 12% – 20%; 4) it is likely that other clinical factors and risk constellations might be of greater clinical importance; and 5) it is unknown whether a specific genetic polymorphism is capable of influencing outcome for the individual patient; genetic profiling cannot be recommended for routine use at present but will remain of considerable scientific interest.

Decrease in high on-treatment platelet reactivity (HPR) prevalence on switching from clopidogrel to prasugrel: Insights from the switching anti-platelet (SWAP) study

The prevalence of high platelet reactivity (HPR) in patients who have switched from clopidogrel to prasugrel during maintenance phase after an acute coronary syndrome (ACS) event is unknown. Therefore, the effect of switching from clopidogrel to prasugrel on the prevalence of HPR was evaluated. This analysis from the previously reported SWAP (SWitching Anti Platelet) study assessed HPR at baseline, 2 and 24 hours, and seven days after switching from clopidogrel to prasugrel maintenance dose (MD), with or without a prasugrel loading dose (LD) using four definitions: maximum platelet aggregation (MPA) >65% (primary endpoint), MPA >50%, P2Y12 reaction units (PRU) >235, and platelet reactivity index (PRI) ≥50%. A total of 95 patients were available for analysis; 56 patients provided DNA for genetic assessments of cytochrome P450 (CYP) 2C19. There were 26 (27.4%) patients with HPR at the end of the clopidogrel run-in (defined as MPA >65%). The HPR prevalence varied by each definition and ranged from 19% (PRU >235) to 68% (PRI ≥50%). A significantly higher HPR prevalence was observed during clopidogrel versus the combined prasugrel therapy groups at seven days as measured by MPA >65% (21.2% vs. 4.5%, p>0.05), PRU >235 (18.8% vs. 0%, p=0.001), and PRI ≥50% (66.7% vs. 7.9%, p<0.0001). There was a significantly higher percentage of subjects carrying at least one reduced function allele with HPR measured by MPA >65% (p=0.02) or PRU >235 (p=0.05) than non-carriers with HPR. Switching ACS patients during maintenance clopidogrel therapy to prasugrel with or without an LD is associated with a reduced HPR prevalence and may provide an alternative strategy to treat patients with HPR, independent of CYP2C19 genotype.

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.

Genetic Polymorphisms of Cytochrome P450 Enzymes and Transport Proteins in a Russian Population and Three Ethnic Groups of Dagestan

AIM

The objective of this study was to investigate the prevalence of polymorphic markers of the CYP2C19, CYP2C9, CYP2D6, SLCO1B1, and ABCB1 genes among the three ethnic groups in Dagestan and compare it with the carrier frequency of these markers among the Russian population living in Moscow.

METHODS

The study involved 186 healthy, unrelated, and chronic medication-free volunteers (53 males and 133 females) of the three ethnic groups in the Dagestan Republic: 46 Laks, 90 Avars, and 50 Dargins. Genotyping was performed using real-time polymerase chain reaction-based methods. The allelic prevalences of the three Dagestan peoples were compared with ethnic Russians from the Moscow region.

RESULTS

Statistically significant differences for the following gene polymorphisms: CYP2C19*17, CYP2C9*3, ABCB1 (C3435T), SLCO1B1*5 were found between the Russian population and the three ethnic groups of the Dagestan republic.

CONCLUSION

The data obtained from this study will help with prioritization genotyping in the region.

Evaluation of baseline frequency of sister chromatid exchanges in an Italian population according to age, sex, smoking habits, and gene polymorphisms

OBJECTIVES

Increased SCEs frequencies in human lymphocytes are an indicator of spontaneous chromosome instability and could be influenced by different exogenous and endogenous factors. In this study, we evaluated the influence of age, sex, smoking habits, and genetic polymorphisms on the background levels of SCEs in peripheral blood lymphocytes.

METHODS

Two hundred-thirty healthy Italian subjects were recruited. Data about age, sex and smoking habits were recorded. Subjects were also genotyped for GSTT1, GSTM1, GSTP1 A/G, CYP1A1 Ile/Val, CYP2C19 G/A, ERCC2/XPD Lys751Gln, XRCC1 Arg194ATrp, XRCC1 Arg399Gln, and XRCC1Arg208His gene polymorphisms.

RESULTS

The frequency of SCEs/cell was 5.15 ± 1.87, with females showing a significantly higher SCEs value with respect to males (5.36 ± 2.10 and 4.82 ± 1.39, respectively). Smokers showed significantly increased levels of SCEs with respect to nonsmokers (5.93 ± 1.75 and 4.70 ± 1.79, respectively) whereas no differences were observed between heavy and light smokers. Age correlated with the RI value (P = .01) but not with the SCEs frequency (P = 07), although the 31-40 age group showed a significantly lower SCEs frequency with respect to the other age groups. A significant association was also found between GSTP2C19-AA, GSTT1-null, GSTM1-null, ERCC2/XPD Gln751Gln, and XRCC1 His208His genotypes, and higher frequencies of SCEs.

CONCLUSION

We describe the association between some phase I, phase II, and DNA-repair gene polymorphisms with increased SCEs frequencies, reinforcing the importance of genetic analysis in biomonitoring studies. Sex and age were found to be important endogenous factors that affect the level of genomic damage and the replicative capacity of cells, respectively.

Effects of CYP2C19 Genetic Polymorphisms on PK/PD Responses of Omeprazole in Korean Healthy Volunteers

The aim of this study was to examine the effects of CYP2C19*2 and *3 genetic polymorphisms on omeprazole pharmacokinetic (PK) and pharmacodynamic (PD) responses. Twenty-four healthy Korean volunteers were enrolled and given 20 mg omeprazole orally once daily for 8 days. The genotypes of CYP2C19 single nucleotide polymorphisms (SNPs) (*2, *3, and *17) were screened. The plasma concentrations of omeprazole, omeprazole sulfone, and 5-hydroxy (5-OH) omeprazole were determined by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The noncompartmental method was used for the determination of PK parameters. Change of mean pH and proportion (%) of time of gastric pH above 4.0 were estimated. The poor metabolizer (PM) group had the lowest metabolic ratio and exhibited the highest area under the curve (AUC) for omeprazole among the CYP2C19 phenotype groups. The PM group showed the greatest change of mean pH and the highest % time of gastric pH above 4.0. The relationship between AUC of omeprazole and % time of gastric pH above 4.0 was confirmed. The study demonstrates that CYP2C19*2 and *3 influence the PKs and PDs of omeprazole in Korean healthy volunteers.

Optimizing clopidogrel dose response: a new clinical algorithm comprising CYP2C19 pharmacogenetics and drug interactions

PURPOSE

Response to clopidogrel varies widely with nonresponse rates ranging from 4% to 30%. A reduced function of the gene variant of the CYP2C19 has been associated with lower drug metabolite levels, and hence diminished platelet inhibition. Drugs that alter CYP2C19 activity may also mimic genetic variants. The aim of the study is to investigate the cumulative effect of CYP2C19 gene polymorphisms and drug interactions that affects clopidogrel dosing, and apply it into a new clinical-pharmacogenetic algorithm that can be used by clinicians in optimizing clopidogrel-based treatment.

METHOD

Clopidogrel dose optimization was analyzed based on two main parameters that affect clopidogrel metabolite area under the curve: different CYP2C19 genotypes and concomitant drug intake. Clopidogrel adjusted dose was computed based on area under the curve ratios for different CYP2C19 genotypes when a drug interacting with CYP2C19 is added to clopidogrel treatment. A clinical-pharmacogenetic algorithm was developed based on whether clopidogrel shows 1) expected effect as per indication, 2) little or no effect, or 3) clinical features that patients experience and fit with clopidogrel adverse drug reactions.

RESULTS

The study results show that all patients under clopidogrel treatment, whose genotypes are different from *1*1, and concomitantly taking other drugs metabolized by CYP2C19 require clopidogrel dose adjustment. To get a therapeutic effect and avoid adverse drug reactions, therapeutic dose of 75 mg clopidogrel, for example, should be lowered to 6 mg or increased to 215 mg in patients with different genotypes.

CONCLUSION

The implementation of clopidogrel new algorithm has the potential to maximize the benefit of clopidogrel pharmacological therapy. Clinicians would be able to personalize treatment to enhance efficacy and limit toxicity.

Clinical evidence for oral antiplatelet therapy in acute coronary syndromes

Platelet-mediated thrombosis is a major pathophysiological mechanism that underlies acute coronary syndromes, and therefore, antiplatelet therapy is an important foundation in the treatment and prevention of recurrence of these syndromes. Nearly 30 years ago, aspirin was the first agent to show a benefit for acute coronary syndromes and is still a key therapeutic agent. The landmark CURE trial showed that the addition of a P2Y12 antagonist, clopidogrel, to aspirin was beneficial in the treatment of acute coronary syndromes. Despite substantial benefits with clopidogrel, limitations include the slow speed of onset, variable response, and a modest antiplatelet effect. Next-generation P2Y12 antagonists, prasugrel and ticagrelor, overcome these limitations and have been shown, in large-scale clinical trials for acute coronary syndromes, to reduce ischaemic events more than clopidogrel, at the expense of an increase in bleeding. Additional agents that target platelets by alternate mechanisms, including the protease-activated receptor-1 antagonist vorapaxar, have shown ischaemic benefit. These large-scale trials inform treatment decisions that need to balance ischaemic benefit and bleeding risk in patients with acute coronary syndromes. This Series paper describes major trial results, implications for clinical practice, and summarises continuing controversy.

Review of clopidogrel dose escalation in the current era of potent P2Y12 inhibitors

Dual anti-platelet therapy with aspirin and a P2Y12 inhibitor is the standard of care for patients with acute coronary syndromes (ACS) and for patients undergoing percutaneous coronary intervention (PCI). Clopidogrel is associated with increased risk of high on-treatment platelet reactivity (HTPR) compared to ticagrelor and prasugrel. Investigators have therefore sought to "escalate" clopidogrel dosing to overcome HTPR to reduce ischemic/thrombotic events. In this review, we will summarize the evidence for dose escalation in the context of genetic determinants of resistance and platelet function data. We will review contemporary clinical trials that have sought to improve delivery of dual antiplatelet therapy to patients with coronary artery disease and discuss the potential of clopidogrel dose escalation in specific populations.

Impact of tailored anti-P2Y12 therapies in acute coronary syndromes

Acute coronary syndromes are a major disease burden and the prognosis has improved over the last decades due to improvement of medical and interventional treatments. Novel P2Y12-ADP-receptor antagonists have been introduced into clinical treatment offering more potent and rapid onset of action with the downside of increased bleeding risk. This special report will focus on interindividual variability of antiplatelet drugs in the setting of acute coronary syndromes and the current impact and potential future of point-of-care testing to personalize therapy aiming to improve prognosis in acute coronary syndrome patients.

Genetics of platelet inhibitor treatment

Dual antiplatelet therapy with aspirin and a P2Y12 receptor antagonist is the standard of care in patients undergoing percutaneous coronary intervention (PCI) and in patients with acute coronary syndromes (ACS) because this regimen has markedly decreased the rate of cardiovascular events. The substantial variability in pharmacodynamic response as well as the moderate antiplatelet efficacy of clopidogrel has raised major concerns, since high on-clopidogrel platelet reactivity has consistently been associated with increased risk for ischaemic events in PCI patients. Baseline demographic and clinical variables contributing to the observed variability have been identified. Besides this, research within the past decade has focused on the impact of genetic polymorphisms encoding transport systems or enzymes involved in the absorption and metabolism of these drugs. Loss-of-function polymorphisms in CYP2C19 are the strongest individual variables affecting pharmacokinetics and antiplatelet response to clopidogrel, but explain no more than 5 to 12% of the variability in adenosine diphosphate-induced platelet aggregation on clopidogrel. No genetic variables contributing to clinical outcomes of patients treated with the newer P2Y12 receptor antagonists, prasugrel or ticagrelor, have been identified so far. This review aims to provide an update on the current status of genotype-based personalized therapy with clopidogrel.

Impact of diabetes mellitus and metabolic syndrome on acute and chronic on-clopidogrel platelet reactivity in patients with stable coronary artery disease undergoing drug-eluting stent placement

BACKGROUND

Previous studies, which compared the prevalence of high on-clopidogrel platelet reactivity (HCPR) in type 2 diabetes mellitus (T2DM) versus non-T2DM and obese versus nonobese patients provided conflicting results.

METHODS

We compared the prevalence of HCPR in patients with T2DM, metabolic syndrome (MS), or neither T2DM nor MS undergoing drug-eluting stent implantation for stable coronary artery disease. Platelet functions were measured after a 600-mg clopidogrel loading dose and after 4 months on clopidogrel 75 mg/d.

RESULTS

The prevalence of HCPR was significantly higher in 63 T2DM and 50 MS patients than in 43 patients with neither T2DM nor MS (46.0% and 52.0% vs 20.9%) after clopidogrel loading dose, whereas, at 4 months, only T2DM patients had a significantly higher prevalence of HCPR (50.8% and 31.3% vs 23.8%). By multivariable analysis, T2DM (odds ratio [OR] 3.62, 95% CI, 1.34-9.80, P = .011), MS (OR 4.00, 95% CI 1.39-11.46, P = .010), and previous chronic treatment with clopidogrel (OR 0.22, 95% CI 0.09-0.49; P < .001) were the main independent predictors of HCPR after clopidogrel loading dose, whereas only T2DM (OR 2.98, 95% CI 1.20-7.41, P = .017) was an important independent predictor of HCPR at 4 months.

CONCLUSIONS

Both MS and T2DM were independent predictors of HCPR after clopidogrel loading dose. On clopidogrel maintenance therapy, only T2DM remained an independent predictor. This observation may be clinically relevant in the current era of antiplatelet therapy.

Antiplatelet and anticoagulation agents in acute coronary syndromes: what is the current status and what does the future hold?

Mortality and morbidity in acute coronary syndromes (ACSs), caused principally by plaque erosion or rupture leading to thrombus formation and myocardial ischemia, have been reduced by a combination of antithrombotic agents (antiplatelet drugs and anticoagulants) and early revascularization. Aspirin is the foundation antiplatelet agent. New P2Y12 receptor inhibitors (prasugrel and ticagrelor) have clear benefits compared with clopidogrel for dual antiplatelet therapy, and cangrelor or vorapaxar, a thrombin receptor inhibitor, may be of value in specific settings. Anticoagulation uses 1 of 4 choices: bivalirudin, unfractionated heparin, enoxaparin, and fondaparinux. Moreover, some patients (such as those who have chronic atrial fibrillation) require triple therapy with aspirin, clopidogrel, plus an anticoagulant, frequently a vitamin K antagonist. New oral anticoagulants have been shown to be at least as effective as vitamin K antagonists in atrial fibrillation and led to fewer bleeding complications. Finally, the combination of aspirin, clopidogrel, and low-dose rivaroxaban has recently been approved by the European Medicines Agency (but not the Food and Drug Administration) for secondary prevention after ACS. Several strategies have been developed to balance the potential benefit of antithrombotic therapy against the risk of bleeding complications, for example, radial access in coronary angiography or restricted use of combination therapy, and others are under investigation, such as discontinuation of aspirin. This overview summarizes the current status of antithrombotic therapy in ACS and describes strategies currently explored to optimize its benefit/risk ratio.

Clinical pharmacokinetics of clopidogrel and its metabolites in patients with cardiovascular diseases

Background and Objective

Approximately 5–40 % of patients treated with clopidogrel do not display an adequate antiplatelet response. Clopidogrel resistance may be caused by insufficient drug absorption or impaired metabolic activation of the drug. The aim of this study was to evaluate the pharmacokinetics of clopidogrel and its metabolites in plasma samples from patients treated with high and low doses of clopidogrel, to obtain a possible explanation for antiplatelet resistance.

Methods

The study included patients receiving either a single 300 mg loading dose of clopidogrel (n = 17) or a 75 mg dose (n = 45) for at least 7 days before sample collection. The concentrations of clopidogrel and its metabolites—the inactive H3 and the pharmacologically active H4 isomers of the thiol metabolite and the inactive carboxylic acid metabolite—in plasma samples (stabilized with 2-bromo-3′-methoxyacetophenone) from three patients after 300 mg and from 41 patients after 75 mg of the drug were determined using a validated high-performance liquid chromatography method with tandem mass spectrometry. The non-stabilized samples from the remaining patients were analysed using a validated capillary electrophoresis method. The calculated concentrations were used to determine the pharmacokinetic parameters of the analytes. The pharmacodynamic response to clopidogrel treatment, expressed as adenosine diphosphate-induced platelet aggregation, was measured using a Multiplate analyser.

Results

The pharmacokinetic parameter values for the H3 and H4 isomers determined in the studied group of patients treated with clopidogrel 75 mg (maximum plasma concentration [C_max] 5.29 ± 5.54 and 7.13 ± 6.32 ng/mL for H3 and H4, respectively; area under the plasma concentration-time curve from time zero to time t [AUC_t] 7.37 ± 6.71 and 11.30 ± 9.58 ng·h/mL for H3 and H4, respectively) were lower than those reported in healthy volunteers, according to the literature data. Platelet aggregation measured with a Multiplate analyser ranged between 37 and 747 AU·min. A significant correlation was found between the C_max of the active H4 isomer and platelet aggregation (p = 0.025).

Conclusion

The C_max of the active H4 isomer and platelet aggregation measured by the Multiplate analyser may serve as markers of the patient response to clopidogrel therapy.

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.

Treatment options for patients with poor clopidogrel response

A significant percentage of patients demonstrate a poor antiplatelet response to clopidogrel. With the emergence of testing for genetic variations in drug-metabolizing enzyme function and testing for platelet function, it is becoming more common to identify patients as poor responders to clopidogrel. This leaves the clinician in a difficult situation when confronted with a patient deemed to be a poor clopidogrel responder as there is no clear therapeutic strategy for treating these patients. In this situation, a number of alternatives to conventional dosing of clopidogrel have been investigated, including increasing the dosage of clopidogrel, switching from clopidogrel to either prasugrel or ticagrelor, or adding cilostazol to clopidogrel therapy. All of these options have demonstrated pharmacologic benefit in terms of greater antiplatelet effects compared with standard clopidogrel dosing in patients with high on-treatment platelet reactivity or a genetic loss-of-function variant of CYP2C19, the main enzyme responsible for clopidogrel activation. However, the impact of each of these alternative therapies on clinical outcomes is poorly understood. Early studies have not shown a clinical benefit by increasing the clopidogrel dosage or switching to prasugrel although there is still much to be discovered in this area. Of the alternatives to standard dosing of clopidogrel, switching to either prasugrel or ticagrelor has the most potential benefit, but again, there is limited evidence to support this practice in patients who demonstrate high on-treatment platelet reactivity while on clopidogrel although the evidence is somewhat more supportive in patients who have a CYP2C19 loss-of-function variant allele. The evidence for increasing the dosage of clopidogrel or adding cilostazol is the least supportive, making these alternatives difficult to justify. Given the limited evidence to support switching treatments, some providers may simply opt to continue standard dosing of clopidogrel pending the results of ongoing trials. Much research is needed and is currently underway in this area, which will be helpful in establishing future treatment protocols for patients with poor clopidogrel response.

Platelet-reactivity tests identify patients at risk of secondary cardiovascular events: a systematic review and meta-analysis

BACKGROUND

Antiplatelet therapy is the standard treatment for the prevention of cardiovascular events (CVEs). High on-treatment platelet reactivity (HPR) is a risk factor for secondary CVEs in patients prescribed aspirin and/or clopidogrel. The present review and meta-analysis was aimed at assessing the ability of individual platelet-function tests to reliably identify patients at risk of developing secondary CVEs.

METHODS AND RESULTS

A systematic literature search was conducted to identify studies on platelet-reactivity measurements and CVEs. The main inclusion criteria were: (i) prospective study design; (ii) study medication, including aspirin and/or clopidogrel; and (iii) a platelet-function test being performed at baseline, before follow-up started. Of 3882 identified studies, 102 (2.6%; reporting on 44 098 patients) were included in the meta-analysis. With regard to high on-aspirin platelet reactivity (HAPR), 22 different tests were discussed in 55 studies (22 441 patients). Pooled analysis showed that HAPR was diagnosed in 22.2% of patients, and was associated with an increased CVE risk (relative risk [RR] 2.09; 95% confidence interval [CI] 1.77-2.47). Eleven HAPR tests independently showed a significantly increased CVE risk in patients with HAPR as compared with those with normal on-aspirin platelet reactivity. As regards high on-clopidogrel platelet reactivity (HCPR), 59 studies (34 776 patients) discussed 15 different tests, and reported that HCPR was present in 40.4% of patients and was associated with an increased CVE risk (RR 2.80; 95% CI 2.40-3.27). Ten tests showed a significantly increased CVE risk.

CONCLUSIONS

Patients with HPR are suboptimally protected against future cardiovascular complications. Furthermore, not all of the numerous platelet tests proved to be able to identify patients at increased cardiovascular risk.

α2A-Adrenergic receptor polymorphism potentiates platelet reactivity in patients with stable coronary artery disease carrying the cytochrome P450 2C19*2 genetic variant

OBJECTIVE

Platelet α2A-adrenergic receptors (ARs) mediate platelet aggregation in response to sympathetic stimulation. The 6.3-kb variant of α2A-AR gene is associated with increased epinephrine-induced platelet aggregation in healthy volunteers. The cytochrome P450 2C19*2 (CYP2C19*2) loss-of-function allele influences P2Y12-mediated platelet inhibition and hence the rate of major adverse cardiovascular events. We assessed the influence of 6.3-kb α2A-AR gene variant on platelet aggregation and its interaction with CYP2C19*2 loss-of-function allele in patients with stable angina on aspirin and clopidogrel (dual antiplatelet therapy).

APPROACH AND RESULTS

Aggregation to 5 increasing doses of epinephrine (from 0.156 to 10 μmol/L) was assessed in aggregation units by Multiplate Analyzer and platelet reactivity in P2Y12 reactivity units and % inhibition by VerifyNow P2Y12 assay before percutaneous revascularization. Gene polymorphisms were analyzed with TaqMan Drug Metabolism assay. Of 141 patients, aggregation was higher in 6.3-kb carriers (n=52) when compared with wild types (n=89) at all epinephrine doses (P<0.05) apart from 10 μmol/L (P=0.077). Percentage inhibition was lower (P=0.048) in 6.3-kb α2A-AR carriers. Percentage inhibition was lower (P=0.005) and P2Y12 reactivity units was higher (P=0.012) in CYP2C19*2 allele carriers. Higher P2Y12 reactivity units (P=0.037) and lower percentage inhibition (P=0.009) were observed in carriers of both 6.3-kb α2A-AR variant and CYP2C19*2 allele when compared with wild-type or with either mutation on its own.

CONCLUSIONS

The 6.3-kb α2A-AR variant is associated with increased platelet reactivity to epinephrine and has an additive effect along with CYP2C19*2 loss-of-function allele on P2Y12-mediated platelet responses in patients with stable angina on dual antiplatelet therapy.

Thromboembolic complications with Pipeline Embolization Device placement: impact of procedure time, number of stents and pre-procedure P2Y12 reaction unit (PRU) value

BACKGROUND

Thromboembolic events after Pipeline Embolization Device (PED) placement remain a feared complication among neuroendovascular surgeons. This study aimed to investigate potential risk factors for thromboembolic events in patients undergoing PED placement.

METHODS

Medical records of patients who underwent PED placement from April 2011 to August 2013 were reviewed. Variables including pre-procedure P2Y12 reaction unit (PRU) value, procedure time, number of PEDs deployed and perioperative neurovascular complications were recorded. Multivariate analysis was performed to identify risk factors for perioperative thromboembolic complications.

RESULTS

Seventy-four patients were identified. Six patients (8.1%) had changes in neurological status after PED placement including five (6.8%) thromboembolic complications and one (1.4%) delayed intracranial hemorrhage; 50.9% of patients had diffusion-weighted imaging (DWI) changes on post-procedural MRI. Longer procedure time (>116 min) and multiple PED placements (>1) were statistically significant risk factors for symptomatic thromboembolic events (p<0.01). A pre-procedural PRU value >208 had an OR of 11.32 (95% CI 0.06 to 212.57) for symptomatic thromboembolic complications, but the result was not statistically significant.

CONCLUSIONS

DWI changes on MRI occurred at a much higher rate than new neurological symptoms following PED placement. Longer procedure time and multiple PED deployment are associated with higher risks of new neurological changes due to thromboembolic events. There was a trend for an increased risk of a symptomatic thromboembolic event in patients with pre-procedural PRU values >208. Reloading (clopidogrel 600 mg) patients with preoperative PRU >208 was safe and may have a protective effect on thromboembolic events.

High residual platelet reactivity on clopidogrel: its significance and therapeutic challenges overcoming clopidogrel resistance

Over the last decade, dual antiplatelet therapy has been the mainstay of the management of Acute Coronary Syndrome, with clopidogrel therapy providing clear benefits over aspirin monotherapy and becoming the agent of choice for the prevention of stent thrombosis. While newer antiplatelet agents have now become available, clopidogrel is still widely used due to its low cost and efficacy. However, many patients still experience recurrent ischemic events. A poor response of the platelets to clopidogrel, called High Residual Platelet Reactivity (HRPR), has been incriminated to account for this dilemma. Despite the absence of a universal definition of HRPR or the gold standard test to quantify it, persistent high platelet reactivity has consistently been associated with recurrence of ischemic events. Clopidogrel metabolism is highly variable, and genetics, comorbidities and drug interactions can affect it. In this article we review all definitions of HRPR, explore the available tests to quantify it, the clinical outcomes associated with it, as well as strategies that have shown success in overcoming it.

Pharmacogenomics in cardiovascular disease: focus on aspirin and ADP receptor antagonists

Antiplatelet agents like aspirin and adenosine diphosphate receptor antagonists are effective in reducing recurrent ischemic events. Considerable inter-individual variability in the platelet inhibition obtained with these drugs has initiated a search for explanatory mechanisms and ways to improve treatment. In recent years, numerous genetic polymorphisms have been linked with reduced platelet inhibition and lack of clinical efficacy of antiplatelet drugs, particularly clopidogrel and aspirin. Consequently, attempts to adjust antiplatelet treatment according to genotype have been made, but the clinical benefit has been modest in studies performed so far. The progress in genome science over the last decade and the declining cost of sequencing technologies hold the promise of enabling genetically tailored antiplatelet therapy. However, more evidence is needed to clarify which polymorphisms may serve as targets to improve treatment. The present review outlines the panel of polymorphisms affecting the benefit of aspirin and adenosine diphosphate receptor antagonists, including novel and ongoing studies evaluating whether genotyping may be beneficial in tailoring antiplatelet therapy.

Comparison of On-Treatment Platelet Reactivity Between Triple Antiplatelet Therapy With Cilostazol and Standard Dual Antiplatelet Therapy in Patients Undergoing Coronary Interventions

Background:

The recent literature has shown that triple antiplatelet therapy with cilostazol in addition to the standard dual antiplatelet therapy with aspirin and clopidogrel may reduce platelet reactivity and improve clinical outcomes following percutaneous coronary intervention. The purpose of this meta-analysis is to compare the efficacy of triple antiplatelet therapy and dual antiplatelet therapy in regard to on-treatment platelet reactivity.

Methods:

Nine studies (n = 2179) comparing on-treatment platelet reactivity between dual antiplatelet therapy (n = 1193) and triple antiplatelet therapy (n = 986) in patients undergoing percutaneous coronary intervention were included. Primary end points were P2Y12 reaction unit (PRU) and platelet reactivity index (PRI). Secondary end points were platelet aggregation with adenosine diphosphate (ADP) 5 and 20 µmol/L and P2Y12% inhibition. Mean difference (MD) and 95% confidence intervals (CI) were computed and 2-sided α error <.05 was considered as a level of significance.

Results:

Compared to dual antiplatelet therapy, triple antiplatelet therapy had significantly lower maximum platelet aggregation with ADP 5 µmol/L (MD: −14.4, CI: −21.6 to −7.2, P < .001) and 20 µmol/L (MD: −14.9, CI: −22.9 to −6.8, P < .001), significantly lower PRUs (MD: −45, CI: −59.4 to −30.6, P < .001) and PRI (MD: −26, CI: −36.8 to −15.2, P < .001), and significantly higher P2Y12% inhibition (MD: 18.5, CI: 2.3 to 34.6, P = .025).

Conclusion:

Addition of cilostazol to conventional dual antiplatelet therapy significantly lowers platelet reactivity and may explain a decrease in thromboembolic events following coronary intervention; however, additional studies evaluating clinical outcomes will be helpful to determine the benefit of triple antiplatelet therapy.

Tailored Thienopyridine therapy: no urgency for CYP2C19 genotyping

Between 20% and 50% of cardiovascular patients treated with clopidogrel, an anti‐P2Y12 drug, display high on‐treatment platelet reactivity (HTPR) and are not adequately protected from major adverse cardiovascular events (MACE). Despite a minor influence of the CYP2C19*2 genetic variant on the pharmacodynamic response to clopidogrel (5% to 12%) and a limited or absent value for predicting stent thrombosis and MACE, this latter polymorphism is currently considered an important candidate to tailor anti‐P2Y12 therapy during percutaneous coronary intervention. Seven studies have examined the value of CYP2C19*2 for predicting HTPR in comparison to a specific pharmacodynamic assay (VASP assay). Overall, the summarized sensitivity of the CYP2C19*2 genotype for predicting HTPR was 37.6% (95% CI: 32.2 to 43.3%), yielding a negative likelihood ratio of only 0.77 (95% CI: 0.68 to 0.86) which confirms its limited value as a routine clinical aid. A tailored anti‐P2Y12 treatment strategy restricted to CYP2C19*2 carriers may be of some help, but this restrictive approach leaves out noncarriers with HTPR. As for platelet function testing, there is currently no convincing data to support that using CYP2C19*2 genotyping as a tailored anti‐P2Y12 treatment would be an effective strategy and there is no urgency for CYP2C19 genotyping in clinical practice. Strategies incorporating genotyping, phenotyping, and clinical data in a stratified and sequential approach may be more promising.

Platelet function tests in clinical cardiology: unfulfilled expectations

This review is a critical evaluation of publications in the past decade on the usefulness of platelet function tests (PFTs) in clinical cardiology, in aiding diagnosis, predicting risk, and monitoring therapy. The ideal PFT should: 1) detect baseline platelet hyperreactivity; 2) allow individualization of antiplatelet medication; 3) predict thrombotic risk; and 4) predict bleeding risk. The practicalities of clinical cardiology demand rapid, accurate, and reliable tests that are simple to operate at the bedside and available 24 h a day, 7 days a week. Point-of-care PFTs most widely evaluated clinically include PFA-100 and VerifyNow. None of these tests can reliably detect platelet hyperreactivity and thus identify a prothrombotic state. Identification of antiplatelet nonresponsiveness or hyporesponsiveness is highly test specific, and does not allow individualization of therapy. The power of PFTs in predicting thrombotic events for a given individual is variable and often modest, and alteration of antithrombotic treatment on the basis of the results of PFTs has not been shown to alter clinical outcome. PFTs in current mainstream use cannot reliably assess bleeding risk. These tests have been in use for over a decade, but the hopes raised by PFTs in clinical practice remain unfulfilled. Although physiologically relevant measurement of platelet function now is more important than ever, a critical reappraisal of available techniques in light of clinical requirements is needed. The use of native blood, global stimulus instead of individual agonists, contribution of thrombin generation by activated platelets to the test results, and establishment of a PFT therapeutic range for each antiplatelet drug should be considered and is discussed.

Pharmaco-mechanic antithrombotic strategies to reperfusion of the infarct-related artery in patients with ST-elevation acute myocardial infarctions

Primary percutaneous coronary intervention is the best treatment of patients with ST elevation myocardial infarction (STEMI). When managing a STEMI patient, our approach must be rapid and aggresive in order to interrupt the pathological process of thrombus formation and stabilization. The therapy must be initiated prior to angiography (pretreatment), continued during the procedure (periprocedural), recovery phase (in-hospital), and follow-up. The treatment strategies resulting in thrombus dissolution/extraction have focused on optimization of both pharmacological and interventional therapies. At present, there is no optimal evidence-based approach to all patients with STEMI, and the treatment of these patients needs to be modified with respect to the risk profile, availability of medical resources, and our experience. In this review, we summarize current pharmacological and interventional strategies used in the setting of STEMI and discuss potential benefits of novel dosing regimens and combinations of drugs and techniques.

CYP2C19 and PON1 polymorphisms regulating clopidogrel bioactivation in Chinese, Malay and Indian subjects

AIM, MATERIALS & METHODS: We investigated the functional significance of CYP2C19*2, *3, *17 and PON1 Q192R SNPs in 89 consecutive Asian patients on clopidogrel treatment and the prevalence of functionally significant polymorphisms among 300 Chinese, Malays and Asian Indians.

RESULTS

Both CYP2C19 loss-of-function alleles (*2 or *3) were associated with higher platelet reactivity while the CYP2C19 gain-of-function allele (*17) had lower platelet reactivity. For PON1, the median PRI was not significantly different between the QQ, QR and RR groups. The allele frequencies of CYP2C19*2, CYP2C19*3 and CYP2C19*17 were 0.280, 0.065 and 0.010 (rare) for Chinese, 0.310, 0.050 and 0.025 for Malays, and 0.375, 0.010 (rare) and 0.165 for Indians, respectively.

CONCLUSION

Our data suggest that genotyping studies to investigate clopidogrel response should include CYP2C19*2 and *3 but not *17 polymorphisms in Chinese, and CYP2C19*2 and *17 polymorphisms but not *3 in Indians. All three polymorphisms should preferably be genotyped in Malays.

Personalizing antiplatelet therapy with clopidogrel

Dual antiplatelet therapy with aspirin and clopidogrel is the accepted standard for prevention of ischemic complications after percutaneous coronary intervention and has been shown to reduce cardiovascular events in patients with acute coronary syndromes (ACSs). There is substantial interindividual variability in antiplatelet response to clopidogrel. Various clinical studies have demonstrated that patients with high on-clopidogrel platelet reactivity incur an increased risk for ischemic events. In recent years, several clinical and demographic variables as well as multiple genetic factors contributing to the variability in antiplatelet response to clopidogrel have been identified. We discuss strategies based on platelet function testing or genotyping for improvement of antiplatelet effects of clopidogrel and thereby clinical outcome.

CYP2C19*2/ABCB1-C3435T polymorphism and risk of cardiovascular events in coronary artery disease patients on clopidogrel: is clinical testing helpful?

BACKGROUND

Studies evaluating CYP2C19*2 and ABCB1-C3435T polymorphisms have shown conflicting results. We performed this meta-analysis to evaluate role of clinical testing for these polymorphisms in CAD patients on clopidogrel.

METHODS

19,601 patients from 14 trials were analyzed. The endpoints were major adverse cardiovascular events (MACE), cardiovascular (CV) death, stent thrombosis (ST), myocardial infarction (MI), stroke and major bleeding. Combined relative risks (RR) with 95% confidence intervals (CI) were computed for each outcome by using standard methods of meta-analysis and test parameters were computed.

RESULTS

CYP2C19*2 polymorphism was associated with higher risk of MACE [RR: 1.28, CI: 1.06-1.54; p=0.009], CV death [RR: 3.21, CI: 1.65-6.23; p=0.001], MI [RR: 1.36, CI: 1.12-1.65; p=0.002], ST [RR: 2.41, CI: 1.69-3.41; p<0.001]. No difference was seen in major bleeding events [RR: 1.02, CI: 0.86-1.20; p=0.83]. Subgroup analysis showed similar results for elective PCI [RR: 1.34, CI: 1.01-1.76; p=0.03], and PCI with DES [RR: 1.53, CI: 1.029-1.269; p=0.03]. CYP2C19*2 polymorphism has very low sensitivity (28-58%), specificity (71-73%), positive predictive value (3-10%) but good negative predictive value (92-99%). ABCB1-C3435T polymorphism analysis revealed similar MACE [RR: 1.13, CI: 0.99-1.29; p=0.06], ST [RR: 0.88, CI: 0.52-1.47; p=0.63] and major bleeding [RR: 1.04, CI: 0.87-1.25; p=0.62] in both groups.

CONCLUSION

In CAD patients on clopidogrel therapy, CYP2C19*2 polymorphism is associated with significantly increased adverse cardiovascular events. However, due to the low positive predictive value, routine genetic testing cannot be recommended at present.

Translational platelet research in patients with coronary artery disease: what are the major knowledge gaps?

Translational platelet function investigations performed in the percutaneous coronary intervention (PCI)-treated population receiving clopidogrel have identified high platelet reactivity to ADP (HPR) as a major risk factor for both acute as well as long-term ischaemic event occurrence, including stent thrombosis. Recent studies have highlighted the relation of single nucleotide polymorphisms of genes involved in clopidogrel absorption and metabolism to reduced pharmacokinetic and pharmacodynamic responses to clopidogrel. CYP 2C19 loss-of-function (LoF) allele carriage has been associated with increased thrombotic risk in the PCI population. However, there is no information regarding the utility of platelet function testing to predict outcomes in patients with stable coronary artery disease and in medically managed patients with acute coronary syndromes. Additionally, few studies have included longitudinal assessment of platelet function to assess a potential time-dependent relation to ischaemic event occurrence and no phase-III antiplatelet-therapy trial has included a large enough platelet function sub-study to examine the relation between on-treatment platelet reactivity, bleeding, and ischaemic event occurrence. Therefore, futher studies are needed to delineate the role of platelet function testing across the spectrum of symptomatic coronary artery disease.

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

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