Influence of Genetic Polymorphisms on the Effect of High- and Standard-Dose Clopidogrel After Percutaneous Coronary Intervention

Protocol for the comparison of triflusal and clopidogrel in secondary prevention of stroke based on cytochrome P450 2C19 genotyping (MASETRO study): A multicenter, randomized, open-label, parallel-group trial

RATIONALE AND AIM

The antiplatelet effect of clopidogrel is reportedly influenced by cytochrome P450 2C19 (CYP2C19) polymorphisms. However, there is no data concerning the relationship between stroke recurrence and CYP2C19 polymorphisms in patients treated with clopidogrel for secondary prevention of ischemic stroke. Triflusal may be an alternative therapy for clopidogrel in patients with poor genotype. The Comparison of Triflusal and Clopidogrel Effects in Secondary Prevention of Stroke Based on Cytochrome P450 2C19 Genotyping (MAESTRO) study will investigate the effect of antiplatelet agents based on CYP2C19 polymorphisms in secondary prevention of ischemic stroke.

SAMPLE SIZE AND DESIGN

Assuming that 55% of patients belong to the poor genotype group, the required sample size is 1080 patients with at least 24 months of follow-up. This study is designed as a prospective, multicenter, randomized, parallel-group, open-label, and blind genotype trial. Patients who experience their first non-cardiogenic ischemic stroke within 30 days prior to screening are eligible. Patients received 300 mg triflusal twice a day or 75 mg clopidogrel once daily during the trial. The study is registered with ClinicalTrials.gov (NCT01174693).

STUDY OUTCOME

The primary outcome is recurrent ischemic stroke or hemorrhagic stroke. Secondary outcomes consist of composite major vascular events including stroke, myocardial infarction, coronary revascularization, or vascular death.

DISCUSSION

Personalized medicine may be essential for patients according to individual drug metabolism abilities. MAESTRO is the first prospective study designed to evaluate the effect of CYP2C19 polymorphism in secondary stroke prevention and will resolve several questions regarding preventive antiplatelet agents for recurrent stroke.

Aspirin resistance and other aspirin-related concerns

Aspirin is a widely used medication and has become a cornerstone for treating cardiovascular disease. Aspirin can significantly reduce the incidence of cardiovascular ischemic events, recurrence and mortality, thereby improving the long-term prognosis of patients. However, there has been a staggering increase in the volume of literature addressing the issue of so-called "aspirin resistance" in recent years, and for some patients, it is difficult to avoid adverse reactions to aspirin. In this review, we present both the historical aspects of aspirin use and contemporary developments in its clinical use.

Cost-effectiveness of clopidogrel, prasugrel and ticagrelor for dual antiplatelet therapy after acute coronary syndrome: a decision-analytic model

BACKGROUND

The use of prasugrel or ticagrelor as part of dual antiplatelet therapy with acetylsalicylic acid after acute coronary syndrome (ACS) improves clinical outcomes relative to clopidogrel. The relative cost-effectiveness of these agents are unknown. We conducted an economic analysis evaluating 12 months of treatment with clopidogrel, prasugrel or ticagrelor after ACS.

METHODS

We developed a fully probabilistic Markov cohort decision-analytic model using a lifetime horizon, from the perspective of the Ontario Ministry of Health and Long-Term Care. The model incorporated risks of death, recurrent ACS, heart failure, major bleeding and other adverse effects of treatment. Data on probabilities and utilities were obtained from the published literature where available. The primary outcome was quality-adjusted life-years (QALYs).

RESULTS

Treatment with clopidogrel was associated with the lowest effectiveness (7.41 QALYs, 95% confidence interval [CI] 1.05-14.79) and the lowest cost ($39 601, 95% CI $8434-$111 186). Ticagrelor treatment had an effectiveness of 7.50 QALYs (95% CI 1.13-14.84) at a cost of $40 649 (95% CI $9327-$111 881). The incremental cost-effectiveness ratio (ICER) for ticagrelor relative to clopidogrel was $12 205 per QALY gained. Prasugrel had an ICER of $57 630 per QALY gained relative to clopidogrel. Ticagrelor was the preferred option in 90% of simulations at a willingness-to-pay threshold of $50 000 per QALY gained.

INTERPRETATION

Ticagrelor was the most cost-effective agent when used as part of dual antiplatelet therapy after ACS. This conclusion was robust to wide variations in model parameters.

Efficacy and safety of cilostazol based triple antiplatelet treatment versus dual antiplatelet treatment in patients undergoing coronary stent implantation: an updated meta-analysis of the randomized controlled trials

The aim of this study was to obtain best estimates of the efficacy and safety of cilostazol-based triple antiplatelet therapy (TAPT: aspirin, clopidogrel and cilostazol) compared with dual antiplatelet therapy (DAPT: aspirin and clopidogrel) in patients undergoing coronary stent implantation. We searched the literature to identify all randomized clinical trials examining efficacy and safety of TAPT versus DAPT in patients undergoing coronary stent implantation. Major efficacy outcomes were death, non-fatal myocardial infarction (MI), ischemic stroke and stent thrombosis (ST) and the safety outcome was bleeding. Data were analyzed using the Review Manager 5.0.0 software. A total of 19 trials involving 7,464 patients were included. TAPT and DAPT were associated with similar rates of death, non-fatal MI, ischemic stroke and ST, but compared with DAPT, TAPT had lower rates of target lesion revascularization (TLR) (RR 0.67, 95 % CI 0.56-0.82, P < 0.0001) and target vessel revascularization (TVR) (RR 0.65, 95 % CI 0.55-0.77, P < 0.00001), as well as less late loss of minimal lumen diameter (mean difference -0.14, 95 % CI -0.17--0.11, P < 0.00001), and less binary angiographic restenosis (RR 0.54, 95 % CI 0.45-0.65, P < 0.00001). TAPT and DAPT had similar rates of bleeding, but TAPT had significantly higher rates of headache, palpitation, rash and gastrointestinal side-effects. Cilostazol-based TAPT compared with DAPT is associated with improved angiographic outcomes and decreased risk of TLR and TVR but does not reduce major cardiovascular events and is associated with an increase in minor adverse events.

Clinical pharmacokinetics and pharmacodynamics of clopidogrel

Acute coronary syndromes (ACS) remain life-threatening disorders, which are associated with high morbidity and mortality. Dual antiplatelet therapy with aspirin and clopidogrel has been shown to reduce cardiovascular events in patients with ACS. However, there is substantial inter-individual variability in the response to clopidogrel treatment, in addition to prolonged recovery of platelet reactivity as a result of irreversible binding to P2Y12 receptors. This high inter-individual variability in treatment response has primarily been associated with genetic polymorphisms in the genes encoding for cytochrome (CYP) 2C19, which affect the pharmacokinetics of clopidogrel. While the US Food and Drug Administration has issued a boxed warning for CYP2C19 poor metabolizers because of potentially reduced efficacy in these patients, results from multivariate analyses suggest that additional factors, including age, sex, obesity, concurrent diseases and drug-drug interactions, may all contribute to the overall between-subject variability in treatment response. However, the extent to which each of these factors contributes to the overall variability, and how they are interrelated, is currently unclear. The objective of this review article is to provide a comprehensive update on the different factors that influence the pharmacokinetics and pharmacodynamics of clopidogrel and how they mechanistically contribute to inter-individual differences in the response to clopidogrel treatment.

Influence of Genetic Polymorphisms on Clopidogrel Response and Clinical Outcomes in Patients with Acute Ischemic Stroke CYP2C19 Genotype on Clopidogrel Response

OBJECTIVES

This study sought to evaluate the influence of the genetic polymorphisms on platelet reactivity and clinical outcomes in acute ischemic stroke patients taking clopidogrel.

BACKGROUND

Little research has been published on relationships between genetic polymorphisms, platelet reactivity, and clinical outcomes in stroke patients treated with clopidogrel.

METHODS

Patients hospitalized in Changhai Hospital with acute ischemic stroke were randomly enrolled into treatment with a 75-mg daily maintenance dose of clopidogrel. Genotyping was detected by the MassARRAY iPLEX genotyping system (Sequenom Inc, San Diego, CA), and platelet reactivity was evaluated by the VerifyNow P2Y12 test (Accumetrics Inc., San Diego, CA). Sixteen single nucleotide polymorphisms (SNPs) within 9 genes were selected and high on-clopidogrel platelet reactivity (HPR) was defined as P2Y12 reaction units (PRU) value ≥230. The primary endpoint was ischemic events, including major adverse cardiac events (MACE), recurrence of stroke, transient ischemic attack (TIA), and the composite of vascular death, and the secondary endpoint was bleeding.

RESULTS

Of the 345 patients recruited, 275 (79.7%) patients were followed up for 1 year and 122 (35.4%) patients were categorized as HPR. Among the SNPs selected, only the CYP2C19*2 allele and the CYP2C19*3 allele were statistically significantly associated with PRU (P < 0.001 and P = 0.003, respectively). Similarly, the prevalence of HPR was associated with CYP2C19*2 and CYP2C19*3 (P < 0.001 and P = 0.001, respectively). During the 1 year of follow-up, a total of 64 (23.3%) cases of clinical events occurred, including 60 ischemic events and 4 bleeding events. There were no correlation between CYP2C19 variant alleles and clinical outcomes (P > 0.05), but a statistically significant relevance was found between the HPR and the ischemic events in 1 year of follow-up (P = 0.001).

CONCLUSIONS

CYP2C19*2 and CYP2C19*3 had a significant impact on clopidogrel response, but was not associated with ischemic events during 1 year of follow-up in patients with acute ischemic stroke. HPR was an independent risk factor for ischemic events, and the VerifyNow P2Y12 test may be available to guide individualized antiplatelet therapies in stroke patients in China.

The pharmacogenetic control of antiplatelet response: candidate genes and CYP2C19

INTRODUCTION

Aspirin, clopidogrel, prasugrel and ticagrelor are antiplatelet agents for the prevention of ischemic events in patients with acute coronary syndromes (ACS), percutaneous coronary intervention (PCI) and other indications. Variability in response is observed to different degrees with these agents, which can translate to increased risks for adverse cardiovascular events. As such, potential pharmacogenetic determinants of antiplatelet pharmacokinetics, pharmacodynamics and clinical outcomes have been actively studied.

AREAS COVERED

This article provides an overview of the available antiplatelet pharmacogenetics literature. Evidence supporting the significance of candidate genes and their potential influence on antiplatelet response and clinical outcomes are summarized and evaluated. Additional focus is directed at CYP2C19 and clopidogrel response, including the availability of clinical testing and genotype-directed antiplatelet therapy.

EXPERT OPINION

The reported aspirin response candidate genes have not been adequately replicated and few candidate genes have thus far been implicated in prasugrel or ticagrelor response. However, abundant data support the clinical validity of CYP2C19 and clopidogrel response variability among ACS/PCI patients. Although limited prospective trial data are available to support the utility of routine CYP2C19 testing, the increased risks for reduced clopidogrel efficacy among ACS/PCI patients that carry CYP2C19 loss-of-function alleles should be considered when genotype results are available.

Cytochrome P450 CYP 2C19*2 Associated with Adverse 1-Year Cardiovascular Events in Patients with Acute Coronary Syndrome

Background

The cytochrome P450 (CYP450) 2C19 681 genotypes affect the antiplatelet activity of clopidogrel. We investigated the correlation of CYP 2C19 681G > A mutation with clopidogrel resistance (CR). Additionally, we studied the effect of CR on clinical prognosis of patients with acute coronary syndrome (ACS).

Methods

One hundred ten ACS patients undergoing percutaneous coronary intervention, who were followed-up for 1 year, were included in the study. The patients were co-administered aspirin 100 mg/d and clopidogrel 75mg/d following a loading dose of 300 mg. CR was assessed on the basis of polymorphism observed in the CYP2C19 subgroup.

Results

Patients in GG genotype group exhibited greater inhibition of platelet aggregation than patients in GA and AA genotype groups (16.2 ± 10.1%; 10.2 ± 9.9%; 8.0 ± 5.9%, respectively, p < 0.01). CYP2C19 681GG genotype group was associated with lower CR than CYP2C19 681A allele (GA + AA) group (9/59 vs. (12+5)/51; p = 0.009). Over a follow-up of 12 months, the incidence of recurrent angina, acute myocardial infarction, and intra-stent thrombosis in CYP2C19 681 GG carriers was significantly lower than that in CYP2C19 681A allele (GA + AA) group (2/59 vs. 8/51, 1/59 vs. 6/51, 0 vs. 4/51, respectively, p < 0.05).

Conclusion

CYP 2C19*2 is associated with reduced clopidogrel antiplatelet activity and might be an important marker for poor prognosis of ACS.

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.

The impact of cytochrome P450 2C19 polymorphism on the occurrence of one-year in-stent restenosis in patients who underwent percutaneous coronary intervention: A case-match study

OBJECTIVE

In this case-match study, we evaluated the impact of the CYP2C19*2 polymorphism in the occurrence of in-stent restenosis during a 1-year follow-up period despite adequate dual anti-platelet therapy in Iranian patients having undergone percutaneous coronary intervention (PCI).

METHODS

This study, conducted at a tertiary referral heart center in Tehran, recruited 100 patients: 50 patients had in-stent restenosis after PCI during a 1-year follow-up and were compared to another 50 patients without in-stent restenosis who were individually matched according to sex. In order to evaluate the impact of the CYP2C19*2 polymorphism, case frequency matching was performed with respect to variables previously shown to be predictors of in-stent restenosis. The CYP2C19*2 polymorphism evaluated using real-time PCR methods.

RESULTS

Among all 100 patients (mean age=60.09 ± 10.29: 72.0% male), 89 (89%) patients had wild (CYP2C19*1/CYP2C19*1) and 11% had a heterozygous (CYP2C19*1/CYP2C19*2) genotypes, and there was no patient with a completely mutant genotype (CYP2C19*2/CYP2C19*2). Conditional logistic regression analysis showed that there was no significant association between genotype CYP2C19*1/CYP2C19*2 and the occurrence of in-stent restenosis after PCI (OR=2.5, p value=0.273).

CONCLUSION

Our findings indicated that carrying a CYP2C19*2 allele with a functional CYP2C19*1 allele had no significant association with in-stent restenosis 1 year after PCI. The antiplatelet treatment strategy for non-functional allele carriers is still a matter of controversy. Further studies with larger sample sizes are necessary to determine the prevalence of non-functional alleles in various populations and to achieve a consensus about the effective treatment strategy.

A prospective randomized evaluation of a pharmacogenomic approach to antiplatelet therapy among patients with ST-elevation myocardial infarction: the RAPID STEMI study

Treatment of carriers of the CYP2C19*2 allele and ABCB1 TT genotype with clopidogrel is associated with increased ischemic complications after percutaneous coronary intervention (PCI). We sought to evaluate a pharmacogenomic strategy among patients undergoing PCI for ST-elevation myocardial infarction (STEMI), by performing a randomized trial, enrolling 102 patients. Point-of-care genetic testing for CYP2C19*2, ABCB1 TT and CYP2C19*17 was performed with carriers of either the CYP2C19*2 allele or ABCB1 TT genotype randomly assigned to a strategy of prasugrel 10 mg daily or an augmented dosing strategy of clopidogrel (150 mg daily for 6 days then 75 mg daily). The primary end point was the proportion of at-risk carriers exhibiting high on-treatment platelet reactivity (HPR), a marker associated with increased adverse cardiovascular events, after 1 month. Fifty-nine subjects (57.8%) were identified as carriers of at least one at-risk variant. Treatment with prasugrel significantly reduced HPR compared with clopidogrel by P2Y12 reaction unit (PRU) thresholds of >234 (0 vs 24.1%, P=0.0046) and PRU>208 (3.3 vs 34.5%, P=0.0025). The sensitivity of point-of-care testing was 100% (95% CI 88.0-100), 100% (86.3-100) and 96.9% (82.0-99.8) and specificity was 97.0% (88.5-99.5), 97.1% (89.0-99.5) and 98.5% (90.9-99.9) for identifying CYP2C19*2, ABCB1 TT and CYP2C19*17, respectively. Logistic regression confirmed carriers as a strong predictor of HPR (OR=6.58, 95% CI 1.24-34.92; P=0.03). We confirmed that concurrent identification of three separate genetic variants in patients with STEMI receiving PCI is feasible at the bedside. Among carriers of at-risk genotypes, treatment with prasugrel was superior to an augmented dosing strategy of clopidogrel in reducing HPR.

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.

The relationship between on-clopidogrel platelet reactivity, genotype, and post-percutaneous coronary intervention outcomes in Chinese patients

BACKGROUND

High on-clopidogrel platelet reactivity reflects a poor response to clopidogrel and is associated with ischemic events, which has been attributed to several factors such as demographic, clinical characteristics and a polymorphism of CYP2C19. Some new platelet assays monitoring on-clopidogrel platelet reactivity are currently available in China, but their relevance to the CYP2C19 genotype and post-percutaneous coronary intervention outcomes remain to be elucidated.

METHODS

Patients were prospectively included if they had a successful percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) and received clopidogrel and aspirin. CYP2C19 loss-of function genotype, adenosine diphosphate (ADP)-induced maximum platelet aggregation rate (MPA ADP) measured by light transmittance aggregometry, ADP-induced platelet-fibrin clot strength (MA ADP) measured by thrombelastography, platelet reactivity index (PRI) measured by vasodilator-stimulated phosphoprotein phosphorylation (VASP), and the occurrence of 6-month major adverse cardiovascular events (MACE) were assessed in 178 patients.

RESULTS

High on-treatment platelet reactivity prevalence defined by MPA ADP > 46.0%, MA ADP > 47 mm and PRI > 50.0% was 27.0%, 24.2%, and 61.2%, respectively. ADP-specific assays (VASP PRI) differed according to CYP2C19 genotype, with a significant gene-dose effect (PMs > IMs > EMs, p < 0.05). Multivariate analysis showed MPA ADP > 46.0% and MA ADP > 47 mm to be independent predictors of MACE at 6 months.

CONCLUSIONS

CYP2C19 loss-of function genotypes with the *2 and/or *3 allele are highly prevalent in the Chinese population and are associated with higher residual platelet reactivity. High on-treatment platelet reactivity defined by MPA ADP or MA ADP predicts an increased risk of MACE for ACS patients undergoing PCI.

Routine screening for CYP2C19 polymorphisms for patients being treated with clopidogrel is not recommended

Recent efforts directed at potential litigation in Hawai'i have resulted in a renewed interest for genetic screening for cytochrome P450 2C19 (CYP2C19) polymorphisms in patients treated with clopidogrel. Clopidogrel is an antiplatelet agent, frequently used in combination with aspirin, for the prevention of thrombotic complications with acute coronary syndrome and in patients undergoing percutaneous coronary interventions. Cytochrome P-450 (CYP) 2C19 is an enzyme involved in the bioactivation of clopidogrel from a pro-drug to an active inhibitor of platelet action. Patients of Asian and Pacific Island background have been reported to have an increase in CYP2C19 polymorphisms associated with loss-of-function of this enzyme when compared to other ethnicities. This has created an interest in genetic testing for CYP2C19 polymorphisms in Hawai'i. Based upon our review of the current literature, we do not feel that there is support for the routine screening for CYP2C19 polymorphisms in patients being treated with clopidogrel; furthermore, the results of genetic testing may not be helpful in guiding therapeutic decisions. We recommend that decisions on the type of antiplatelet treatment be made based upon clinical evidence of potential differential outcomes associated with the use of these agents rather than on the basis of genetic testing.

Pharmacogenomics of antiplatelet drugs

Clopidogrel, a platelet P2Y12 inhibitor, is one of the most widely prescribed drugs in cardiovascular medicine because it reduces ischemic and thrombotic complications. It is a prodrug requiring biotransformation into the active metabolite by the hepatic cytochrome 450 system, especially the CYP2C19 enzyme. Candidate gene studies and genome-wide association studies have identified loss-of-function CYP2C19 variants to be associated with a diminished pharmacologic response. Specifically, compared with noncarriers, carriers of at least one copy of a loss-of-function CYP2C19 allele have ∼30% lower levels of active clopidogrel metabolite and ∼25% relatively less platelet inhibition with clopidogrel. Moreover, in patients treated with clopidogrel predominantly for percutaneous coronary intervention, carriers of 1 or 2 CYP2C19 loss-of-function alleles are at increased risk for major adverse cardiovascular outcomes, with an ∼1.5-fold increase in the risk of cardiovascular death, myocardial infarction, or stroke as well as an ∼3-fold increase in risk for stent thrombosis. Tripling the dose of clopidogrel in carriers of a CYP2C19 loss-of-function allele can achieve on-treatment platelet reactivity comparable to that seen with the standard 75 mg dose in wild-type individuals, but the impact on clinical outcomes remains unknown. Alternatively, 2 third-generation P2Y12 inhibitors are available: prasugrel and ticagrelor. These drugs are superior to clopidogrel in reducing ischemic outcomes and are unaffected by CYP2C19 loss-of-function alleles.

Characterization of patients with angioscopically-detected in-stent mural thrombi – genetics of clopidogrel responsiveness and generations of drug-eluting stents

BACKGROUND

The loss-of-function genotype of cytochrome P450 2C19 (CYP2C19) has been proposed as a risk factor for stent thrombosis in patients with drug-eluting stent implantation. The aim of this study was to clarify the clinical features of patients with angioscopically-detected in-stent mural thrombi (ISMT).

METHODS AND RESULTS

Enrolled were 100 stented segments in 55 patients with stable angina (20 bare-metal stents; 39 Cypher sirolimus-eluting stents [SES]; 26 Endeavor zotarolimus-eluting stents [ZES]; 13 Xience V everolimus-eluting stents; and 2 Nobori biolimus-eluting stents). Dual antiplatelet therapy (100 mg aspirin+75 mg clopidogrel once daily) had been continued since stenting. A poor metabolizer (PM) of clopidogrel was defined as a homozygote of CYP2C19 loss-of-function alleles. Coronary angioscopy revealed ISMT in 6 patients (5 SES, 1 ZES). Between the ISMT group and control group (n=49), there were no significant differences with regards to the VerifyNow P2Y12platelet function assay or in-stent endothelial coverage grade. Exact logistic regression analyses with stepwise forward selection at a significance level of 0.10 were performed to reveal predictive variables for ISMT (respectively: odds ratio, 95% confidence interval, P value: CYP2C19 PM genotype (3.28, 0.88-24.80, 0.09), SES implantation (3.37, 0.90-28.09, 0.08), and presence of yellow plaque (3.69, 1.14-25.70, 0.02).

CONCLUSIONS

Patients with ISMT were characterized by SES implantation, poor clopidogrel metabolism, and in-stent yellow plaque.

Role of genetic factors on the effect of additional loading doses and two maintenance doses used to overcome clopidogrel hyporesponsiveness

BACKGROUND AND OBJECTIVE

Additional loading doses and higher maintenance doses (MDs) have been used to overcome hyporesponsiveness of clopidogrel. We aimed to investigate whether genetic polymorphisms of two cytochromes (CYP2C19 and CYP2C9) and ABCB1 modify effect of such dose-adjustment strategy.

MATERIALS AND METHODS

We enrolled 118 patients undergoing elective or acute percutaneous coronary intervention (PCI) with drug eluting stent (DES). Platelet reactivity index (PRI) was measured using the vasodilator-stimulated phosphoprotein (VASP) index and a cut-off value of ≥ 60% was defined as hyporesponsiveness. Polymorphism of two cytochromes (CYP2C19, CYP2C9) and gene ABCB1 were determined. In patients hyporesponsive to the initial LD the dose-adjustment was performed using up to 3 additional 600 mg LDs in order to achieve PRI <60%, and both 150 mg and 75 mg MD were tested at the follow-up.

RESULTS

Patients with at least one CYP2C19*2 allele had higher baseline PRI after the initial LD (78.2 ± 13.1 vs. 65.3 ± 19.5, P=0.005). The PRI reduction with additional LD was significantly smaller in carriers of the CYP2C19*2 (25.2 ± 15.6 vs. 35.5 ± 16.8, P=0.025) and similar trend was observed with subsequent additional LDs. Both MDs were less effective in presence of CYP2C19*2. Target PRI was, however, more frequently achieved with higher MD even in presence of CYP2C19*2 (in 70.6% vs. 23.5% of hyporesponders, P=0.008). No such differences were observed for other polymorphisms.

CONCLUSIONS

In patients hyporesponsive to a routine clopidogrel doses the potency of additional LD and higher MD of clopidogrel is compromised by presence of CYP2C19*2 allele. The dose-adjustment strategy is not affected by ABCB1 C3435T or CYP2C9 genotypes.

Relationships between PON1 Q192R polymorphism and clinical outcome of antiplatelet treatment after percutaneous coronary intervention: a meta-analysis

This meta-analysis was performed to assess the relationships between the PON1 Q192R (rs662 T>C) polymorphism and the clinical outcome of antiplatelet treatment after percutaneous coronary intervention (PCI). A range of electronic databases were searched: Web of Science (1945-2013), the Cochrane Library Database (Issue 12, 2013), PubMed (1966-2013), EMBASE (1980-2013), CINAHL (1982-2013) and the Chinese Biomedical Database (CBM) (1982-2013) without language restrictions. Meta-analysis was conducted using the STATA 12.0 software. The crude odds ratio (OR) with their 95 % confidence interval (CI) were calculated. Six clinical cohort studies with a total number of 5,189 patients undergoing PCI for coronary heart disease were included. Our meta-analysis revealed that the PON1 Q192R polymorphism was correlated with an increased risk of major adverse cardiovascular events (MACE) in patients receiving antiplatelet treatment after PCI (C allele vs. T allele: OR = 1.22, 95 % CI 1.04-1.43, P = 0.014; CT+CC vs. TT: OR = 1.38, 95 % CI 1.03-1.86, P = 0.029; CC vs. TT: OR = 1.45, 95 % CI 1.05-1.99, P = 0.024; respectively), especially among Asians. Furthermore, we found significantly positive correlations between the PON1 Q192R polymorphism and the incidence of stent thrombosis in patients receiving antiplatelet treatment after PCI (C allele vs. T allele: OR = 1.42, 95 % CI 1.08-1.87, P = 0.011; CT+CC vs. TT: OR = 1.93, 95 % CI 1.01-3.67, P = 0.046; CC vs. TT: OR = 2.18, 95 % CI 1.09-4.35, P = 0.027; respectively). Our meta-analysis of clinical cohort studies provides evidence that the PON1 Q192R polymorphism may increase the risk of MACE and stent thrombosis in patients receiving antiplatelet treatment after PCI.

Role of phenotypic and genetic testing in managing clopidogrel therapy

The P2Y12 inhibitors, clopidogrel, prasugrel, and ticagrelor, are administered in fixed doses without laboratory monitoring. Randomized trials in acute coronary syndrome have shown that prasugrel and ticagrelor are more effective than standard-dose clopidogrel. Nonetheless, standard-dose clopidogrel remains widely used because it causes less bleeding and is less expensive. Patients treated with standard-dose clopidogrel have substantial variability in platelet inhibition, which is partly explained by genetic polymorphisms encoding CYP2C19, the hepatic enzyme involved in biotransformation of clopidogrel to its active metabolite. Some advocate tailoring P2Y12 inhibitor therapy according to the results of routine laboratory testing. Although there is good evidence for analytic, biological, and clinical validity of several phenotypic and genotypic biomarkers, the benefit of a management strategy that incorporates routine biomarker testing over standard of care without such testing remains unproven. Appropriately designed, adequately powered trials are needed but face the challenges of feasibility, cost, and the progressive switch from clopidogrel to prasugrel or ticagrelor.

ABCB1 C3435T and CYP2C19*2 polymorphisms in a Palestinian and Turkish population: A pharmacogenetic perspective to clopidogrel

Clopidogrel is an antiplatelet drug used to prevent recurrent ischemic events after acute coronary syndrome and/or coronary stent implantation. Single nucleotide polymorphisms (SNPs) such as CYP2C19*2 and ABCB1 C3435T have been found to play a role in different individual responses to clopidogrel. Since the prevalence of these SNPs is generally known to differ from one population to another, the aim of this study was to examine their prevalence in both a Palestinian and Turkish population. One hundred unrelated Palestinian subjects and 100 unrelated Turkish subjects were analyzed for CYP2C19*2 and ABCB1 C3435T polymorphisms by the amplification refractory mutation system (ARMS). Results showed an ABCB1 3435 T allele frequency of 0.46 (95% CI 0.391 to 0.529) in the Palestinian sample and 0.535 (95% CI 0.4664 to 0.6036) in the Turkish sample. CYP2C19*2 allele frequency was 0.095 (95% CI 0.0558 to 0.134) in the Palestinian sample and 0.135 (95% CI 0.088 to 0.182) in the Turkish sample. Our results provide information about the prevalence of the polymorphisms related to clopidogrel response in both the Palestinian and Turkish populations, in order to improve the safety and efficacy of clopidogrel through use of genetically guided, individualized treatment. The prevalence of these clinically significant alleles shed light on the importance of testing them before prescribing clopidogrel.

A comprehensive acute coronary syndrome algorithm for centers with percutaneous coronary intervention capability

A comprehensive acute coronary syndrome (ACS) protocol was developed to improve the quality of care for patients admitted with definite or probable ACS. These protocols were constructed to streamline the practice for diverse clinicians who care for ACS patients across a variety of clinical settings. They are applicable in the emergency department, the cardiac catheterization laboratory, and the inpatient settings for hospitals with primary percutaneous coronary intervention capability. These protocols standardized the care by selecting the best therapy for each clinical scenario based on available established guidelines to insure the safest and highest value (quality/cost) medical care.

Clinical pharmacogenetics implementation: approaches, successes, and challenges

Current challenges exist to widespread clinical implementation of genomic medicine and pharmacogenetics. The University of Florida (UF) Health Personalized Medicine Program (PMP) is a pharmacist-led, multidisciplinary initiative created in 2011 within the UF Clinical Translational Science Institute. Initial efforts focused on pharmacogenetics, with long-term goals to include expansion to disease-risk prediction and disease stratification. Herein we describe the processes for development of the program, the challenges that were encountered and the clinical acceptance by clinicians of the genomic medicine implementation. The initial clinical implementation of the UF PMP began in June 2012 and targeted clopidogrel use and the CYP2C19 genotype in patients undergoing left heart catheterization and percutaneous-coronary intervention (PCI). After 1 year, 1,097 patients undergoing left heart catheterization were genotyped preemptively, and 291 of those underwent subsequent PCI. Genotype results were reported to the medical record for 100% of genotyped patients. Eighty patients who underwent PCI had an actionable genotype, with drug therapy changes implemented in 56 individuals. Average turnaround time from blood draw to genotype result entry in the medical record was 3.5 business days. Seven different third party payors, including Medicare, reimbursed for the test during the first month of billing, with an 85% reimbursement rate for outpatient claims that were submitted in the first month. These data highlight multiple levels of success in clinical implementation of genomic medicine.

Genotype-guided use of oral antithrombotic therapy: a pharmacoeconomic perspective

Pharmacogenomics focuses on tailoring therapy to the individual as opposed to the historical model of fitting the individual to the therapy, and it offers the potential to maximize medication efficacy while reducing adverse events. By its very nature, personalized medicine is conducive to a patient-centered care model. Oral antithrombotics as a class could benefit immensely from this type of approach because an imbalance of safety and efficacy in either direction can yield deadly consequences. Since the current healthcare climate in the USA requires thoughtful allocation of resources, pharmacoeconomic analysis has become critical for all stakeholders, and the adoption of new technologies hinges upon economic impact. This article summarizes the current state of genetics in oral antithrombotic therapy, including clinical relevance as well as cost-effectiveness from a US healthcare system perspective, and provides insight into the future of pharmacogenomics in treating and preventing thromboembolic disorders.

Monitoring aspirin and clopidogrel response: testing controversies and recommendations

Antiplatelet therapy is the cornerstone of the treatment for patients with coronary artery disease (CAD). Dual therapy with clopidogrel and aspirin is currently the standard treatment after percutaneous coronary interventions. However, despite the use of clopidogrel, a considerable number of patients continue to suffer major adverse cardiac events. There is a growing degree of evidence supporting high on-treatment platelet reactivity (HPR) as a predictive factor for recurrent ischemic complications. Numerous studies have shown an interindividual variability of responsiveness to clopidogrel and aspirin, which is one of the reasons for HPR. There is yet to be established an assay for antiplatelet drug response as the gold standard. This paper provides a background to the current controversies surrounding the issue of testing for the effectiveness of antiplatelet therapy and reviews the various genetic and phenotype-based laboratory tests to measure aspirin and clopidogrel response and their correlation with clinical outcomes. On the basis of the current evidence and trying to be cost-effective, testing should be considered on a case-by-case basis, especially in patients who present with an acute coronary syndrome or stent thrombosis. In the case of stable CAD, we think that testing might be helpful in particular risk groups of patients to avoid ischemic or bleeding complications.

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.

Clopidogrel, prasugrel, or ticagrelor? a practical guide to use of antiplatelet agents in patients with acute coronary syndromes

Aspirin is a cornerstone of therapy in the treatment of patients with acute coronary syndromes (ACS). However, dual antiplatelet therapy reduces the risk of stent thrombosis and cardiovascular events compared with aspirin alone in the treatment of patients with ACS. Recently, there has been debate as to which antiplatelet agent should be added to aspirin in the ACS treatment regimen. This review summarizes the pharmacologic and clinical data comparing clopidogrel, prasugrel, and ticagrelor, and provides a practical guide to clinicians for determining which antiplatelet to use for patients with ACS.

Pharmacogenomics in Interventional Pharmacology: Present Status and Future Directions

Pharmacogenomics offers the possibility of tailoring a drug to a patient's unique genetic signature, improving the likelihood of clinical efficacy while minimizing risks. Clopidogrel, a platelet P2Y12 receptor inhibitor that forms the cornerstone of dual antiplatelet therapy in patients with unstable coronary artery disease and those undergoing percutaneous coronary intervention, is the first broadly used drug in cardiovascular medicine in which genotyping may help optimize outcomes. This article describes techniques to identify the genetic determinants of drug response, their application (ie, clopidogrel), and the challenges to integration of pharmacogenomics into the practice of interventional cardiology.

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.

A review of pharmacogenetics of adverse drug reactions in elderly people

Older adults are more susceptible to the prevalence of therapeutic failure and adverse drug reactions (ADRs). Recent advances in genomic research have shed light on the crucial role of genetic variants, mainly involving genes encoding drug-metabolizing enzymes, drug transporters and genes responsible for a compound's mechanism of action, in driving different treatment responses among individuals, in terms of therapeutic efficacy and safety. The interindividual variations of these genes may account for the differences observed in drug efficacy and the appearance of ADRs in elderly people. The advent of whole genome mapping techniques has allowed researchers to begin to characterize the genetic components underlying serious ADRs. The identification and validation of these genetic markers will enable the screening of patients at risk of serious ADRs and to establish personalized treatment regimens.The aim of this review was to provide an update on the recent developments in geriatric pharmacogenetics in clinical practice by reviewing the available evidence in the PubMed database to September 2012. A Pubmed search was performed (years 1999-2012) using the following two search strategies: ('pharmacogenomic' OR 'pharmacogenetic ') AND ('geriatric' or 'elderly ') AND 'adverse drug reactions'; [gene name] AND ('geriatric' or 'elderly ') AND 'adverse drug reactions', in which the gene names were those contained in the Table of Pharmacogenomic Biomarkers in Drug Labels published online by the US Food and Drug Administration ( http://www.fda.gov/drugs/scienceresearch/researchareas/pharmacogenetics/ucm083378.htm ). Reference lists of included original articles and relevant review articles were also screened. The search was limited to studies published in the English language.

Aspirin, Platelet P2Y12 Receptor Inhibitors, and Other Oral Antiplatelets: Comparative Pharmacology and Role in Elective PCI

Angina pectoris accounts for a large burden of disease worldwide. Antiplatelet agents play a crucial role in inhibiting the platelet response to vascular injury after percutaneous coronary intervention (PCI) for the management of coronary artery disease. Antiplatelet agents are also essential in the longer term, because the metallic structure of stents is inherently thrombogenic. This article examines the use of aspirin, P2Y12 inhibitors, and other oral antiplatelets in the setting of elective PCI. Dual antiplatelet therapy in elective PCI is now standard therapy. The clinical use of novel antiplatelet therapy in the setting requires further evaluation.

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.

Platelet function monitoring and clopidogrel

Antiplatelet therapy with aspirin and a platelet P2Y12 receptor antagonist reduces thrombotic and ischemic events after percutaneous coronary intervention and acute coronary syndrome. The platelet inhibitory effect of the thienopyridine clopidogrel varies widely among individuals, and high on-treatment platelet reactivity has been associated with a substantial hazard for post-PCI cardiovascular events, including stent thrombosis. The clinical availability of ex vivo methods to measure the antiplatelet effect of P2Y12 antagonists raises the possibility that incorporating platelet function testing into clinical practice could facilitate a stratified and efficient approach to antiplatelet therapy following PCI, although data from definitive randomized trials supporting a routine approach are currently lacking.

Pharmacogenetics and cardiovascular disease--implications for personalized medicine

The past decade has seen tremendous advances in our understanding of the genetic factors influencing response to a variety of drugs, including those targeted at treatment of cardiovascular diseases. In the case of clopidogrel, warfarin, and statins, the literature has become sufficiently strong that guidelines are now available describing the use of genetic information to guide treatment with these therapies, and some health centers are using this information in the care of their patients. There are many challenges in moving from research data to translation to practice; we discuss some of these barriers and the approaches some health systems are taking to overcome them. The body of literature that has led to the clinical implementation of CYP2C19 genotyping for clopidogrel, VKORC1, CYP2C9; and CYP4F2 for warfarin; and SLCO1B1 for statins is comprehensively described. We also provide clarity for other genes that have been extensively studied relative to these drugs, but for which the data are conflicting. Finally, we comment briefly on pharmacogenetics of other cardiovascular drugs and highlight β-blockers as the drug class with strong data that has not yet seen clinical implementation. It is anticipated that genetic information will increasingly be available on patients, and it is important to identify those examples where the evidence is sufficiently robust and predictive to use genetic information to guide clinical decisions. The review herein provides several examples of the accumulation of evidence and eventual clinical translation in cardiovascular pharmacogenetics.

Pharmacotherapy for the reduction of stent thrombosis

The benefits of percutaneous coronary intervention (PCI) can be offset by periprocedural complications such as acute vessel closure and stent thrombosis in the absence of adequate antiplatelet and antithrombotic therapy. Additionally, conditions occurring after 30 days post-PCI, such as in-stent restenosis or late stent thrombosis can occur. Excess antithrombotic therapy, on the other hand, carries a risk of major gastrointestinal or intracranial bleeding as well as vascular access site bleeding complications. In this review, evidence related to the various pharmacological agents for reduction of stent thrombosis available to clinicians during and after PCI will be explored.

Association of PON1 genotype and haplotype with susceptibility to coronary artery disease and clinical outcomes in dual antiplatelet-treated Han Chinese patients

PURPOSE

The aim of this study was to evaluate the association of PON1 genetic variants with the susceptibility to coronary artery disease (CAD) and with the clinical endpoints in aspirin and clopidogrel (dual antiplatelet therapy)-treated Han Chinese patients with CAD after percutaneous coronary intervention (PCI).

METHODS

A total of 538 Han Chinese patients undergoing PCI and receiving dual-antiplatelet therapy were sequentially recruited to the study and followed for up to 1 year. Healthy controls (n = 539) were enrolled during the same period. All study participants were genotyped for five genetic variants in PON1 and the cytochrome P450 2C19*2 mutation (CYP2C19*2). The effect of genetic variants on disease risk and clinical outcome of major adverse cardiac events (MACE) within 1 year or bleeding within 6 months was assessed.

RESULTS

CYP2C19*2 was associated with a higher risk of MACE (adjusted P = 0.0098), but a lower risk of bleeding events (adjusted P = 0.0016). The PON1 Q192R polymorphism was significantly associated with a lower risk of bleeding events [odds ratio (OR) 0.61, 95% confidence interval (CI) 0.43-0.87, adjusted P = 0.0066). The haplotype bearing the PON1 -126C allele was associated with a higher risk to CAD (OR 1.48, 95% CI 1.04-2.09, P = 0.029) and a higher risk of bleeding events (OR 1.68, 95% CI 1.10-2.56, P = 0.017) compared to the most frequent haplotype. The transcription activity of haplotype p-162A-126C-108C in the PON1 promoter was 2.6-fold higher than that of the most frequent haplotype (p-162G-126G-108T).

CONCLUSIONS

Based on these results, we suggest that the haplotype-bearing PON1 -126C allele contributes to the disease risk and the risk of bleeding events in dual antiplatelet-treated CAD patients after PCI.

The role of clopidogrel in the management of ischemic heart disease

PURPOSE OF REVIEW

Placebo-controlled randomized trials have demonstrated the efficacy of clopidogrel in combination with aspirin across a broad range of clinical presentations. Recent trials have addressed several remaining issues regarding clopidogrel therapy.

RECENT FINDINGS

Three randomized trials examined the role of platelet function testing (PFT) in clopidogrel-treated patients. The results do not support the use of PFT to adjust clopidogrel dose after percutaneous coronary intervention (PCI), particularly in patients with stable angina or ischemia, in whom event rates are low irrespective of on-treatment reactivity. Doses greater than clopidogrel 150  mg daily are required to sufficiently overcome high reactivity in CYP2C19 loss-of-function (LOF) allele carriers. Clopidogrel response variability also influences the time to platelet recovery after drug discontinuation, and a proof-of-principle study supports the concept of using PFT for surgical timing. Unlike its efficacy in the setting of acute coronary syndrome (ACS) and PCI, prasugrel was not superior to clopidogrel in medically treated patients recovering from ACS.

SUMMARY

Current data do not support routine PFT to guide antiplatelet therapy in patients undergoing nonurgent PCI. The role of PFT to optimize therapy in ACS patients remains unaddressed, and further study is needed to confirm its promise in guiding surgical timing in patients who have discontinued therapy. Clopidogrel remains an important therapeutic option for patients presenting after an ACS who did not undergo initial revascularization.

Role of CYP450 in Antiplatelet Therapy: Considerations for Patients at Risk for Further Cardiovascular or Cerebrovascular Problems

Objective:

To determine how interactions with cytochrome P450 ( CYP450) isoenzyme pathways may influence the selection of antiplatelet therapy in patients with cardiovascular and cerebrovascular disease.

Data Sources:

A MEDLINE search (1966-September 2012) was performed using the following MeSH search terms: clopidogrel, prasugrel, ticagrelor, aspirin, dipyridamole, drug interactions, polymorphism, cytochrome P450, platelets, platelet reactivity testing, and platelet function. In addition, reference citations were reviewed.

Study Selection and Data Extraction:

Selected studies analyzed the effects of CYP450 isoenzymes on the efficacy of antiplatelet therapy and potential drug-drug interactions.

Data Synthesis:

Antiplatelet therapy is pivotal in reducing the risk of acute coronary syndromes. Thienopyridines are commonly prescribed for antiplatelet drug therapy; however, a multitude of factors can influence their efficacy, given that thienopyridines require activation through CYP450 isoenzymes. Genetic polymorphisms in CYP450 isoenzymes and the susceptibility of drug-drug interactions mediated through the CYP450 system have led to variability in antiplatelet response. Two factors in particular have been prime targets in elucidating the role of CYP450 isoenzymes on thienopyridine activity and bioavailability: CYP2C19*2 polymorphisms and drug interactions with proton pump inhibitors. Additionally, many studies have surfaced in an attempt to quantify a patient's response to antiplatelet therapy but, to date, none has determined whether platelet reactivity testing is mandatory prior to initiation of therapy or whether it correlates with clinical efficacy. This review spotlights the pharmacokinetic and pharmacodynamic influences that CYP450 isoenzymes exert on antiplatelet therapies and attempts to categorize the role of platelet reactivity testing in determining the clinical significance of drug interactions.

Conclusions:

Suboptimal responses to antiplatelet therapy may occur because of interactions with CYP450 isoenzyme pathways. Further studies are warranted to clarify the impact of genetic polymorphisms and drug-drug interactions on clinical outcomes in patients with cardiovascular/cerebrovascular disease.

Mutational analysis clopidogrel resistance and platelet function in patients scheduled for coronary artery bypass grafting

Clopidogrel is an oral antiplatelet pro-drug prescribed to 40 million patients worldwide who are at risk for thrombotic events or receiving percutaneous coronary intervention (PCI). However about a fifth of patients treated with clopidogrel do not respond adequately to the drug. From a cohort of 105 patients on whom we had functional data on clopidogrel response, we used ultra-high throughput sequencing to assay mutations in CYP2C19 and ABCB1, the two genes genetically linked to respond. Testing for mutations in CYP2C19, as recommended by the FDA, only correctly predicted if a patient would respond to clopidogrel 52.4% of the time. Similarly, testing of the ABCB1 gene only correctly foretold response in 51 (48.6%) patients. These results are clinically relevant and suggest that until additional genetic factors are discovered that predict response more completely, functional assays are more appropriate for clinical use.