Supplement article
Genetic and nongenetic factors influencing the response to clopidogrel Maria F. Notarangeloa, Federico Bontardellia and Piera Angelica Merlinib The antiplatelet drug clopidogrel is a commonly prescribed therapy in patients with acute coronary syndrome. However, its clinical efficacy is hampered by a wide inter-patient response variability, with over 30% of patients treated with this drug experiencing an inadequate antiplatelet response. There are growing evidences that clopidogrel response variability is associated with cytochrome P450 (CYP) enzyme genetic polymorphisms, primarily CYP2C19 which is responsible for the conversion of clopidogrel into its active metabolite. All of the CYP2C19 polymorphism data suggest that carriers of allele 2 or 17 are at greater risk of ischemic or bleeding events, particularly in patients with acute coronary syndrome undergoing percutaneous coronary intervention. Yet, CYP2C19 status explains only 12% of clopidogrel response variability, indicating that genetic variants other than CYP2C19 might be important. Clopidogrel undergoes intestinal efflux via P-glycoprotein, encoded by the ABCB1 gene. The C3435T polymorphism in this gene affects the bioavailability of clopidogrel, however, its effects on clinical outcomes are inconclusive. Similarly, a polymorphism in the gene encoding PON1, a rate-limiting
Introduction Platelet activation and aggregation play a central role in the pathogenesis of thrombosis, particularly stent thrombosis after percutaneous coronary intervention (PCI).1–3 Clopidogrel is a second-generation thienopyridine that inhibits platelet aggregation by selectively and irreversibly blocking the P2Y12 adenosine diphosphate (ADP) receptor on the platelet surface.4 Clopidogrel, usually in combination with aspirin, is the standard of care for the prevention of stent thrombosis after PCI and for reducing major adverse cardiovascular events (MACE) in patients with acute coronary syndrome (ACS).5–7 Clopidogrel is a prodrug that is absorbed in the intestine by a transporter and converted into its active metabolite by the hepatic cytochrome P450 (CYP). The conversion involves oxidation of clopidogrel into 2-oxo-clopidogrel, which is further oxidized into an active thiol group. The two-step conversion involves a number of enzymes such as CYP1A2, CYP2C19, CYP2B6, CYP2C9, CYP3A4, CYP35 and PON1, of which CYP2C19 is thought to be involved in both steps.8 Only about 15% of clopidogrel is converted into its active form, and the rest is hydrolyzed by esterases into an inactive carboxylic acid derivative. Clopidogrel clinical efficacy is hindered by variability in inter-patient pharmacodynamic response.9 Despite 1558-2027 ß 2013 Italian Federation of Cardiology
enzyme for clopidogrel bioactivation, also affects the response to clopidogrel. Among nongenetic factors, an adverse drug interaction between proton pump inhibitors and clopidogrel is often reported, but evidence is inconclusive. A genetic test to identify potential responders to clopidogrel might be useful. However, the use of such tests is currently limited because they focus mainly on CYP2C19 loss-of-function alleles, and there is no empirical evidence yet for genotype-guided clopidogrel therapy. J Cardiovasc Med 2013, 14 (suppl 1):S1–S7 Keywords: clopidogrel resistance, genetic polymorphisms, genotyping, pharmacogenomics, platelet aggregation a
Division of Cardiology, Azienda Ospedaliero-Universitaria of Parma, Italy and Director, Cardiovascular Genetics Unit, Department of Cardiology, Azienda Ospedaliera Ospedale Niguarda Ca` Granda, Milan, Italy
b
Correspondence to Dr Maria F. Notarangelo, Division of Cardiology, Azienda Ospedaliero-Universitaria of Parma, Via Gramsci 14, 43126, Parma, Italy Tel: +39 0521 702070; fax: +39 0521 702189; e-mail: [email protected] Received 18 June 2013 Accepted 26 June 2013
adequate treatment with a standard loading dose of clopidogrel 300 mg followed by a maintenance dose of 75 mg, about 30% of patients display persistent high platelet reactivity (defined as A, which results in a protein with no enzymatic activity. This variant is designated as CYP2C192 (2 or loss-of-function allele).23 In contrast, the variant resulting from an SNP at the 806C>T location results in a protein with increased enzymatic activity (CYP2C1917 or 17; gain-of-function allele). The other less common variants include CYP2C193, CYP2C194, CYP2C195, CYP2C196, CYP2C197 and CYP2C198, all of which are associated with decreased enzymatic activity. The prevalence of CYP2C19 polymorphisms varies by ethnicity, and the most common variants are 2 and 17.21,24 Based on the enzyme activity, patients can be classified into categories of metabolizing phenotypes. Patients carrying two normal alleles (1/1) are extensive metabolizers; those with one reduced-function allele (1/2) are intermediate metabolizers; those carrying two reduced-function alleles (2/2) are poor metabolizers; and those carrying one or two increased-function alleles (1/17 or 17/17) are ultra-rapid metabolizers.21
carriers of at least one CYP2C19 reduced-function allele showed a relative reduction of 32.4% in plasma exposure of the active metabolite of clopidogrel, and an absolute reduction in maximal platelet aggregation that was 9% less than that seen in noncarriers (P < 0.001 for both comparisons).21. Gurbel et al.22 showed that CYP2C19 genotype and high platelet reactivity together may help to stratify the cardiovascular risk, but they did not correlate well with each other, in stented patients receiving clopidogrel plus aspirin. Within the six CYP2C19 diplotypes, platelet aggregation and the prevalence of high platelet reactivity in the presence of 5 and 20 mM ADP increased with 2 doses and decreased with 17 doses; however, the wide variability seen within the diplotype groups indicated that CYP2C19 genotype did not correlate well with high platelet reactivity (Fig. 1).22 MACE
Among the clopidogrel-treated subjects in TRITON– TIMI 38 (TRial to assess Improvement in Therapeutic Outcomes by optimizing platelet InhibitioN with prasugrel Thrombolysis In Myocardial Infarction 38) trial, carriers of at least one CYP2C19 loss-of-function allele showed a relative 53% increase in the composite primary efficacy outcome of the risk of death from cardiovascular causes, MI or stroke (hazard ratio [HR] 1.53; 95% confidence interval [CI] 1.07–2.19; P ¼ 0.01), and a 3-fold increase in the risk of stent thrombosis (HR 3.09; 95% CI 1.19–8.00; P ¼ 0.02).21 Similar results were reported also from a meta-analysis of nine studies involving 9685 patients (91.3% underwent PCI and 54.5% had ACS) treated with clopidogrel.26 In this analysis, the risk of the composite endpoint was Fig. 1
Pharmacokinetics and pharmacodynamic response
Pharmacokinetics studies have shown that metabolism of clopidogrel to its active metabolite is diminished in carriers of the CYP2C19 loss of function alleles and platelet function studies have found that these alleles are associated with higher levels of platelet aggregation after clopidogrel treatment. Hulot et al.25 found that 10 mM ADP-induced platelet aggregation decreased gradually from baseline during treatment with clopidogrel 75 mg once daily in wild-type (1/1), young, healthy male volunteers, but did not change in carriers of at least one loss-of-function allele (1/2). Mega et al.21 clearly showed that genetic variants of CYP2C19 are associated with differences in the bioavailability of the active metabolite of clopidogrel, its antiplatelet effects and clinical outcomes. In a cohort of 162 healthy volunteers treated with clopidogrel,
Adenosine diphosphate (ADP)-induced platelet aggregation and the prevalence of high platelet reactivity (HPR) with CYP2C19 diplotype status in stented patients receiving clopidogrel plus aspirin. Figure reproduced with permission from Gurbel et al.22
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S3
significantly higher in carriers of one 2 allele (HR 1.55; 95% CI 1.11–2.17; P ¼ 0.01), and even higher in carriers of two 2 alleles (1.76; 95% CI 1.24–2.50; P ¼ 0.002), compared with noncarriers. The risk of stent thrombosis was also increased by 2.67- and 3.97-fold in one and two 2 allele carriers, respectively. Clinical outcome data concerning the relevance of CYP2C192 carrier status are also available in the setting of coronary stenting. Among patients undergoing coronary stent placement after pretreatment with clopidogrel (n ¼ 2485), carriers of CYP2C192 (1/2 or 2/2) had significantly higher risk of definite stent thrombosis, compared with noncarriers (HR 3.81, 95% CI 1.45– 10.02; P ¼ 0.006).27 A significant gene-dose effect, with 2/ 2 carriers being at highest risk, was also reported in this study. Data from the GIFT (Genotype Information and Functional Testing) sub-study of the GRAVITAS (Gauging Responsiveness With A VerifyNow AssayImpact On Thrombosis And Safety) trial showed that the adjusted HRs (95% CI) for cardiovascular death, MI or stent thrombosis in carriers of one and two 2 alleles were 1.07 (0.91–1.25) and 1.67 (1.09–2.56), respectively, compared with noncarriers.28 Conversely, large-scale analysis of the CURE (Clopidogrel in Unstable angina to prevent Recurrent Events) trial population showed that the effect of clopidogrel, as compared with placebo, was consistent, irrespective of CYP2C19 loss-of-function carrier status.29 In contrast with previous studies, which purely compared carriers of loss-of-function alleles versus noncarriers among clopidogrel-treated patients, the CURE analysis included a randomized control group, and clearly showed that the effect of clopidogrel in reducing the rate of the primary efficacy outcome was consistent among patients treated with clopidogrel, irrespective of the genetically determined metabolizer phenotype (P ¼ 0.12 for heterogeneity). The strongest association between CYP2C19 loss-of-function allele status and MACE therefore seems to be limited to patients with ACS undergoing PCI with stenting. Thus, a reasonable explanation for the controversial data of the CURE population analysis may be that only 18% of patients in the CURE population underwent PCI, and stenting was less extensively used (14.5%). There are only few data concerning the relationship between an increased response to clopidogrel and bleeding events. Sibbing et al.30 reported that CYP2C1917 carrier status is significantly associated with an enhanced response to clopidogrel treatment and a 4-fold increase in the risk of bleeding events, and has no protective effect on the occurrence of ischemic events.
Genetic variability in response to clopidogrel: beyond CYP2C19 genotype CYP2C19 genotype accounts only for a minor proportion of variation in clopidogrel response. A genome-wide
association study in 429 healthy Amish subjects identified genes responsible for variation in ADP-stimulated platelet aggregation in response to standard clopidogrel therapy.20 Interestingly, the strongest association with a diminished clopidogrel response was found for the rs12777823 polymorphism, which is in linkage disequilibrium with CYP2C192. However, the CYP2C192 genotype (30.8% heterozygous and 2.1% homozygous in the study population) explained only 12% of the variation in clopidogrel response. An additional 10% of variation was due to age, body mass index and triglyceride levels. Thus approximately 78% of variation remained unexplained, suggesting that genetic variants other than CYP2C19 might be important.20 The gut absorption of clopidogrel is opposed by the drug efflux pump P-glycoprotein (P-gp), encoded by the ABCB1 gene. It has been hypothesized that variations in the ABCB1 gene resulting in the overexpression of P-gp may affect responses to clopidogrel and clinical outcomes through decreased intestinal absorption of the drug. However, data concerning this genetic variant are still partial, and clinical studies have led to mixed results. Several studies have shown that C3435T polymorphism in the ABCB1 gene significantly influences the bioavailability of clopidogrel. Among patients with coronary artery disease (CAD) who had undergone PCI (n ¼ 60) and received a single loading dose of clopidogrel 600 mg, homozygous carriers of the variant C3435T (TT) had significantly lower clopidogrel Cmax and AUC than the combined group of heterozygous carriers (CT) and wild-type patients (CC) (P ¼ 0.001 for Cmax, P ¼ 0.0006 for AUC). The Cmax and AUC of clopidogrel active metabolite followed a similar pattern (P ¼ 0.011 for both).17 Another study showed that among patients with ACS undergoing PCI, carriers of TT were more likely to have an higher platelet reactivity despite clopidogrel therapy, than wild-type patients (odds ratio [OR] 5.23, 95% CI 1.34–20.45; P ¼ 0.017).31 These data are consistent with the pharmacogenetic analysis of the TRITON-TIMI 38 population,32 which indicated that clopidogrel-treated TT carriers had lower concentrations of the active drug metabolite and reduced platelet inhibition.32 Available evidence regarding the effect of C3435CT status on the clinical outcome is inconclusive, however. The study by Spiewak et al.31 and the genetic substudy of the PLATO trial33 found that the risk for an adverse outcome was not affected by C3435T variant, either homozygous or heterozygous. In contrast, the FAST-MI (French registry of Acute ST-elevation and non-ST-elevation-myocardial infarction) investigators reported that the risk for the composite endpoint of death, acute MI or stroke was 72% higher in carriers of the C3435T variant (CT or TT) compared with the wild-type allele, among patients with acute MI receiving clopidogrel therapy.34 On the other hand, the
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
S4 Journal of Cardiovascular Medicine 2013, Vol 14 (suppl 1)
Overcoming 2 status with high-dose clopidogrel Results from the CLOVIS-2 (CLOpidogrel and response Variability Investigation Study 2) trial showed that increasing the loading dose of clopidogrel was not effective in CYP2C19 2/2 carriers.36 This trial assessed the antiplatelet effect of high (900 mg) or standard (300 mg) loading doses of clopidogrel, according to genotype, in patients who had had an MI and had received maintenance doses of clopidogrel 75 mg for 3 months (n ¼ 106; mean age 40.1 years). The primary endpoint was the relative reduction in residual platelet aggregation (RR-RPA %) by genotype. Baseline RR-RPA was significantly different between genotypes in patients who had previously received clopidogrel maintenance doses, but not in clopidogrel-naı¨ve patients. The highest RR-RPA was seen in 2/2 carriers and the lowest in wildtype carriers (1/1) (Fig. 2a). After the clopidogrel 300 mg loading dose there was a significant gene-dose effect, with 1/1 carriers having the highest RR-RPA and 2/2 carriers the lowest (Fig. 2b). The clopidogrel 900 mg loading dose improved RR-RPA in 1/2 carriers but not in 2/2 carriers (Fig. 2b). The plasma concentration (AUC0–6) of clopidogrel active metabolite followed a pattern similar to RR-RPA. In the GIFT study, doubling the maintenance dose of clopidogrel to 150 mg was not effective in carriers of one or two CYP2C19 2 alleles.28 With the 150 mg dose, the OR (95% CI) for platelet reaction units (PRU) >230 was 1.62 (0.93–2.85) in 1/2 carriers and 11.20 (2.02– 62.09) in 2/2 carriers, compared with noncarriers. The ELEVATE-TIMI 56 (Escalating Clopidogrel by Involving a Genetic Strategy - Thrombolysis In
(a) p < 0.02 for all p = 0.16
p < 0.04
100
p = 0.03
ADP 20µmol/L-induced residual platelet aggregation (%)
Paraoxonase-1 (PON1) has been identified as the ratedetermining enzyme for clopidogrel bioactivation in vitro, and the Q192R polymorphism in the PON1 gene has been shown to affect the rate of clopidogrel active metabolite formation.35 Among patients with CAD who had undergone PCI and received clopidogrel therapy, carriers of the homozygous Q192R variant (QQ) had less plasma PON1 activity, lower plasma concentrations of the active metabolite, and a lower degree of platelet inhibition, than heterozygote carriers (QR) or wild-type patients (RR). Carriers of QQ were at considerably higher risk for stent thrombosis, than QR carriers or wild-type patients (OR 3.6; 95% CI 1.6–7.9; P ¼ 0.003).35
Fig. 2
75
50
25
0 wt/wt
wt/*2
*2/*2
CYP2C19*2 genotype
(b) 300mg-LD < 0.003 for all*
Relative change of ADP 20µmol/L-induced residual platelet aggregation (%)
TRITON-TIMI 38 pharmacogenetic analysis showed that carriers of TT had a higher risk for the composite of cardiovascular death, MI or stroke than carriers of CT or wild-type patients (OR 1.72, 95% CI 1.22–2.44; P ¼ 0.002).32 The authors of this study noted that variants of both the ABCB1 and CYP2C19 genes were significant independent predictors of cardiovascular risk, and provide complementary information about this risk.
0.03
100
900mg-LD < 0.0005 for all*
0.04
0.20
p = 0.0045
< 0.001
p < 0.001
75
50
25
0 wt/wt
wt/*2
*2/*2
wt/wt
wt/*2
*2/*2
CYP2C19*2 genotype
Effect of CYP2C19 2 allele status on residual platelet aggregation in patients with myocardial infarction. A. Baseline levels after clopidogrel 75 mg maintenance therapy; B. after 300 mg and 900 mg clopidogrel loading dose. ADP, Adenosine diphosphate; LD, loading dose; wt, wild type. Figure reproduced with permission from Collet et al.36
Myocardial Infarction 56) trial demonstrated that tripling the maintenance dose of clopidogrel to 225 mg in carriers of one CYP2C19 2 allele achieved the same level of platelet reactivity as noncarriers treated with the standard 75 mg maintenance dose. However, even doses of up to 300 mg did not achieve the same level of platelet reactivity in 2/2 carriers.37 In this trial, 315 patients with known cardiovascular disease (MI and/or PCI within 4–6 weeks before enrollment) received clopidogrel 75, 150, 225 or 300 mg daily for 14 days (all with aspirin 81– 325 mg). Response to clopidogrel was measured using on-treatment vasodilator-stimulated phosphoprotein platelet reactivity index (VASP PRI) and platelet function test (VerifyNow P2Y12) reported as PRU. After treatment with clopidogrel 75 mg, carriers of 1/2 and
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S5
2/2 had significantly higher VASP PRI (70.0% and 86.6%, respectively versus 57.5%) and PRU (225.6 and 328.8, respectively versus 163.6) than noncarriers (P < 0.001 for all comparisons). Carriers of 1/2 treated with clopidogrel 225 mg had a similar reduction in platelet reactivity to noncarriers treated with 75 mg (VASP PRI 52.7% and 57.5%, respectively; PRU 152.9 and 163.6, respectively). However, carriers of 2/2 treated with clopidogrel doses as high as 300 mg still had high VASP PRI (68.3%) and PRU (287.0). The above findings indicate that increasing the loading or maintenance dose of clopidogrel does not achieve adequate antiplatelet effect in homozygous carriers of CYP2C19 loss-of-function alleles, and these patients should be treated with alternative P2Y12 inhibitors.
Alternative therapies Ticagrelor and prasugrel provide a more homogenous antiplatelet effect than clopidogrel across individuals carrying different CYP2C19 genotypes (Table 1).21,33,38 In the pharmacogenetic analysis of the TRITON-TIMI 38 population, the incidence of MACE was significantly higher in carriers of at least one loss-of-function allele in CYP genes than noncarriers treated with clopidogrel (12.1% versus 8%; P < 0.01).21 However, the MACE rate was similar between carriers and noncarriers treated with prasugrel (8.5% versus 9.8%).38 The genetic substudy of the PLATO (PLATelet inhibition and patient Outcomes) trial showed that the incidence of MACE was similar between carriers and noncarriers of any loss-offunction allele treated with ticagrelor (8.8% and 8.6%, respectively).33 Furthermore, this study showed that ticagrelor had significantly greater antiplatelet effect than clopidogrel in both carriers and noncarriers of CYP2C19 and ABCB1 polymorphisms.
Effect of proton pump inhibitors on clopidogrel response Concerns have been raised about the clinical impact of the interaction between clopidogrel and proton pump inhibitors (PPIs). Ex vivo biological studies have suggested that PPIs, especially omeprazole, might decrease the antiplatelet effect of clopidogrel, by means of the inhibition of the hepatic CYP2C19 and therefore the conversion of clopidogrel into its active metabolite through competition for the same substrate. Although there is a mechanistic basis, and pharmacodynamic data support Incidence of cardiovascular death, myocardial infarction and stroke (N) by CYP2C19 2 status in patients treated with clopidogrel, prasugrel or ticagrelor Table 1
% (n) Clopidogrel Prasugrel Ticagrelor
Carriers 12.1% (395) 8.5% (407) 8.8% (1384)
Noncarriers 8.0% (1064) 9.8% (1048) 8.6% (3551)
P value 0.01 0.27 0.46
Reference 21 38 32
an interaction between PPIs and clopidogrel, clinical significance of this interaction is still unclear.39 In a cross-sectional observational study (n ¼ 1000), omeprazole, but not pantoprazole or esomeprazole, significantly reduced the antiplatelet effect of clopidogrel in patients who previously received coronary stent placement and long-term clopidogrel treatment.40 Moreover, a retrospective analysis of data from a registry (n ¼ 2066) showed that concomitant use of a PPI with clopidogrel was associated with a higher risk of rehospitalization for MI or stent placement, than clopidogrel alone.41 However, these data were not confirmed in the post hoc analysis of TRITON TIMI-38 trial. In this large population of patients with ACS, despite the observed attenuation of the in-vitro antiplatelet effect of clopidogrel, the use of a PPI was not independently associated with an increased risk of adverse clinical outcomes after adjusting for potential confounders and the propensity to be treated with a PPI (HR 0.94, 95% CI 0.80–1.11).42 Moreover, the COGENT trial, the first randomized phase 3 study testing a combination of 20 mg omeprazole and clopidogrel versus placebo and clopidogrel in patients requiring clopidogrel for at least 12 months, showed that the negative influence of PPIs on the antiplatelet effect of clopidogrel did not translate into worse clinical outcomes. After only 133 days of follow-up, due to early termination of the trial, the patients assigned to omeprazole had a lower number of upper gastrointestinal clinical events, but there were no differences in clinical endpoints of cardiovascular death and MI between the two groups (HR 1.02, 95% CI 0.70–1.51; P ¼ NS).43
Interaction between CYP2C19 genotype and PPI In the FAST-MI study, clopidogrel plus PPI use was associated with poor outcomes in CYP2C19 2/2 carriers, but not in 1/2 carriers.44 The FAST-MI registry study collected outcome data from 3670 patients with MI. The outcomes were in-hospital events (proportion of death, reinfarction, stroke, major bleeding and transfusion) and the proportion of death, MI/stroke at 1 year. Among 2353 patients who were clopidogrel- and PPI-naı¨ve at admission and received clopidogrel within 48 h, treatment outcomes were compared with respect to clopidogrel use, PPI use and CYP2C19 genotype. Overall, PPI use did not increase the risk of adverse outcomes, irrespective of genotype. However, the 1-year event rate was higher with PPI use versus no PPI use in 2/2 carriers (15.8% versus 6.7%). Furuta et al.45 assessed the influence of three different PPIs on the response to clopidogrel according to CYP2C19 genotype status and found that carriers of CYP2C19 2 and/or 3 alleles were more likely to change from responder to nonresponder to clopidogrel when PPIs were added. Interestingly, addition of omeprazole and rabeprazole significantly decreased the efficacy of clopidogrel in noncarriers, but not in carriers.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
S6 Journal of Cardiovascular Medicine 2013, Vol 14 (suppl 1)
It was also observed that, in carriers of CYP2C19 2 and/or 3 alleles, separate dosing of clopidogrel and a PPI (i.e. clopidogrel in the morning and the PPI in the evening) did not prevent the problematic drug-drug interaction.45
Genotyping for risk stratification In March 2010, the US Food and Drug Administration (FDA) issued a black-box warning, noting that carriers of two loss-of-function CYP2C19 alleles show a diminished response to standard doses of clopidogrel. It also pointed out that tests are available to identify patients with genetic polymorphisms, for whom alternative treatment strategies should be considered. However, the FDA did not explicitly recommend CYP2C19 genetic testing in patients prescribed clopidogrel, and did not offer any specific guidance on drug dosing in carriers of the CYP2C19 variant allele, thus leaving it uncertain as to how the warning should be translated into clinical practice. In July 2010, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) published a Clinical Alert in response to the FDA’s black box warning on clopidogrel stating that ‘the evidence base is insufficient to recommend routine genetic or platelet function testing at the present time’, but it ‘may be considered before starting clopidogrel therapy in patients believed to be at moderate or high risk of a poor outcome.’ Currently, the benefits of genetic testing are limited due to several reasons. Many tests focus on the CYP2C192 allele which only accounts for 12% variation in the platelet reactivity. Although a number of commercial assays do also check for other loss-of-function alleles, few detect the CYP2C1917 allele and none the ABCB1 and PON1 variants. Furthermore, the predictive capacity of the CYP2C192 genotype for an inadequate antiplatelet response is also generally weak. Geisler et al.13 found that the residual platelet aggregation after clopidogrel therapy is significantly correlated not only with CYP2C19 2 status, but also with age, diabetic status, decreased left ventricular function, renal failure and ACS. Interestingly, CYP2C192 status explained only 5.2% of an insufficient antiplatelet response in a population of 760 clopidogrel-treated subjects undergoing elective coronary stent implantation.46 A case-control study showed that CYP2C19, ABCB1 and ITGB3 genes, clopidogrel loading dose and PPI use were independent factors associated with early stent thrombosis in patients who have undergone PCI.47 In this study, risk stratification for stent thrombosis improved when genetic and clinical factors were combined. However, the authors cautioned that a further validation of such risk stratification is required in independent cohorts before it can be used as a basis for treatment adjustment.
Conclusion Information on patients’ genotypes that affect their response to clopidogrel may be critical for clinicians. For this reason, targeting clopidogrel therapy towards sensitive and away from resistant patients by means of genetic testing may become a reasonable treatment strategy. Such a one-time test will also allow the effective use of clopidogrel in a population that is sensitive to this drug, as an alternative to the newer drugs in this class, and therefore provide a significant pharmacoeconomic benefit. The current clinical question is whether CYP enzyme genotype information alone is enough to identify poor responders to clopidogrel and justify the use of alternative treatment. It has been estimated that 83% of the individual variance in clopidogrel responses is attributable to genetic effects, but the gene variants so far investigated explain only a small proportion of the variability. The CYP2C19 variants alone do not account for all of the genetic variability in the pharmacodynamic, pharmacokinetic or clinical responses to clopidogrel, but variants in other genes, such as ABCB1 or PON1 also seem to be important. Finally, the impact of genotype-guided algorithms for the use of clopidogrel on clinical outcomes has not yet been adequately tested in prospective controlled trials. Only when there are clinical data to support the hypothesis that genotype-guided therapy reduces the rate of ischemic and bleeding events it will be possible to justify the use of genetic testing in all potential patients. When that happens, genotype-guided antiplatelet therapy will also be available in the field of cardiovascular medicine.
Acknowledgements The authors would like to thank Yahiya Syed of in Science Communications, a Springer Healthcare business, who provided medical writing assistance. This support was funded by AstraZeneca (Italy). The authors have no conflicts of interest to declare. This article was published in a supplement sponsored by AstraZeneca (Italy).
References 1 2
3
4
5
Furie B, Furie BC. Mechanisms of thrombus formation. N Engl J Med 2008; 359:938–949. Mak KH, Belli G, Ellis SG, Moliterno DJ. Subacute stent thrombosis: evolving issues and current concepts. J Am Coll Cardiol 1996; 27:494– 503. Steg PG, James SK, Atar D, et al. ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force on the management of ST-segment elevation acute myocardial infarction of the European Society of Cardiology (ESC). Eur Heart J 2012; 33:2569–2619. Savi P, Pereillo JM, Uzabiaga MF, et al. Identification and biological activity of the active metabolite of clopidogrel. Thromb Haemost 2000; 84:891– 896. Bassand JP, Hamm CW, Ardissino D, et al. Guidelines for the diagnosis and treatment of non-ST-segment elevation acute coronary syndromes. Eur Heart J 2007; 28:1598–1660.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S7
6
7
8
9
10 11 12
13
14
15
16
17 18 19
20
21 22
23 24 25
26
27
Hamm CW, Bassand JP, Agewall S, et al. ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J 2011; 32:2999–3054. Kushner FG, Hand M, Smith SC Jr, et al. 2009 focused updates: ACC/ AHA guidelines for the management of patients with ST-elevation myocardial infarction (updating the 2004 guideline and 2007 focused update) and ACC/AHA/SCAI guidelines on percutaneous coronary intervention (updating the 2005 guideline and 2007 focused update) a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2009; 54:2205–2241. Kazui M, Nishiya Y, Ishizuka T, et al. Identification of the human cytochrome P450 enzymes involved in the two oxidative steps in the bioactivation of clopidogrel to its pharmacologically active metabolite. Drug Metab Dispos 2010; 38:92–99. Serebruany VL, Steinhubl SR, Berger PB, et al. Variability in platelet responsiveness to clopidogrel among 544 individuals. J Am Coll Cardiol 2005; 45:246–251. Nguyen TA, Diodati JG, Pharand C. Resistance to clopidogrel: a review of the evidence. J Am Coll Cardiol 2005; 45:1157–1164. Gurbel PA, Tantry US. Clopidogrel resistance? Thromb Res 2007; 120:311–321. Snoep JD, Hovens MM, Eikenboom JC, et al. Clopidogrel nonresponsiveness in patients undergoing percutaneous coronary intervention with stenting: a systematic review and meta-analysis. Am Heart J 2007; 154:221–231. Geisler T, Schaeffeler E, Dippon J, et al. CYP2C19 and nongenetic factors predict poor responsiveness to clopidogrel loading dose after coronary stent implantation. Pharmacogenomics 2008; 9:1251–1259. Hulot JS, Collet JP, Silvain J, et al. Cardiovascular risk in clopidogrel-treated patients according to cytochrome P450 2C19 2 loss-of-function allele or proton pump inhibitor coadministration: a systematic meta-analysis. J Am Coll Cardiol 2010; 56:134–143. Lau WC, Waskell LA, Watkins PB, et al. Atorvastatin reduces the ability of clopidogrel to inhibit platelet aggregation: a new drug-drug interaction. Circulation 2003; 107:32–37. Serebruany VL, Midei MG, Malinin AI, et al. Absence of interaction between atorvastatin or other statins and clopidogrel: results from the interaction study. Arch Intern Med 2004; 164:2051–2057. Taubert D, von Beckerath N, Grimberg G, et al. Impact of P-glycoprotein on clopidogrel absorption. Clin Pharmacol Ther 2006; 80:486–501. Tentzeris I, Siller-Matula J, Farhan S, et al. Platelet function variability and nongenetic causes. Thromb Haemost 2011; 105 (Suppl 1):S60–S66. Bauer T, Bouman HJ, van Werkum JW, et al. Impact of CYP2C19 variant genotypes on clinical efficacy of antiplatelet treatment with clopidogrel: systematic review and meta-analysis. Bmj 2011; 343:d4588. Shuldiner AR, O’Connell JR, Bliden KP, et al. Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy. Jama 2009; 302:849–857. Mega JL, Close SL, Wiviott SD, et al. Cytochrome p-450 polymorphisms and response to clopidogrel. N Engl J Med 2009; 360:354–362. Gurbel PA, Shuldiner AR, Bliden KP, et al. The relation between CYP2C19 genotype and phenotype in stented patients on maintenance dual antiplatelet therapy. Am Heart J 2011; 161:598–604. Sangkuhl K, Klein TE, Altman RB. Clopidogrel pathway. Pharmacogenet Genomics 2010; 20:463–465. Shah SH, Voora D. Clopidogrel Dosing and CYP2C19. 2011 Medscape. Hulot JS, Bura A, Villard E, et al. Cytochrome P450 2C19 loss-of-function polymorphism is a major determinant of clopidogrel responsiveness in healthy subjects. Blood 2006; 108:2244–2247. Mega JL, Simon T, Collet JP, et al. Reduced-function CYP2C19 genotype and risk of adverse clinical outcomes among patients treated with clopidogrel predominantly for PCI: a meta-analysis. Jama 2010; 304:1821–1830. Sibbing D, Stegherr J, Latz W, et al. Cytochrome P450 2C19 loss-offunction polymorphism and stent thrombosis following percutaneous coronary intervention. Eur Heart J 2009; 30:916–922.
28
29 30
31
32
33
34
35 36
37
38
39
40
41
42
43
44
45
46
47
Price MJ. Primary results from genotype information and functional testing (GIFT): A prospective pharmacogenomic analysis of clopidogrel therapy. 2011. Presented at American College of Cardiology Meeting 2011 at New Orleans, USA. Pare G, Mehta SR, Yusuf S, et al. Effects of CYP2C19 genotype on outcomes of clopidogrel treatment. N Engl J Med 2010; 363:1704–1714. Sibbing D, Koch W, Gebhard D, et al. Cytochrome 2C19 17 allelic variant, platelet aggregation, bleeding events, and stent thrombosis in clopidogreltreated patients with coronary stent placement. Circulation 2010; 121:512–518. Spiewak M, Malek LA, Kostrzewa G, et al. Influence of C3435T multidrug resistance gene-1 (MDR-1) polymorphism on platelet reactivity and prognosis in patients with acute coronary syndromes. Kardiol Pol 2009; 67:827–834. Mega JL, Close SL, Wiviott SD, et al. Genetic variants in ABCB1 and CYP2C19 and cardiovascular outcomes after treatment with clopidogrel and prasugrel in the TRITON-TIMI 38 trial: a pharmacogenetic analysis. Lancet 2010; 376:1312–1319. Wallentin L, James S, Storey RF, et al. Effect of CYP2C19 and ABCB1 single nucleotide polymorphisms on outcomes of treatment with ticagrelor versus clopidogrel for acute coronary syndromes: a genetic substudy of the PLATO trial. Lancet 2010; 376:1320–1328. Simon T, Verstuyft C, Mary-Krause M, et al. Genetic determinants of response to clopidogrel and cardiovascular events. N Engl J Med 2009; 360:363–375. Bouman HJ, Schomig E, van Werkum JW, et al. Paraoxonase-1 is a major determinant of clopidogrel efficacy. Nat Med 2011; 17:110–116. Collet JP, Hulot JS, Anzaha G, et al. High doses of clopidogrel to overcome genetic resistance: the randomized crossover CLOVIS-2 (Clopidogrel and Response Variability Investigation Study 2). JACC Cardiovasc Interv 2011; 4:392–402. Mega JL, Hochholzer W, Frelinger AL 3rd, et al. Dosing clopidogrel based on CYP2C19 genotype and the effect on platelet reactivity in patients with stable cardiovascular disease. Jama 2011; 306:2221–2228. Mega JL, Close SL, Wiviott SD, et al. Cytochrome P450 genetic polymorphisms and the response to prasugrel: relationship to pharmacokinetic, pharmacodynamic, and clinical outcomes. Circulation 2009; 119:2553–2560. Chua D, Shalansky SJ, Legal MG, Jung J. Conflicting evidence surrounding the clopidogrel and proton pump inhibitor drug interaction. Arch Intern Med 2010; 170:1507–1508; author reply 1508. Sibbing D, Morath T, Stegherr J, et al. Impact of proton pump inhibitors on the antiplatelet effects of clopidogrel. Thromb Haemost 2009; 101:714– 719. Stockl KM, Le L, Zakharyan A, et al. Risk of rehospitalization for patients using clopidogrel with a proton pump inhibitor. Arch Intern Med 2010; 170:704–710. O’Donoghue ML, Braunwald E, Antman EM, et al. Pharmacodynamic effect and clinical efficacy of clopidogrel and prasugrel with or without a protonpump inhibitor: an analysis of two randomised trials. Lancet 2009; 374:989–997. Bhatt DL, Cryer BL, Contant CF, et al. Clopidogrel with or without omeprazole in coronary heart disease. New Eng J Med 2010; 363:1909– 1917. Simon T, Steg PG, Gilard M, et al. Clinical events as a function of proton pump inhibitor use, clopidogrel use, and cytochrome P450 2C19 genotype in a large nationwide cohort of acute myocardial infarction: results from the French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction (FAST-MI) registry. Circulation 2011; 123:474–482. Furuta T, Iwaki T, Umemura K. Influences of different proton pump inhibitors on the antiplatelet function of clopidogrel in relation to CYP2C19 genotypes. Br J Clin Pharmacol 2010; 70:383–392. Hochholzer W, Trenk D, Fromm MF, et al. Impact of cytochrome P450 2C19 loss-of-function polymorphism and of major demographic characteristics on residual platelet function after loading and maintenance treatment with clopidogrel in patients undergoing elective coronary stent placement. J Am Coll Cardiol 2010; 55:2427–2434. Cayla G, Hulot JS, O’Connor SA, et al. Clinical, angiographic, and genetic factors associated with early coronary stent thrombosis. Jama 2011; 306:1765–1774.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Genetic and nongenetic factors influencing the response to clopidogrel Maria F. Notarangeloa, Federico Bontardellia and Piera Angelica Merlinib The antiplatelet drug clopidogrel is a commonly prescribed therapy in patients with acute coronary syndrome. However, its clinical efficacy is hampered by a wide inter-patient response variability, with over 30% of patients treated with this drug experiencing an inadequate antiplatelet response. There are growing evidences that clopidogrel response variability is associated with cytochrome P450 (CYP) enzyme genetic polymorphisms, primarily CYP2C19 which is responsible for the conversion of clopidogrel into its active metabolite. All of the CYP2C19 polymorphism data suggest that carriers of allele 2 or 17 are at greater risk of ischemic or bleeding events, particularly in patients with acute coronary syndrome undergoing percutaneous coronary intervention. Yet, CYP2C19 status explains only 12% of clopidogrel response variability, indicating that genetic variants other than CYP2C19 might be important. Clopidogrel undergoes intestinal efflux via P-glycoprotein, encoded by the ABCB1 gene. The C3435T polymorphism in this gene affects the bioavailability of clopidogrel, however, its effects on clinical outcomes are inconclusive. Similarly, a polymorphism in the gene encoding PON1, a rate-limiting
Introduction Platelet activation and aggregation play a central role in the pathogenesis of thrombosis, particularly stent thrombosis after percutaneous coronary intervention (PCI).1–3 Clopidogrel is a second-generation thienopyridine that inhibits platelet aggregation by selectively and irreversibly blocking the P2Y12 adenosine diphosphate (ADP) receptor on the platelet surface.4 Clopidogrel, usually in combination with aspirin, is the standard of care for the prevention of stent thrombosis after PCI and for reducing major adverse cardiovascular events (MACE) in patients with acute coronary syndrome (ACS).5–7 Clopidogrel is a prodrug that is absorbed in the intestine by a transporter and converted into its active metabolite by the hepatic cytochrome P450 (CYP). The conversion involves oxidation of clopidogrel into 2-oxo-clopidogrel, which is further oxidized into an active thiol group. The two-step conversion involves a number of enzymes such as CYP1A2, CYP2C19, CYP2B6, CYP2C9, CYP3A4, CYP35 and PON1, of which CYP2C19 is thought to be involved in both steps.8 Only about 15% of clopidogrel is converted into its active form, and the rest is hydrolyzed by esterases into an inactive carboxylic acid derivative. Clopidogrel clinical efficacy is hindered by variability in inter-patient pharmacodynamic response.9 Despite 1558-2027 ß 2013 Italian Federation of Cardiology
enzyme for clopidogrel bioactivation, also affects the response to clopidogrel. Among nongenetic factors, an adverse drug interaction between proton pump inhibitors and clopidogrel is often reported, but evidence is inconclusive. A genetic test to identify potential responders to clopidogrel might be useful. However, the use of such tests is currently limited because they focus mainly on CYP2C19 loss-of-function alleles, and there is no empirical evidence yet for genotype-guided clopidogrel therapy. J Cardiovasc Med 2013, 14 (suppl 1):S1–S7 Keywords: clopidogrel resistance, genetic polymorphisms, genotyping, pharmacogenomics, platelet aggregation a
Division of Cardiology, Azienda Ospedaliero-Universitaria of Parma, Italy and Director, Cardiovascular Genetics Unit, Department of Cardiology, Azienda Ospedaliera Ospedale Niguarda Ca` Granda, Milan, Italy
b
Correspondence to Dr Maria F. Notarangelo, Division of Cardiology, Azienda Ospedaliero-Universitaria of Parma, Via Gramsci 14, 43126, Parma, Italy Tel: +39 0521 702070; fax: +39 0521 702189; e-mail: [email protected] Received 18 June 2013 Accepted 26 June 2013
adequate treatment with a standard loading dose of clopidogrel 300 mg followed by a maintenance dose of 75 mg, about 30% of patients display persistent high platelet reactivity (defined as A, which results in a protein with no enzymatic activity. This variant is designated as CYP2C192 (2 or loss-of-function allele).23 In contrast, the variant resulting from an SNP at the 806C>T location results in a protein with increased enzymatic activity (CYP2C1917 or 17; gain-of-function allele). The other less common variants include CYP2C193, CYP2C194, CYP2C195, CYP2C196, CYP2C197 and CYP2C198, all of which are associated with decreased enzymatic activity. The prevalence of CYP2C19 polymorphisms varies by ethnicity, and the most common variants are 2 and 17.21,24 Based on the enzyme activity, patients can be classified into categories of metabolizing phenotypes. Patients carrying two normal alleles (1/1) are extensive metabolizers; those with one reduced-function allele (1/2) are intermediate metabolizers; those carrying two reduced-function alleles (2/2) are poor metabolizers; and those carrying one or two increased-function alleles (1/17 or 17/17) are ultra-rapid metabolizers.21
carriers of at least one CYP2C19 reduced-function allele showed a relative reduction of 32.4% in plasma exposure of the active metabolite of clopidogrel, and an absolute reduction in maximal platelet aggregation that was 9% less than that seen in noncarriers (P < 0.001 for both comparisons).21. Gurbel et al.22 showed that CYP2C19 genotype and high platelet reactivity together may help to stratify the cardiovascular risk, but they did not correlate well with each other, in stented patients receiving clopidogrel plus aspirin. Within the six CYP2C19 diplotypes, platelet aggregation and the prevalence of high platelet reactivity in the presence of 5 and 20 mM ADP increased with 2 doses and decreased with 17 doses; however, the wide variability seen within the diplotype groups indicated that CYP2C19 genotype did not correlate well with high platelet reactivity (Fig. 1).22 MACE
Among the clopidogrel-treated subjects in TRITON– TIMI 38 (TRial to assess Improvement in Therapeutic Outcomes by optimizing platelet InhibitioN with prasugrel Thrombolysis In Myocardial Infarction 38) trial, carriers of at least one CYP2C19 loss-of-function allele showed a relative 53% increase in the composite primary efficacy outcome of the risk of death from cardiovascular causes, MI or stroke (hazard ratio [HR] 1.53; 95% confidence interval [CI] 1.07–2.19; P ¼ 0.01), and a 3-fold increase in the risk of stent thrombosis (HR 3.09; 95% CI 1.19–8.00; P ¼ 0.02).21 Similar results were reported also from a meta-analysis of nine studies involving 9685 patients (91.3% underwent PCI and 54.5% had ACS) treated with clopidogrel.26 In this analysis, the risk of the composite endpoint was Fig. 1
Pharmacokinetics and pharmacodynamic response
Pharmacokinetics studies have shown that metabolism of clopidogrel to its active metabolite is diminished in carriers of the CYP2C19 loss of function alleles and platelet function studies have found that these alleles are associated with higher levels of platelet aggregation after clopidogrel treatment. Hulot et al.25 found that 10 mM ADP-induced platelet aggregation decreased gradually from baseline during treatment with clopidogrel 75 mg once daily in wild-type (1/1), young, healthy male volunteers, but did not change in carriers of at least one loss-of-function allele (1/2). Mega et al.21 clearly showed that genetic variants of CYP2C19 are associated with differences in the bioavailability of the active metabolite of clopidogrel, its antiplatelet effects and clinical outcomes. In a cohort of 162 healthy volunteers treated with clopidogrel,
Adenosine diphosphate (ADP)-induced platelet aggregation and the prevalence of high platelet reactivity (HPR) with CYP2C19 diplotype status in stented patients receiving clopidogrel plus aspirin. Figure reproduced with permission from Gurbel et al.22
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S3
significantly higher in carriers of one 2 allele (HR 1.55; 95% CI 1.11–2.17; P ¼ 0.01), and even higher in carriers of two 2 alleles (1.76; 95% CI 1.24–2.50; P ¼ 0.002), compared with noncarriers. The risk of stent thrombosis was also increased by 2.67- and 3.97-fold in one and two 2 allele carriers, respectively. Clinical outcome data concerning the relevance of CYP2C192 carrier status are also available in the setting of coronary stenting. Among patients undergoing coronary stent placement after pretreatment with clopidogrel (n ¼ 2485), carriers of CYP2C192 (1/2 or 2/2) had significantly higher risk of definite stent thrombosis, compared with noncarriers (HR 3.81, 95% CI 1.45– 10.02; P ¼ 0.006).27 A significant gene-dose effect, with 2/ 2 carriers being at highest risk, was also reported in this study. Data from the GIFT (Genotype Information and Functional Testing) sub-study of the GRAVITAS (Gauging Responsiveness With A VerifyNow AssayImpact On Thrombosis And Safety) trial showed that the adjusted HRs (95% CI) for cardiovascular death, MI or stent thrombosis in carriers of one and two 2 alleles were 1.07 (0.91–1.25) and 1.67 (1.09–2.56), respectively, compared with noncarriers.28 Conversely, large-scale analysis of the CURE (Clopidogrel in Unstable angina to prevent Recurrent Events) trial population showed that the effect of clopidogrel, as compared with placebo, was consistent, irrespective of CYP2C19 loss-of-function carrier status.29 In contrast with previous studies, which purely compared carriers of loss-of-function alleles versus noncarriers among clopidogrel-treated patients, the CURE analysis included a randomized control group, and clearly showed that the effect of clopidogrel in reducing the rate of the primary efficacy outcome was consistent among patients treated with clopidogrel, irrespective of the genetically determined metabolizer phenotype (P ¼ 0.12 for heterogeneity). The strongest association between CYP2C19 loss-of-function allele status and MACE therefore seems to be limited to patients with ACS undergoing PCI with stenting. Thus, a reasonable explanation for the controversial data of the CURE population analysis may be that only 18% of patients in the CURE population underwent PCI, and stenting was less extensively used (14.5%). There are only few data concerning the relationship between an increased response to clopidogrel and bleeding events. Sibbing et al.30 reported that CYP2C1917 carrier status is significantly associated with an enhanced response to clopidogrel treatment and a 4-fold increase in the risk of bleeding events, and has no protective effect on the occurrence of ischemic events.
Genetic variability in response to clopidogrel: beyond CYP2C19 genotype CYP2C19 genotype accounts only for a minor proportion of variation in clopidogrel response. A genome-wide
association study in 429 healthy Amish subjects identified genes responsible for variation in ADP-stimulated platelet aggregation in response to standard clopidogrel therapy.20 Interestingly, the strongest association with a diminished clopidogrel response was found for the rs12777823 polymorphism, which is in linkage disequilibrium with CYP2C192. However, the CYP2C192 genotype (30.8% heterozygous and 2.1% homozygous in the study population) explained only 12% of the variation in clopidogrel response. An additional 10% of variation was due to age, body mass index and triglyceride levels. Thus approximately 78% of variation remained unexplained, suggesting that genetic variants other than CYP2C19 might be important.20 The gut absorption of clopidogrel is opposed by the drug efflux pump P-glycoprotein (P-gp), encoded by the ABCB1 gene. It has been hypothesized that variations in the ABCB1 gene resulting in the overexpression of P-gp may affect responses to clopidogrel and clinical outcomes through decreased intestinal absorption of the drug. However, data concerning this genetic variant are still partial, and clinical studies have led to mixed results. Several studies have shown that C3435T polymorphism in the ABCB1 gene significantly influences the bioavailability of clopidogrel. Among patients with coronary artery disease (CAD) who had undergone PCI (n ¼ 60) and received a single loading dose of clopidogrel 600 mg, homozygous carriers of the variant C3435T (TT) had significantly lower clopidogrel Cmax and AUC than the combined group of heterozygous carriers (CT) and wild-type patients (CC) (P ¼ 0.001 for Cmax, P ¼ 0.0006 for AUC). The Cmax and AUC of clopidogrel active metabolite followed a similar pattern (P ¼ 0.011 for both).17 Another study showed that among patients with ACS undergoing PCI, carriers of TT were more likely to have an higher platelet reactivity despite clopidogrel therapy, than wild-type patients (odds ratio [OR] 5.23, 95% CI 1.34–20.45; P ¼ 0.017).31 These data are consistent with the pharmacogenetic analysis of the TRITON-TIMI 38 population,32 which indicated that clopidogrel-treated TT carriers had lower concentrations of the active drug metabolite and reduced platelet inhibition.32 Available evidence regarding the effect of C3435CT status on the clinical outcome is inconclusive, however. The study by Spiewak et al.31 and the genetic substudy of the PLATO trial33 found that the risk for an adverse outcome was not affected by C3435T variant, either homozygous or heterozygous. In contrast, the FAST-MI (French registry of Acute ST-elevation and non-ST-elevation-myocardial infarction) investigators reported that the risk for the composite endpoint of death, acute MI or stroke was 72% higher in carriers of the C3435T variant (CT or TT) compared with the wild-type allele, among patients with acute MI receiving clopidogrel therapy.34 On the other hand, the
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
S4 Journal of Cardiovascular Medicine 2013, Vol 14 (suppl 1)
Overcoming 2 status with high-dose clopidogrel Results from the CLOVIS-2 (CLOpidogrel and response Variability Investigation Study 2) trial showed that increasing the loading dose of clopidogrel was not effective in CYP2C19 2/2 carriers.36 This trial assessed the antiplatelet effect of high (900 mg) or standard (300 mg) loading doses of clopidogrel, according to genotype, in patients who had had an MI and had received maintenance doses of clopidogrel 75 mg for 3 months (n ¼ 106; mean age 40.1 years). The primary endpoint was the relative reduction in residual platelet aggregation (RR-RPA %) by genotype. Baseline RR-RPA was significantly different between genotypes in patients who had previously received clopidogrel maintenance doses, but not in clopidogrel-naı¨ve patients. The highest RR-RPA was seen in 2/2 carriers and the lowest in wildtype carriers (1/1) (Fig. 2a). After the clopidogrel 300 mg loading dose there was a significant gene-dose effect, with 1/1 carriers having the highest RR-RPA and 2/2 carriers the lowest (Fig. 2b). The clopidogrel 900 mg loading dose improved RR-RPA in 1/2 carriers but not in 2/2 carriers (Fig. 2b). The plasma concentration (AUC0–6) of clopidogrel active metabolite followed a pattern similar to RR-RPA. In the GIFT study, doubling the maintenance dose of clopidogrel to 150 mg was not effective in carriers of one or two CYP2C19 2 alleles.28 With the 150 mg dose, the OR (95% CI) for platelet reaction units (PRU) >230 was 1.62 (0.93–2.85) in 1/2 carriers and 11.20 (2.02– 62.09) in 2/2 carriers, compared with noncarriers. The ELEVATE-TIMI 56 (Escalating Clopidogrel by Involving a Genetic Strategy - Thrombolysis In
(a) p < 0.02 for all p = 0.16
p < 0.04
100
p = 0.03
ADP 20µmol/L-induced residual platelet aggregation (%)
Paraoxonase-1 (PON1) has been identified as the ratedetermining enzyme for clopidogrel bioactivation in vitro, and the Q192R polymorphism in the PON1 gene has been shown to affect the rate of clopidogrel active metabolite formation.35 Among patients with CAD who had undergone PCI and received clopidogrel therapy, carriers of the homozygous Q192R variant (QQ) had less plasma PON1 activity, lower plasma concentrations of the active metabolite, and a lower degree of platelet inhibition, than heterozygote carriers (QR) or wild-type patients (RR). Carriers of QQ were at considerably higher risk for stent thrombosis, than QR carriers or wild-type patients (OR 3.6; 95% CI 1.6–7.9; P ¼ 0.003).35
Fig. 2
75
50
25
0 wt/wt
wt/*2
*2/*2
CYP2C19*2 genotype
(b) 300mg-LD < 0.003 for all*
Relative change of ADP 20µmol/L-induced residual platelet aggregation (%)
TRITON-TIMI 38 pharmacogenetic analysis showed that carriers of TT had a higher risk for the composite of cardiovascular death, MI or stroke than carriers of CT or wild-type patients (OR 1.72, 95% CI 1.22–2.44; P ¼ 0.002).32 The authors of this study noted that variants of both the ABCB1 and CYP2C19 genes were significant independent predictors of cardiovascular risk, and provide complementary information about this risk.
0.03
100
900mg-LD < 0.0005 for all*
0.04
0.20
p = 0.0045
< 0.001
p < 0.001
75
50
25
0 wt/wt
wt/*2
*2/*2
wt/wt
wt/*2
*2/*2
CYP2C19*2 genotype
Effect of CYP2C19 2 allele status on residual platelet aggregation in patients with myocardial infarction. A. Baseline levels after clopidogrel 75 mg maintenance therapy; B. after 300 mg and 900 mg clopidogrel loading dose. ADP, Adenosine diphosphate; LD, loading dose; wt, wild type. Figure reproduced with permission from Collet et al.36
Myocardial Infarction 56) trial demonstrated that tripling the maintenance dose of clopidogrel to 225 mg in carriers of one CYP2C19 2 allele achieved the same level of platelet reactivity as noncarriers treated with the standard 75 mg maintenance dose. However, even doses of up to 300 mg did not achieve the same level of platelet reactivity in 2/2 carriers.37 In this trial, 315 patients with known cardiovascular disease (MI and/or PCI within 4–6 weeks before enrollment) received clopidogrel 75, 150, 225 or 300 mg daily for 14 days (all with aspirin 81– 325 mg). Response to clopidogrel was measured using on-treatment vasodilator-stimulated phosphoprotein platelet reactivity index (VASP PRI) and platelet function test (VerifyNow P2Y12) reported as PRU. After treatment with clopidogrel 75 mg, carriers of 1/2 and
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S5
2/2 had significantly higher VASP PRI (70.0% and 86.6%, respectively versus 57.5%) and PRU (225.6 and 328.8, respectively versus 163.6) than noncarriers (P < 0.001 for all comparisons). Carriers of 1/2 treated with clopidogrel 225 mg had a similar reduction in platelet reactivity to noncarriers treated with 75 mg (VASP PRI 52.7% and 57.5%, respectively; PRU 152.9 and 163.6, respectively). However, carriers of 2/2 treated with clopidogrel doses as high as 300 mg still had high VASP PRI (68.3%) and PRU (287.0). The above findings indicate that increasing the loading or maintenance dose of clopidogrel does not achieve adequate antiplatelet effect in homozygous carriers of CYP2C19 loss-of-function alleles, and these patients should be treated with alternative P2Y12 inhibitors.
Alternative therapies Ticagrelor and prasugrel provide a more homogenous antiplatelet effect than clopidogrel across individuals carrying different CYP2C19 genotypes (Table 1).21,33,38 In the pharmacogenetic analysis of the TRITON-TIMI 38 population, the incidence of MACE was significantly higher in carriers of at least one loss-of-function allele in CYP genes than noncarriers treated with clopidogrel (12.1% versus 8%; P < 0.01).21 However, the MACE rate was similar between carriers and noncarriers treated with prasugrel (8.5% versus 9.8%).38 The genetic substudy of the PLATO (PLATelet inhibition and patient Outcomes) trial showed that the incidence of MACE was similar between carriers and noncarriers of any loss-offunction allele treated with ticagrelor (8.8% and 8.6%, respectively).33 Furthermore, this study showed that ticagrelor had significantly greater antiplatelet effect than clopidogrel in both carriers and noncarriers of CYP2C19 and ABCB1 polymorphisms.
Effect of proton pump inhibitors on clopidogrel response Concerns have been raised about the clinical impact of the interaction between clopidogrel and proton pump inhibitors (PPIs). Ex vivo biological studies have suggested that PPIs, especially omeprazole, might decrease the antiplatelet effect of clopidogrel, by means of the inhibition of the hepatic CYP2C19 and therefore the conversion of clopidogrel into its active metabolite through competition for the same substrate. Although there is a mechanistic basis, and pharmacodynamic data support Incidence of cardiovascular death, myocardial infarction and stroke (N) by CYP2C19 2 status in patients treated with clopidogrel, prasugrel or ticagrelor Table 1
% (n) Clopidogrel Prasugrel Ticagrelor
Carriers 12.1% (395) 8.5% (407) 8.8% (1384)
Noncarriers 8.0% (1064) 9.8% (1048) 8.6% (3551)
P value 0.01 0.27 0.46
Reference 21 38 32
an interaction between PPIs and clopidogrel, clinical significance of this interaction is still unclear.39 In a cross-sectional observational study (n ¼ 1000), omeprazole, but not pantoprazole or esomeprazole, significantly reduced the antiplatelet effect of clopidogrel in patients who previously received coronary stent placement and long-term clopidogrel treatment.40 Moreover, a retrospective analysis of data from a registry (n ¼ 2066) showed that concomitant use of a PPI with clopidogrel was associated with a higher risk of rehospitalization for MI or stent placement, than clopidogrel alone.41 However, these data were not confirmed in the post hoc analysis of TRITON TIMI-38 trial. In this large population of patients with ACS, despite the observed attenuation of the in-vitro antiplatelet effect of clopidogrel, the use of a PPI was not independently associated with an increased risk of adverse clinical outcomes after adjusting for potential confounders and the propensity to be treated with a PPI (HR 0.94, 95% CI 0.80–1.11).42 Moreover, the COGENT trial, the first randomized phase 3 study testing a combination of 20 mg omeprazole and clopidogrel versus placebo and clopidogrel in patients requiring clopidogrel for at least 12 months, showed that the negative influence of PPIs on the antiplatelet effect of clopidogrel did not translate into worse clinical outcomes. After only 133 days of follow-up, due to early termination of the trial, the patients assigned to omeprazole had a lower number of upper gastrointestinal clinical events, but there were no differences in clinical endpoints of cardiovascular death and MI between the two groups (HR 1.02, 95% CI 0.70–1.51; P ¼ NS).43
Interaction between CYP2C19 genotype and PPI In the FAST-MI study, clopidogrel plus PPI use was associated with poor outcomes in CYP2C19 2/2 carriers, but not in 1/2 carriers.44 The FAST-MI registry study collected outcome data from 3670 patients with MI. The outcomes were in-hospital events (proportion of death, reinfarction, stroke, major bleeding and transfusion) and the proportion of death, MI/stroke at 1 year. Among 2353 patients who were clopidogrel- and PPI-naı¨ve at admission and received clopidogrel within 48 h, treatment outcomes were compared with respect to clopidogrel use, PPI use and CYP2C19 genotype. Overall, PPI use did not increase the risk of adverse outcomes, irrespective of genotype. However, the 1-year event rate was higher with PPI use versus no PPI use in 2/2 carriers (15.8% versus 6.7%). Furuta et al.45 assessed the influence of three different PPIs on the response to clopidogrel according to CYP2C19 genotype status and found that carriers of CYP2C19 2 and/or 3 alleles were more likely to change from responder to nonresponder to clopidogrel when PPIs were added. Interestingly, addition of omeprazole and rabeprazole significantly decreased the efficacy of clopidogrel in noncarriers, but not in carriers.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
S6 Journal of Cardiovascular Medicine 2013, Vol 14 (suppl 1)
It was also observed that, in carriers of CYP2C19 2 and/or 3 alleles, separate dosing of clopidogrel and a PPI (i.e. clopidogrel in the morning and the PPI in the evening) did not prevent the problematic drug-drug interaction.45
Genotyping for risk stratification In March 2010, the US Food and Drug Administration (FDA) issued a black-box warning, noting that carriers of two loss-of-function CYP2C19 alleles show a diminished response to standard doses of clopidogrel. It also pointed out that tests are available to identify patients with genetic polymorphisms, for whom alternative treatment strategies should be considered. However, the FDA did not explicitly recommend CYP2C19 genetic testing in patients prescribed clopidogrel, and did not offer any specific guidance on drug dosing in carriers of the CYP2C19 variant allele, thus leaving it uncertain as to how the warning should be translated into clinical practice. In July 2010, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) published a Clinical Alert in response to the FDA’s black box warning on clopidogrel stating that ‘the evidence base is insufficient to recommend routine genetic or platelet function testing at the present time’, but it ‘may be considered before starting clopidogrel therapy in patients believed to be at moderate or high risk of a poor outcome.’ Currently, the benefits of genetic testing are limited due to several reasons. Many tests focus on the CYP2C192 allele which only accounts for 12% variation in the platelet reactivity. Although a number of commercial assays do also check for other loss-of-function alleles, few detect the CYP2C1917 allele and none the ABCB1 and PON1 variants. Furthermore, the predictive capacity of the CYP2C192 genotype for an inadequate antiplatelet response is also generally weak. Geisler et al.13 found that the residual platelet aggregation after clopidogrel therapy is significantly correlated not only with CYP2C19 2 status, but also with age, diabetic status, decreased left ventricular function, renal failure and ACS. Interestingly, CYP2C192 status explained only 5.2% of an insufficient antiplatelet response in a population of 760 clopidogrel-treated subjects undergoing elective coronary stent implantation.46 A case-control study showed that CYP2C19, ABCB1 and ITGB3 genes, clopidogrel loading dose and PPI use were independent factors associated with early stent thrombosis in patients who have undergone PCI.47 In this study, risk stratification for stent thrombosis improved when genetic and clinical factors were combined. However, the authors cautioned that a further validation of such risk stratification is required in independent cohorts before it can be used as a basis for treatment adjustment.
Conclusion Information on patients’ genotypes that affect their response to clopidogrel may be critical for clinicians. For this reason, targeting clopidogrel therapy towards sensitive and away from resistant patients by means of genetic testing may become a reasonable treatment strategy. Such a one-time test will also allow the effective use of clopidogrel in a population that is sensitive to this drug, as an alternative to the newer drugs in this class, and therefore provide a significant pharmacoeconomic benefit. The current clinical question is whether CYP enzyme genotype information alone is enough to identify poor responders to clopidogrel and justify the use of alternative treatment. It has been estimated that 83% of the individual variance in clopidogrel responses is attributable to genetic effects, but the gene variants so far investigated explain only a small proportion of the variability. The CYP2C19 variants alone do not account for all of the genetic variability in the pharmacodynamic, pharmacokinetic or clinical responses to clopidogrel, but variants in other genes, such as ABCB1 or PON1 also seem to be important. Finally, the impact of genotype-guided algorithms for the use of clopidogrel on clinical outcomes has not yet been adequately tested in prospective controlled trials. Only when there are clinical data to support the hypothesis that genotype-guided therapy reduces the rate of ischemic and bleeding events it will be possible to justify the use of genetic testing in all potential patients. When that happens, genotype-guided antiplatelet therapy will also be available in the field of cardiovascular medicine.
Acknowledgements The authors would like to thank Yahiya Syed of in Science Communications, a Springer Healthcare business, who provided medical writing assistance. This support was funded by AstraZeneca (Italy). The authors have no conflicts of interest to declare. This article was published in a supplement sponsored by AstraZeneca (Italy).
References 1 2
3
4
5
Furie B, Furie BC. Mechanisms of thrombus formation. N Engl J Med 2008; 359:938–949. Mak KH, Belli G, Ellis SG, Moliterno DJ. Subacute stent thrombosis: evolving issues and current concepts. J Am Coll Cardiol 1996; 27:494– 503. Steg PG, James SK, Atar D, et al. ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force on the management of ST-segment elevation acute myocardial infarction of the European Society of Cardiology (ESC). Eur Heart J 2012; 33:2569–2619. Savi P, Pereillo JM, Uzabiaga MF, et al. Identification and biological activity of the active metabolite of clopidogrel. Thromb Haemost 2000; 84:891– 896. Bassand JP, Hamm CW, Ardissino D, et al. Guidelines for the diagnosis and treatment of non-ST-segment elevation acute coronary syndromes. Eur Heart J 2007; 28:1598–1660.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
Variability in clopidogrel response Notarangelo et al. S7
6
7
8
9
10 11 12
13
14
15
16
17 18 19
20
21 22
23 24 25
26
27
Hamm CW, Bassand JP, Agewall S, et al. ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J 2011; 32:2999–3054. Kushner FG, Hand M, Smith SC Jr, et al. 2009 focused updates: ACC/ AHA guidelines for the management of patients with ST-elevation myocardial infarction (updating the 2004 guideline and 2007 focused update) and ACC/AHA/SCAI guidelines on percutaneous coronary intervention (updating the 2005 guideline and 2007 focused update) a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2009; 54:2205–2241. Kazui M, Nishiya Y, Ishizuka T, et al. Identification of the human cytochrome P450 enzymes involved in the two oxidative steps in the bioactivation of clopidogrel to its pharmacologically active metabolite. Drug Metab Dispos 2010; 38:92–99. Serebruany VL, Steinhubl SR, Berger PB, et al. Variability in platelet responsiveness to clopidogrel among 544 individuals. J Am Coll Cardiol 2005; 45:246–251. Nguyen TA, Diodati JG, Pharand C. Resistance to clopidogrel: a review of the evidence. J Am Coll Cardiol 2005; 45:1157–1164. Gurbel PA, Tantry US. Clopidogrel resistance? Thromb Res 2007; 120:311–321. Snoep JD, Hovens MM, Eikenboom JC, et al. Clopidogrel nonresponsiveness in patients undergoing percutaneous coronary intervention with stenting: a systematic review and meta-analysis. Am Heart J 2007; 154:221–231. Geisler T, Schaeffeler E, Dippon J, et al. CYP2C19 and nongenetic factors predict poor responsiveness to clopidogrel loading dose after coronary stent implantation. Pharmacogenomics 2008; 9:1251–1259. Hulot JS, Collet JP, Silvain J, et al. Cardiovascular risk in clopidogrel-treated patients according to cytochrome P450 2C19 2 loss-of-function allele or proton pump inhibitor coadministration: a systematic meta-analysis. J Am Coll Cardiol 2010; 56:134–143. Lau WC, Waskell LA, Watkins PB, et al. Atorvastatin reduces the ability of clopidogrel to inhibit platelet aggregation: a new drug-drug interaction. Circulation 2003; 107:32–37. Serebruany VL, Midei MG, Malinin AI, et al. Absence of interaction between atorvastatin or other statins and clopidogrel: results from the interaction study. Arch Intern Med 2004; 164:2051–2057. Taubert D, von Beckerath N, Grimberg G, et al. Impact of P-glycoprotein on clopidogrel absorption. Clin Pharmacol Ther 2006; 80:486–501. Tentzeris I, Siller-Matula J, Farhan S, et al. Platelet function variability and nongenetic causes. Thromb Haemost 2011; 105 (Suppl 1):S60–S66. Bauer T, Bouman HJ, van Werkum JW, et al. Impact of CYP2C19 variant genotypes on clinical efficacy of antiplatelet treatment with clopidogrel: systematic review and meta-analysis. Bmj 2011; 343:d4588. Shuldiner AR, O’Connell JR, Bliden KP, et al. Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy. Jama 2009; 302:849–857. Mega JL, Close SL, Wiviott SD, et al. Cytochrome p-450 polymorphisms and response to clopidogrel. N Engl J Med 2009; 360:354–362. Gurbel PA, Shuldiner AR, Bliden KP, et al. The relation between CYP2C19 genotype and phenotype in stented patients on maintenance dual antiplatelet therapy. Am Heart J 2011; 161:598–604. Sangkuhl K, Klein TE, Altman RB. Clopidogrel pathway. Pharmacogenet Genomics 2010; 20:463–465. Shah SH, Voora D. Clopidogrel Dosing and CYP2C19. 2011 Medscape. Hulot JS, Bura A, Villard E, et al. Cytochrome P450 2C19 loss-of-function polymorphism is a major determinant of clopidogrel responsiveness in healthy subjects. Blood 2006; 108:2244–2247. Mega JL, Simon T, Collet JP, et al. Reduced-function CYP2C19 genotype and risk of adverse clinical outcomes among patients treated with clopidogrel predominantly for PCI: a meta-analysis. Jama 2010; 304:1821–1830. Sibbing D, Stegherr J, Latz W, et al. Cytochrome P450 2C19 loss-offunction polymorphism and stent thrombosis following percutaneous coronary intervention. Eur Heart J 2009; 30:916–922.
28
29 30
31
32
33
34
35 36
37
38
39
40
41
42
43
44
45
46
47
Price MJ. Primary results from genotype information and functional testing (GIFT): A prospective pharmacogenomic analysis of clopidogrel therapy. 2011. Presented at American College of Cardiology Meeting 2011 at New Orleans, USA. Pare G, Mehta SR, Yusuf S, et al. Effects of CYP2C19 genotype on outcomes of clopidogrel treatment. N Engl J Med 2010; 363:1704–1714. Sibbing D, Koch W, Gebhard D, et al. Cytochrome 2C19 17 allelic variant, platelet aggregation, bleeding events, and stent thrombosis in clopidogreltreated patients with coronary stent placement. Circulation 2010; 121:512–518. Spiewak M, Malek LA, Kostrzewa G, et al. Influence of C3435T multidrug resistance gene-1 (MDR-1) polymorphism on platelet reactivity and prognosis in patients with acute coronary syndromes. Kardiol Pol 2009; 67:827–834. Mega JL, Close SL, Wiviott SD, et al. Genetic variants in ABCB1 and CYP2C19 and cardiovascular outcomes after treatment with clopidogrel and prasugrel in the TRITON-TIMI 38 trial: a pharmacogenetic analysis. Lancet 2010; 376:1312–1319. Wallentin L, James S, Storey RF, et al. Effect of CYP2C19 and ABCB1 single nucleotide polymorphisms on outcomes of treatment with ticagrelor versus clopidogrel for acute coronary syndromes: a genetic substudy of the PLATO trial. Lancet 2010; 376:1320–1328. Simon T, Verstuyft C, Mary-Krause M, et al. Genetic determinants of response to clopidogrel and cardiovascular events. N Engl J Med 2009; 360:363–375. Bouman HJ, Schomig E, van Werkum JW, et al. Paraoxonase-1 is a major determinant of clopidogrel efficacy. Nat Med 2011; 17:110–116. Collet JP, Hulot JS, Anzaha G, et al. High doses of clopidogrel to overcome genetic resistance: the randomized crossover CLOVIS-2 (Clopidogrel and Response Variability Investigation Study 2). JACC Cardiovasc Interv 2011; 4:392–402. Mega JL, Hochholzer W, Frelinger AL 3rd, et al. Dosing clopidogrel based on CYP2C19 genotype and the effect on platelet reactivity in patients with stable cardiovascular disease. Jama 2011; 306:2221–2228. Mega JL, Close SL, Wiviott SD, et al. Cytochrome P450 genetic polymorphisms and the response to prasugrel: relationship to pharmacokinetic, pharmacodynamic, and clinical outcomes. Circulation 2009; 119:2553–2560. Chua D, Shalansky SJ, Legal MG, Jung J. Conflicting evidence surrounding the clopidogrel and proton pump inhibitor drug interaction. Arch Intern Med 2010; 170:1507–1508; author reply 1508. Sibbing D, Morath T, Stegherr J, et al. Impact of proton pump inhibitors on the antiplatelet effects of clopidogrel. Thromb Haemost 2009; 101:714– 719. Stockl KM, Le L, Zakharyan A, et al. Risk of rehospitalization for patients using clopidogrel with a proton pump inhibitor. Arch Intern Med 2010; 170:704–710. O’Donoghue ML, Braunwald E, Antman EM, et al. Pharmacodynamic effect and clinical efficacy of clopidogrel and prasugrel with or without a protonpump inhibitor: an analysis of two randomised trials. Lancet 2009; 374:989–997. Bhatt DL, Cryer BL, Contant CF, et al. Clopidogrel with or without omeprazole in coronary heart disease. New Eng J Med 2010; 363:1909– 1917. Simon T, Steg PG, Gilard M, et al. Clinical events as a function of proton pump inhibitor use, clopidogrel use, and cytochrome P450 2C19 genotype in a large nationwide cohort of acute myocardial infarction: results from the French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction (FAST-MI) registry. Circulation 2011; 123:474–482. Furuta T, Iwaki T, Umemura K. Influences of different proton pump inhibitors on the antiplatelet function of clopidogrel in relation to CYP2C19 genotypes. Br J Clin Pharmacol 2010; 70:383–392. Hochholzer W, Trenk D, Fromm MF, et al. Impact of cytochrome P450 2C19 loss-of-function polymorphism and of major demographic characteristics on residual platelet function after loading and maintenance treatment with clopidogrel in patients undergoing elective coronary stent placement. J Am Coll Cardiol 2010; 55:2427–2434. Cayla G, Hulot JS, O’Connor SA, et al. Clinical, angiographic, and genetic factors associated with early coronary stent thrombosis. Jama 2011; 306:1765–1774.
Copyright © Italian Federation of Cardiology. Unauthorized reproduction of this article is prohibited.
