how to improve the concept of individualised antiplatelet therapy with...

© Schattauer 2015 Thrombosis and Haemostasis 113.1/2015

37Review Article

How to improve the concept of individualised antiplatelet therapy with P2Y12 receptor inhibitors – is an algorithm the answer?Jolanta M. Siller-Matula1; Dietmar Trenk2; Karsten Schrör3; Meinrad Gawaz4; Steen D. Kristensen5; Robert F. Storey6; Kurt Huber7; for the European Platelet Academy1Department of Cardiology, Medical University of Vienna, Austria; 2Clinics of Cardiology and Angiology II, Universitaets-Herzzentrum Freiburg ∙ Bad Krozingen, Bad Krozingen, Germany; 3Institut für Pharmakologie und Klinische Pharmakologie, Heinrich-Heine-Universität, Düsseldorf, Germany; 4Medizinische Klinik III, Department of Cardiology and Cardiovascular Diseases, Eberhard Karls University, Tübingen, Germany; 5Department of Cardiology, Aarhus University Hospital, Denmark; 6Department of Cardiovascular Science, University of Sheffield, UK; 73rd Medical Department, Cardiology and Emergency Medicine, Wilhelminenhospital, Vienna, Austria

SummaryWithin the past decade, high on-treatment platelet reactivity (HTPR) on clopidogrel and its clinical implications have been frequently dis-cussed. Although it has been previously assumed that HTPR is a phe-nomenon occurring only in patients treated with clopidogrel, recent data show that HTPR might also occur during treatment with prasu-grel or ticagrelor in the acute phase of ST-elevation myocardial infarc-tion. Moreover, it has been postulated that there is a therapeutic window for P2Y12 receptor blockers, thus indicating that HTPR is as-sociated with thrombotic events whereas low on-treatment platelet reactivity (LTPR) is associated with bleeding events. The current paper focuses on tools to identify risk factors for HTPR (pharmacogenomic

testing, clinical scoring and drug-drug interactions) and on the use of platelet function testing in order to identify patients who might not re-spond adequately to clopidogrel. The majority of recent clinical rando-mised trials have not supported the hypothesis that platelet function testing and tailored antiplatelet therapy are providing a favourable clinical outcome. These trials, mainly performed in low-to-moderate risk patients, will be reviewed and discussed. Finally, an algorithm based on current knowledge is suggested, which might be of use for design of clinical trials.

KeywordsPlatelet reactivity, clopidogrel, prasugrel, ticagrelor

Correspondence to:Jolanta Siller-Matula, MD PhDDepartment of Cardiology, Medical University of Vienna, AustriaE-mail: [email protected]

Received: March 16, 2014Accepted after major revision: July 22, 2014Epub ahead of print: September 18, 2014

http://dx.doi.org/10.1160/TH14-03-0238Thromb Haemost 2015; 113: 37–52

Purpose of this review

The purpose of this review is to: i) provide a critical literature re-view regarding high on-treatment platelet reactivity (HTPR) to P2Y12 receptor inhibitors, ii) to discuss studies, which applied per-sonalised antiplatelet treatment with P2Y12 receptor inhibitors, iii) to provide possible explanations why has the concept of person-alised anti-platelet therapy with P2Y12 receptor inhibitors failed so far, and iv) to propose an algorithm for personalised antiplatelet treatment with P2Y12 receptor inhibitors, which might be of inter-est when designing future trials.

Introduction

Platelet function studies have shown that 30–50 % of patients (de-pendent on the assay used) have HTPR while on clopidogrel treat-ment (1, 2). Studies including more than 20,000 patients have demonstrated an association between HTPR and adverse is-chaemic events with the strongest association for short-term thrombotic events in patients undergoing percutaneous coronary intervention (PCI) (odds ratio [OR] 2–10) (3–13). Adenosine dip-hosphate (ADP)-induced platelet function testing has been estab-

lished as the best predictor of ischaemic events in patients treated with dual antiplatelet therapy (5, 9, 11, 14–17). Nevertheless, al-though associations have been reported, an independent associ-ation between HTPR, platelet reactivity and outcome has not been consistently demonstrated. Although it has been previously as-sumed that HTPR is a phenomenon occurring only on treatment with clopidogrel, recent data show that in special clinical situations such as in the acute phase of ST-elevation myocardial infarction (STEMI) a substantial proportion (30–40 %) of patients treated with prasugrel or ticagrelor exhibited HTPR (18–24), which was associated with adverse ischaemic outcome in one of these studies (20). In detail, roughly 46 % (ticagrelor) and 37 % (prasugrel) of patients suffering from STEMI and treated with one of the new P2Y12-receptor antagonists exhibited HTPR when assessed 2 hours (h) after the loading dose, thus demonstrating no consistent effi-cacy in reducing platelet function during or shortly after primary PCI (23).

Some recent studies postulate that there might be a therapeutic window for P2Y12 receptor blockers, indicating that HTPR is as-sociated with thrombotic events, whereas low on-treatment pla-telet reactivity (LTPR) may be related to bleeding events (25–30) (▶ Figure 1). For better understanding of its clinical importance, this association has to be confirmed in future trials.

For personal or educational use only. No other uses without permission. All rights reserved.Downloaded from www.thrombosis-online.com on 2015-01-09 | ID: 1000467415 | IP: 128.104.209.86

Thrombosis and Haemostasis 113.1/2015 © Schattauer 2015

38 Siller-Matula et al. Personalised antiplatelet treatment

Several clinical and demographic variables are associated with HTPR in patients treated with clopidogrel. These factors include obesity, renal dysfunction, diabetes, higher age, reduced left ven-tricular function, inflammation and the presence of an acute cor-onary syndrome (ACS) (31–36) (▶ Figure 2). Drug-drug interac-tions may also contribute to variability in response to clopidogrel or ticagrelor. For instance, certain proton-pump inhibitors such as omeprazole, calcium channel blockers, ketoconazole or rifampicin interact with clopidogrel metabolism (33, 37–46). Whereas keto-conazole, rifampicin, clarithromycin or dexamethasone have an impact on ticagrelor pharmacokinetics, ticagrelor itself increases the plasma levels of the CYP3A4 substrates simvastatin and lovas-tatin, of the p-glycoprotein substrate digoxin and also of cyclospo-rine (45). Interestingly, concomitant use of morphine was a strong predictor of HTPR in patients treated with clopidogrel, prasugrel and ticagrelor, indicating that impaired or delayed absorption of those drugs induced by morphine might be the underlying mech-anism of slower action onset in STEMI patients (24, 47).

From multiple candidate genes being involved in absorption, activation, and inhibition of the receptor by P2Y12 antagonists, CYP2C19*2 (loss of function allele) has been associated with a re-duced antiplatelet effect of clopidogrel and increased risk for ad-verse cardiovascular events in several studies (33, 48–52). How-ever, other reports could not confirm the impact of CYP2C19*2 on clinical outcome (15, 53). This discrepancy might be explained by the fact that the CYP2C19*2 allele accounts only for 5–12 % of the variation in the response to clopidogrel (39, 52). Moreover, while the majority of heterozygote carriers had a sufficient level of pla-telet inhibition by increased clopidogrel dosage, a much higher proportion of homozygotes failed to respond (i. e. < 230 P2Y12 reaction units (PRU) by VerifyNow test) despite daily doses of 300

mg clopidogrel (54). Other CYP2C19 variants (*3 -*8) have a low allele frequency in Caucasians (< 1 %) and contribute thereby only to a minor extent to HTPR (55–57). In contrast, in East Asians up to 17 % of patients are carriers of the CYP2C19*3 allele, which also plays a role as a predictor of HTPR (57). Another explanation might be that the CYP2C19*2 allele has been shown to be impor-tant mainly in the acute phase of myocardial infarction, whereas in a chronic stable phase it does not appear to be significant (58). Data on the clinical impact of a gain-of-function mutation (CYP2C19*17), which is responsible for an intensified activation of clopidogrel, are conflicting so far (15, 27, 53, 59, 60). Whether polymorphisms of other genes are involved in the metabolism or action of clopidogrel (e. g. the intestinal efflux transport pump P-glycoprotein pump encoded by the ABCB1 gene (33, 55, 58, 61–63), the ITGB3 encoding the integrin Beta3 of the GpIIb/IIIa receptor (33, 55), the P2Y12 receptor (33, 55, 64) is a matter of de-bate. Although the P-glycoprotein pump and the CYPP450 system are also involved in the transport and metabolism of prasugrel and ticagrelor (▶ Figure 3), polymorphisms of the responsive gens did not impact on clinical outcome of ticagrelor or prasugrel treated patients (58, 65).

Studies investigating personalised antiplatelet treatment

Undoubtedly, a growing body of evidence underlines a considerable concern surrounding the one-size-fits-all strategy with clopidogrel. The majority of published data linked clopidogrel non-responsive-ness to adverse ischaemic events especially in patients undergoing PCI, which led to the suggestion that the magnitude of platelet in-

Figure 1: A hypotheti-cal model suggesting a therapeutic window for platelet inhibition by adenosine diphos-phate (ADP)-receptor blockers. Multiple Elec-trode Aggregometry (MEA), Light transmission aggregometry (LTA; 10 µM ADP), Vasodilator ac-tivated phosphoprotein (VASP) phopholyration assay, cytochrome P450 (CYP), maximum ampli-tude in thromb -elastography (TEG-MA), VerifyNow (VN).



39Siller-Matula et al. Personalised antiplatelet treatment

hibition by clopidogrel can be monitored and adjusted appropri-ately using different approaches. Several studies have demonstrated that the inhibition of ADP-induced platelet aggregation in patients on standard doses of clopidogrel can be improved with higher load-ing or maintenance doses of clopidogrel, or by switching to prasu-grel or ticagrelor (▶ Table 1). Administration of a 150 mg mainten-ance dose of clopidogrel resulted in more intense inhibition of pla-telet aggregation than administration of the 75 mg maintenance dose in a major subset of patients but not in all (66–68). In line with these findings, tailored treatment with up to four repeated loading doses of clopidogrel or a single reloading and a double maintenance dose of clopidogrel overcame HTPR to the conventional-dose clopidogrel therapy (69–71). Nevertheless, doubling the clopidogrel maintenance dose did not reach the same inhibition level as the one achieved in patients with an adequate response (67, 68, 72, 73). Moreover, the enhanced platelet reactivity persisted over time in some patients and the antiplatelet effect was not uniform (67, 68, 73). Interestingly, adding cilostazol to aspirin and clopidogrel was more effective than 150 mg maintenance dose of clopidogrel (74). Novel P2Y12 receptor inhibitors achieved stronger platelet in-hibition in patients with HTPR to clopidogrel, but only prasugrel and ticagrelor are currently approved for clinical use. With regard to genotype-based personalised treatment, increased loading doses of clopidogrel up to 900 mg or maintenance doses up to 300 mg have been show to overcome HTPR under clopidogrel treatment in heterozygous carriers of CYP2C19*2 allele but not in homozygous carriers (54, 75).

An impact on clinical outcome with individualised antiplatelet therapy has been tested in some smaller studies (▶ Table 1).

Guided therapy with up to four clopidogrel re-loadings in the group of patients with HTPR resulted in a reduction of major ad-verse cardiac events without an increase in major bleeding compli-cations (69–71). In line with this finding, intensified platelet in-hibition with GPIIb/IIIa antagonists lowered the incidence of major adverse cardiac events without increased bleeding rates (76, 77). In contrast, guided antiplatelet therapy did not improve patient out-comes in the large-scale GRAVITAS [Gauging Responsiveness With A VerifyNow Assay-Impact On Thrombosis And Safety] trial (78). Patients with HTPR under clopidogrel treatment were rando-mised to standard dosing of clopidogrel or to receive a second clopidogrel loading dose of 600 mg and were treated with a double maintenance dose of 150 mg of clopidogrel throughout the study. This approach, tested in more than 2.200 patients, showed no dif-ferences in event rates during six months follow-up in a patient population with a low-to-moderate thrombotic risk.

The TRIGGER-PCI [Testing Platelet Reactivity In Patients Undergoing Elective Stent Placement on Clopidogrel to Guide Al-ternative Therapy With Prasugrel] trial, which compared prasugrel versus clopidogrel in patients with HTPR to clopidogrel after elec-tive DES implantation without procedural complications (low thrombotic risk), was stopped prematurely for futility after rando-misation of 423 patients, because an interim analysis indicated a lower than expected incidence of the primary endpoint. However, platelet aggregation data from TRIGGER-PCI clearly demon-strated that HTPR could be corrected by switching from clopido-grel to prasugrel (79).

The TRILOGY ACS [The Targeted Platelet Inhibition to Clarify the Optimal Strategy to Medically Manage Acute Coronary Syn-

Figure 2: Factors linked to clopidogrel response variability. Adenosine diphosphate (ADP), cytochrome P450 (CYP).




dromes] platelet substudy among medically managed patients with ACS but no ST-segment elevation, confirmed that the use of pra-sugrel was associated with lower platelet reactivity than clopido-grel. Although platelet reactivity showed association with the oc-currence of ischaemic outcomes in univariate and survival ana-lyses, there was no independent association between platelet reac-tivity and ischaemic events (80).

In contrast, a meta-analysis of 10 randomised trials in 4,213 pa-tients showed that the intensified antiplatelet treatment was as-sociated with a significant reduction in cardiovascular mortality, stent thrombosis and myocardial infarction (81). Interestingly, meta-regression analysis revealed that the net clinical benefit of the intensified treatment significantly depended on the baseline risk for stent thrombosis.

In the recently published open-label ARCTIC [Double Rando-misation of a Monitoring Adjusted Antiplatelet Treatment Versus a Common Antiplatelet Treatment for DES Implantation, and Inter-ruption Versus Continuation of Double Antiplatelet Therapy] trial, 2,440 patients scheduled for coronary stenting, who were at low-to-moderate thrombotic risk, were randomised to bedside platelet function monitoring versus no monitoring. In the moni-toring arm, antiplatelet therapy could be intensified in patients with HTPR under aspirin or clopidogrel, either by increasing the dose of aspirin or an additional loading dose followed by an in-creased maintenance dose of clopidogrel, by switching to prasu-grel, or by additional treatment with GP IIb/IIIa inhibitors. Des-pite the fact that platelet reactivity could be reduced, the strategy of therapy adjustment based on platelet function monitoring did not

Figure 3: Metabolic pathways and binding to the P2Y12 receptor by clopidogrel, prasugrel and ticagrelor. Adenosine diphosphate (ADP), cyto -chrome P450 (CYP).




lead to any improvement in the composite endpoint of coronary ischaemic events (82).

Currently, several studies are underway to evaluate the associ-ation between genetic profiling or platelet function testing and clinical outcome (▶ Table 2). With respect to genetic testing, it has to be mentioned that it is currently not clear whether a combi-nation of different polymorphisms (e. g. CYP2C19*2 and CYP2C19*17) have any clinical implication and that the determi-nation of single polymorphisms therefore might not represent the full truth.

Why has the concept of individualised anti-platelet therapy failed so far?Reasons related to risk classification of the study population

The ADAPT-DES [Assessment of Dual AntiPlatelet Therapy With Drug Eluting Stents] registry indicated that platelet function as-sessment in patients with stable CAD treated with clopidogrel is unlikely to provide benefit, whereas this approach may be feasible in patients with high-risk ACS (83). In line with the latter, a meta-regression analysis revealed that the net clinical benefit of the in-tensified treatment largely depends on the baseline risk for stent thrombosis (81). Importantly, large randomised controlled trials (GRAVITAS, TRIGGER-PCI, ARCTIC, TRILOGY- ACS) in-cluded low-to-moderate risk patients whereas high-risk patients, such as those with STEMI, were excluded (▶ Table 1). In the ARC-TIC study, patients with NSTE-ACS represented only 25 % of the study population (84). The TRIGGER-PCI trial included only pa-tients with elective DES-PCI without procedural complications (79). Also the GRAVITAS trial enrolled stable patients undergoing elective PCI (60 %) and a minor proportion of patients with NSTE-ACS (40 %) (78). In the TRILOGY ACS platelet substudy, the post-ACS patients treated conservatively (about half without diagnostic angiography) probably also are low- or moderate-risk patients (80). Therefore, exclusion of high-risk patients may have ac-counted for the negative study results.

Based on the above considerations, intensified antiplatelet treatment does not seem to be efficacious in patients with a low-to-moderate risk for thrombotic events (such as elective PCI or conservatively-treated patients included days after a NSTE-ACS) but might improve outcome in higher-risk patients or in those with a high risk for stent thrombosis (predisposing factors: dia-betes, ACS, multiple stenting and multivessel disease).

Reasons related to the limitations of platelet function testing

The one major limitation of platelet function testing is the lack of consensus regarding the optimal cut-off for HTPR and low stan-dardisation of methods (▶ Table 3). Another problem with platelet function testing arises as some factors can influence the results, the most important of which are technical (anticoagulant used and time delay) and chemical (agonist used and its concentration) (85, 86).

Another shortcoming of platelet function testing ex vivo are the experimental conditions under which most of these assays are per-formed. Platelets are taken out from their natural environment and subsequently re-stimulated by one selected stimulus, in case of ADP-antagonist, by ADP and clot formation is then determined. These procedures ignore the multiplicity of platelet stimuli, acting simultaneously in vivo as well as the secretory function of platelets, i. e. the paracrine release of mediators (e. g. thromboxane A2, sero-tonin, others), which might act on non-platelet targets with conse-quences for the clinical outcome. These procedures also ignore the different platelet-activating situations in ACS vs stable angina as well as the interaction with white cells or plasmatic cytokines (87). They do allow predictions for the pharmacological efficacy of a given drug – an ADP-antagonist: if the drug does not block ADP-induced aggregation in vitro, it will also fail to do so in vivo. How-ever, the opposite conclusion cannot be drawn – i. e. that a com-pound that works in vitro is also expected to work in vivo to pre-vent platelet-dependent thrombus formation. The latter, however, is what investigators and physicians really want to know, at least with some predictive certainty. To improve this certainty is the goal of individualised antiplatelet treatment by platelet function testing. However, this goal is clearly not reached by performing platelet function assays as surrogates of the efficacy of antithrom-botic treatment in all cardiovascular patients at risk of thrombosis. High-risk patients on clopidogrel, such as diabetics, might be one group where platelet function testing is useful but still not predic-tive enough because of the very low event-rate in patients on stable conditions. In any case, general agreement on the type of assay to be performed and its cut-off values is another highly desirable pre-caution. Although it is already proven that platelet hyperreactivity is a key risk factor for arterial thrombosis, the question remains, whether and for what extent this hyperreactivity remains because non-ADP-agonists, such as thrombin, are major stimuli for pla-telet-dependent thrombus formation in certain clinical conditions. For example, thrombin contributes to initial platelet activation in ACS. Huge amounts of thrombin can be generated after gener-ation and release of tissue factor from the ruptured plaque area (88). One possible solution would be to use modified thrombelas-tography (TEG) assay (e. g. a platelet mapping assay), which allows measurement of platelet–fibrin clot strength and is sensitive to P2Y12 receptor inhibition as the contribution of P2Y12 receptor to the thrombus formation is measured by the addition ADP. The ad-vantage with TEG is the fact that the test assesses several aspects of thrombus formation and the interaction between platelets and co-agulation system. Nevertheless, still the disadvantage of the modi-fied TEG is a low standardisation. Therefore, the tests might pro-vide only incomplete answers to the really burning question of clinical efficacy of antiplatelet drugs and its predictability. Another problem arises as platelet function testing represents predictive tests (pre-symptomatic testing: the condition is not present at the time of testing) for which no established measures of performance are given. Therefore, it might not be surprising that the positive predictive values (PPV) of phenotyping are low for stent thrombo-sis when assessed before the event occurs (pre-symptomatic test-ing: PPV=5–15 %), whereas it increases when the test is performed




at the time of stent thrombosis (symptomatic testing: PPV=50 %) (11).

Noteworthy, in the larger trials investigating intensified antipla-telet treatment, which were in most cases negative, the VerifyNow assay system was used (▶ Table 1). Whether the use of other assay methods with subsequent intensification of antiplatelet treatment will improve outcome has to be investigated in future studies. Also, the use of hirudin anticoagulation might enhance the accuracy of the VerifyNow P2Y12 assay in a clinical trial setting (86).

Reasons related to the choice of a diagnostic strategy

Up to now, most studies investigating personalised antiplatelet treatment were based on measurement of platelet function (phe-notyping; ▶ Table 2). Genotype-guided comparison of clopidogrel in CYP2C19*2 carriers versus prasugrel on cardiovascular out-comes in patients with ACS was studied in the GIANT trial ([Ge-

Study author/ -Acronym (ref.)

GRAVITAS (78)

TRIGGER-PCI (79)

Valgimigli et al. (76)

Alexopolus et al. (21)

Alexopolus et al. (22)

ARCTIC (82)

Capranzano et al. (115)

Bonello et al. (70)

Bonello et al. (69)

VASP-02 (73)

Ferreiro et al. (116)

Kozinski et al. (117)

Trenk et al. (72)

ACCEL-RESISTANCE (74)

Cuisset et al. (77)

Population

PCI for CAD or NSTE-ACS

elective PCI

elective PCI

CAD with clopi-dogrel treatment

HD with clopido-grel treatment

PCI with DES

clopidogrel treat-ment + age > 75

PCI

PCI

elective PCI

DMII

ACS+PCI

elective PCI

PCI

elective PCI

n

2214

423

263

31

21

2440

100

162

429

153

30

71

117

60

149

Follow-up

6 months

6 months

in hospital

1 month

1 month

1 year

1 month

1 month

1 month

1 month

14 days

1 month

1 month

Outcome

MACE

MACEc, bleeding

MACE

level of platelet inhibition


MACE


MACE

MACE, ST, bleed-ing

MACE, level of platelet in-hibition





MACE

Method

VerifyNow

VerifyNow

VerifyNow

VerifyNow

VerifyNow

VerifyNow

VerifyNow

VASP assay

VASP assay

VASP assay

VASP assay

VASP assay

LTA

LTA

LTA

Cut-off value

230 PRU

208 PRU

235 PRU

235 PRU

235 PRU

235 PRU

230 PRU

50 %

50 %

69 %

50 %

50 %

14 %

50 %

70 %

Study type

CRT: 300/75 mg clopidogrel vs 600/75 mg clopidogrel in patients with HTPR

CRT: prasugrel (loading of 60 mg and maintenance 10 mg) vs. clopidogrel (maintenance 75 mg) in pa-tients with HTPR

CRT: tirofiban vs placebo in patients with HTPR

randomised, crossover: 10 mg prasugrel vs 150 mg clopidogrel in patients with HTPR

randomised, crossover: 10 mg prasugrel vs 150 mg clopidogrelc

CRT: guided: clopidogrel (600 mg reloading and 75 mg or 150 mg maintenance) or prasugrel (60 mg loading and 10 mg maintenance) or GP IIb/IIIa in-hibitors vs non-guided: clopidogrel (maintenance 75 mg) in patients with HTPR

observational: prasugrel in patients with HTPR

CRT: guided (repeated loading with clopidogrel 600 mg) vs non-guided group

CRT: guided (repeated loading with clopidogrel 600mg) vs. non-guided group

observational: 150 mg clopidogrel in patients with HTPR

observational: cilostazol vs 150 mg clopidogrel in pa-tients with HTPR

parallel-group, open-label study: patients with HTPR were assigned to prasugrel (30 mg loading dose, 10 mg maintenance dose) or clopidogrel (150 mg main-tenance dose for 6 days and thereafter 75 mg main-tenance dose)

observational: 150 mg clopidogrel vs control in pa-tients with HTPR

CRT: adjunctive cilostazol vs 150 mg clopidogrel in patients with HTPR

CRT: GP IIb/IIIa antagonists vs control in patients with HTPR

Table 1: Studies investigating guided antiplatelet treatment. ACS=acute coronary syndrome, IA=impedance aggregometry, CAD=coron-ary artery disease, CYP=cytochrome P450, CRT=controlled randomized trial, DM=diabetes mellitus, HD=haemodialysis, LTA=light transmission aggrego-

metry, MEA=multiple electrode aggregometry, NSTE-ACS=non ST elevation acute coronary syndrome, PCI=percutaneous coronary intervention, TIMI=thrombolysis in myocardial inferction, VASP=vasodilator stimulated phosphoprotein.




notyping Infarct Patients to Adjust and Normalize Thienopyridine Treatment], and another trial evaluating ticagrelor use in patients with the CYP2C19 loss of function allele in PCI patients is still on-going (TAILOR-PCI [Tailored Antiplatelet Therapy Following PCI]). In the GIANT trial, which has been presented at Transca-theter Cardiovascular Therapeutics 25th Annual Scientific Sympo-sium, 272 patients received assay-guided antiplatelet therapy ad-justment. The one-year composite endpoint was about five times higher for the CYP2C19 loss of function allele patients whose anti-platelet therapy was not changed based on the assay as compared to patients with the assay-guided antiplatelet therapy changes (89). These are the first clinical-trial data showing the usefulness of ge-notyping. Nevertheless, we are still awaiting the publication of the original paper.

Nevertheless, prospective randomised double-blind trials with use of pharmacogenetic profiling to guide antiplatelet drug regimen are, to our knowledge, not yet registered. It seems that both genotyping and phenotyping provide complementary infor-mation to stratify risk (90). The TARGET-PCI [Thrombocyte Ac-tivity Reassessment and GEnoTyping for PCI] study, a randomised open label study to guide antiplatelet therapy, was designed to in-

vestigate a strategy of simultaneous pheno- and genotyping. Un-fortunately, the trial has been terminated due to the lack of finan-cial support.

Reasons related to the protocol for personalised therapy

Another possible explanation for the negative results of some re-cent large trials is the fact that the study protocols allowed only singular switch to other drug or dose (▶ Table 2). The latter aspect is mirrored in the GRAVITAS trial, in which 40 % of patients in the guided group displayed HTPR phenotype despite high dose clopidogrel (78). Interestingly, in TRIGGER-PCI, less than 6 % of patients with HTPR on clopidogrel had still HTPR after switching to prasugrel (79). Therefore, it is not surprising that this inad-equate personalised therapy failed to show a significant benefit. Although in the ARCTIC trial platelet function was measured re-peatedly, other aspects might have accounted for unsuccessful out-come as the fact that only 3.3 % of patients were switched to prasu-grel whereas 88 % received higher doses of clopidogrel (84). In the GRAVITAS trial, all patients received a double dose of clopidogrel

Study author/ -Acronym (ref.)

Matezky et al. (118)

Gurbel et al. (119)

RESPOND (120)

MADONNA (71)

Aradi et al. (91)

Neubauer (121)

BOCLA Plan (34)

CLOVIS-2 (75)

ELEVATE TIMI-56 (54)

RAPID-GENE (122)

ACCEL-AMI-2C19 (123)

ACCEL-2C19 (124)

Population

MI

stable CAD + previous PCI

stable CAD + clopidogrel

PCI

ACS+PCI

elective PCI

PCI

MI

clopidogrel treatment

PCI

MI

elective PCI

n

200

20

41

798

741

161

504

109

333

200

126

134

Follow-up

10 weeks

7 days

1 month

1 month

1 year

in hospital

1 month

7 days

30 days

30 days

Outcome




ST, MACE, TIMI major bleeding

ST, MACE, BARC major bleeding








Method

LTA

LTA

LTA

MEA

MEA

IA

IA

CYP2C19*2

CYP2C19*2

CYP2C19*2

CYP2C19*2

CYP2C19*2/*3

Cut-off value

80 %

43 %

43 %

50 U

46 U

5 U

5 U

*1/*2 and *2/*2

*1/*2 and *2/*2

*1/*2 and *2/*2

*1/*2 and *2/*2

*1/*2 and *2/*2 and *2/*3

Study type

observational: 600/150 mg clopidogrel in patients with HTPR

observational: single dose elinogrel 60 mg in patients with HTPR

CRT crossover: ticagrelor 180/90 mg vs clopidogrel 600/75 mg

Non-randomised, controlled: non-guided vs guided group (up to 4 loading doses with 600 mg clopido-grel or 1 loading dose with prasugrel in patients with HTPR)

observational: 600/150 mg clopidogrel vs prasugel in patients with HTPR

observational: 600/150 mg clopidogrel vs ticlopidine in patients with HTPR

observational: 600/150 mg clopidogrel vs ticlopidine vs prasugrel in patients with HTPR

CRT: 300 vs 900 mg clopidogrel

CRT: 75, 150, 225, or 300 mg clopidogrel in *2 car-riers vs. 75 or 150 mg clopidogrel in *2 non-carriers

CRT: 10 mg prasugrel in *2 carriers vs 75 mg clopido-grel in *2 non-carriers

CRT: adjunctive cilostazol vs high maintenance-dose clopidogrel

CRT: adjunctive cilostazol vs high maintenance-dose clopidogrel

Table 1: Continued




Table 2: Ongoing (or terminated) studies investigating guided antiplatelet treatment. ACS=acute coronary syndrome, AF=atrial fibrillation, CAD=coronary artery disease, CYP=cytochrome P450, MEA=multiple electrode aggregometry, MI=myocardial infarction, NSTEMI=non ST elevation myo-cardial infarction, PCI=percutaneous coronary intervention, ST=stent thrombosis, STEMI=ST elevation myocardial infarction.

Identifier

NCT00774475

NCT01515345

NCT00995514terminated

NCT01452152terminated

NCT01097343

NCT01134380

NCT01538446

NCT01643031

NCT01742117

NCT01959451

Acronym

DANTE

IDEAL-PCI

GeCCO

PAPI-2

GIANT

ANTARC-TIC

MATTIS-D

TAILOR-PCI

TROPICAL-ACS

Title

Dual Antiplatelet Therapy Tailored on the Extent of Platelet Inhibition

Individualizing Dual Anti platelet Therapy after PCI

Genotype Guided Com-parison of Clopidogrel and Prasugrel Outcomes Study

Pharmacogenomics of Anti-platelet Interven-tion-2

Clopidogrel Pharma-cogenomics Project

Genotyping Infarct Patients to Adjust and Normalize Thienopyri-dine Treatment

Tailored Antiplatelet Therapy Versus Recommended Dose of Prasugrel

Effect of Modifying Anti- platelet Treatment to Ticagrelor in Patients With Diabetes and Low Response to Clopidogrel

Tailored Antiplatelet Therapy Following PCI

Testing Responsiveness to Platelet Inhibition on Chronic Antiplatelet Treatment For Acute Coronary Syndromes Trial

Population

UA/NSTEMI undergoing PCI with stent implantation

PCI

ACS

PCI

clopidogrel in-take

STEMI+pri-mary PCI

ACS

Diabetes with elective PCI

PCI

ACS with PCI

Test

VerifyNow

MEA

CYP2C19*2

CYP2C19*2

CYP2C19*2

CYP2C19*2

VerifyNow

VerifyNow

CYP2C19*2 or *3

MEA

n

442

1,000

14,600

7,200

200

1,500

962

500

5,945

2,600

Treatment strategy

Active Comparator: clopidogrel 150 mg/day; Control Com-parator: clopidogrel 75 mg/day

Switch to prasugrel or ticagre-lor in patients with HTPR

Active comparator: prasugrel 10mg/day; Control comparator: clopidogrel 75mg/day

Intervention group: CYP2C19 intermediate metabolisers: clopidogrel; Intervention group: CYP2C19 intermediate metabo-lisers: prasugrel; observational group: no Intervention

Active Comparator: clopidogrel 150 mg/day; Control Com-parator: clopidogrel 75 mg/day

Increase of the clopidogrel do-sage, prasugrel or clopidogrel

Down-adjustment of the dose of prasugrel in high responders and up-adjustment of the dose of prasugrel in low responders as compared to a fixed dose of 5 mg to every patient without monitoring

Switch to ticagrelor in patients with HTPR to clopidogrel for 30 days (followed by continued clopidogrel therapy) versus clopidogrel

Patients with the wild type CYP2C19 allele will be assigned to receive clopidogrel 75 mg. Patients with the CYP2C19*2 and *3 will be assigned to receive ticagrelor 90 mg.

1 week prasugrel treatment and switch over to clopidogrel treat-ment in adequate responders to clopidogrel versus standard treatment with prasugrel

Primary endpoint

Composite of cardiovascular death, non-fatal myocardial infarction, target lesion vessel revascularisation by PCI or coronary bypass at 6 and 12 months

ST, bleedings

Composite of cardiovascular death, nonfatal MI, or non-fatal stroke at 6 months

Composite of non-fatal myo-cardial infarction, non-fatal stroke, definite or probable stent thrombosis and death secondary to any cardiovascular cause at 1 year

Level of platelet inhibition

Composite of death, MI and stent thrombosis at 12 months

Composite of cardiovascular death, MI, stroke, ST, urgent revascularisation or bleeding

Elevation of troponin or CK-MB (above the upper limit of normal, and above 3 times the upper limit of normal) measured 20–24 hours after the PCI

Composite of non-fatal MI, non-fatal stroke, cardiovascular mortality, severe recurrent ischaemia, and stent thromb -osis

The combined incidence of bleeding and thrombotic complications during 12 months




(78). A registry data suggested that prasugrel use in patients with HTPR resulted in a better outcome compared to use of high-dose clopidogrel (91). Therefore, the accumulating evidence suggests that when intensified antiplatelet treatment is tested, the more po-tent drugs prasugrel or ticagrelor should be preferred over doubl-ing the maintenance dose of clopidogrel or use of repeated loading doses of clopidogrel. Importantly, repeated testing after switch to a more potent drug might be crucial in order to ensure sufficient level of platelet inhibition, as it has been performed in a small scale MADONNA [Multiple electrode Aggregometry in patients receiv-ing Dual antiplatelet therapy to guide treatment with Novel pla-telet Antagonists] study (71).

Reasons related to the definition of the primary endpoint

The primary endpoint in the ARTIC trial was mainly based on the incidence of peri-procedural myocardial infarction (MI), which was defined as a documented rise in cardiac biomarkers (cardiac troponins or CK-MB measured 6 h after PCI higher than three-fold the upper reference limit). Indeed, the primary endpoint (34.6 %) was driven by the occurrence of MI (30.3 %) and the vis-ual inspection of the survival analyses confirms that the peri-pro-cedural MI was the major driver of the primary endpoint (as sug-gested by the vast majority of events occurring immediately after inclusion). Therefore, it might well be that the inclusion of cardiac biomarker rise in the definition of MI in the ARCTIC study ex-plains the difference in the incidence of MI between the trials: ARCTIC (30.2 %), GRAVITAS (1.8 %) and TRIGGER-PCI (0 %) (78, 79, 82, 92).

As some studies proposed the concept of a therapeutic window for P2Y12 receptor inhibition, which shows that a moderate level of platelet reactivity corresponds best with a net clinical benefit (20, 25, 26, 93), it might be an option to target a moderate level of pla-telet inhibition. This hypothesis is based on a rationale that pa-tients with ACS treated with prasugrel or ticagrelor have a benefit in terms of a reduction of ischaemic events, but, for both drugs, at the cost of an increased rate of spontaneous bleeding events. Thus there might still be room for optimisation of antiplatelet therapy. Tempered against this hypothesis is the uncertainty about the mechanisms by which ticagrelor reduces mortality compared to clopidogrel therapy and the possibility that pleiotropic effects un-related to platelet inhibition may be contributory (94).

Reasons related to the time point of participants inclusion

Inhibition of platelet function might depend on the time from drug intake to blood sampling and on the time between ACS/PCI and blood sampling (95–97). One must be aware of the circum-stance that randomisation was performed 12–24 h after PCI in the GRAVITAS trial and 2–7 h after the first clopidogrel maintenance dose intake the day after successful PCI in the TRIGGER-PCI trial. Therefore, patients experiencing peri-procedural events, early after PCI or those with unsuccessful or complicated PCI procedures

were not eligible for GRAVITAS or TRIGGER-PCI. In the TRIL-OGY ACS platelet substudy, post-ACS patients were treated up to seven days after the index event with non-study clopidogrel and then randomised to either clopidogrel or prasugrel (80). Therefore, it seems that timing of testing and eventual switching to more po-tent drugs should be set before or at least very early after stenting, as HTPR seems to play the most important role in the early phase.

Reasons related to the statistical power of the studies

Inappropriate power of the studies might be another reason why testing and adjustment was not effective. As mentioned the TRIGGER-PCI trial was stopped prematurely for futility after ran-domisation of 423 patients because an interim analysis indicated a lower than expected incidence of the primary endpoint (assumed: 4.7 %, occurred: 0.4 % after inclusion of only 20 % of planed study population) (79). Concordantly, the event rates for the composite endpoint in GRAVITAS trial were also substantially lower than ex-pected (assumed: 5 %, observed: 2.3 %) (78). It has also been sug-gested that the ARCTIC trial was not properly powered. If the traditional composite end point (death, MI, or stroke) had been selected, the investigators would have needed to enroll 17,540 pa-tients with non–ST-elevation ACS in each study group (98).

Proposed algorithm for future personalised antiplatelet treatment

In general, current guidelines recommend a “one-size-fits-all” ap-proach for antiplatelet agents due to lack of prospective double-blind randomised studies demonstrating an improvement in clini-cal outcome by personalised antiplatelet therapy. P2Y12 receptor inhibitors are recommended on top of aspirin. The ACCF/AHA/SCAI and ESC guidelines issue a Class IIb recommendation for platelet function testing to facilitate the choice of P2Y12 inhibitor in selected patients with high risk for thrombotic events following PCI, whereas routine testing is not recommended (Class III) (99–101).In patients presenting with an ACS, the novel platelet inhibitors prasugrel and ticagrelor provide superior inhibition of platelet reactivity and a reduction of thrombotic events, although at costs of increased spontaneous bleeding risk (102, 103). Indeed, it could be a valuable approach to use these potent drugs in almost all ACS patients as it was demonstrated for both compounds in high-risk patients, and as it is recommended by the current ESC guidelines (recommendation: prasugrel IB or ticagrelor IB over clopidogrel IC) (100, 104). In contrast, the ACC/AHA guidelines recommend either clopidogrel or ticagrelor or prasugrel in interventionally managed ACS (recommendation IB for all three agents) (105). As different guidelines exist world-wide and the American guidelines do not prefer one antiplatelet agent over other for ACS with stent-ing (106), it is possible that personalised antiplatelet treatment would be of interest at least in countries following the ACC/AHA guidelines. Moreover, there are several other reasons, which might




support the usefulness of an algorithm for personalised antiplatelet therapy, also in Europe: • A therapeutic window for P2Y12 receptor inhibitors has been

proposed, which indicates that more likely a moderate level of platelet inhibition correlates bests with the net benefit (20, 25, 26, 93).

• Clopidogrel is still the only P2Y12 receptor blocker used in elec-tive patients (107).

• Clopidogrel is currently recommended in ACS patients with a need for oral anticoagulation.

• Clopidogrel is also the P2Y12 receptor blocker of choice in pa-tients with a high bleeding risk (104).

• Clopidogrel is the P2Y12 receptor blocker of choice in patients with contraindications to the novel antiplatelet drugs (up to 40 % of patients) (100, 104, 108).

• Clopidogrel is already available as a generic. Several countries have financial constraints and the authorities start to discuss the need of new antiplatelet agents, especially with respect to the long-term use.

• Many countries in the world have currently no access to ticagrelor or prasugrel at all. Therefore, a personalised approach to antiplatelet treatment strategy might by a strategy in ACS pa-tients in these countries considering the costs of novel antipla-telet drugs.

Based on these considerations and until ongoing trials (e. g. ANT-ARCTIC [Tailored Antiplatelet Therapy Versus Recommended Dose of Prasugrel], MATTIS-D [Effect of Modifying Anti-platelet Treatment to Ticagrelor in Patients With Diabetes and Low Re-sponse to Clopidogrel], TAILOR-PCI; ▶ Table 3) will show whether patients benefit from personalised antiplatelet therapy, we propose an algorithm that might be appropriate for design of fu-ture clinical trials. It is important to emphasise that the proposed algorithm is hypothetical. Additionally, although platelet function testing with the available test systems should not be recommended routinely, it might be considered as valuable diagnostic tool on a case-by-case basis, especially in patients who are at high throm-botic risk (e. g. diabetics), eventually also in patients scheduled for high-risk PCI (e. g. left main stenting or stenting of proximal bifur-

Table 3: Methods used for assessment of the effect of antiplatelet drugs. AA=arachidonic acid, ADP=adenosine diphosphate, AA, PAC-1= antibody that binds to the active conformation of integrin αIIbβ3, PGE1=prastaglandin E1, TRAP-6=thrombic receptor activating peptide 6, TXA2=thromboxane.

Test

Light transmission aggregometry (LTA)

Multiplate analyzer (MEA)

Vasodilator activated phosphoprotein (VASP) phopholyration assay

Platelet surface receptors:P-Selectin, PAC-1

VerifyNow

Impact (Cone and Platelet Analyzer; CPA)

PFA-100

Plateletworks

Thrombelastography (TEG)

Principle

optical aggregometry

impedance aggregometry

flow cytometry

flow cytometry

Turbidimetry: microbead agglutination

Shear induced aggregation

Shear induced aggregation

counting of ag-gregated platelets

quantification of platelet-fibrin clot strength

Measured parameter

% platelet aggregation

area under the aggregation curve AUC=AU*min(1 U=10 AU*min)

platelet reactivity index PRI=VASP-P induced by ADP minus VASP-P induced by ADP+PGE1

activaton of platelet receptors

reaction units

platelet adhesion

closure time

platelet count

clot strength-maximal amplitude (mm)

Material

platelet-rich plasma

whole blood

whole blood

whole blood

whole blood

whole blood

whole blood

whole blood

whole blood

Agonist

ADP, AA, collagen, epi-nephrine, TXA2

ADP, ADP+PGE1, AA, collagen, TRAP-6, ris-tocetin

ADP and ADP+PGE1

ADP, AA, TRAP-6

ADP+PGE1, AA, TRAP-6

ADP, ADP+PGE1, AA

ADP+collagen, ADP+PGE1+collagen, AA+collagen

ADP, AA, collagen

ADP+reptilase+FXIIIa,AA+reptilase+FXIIIa

Sensitivity for antiplatelet agents

P2Y12 inhibitors, aspirin, GpIIb/IIIA inhibitors


P2Y12 inhibitors

P2Y12 inhibitors, aspirin


P2Y12 inhibitors, aspirin (+platelet function disorders)

P2Y12 inhibitors, aspirin



References

(4, 11, 14, 16, 17, 19, 34, 110, 121, 125–134)

(91, 95, 135–141)

(5, 69, 70, 73, 142)

(125, 143–145)

(27, 110, 126, 128, 146–148)

(15, 97, 149–151)

(15, 149, 150, 152–155)

(110)

(156–160)



47

cations in elective cases), and specifically in those experiencing re-current ischaemic events including stent thrombosis. However, randomised double-blinded clinical studies demonstrating a clini-cal benefit for this approach are lacking so far.

Patients might benefit from a global risk algorithm based on clinical (PREDICT score), biological (platelet function) and gen-etic (CYP2C19*2 carrier status) information (▶ Figure 2). How-ever, complementary information received from phenotyping and genotyping would provide a reassurance mainly about the clopido-grel response status and such an approach is time consuming and costly. Whereas platelet function testing identifies patients who do not respond sufficiently to clopidogrel, pharmacogenomic testing provides only a risk marker for HTPR. Genotyping alone may help guiding antiplatelet treatment in some specific clinical scenarios, e. g. for planned stenting of complex lesions or of the left main be-fore intake of clopidogrel, especially when the patient is homozy-gous for the CYP2C19*2 allele, as those patients have a high prob-ability for HTPR under clopidogrel treatment. Nevertheless, the major shortcoming of genotyping is the uncertainty in the predic-tion of the phenotype of clopidogrel response. Moreover, the re-sponse to clopidogrel is even less predictable in individuals with a wild type or heterozygous for CYP2C19*2. Based on these con-siderations, homozygote carriers of CYP2C19*2 may benefit by treatment with the more potent antiplatelet agents prasugrel or ti-cagrelor, while in wild type or heterozygous carriers of CYP2C19*2 platelet function testing might provide an adjunctive information.

Platelet function testing provides more comprehensive infor-mation than genotyping, as it reflects the influence of intrinsic (co-morbidities, genetic polymorphisms) and extrinsic factors (ciga-rette smoking, drug-drug interactions) on platelet reactivity. How-ever, it is still a matter of ongoing investigations to define those pa-tient cohorts, in whom ADP-related platelet function testing is of clinical importance. As platelet function testing has been shown to be a good risk stratifier for adverse events, phenotyping takes a central position in the algorithm (▶ Figure 4). Judgment whether to perform platelet function testing might be based on the scores predicting the individual risk for non-responsiveness to antipla-telet drugs. For example, the PREDICT score offers a tool to indi-vidualise antiplatelet therapy (32). Several clinical variables are in-cluded into the score: age > 65 years, ACS at admission, diabetes mellitus, renal dysfunction (serum creatinine > 1.5 mg dL-1), and reduced left ventricular function (LVF; ejection fraction [EF]< 50 %). Although reduced LVF has been indicated as a pre-dictor of HTPR in a minority of studies (32, 33, 109), three points are assigned to the reduced LVF in the PREDICT score (32). Pla-telet function testing might be also taken into consideration in pa-tients scheduled for high risk PCI and in those experiencing recur-rent ischaemic events despite good compliance. If the test ident-ifies a patient with HTPR, and known drug-drug interactions could be excluded, other therapies, particularly novel platelet in-hibitors as prasugrel or ticagrelor might be considered. Repeated loading with clopidogrel and double maintenance dose might be considered in patients with high bleeding risk or when novel anti-platelet drugs are unavailable. One must be aware, however, of the circumstance that the latter strategy might not achieve the

required level of platelet inhibition and up to four repeated load-ings with clopidogrel could be necessary in some patients (67, 68, 73) thus delaying the time until optimal platelet function in-hibition. Importantly, repeated testing after switching to a more potent drug might be crucial in order to ensure sufficient level of platelet inhibition and to prevent LTPR. In patients who develop life-threatening bleeding because of treatment with prasugrel or ti-cagrelor, the switch to clopidogrel might be an option. Another op-tion would be to reduce the dose of ticagrelor or prasugrel. How-ever, this approach has not been tested elsewhere. In summary, phenotyping of the response to antiplatelet agents with a subse-quent modification of therapy in patients with coronary artery dis-ease treated with P2Y12 receptor antagonists might be considered.

The next question to be addressed is to define the optimal pla-telet assay for use in a daily clinical practice beyond the different platelet function tests that can be used (▶ Table 3). Unfortunately, cross validation of the assays is limited. Only two bigger studies compared different methods for prediction of events: in the PE-GASUS-PCI (Phenotyping versus Genotyping for prediction of cardiac Adverse events in patients Undergoing Percutaneous Cor-onary Intervention) study multiple electrode aggregometry (MEA) was most predictive for stent thrombosis and MACE whereas in the POPULAR (Do Platelet Function Assays Predict Clinical Out-comes in Clopidogrel-Pretreated Patients Undergoing Elective PCI) study LTA, Plateletworks and VerifyNow were shown to have the best predictive values for ischaemic events (15, 110). In a small single centre study it was shown that the VASP assay exhibited a good prediction of future ischaemic events (111). Nevertheless, a good prediction of future ischaemic events by the VASP assay may be related to the low cut-off value of HTPR (platelet reactivity index [PRI] < 50 %) based on the small number of initial clinical data, and might therefore overestimate the patients risk for HTPR (5, 112). Reflecting the growing body of evidence, the test should be judged based on the following properties: predictive value for clinical outcome, reliability and reproducibility of results, known threshold with the best predictive value, operator skills for running tests and time necessary for testing. A fundamental patient care issue remains that the cost for these tests are typically not re-im-bursed. The above aspects require careful consideration. In regards to feasibility of the most frequently used tests, light transmission aggregometry and the VASP assay seem to be too labour-intensive to be performed on a daily basis. In contrast, the results of Ver-ifyNow and MEA are available within a few minutes. The major shortcoming of VerifyNow, however, is the cost of a single measurement. Moreover, the additional limitation of VerifyNow is the poor correlation with the P2Y12 receptor occupancy, where the sensitivity of the VerifyNow P2Y12 assay decreased at higher clopi-dogrel responses (113). MEA, on the other side, is not strictly speaking point of care test, as the test is relatively labour-intensive (reagent preparation, blood dilution, multiple pipetting steps). MEA has also been reported to show a relatively high value of co-efficient of variation (11 %) (114). As none of the currently avail-able tests have yet been evaluated in a randomised trial for su-periority over another test, no special recommendation concern-ing the type of assay can be given at the present time.

Siller-Matula et al. Personalised antiplatelet treatment



48

Figure 4: A proposed algorithm for personalised antiplatelet treatment with P2Y12 receptor blockers. *The PREDICT score might be used when ti-cagrelor or prasugrel are not available or contraindicated. Acute coronary syndrome (ACS), calcium channel blocker (CCB), left ventricular function (LVF), per-cutaneous coronary intervention (PCI), proton pump inhibitor (PPI).




49

As stated before, it is necessary to confirm the usefulness of our algorithm in prospective trials. Whether use of a blinded design will be feasible remains unclear at the moment. This possible diffi-culty is based on the observation of the TRIGGER trial, in which one third of patients declined participation after being identified as having HTPR (79). This underlines on the other hand the con-sideration whether it is ethically correct to randomise patients with HTPR to clopidogrel. A possible solution would be to per-form non-inferiority trials, comparing e. g. novel platelet inhibitors versus personalised treatment with the net clinical benefit as out-come variable.

Conflicts of interestJolanta M. Siller-Matula has received lecture or consultant fees from AstraZeneca, Daiichi Sankyo and Eli Lilly. Dietmar Trenk has received consulting fees or paid advisory board fees and lec-ture fees from Eli Lilly, Daiichi Sankyo, AstraZeneca, and Bayer and lecture fees from Boehringer Ingelheim KG, Bristol Myers Squibb, and Merck Sharp & Dohme. Karsten Schrör has received lecture or consulting fees from AstraZeneca, Bayer, Eli Lilly/Daiic-hi-Sankyo, IROKO. Meinrad Gawaz has received lecture or con-sulting fees from AstraZeneca, Boehringer-Ingelheim, Bayer, Eli Lilly/Daiichi-Sankyo. Steen Kristensen has received lecture fees from AZ, Bristol Myers Squibb, BAYER, Boehringer-Ingelheim, Eli-Lilly, IROKO, Merck, Pfizer, Sanofi, The Medicines Company. Robert Storey has received honoraria, consultancy fees and/or in-stitutional grants from AstraZeneca, Merck, Accumetrics, Eli Lilly, Daiichi Sankyo, Sanofi Aventis, Regeneron, Bristol Myers Squibb, Iroko, Medscape, Novartis and Roche. Kurt Huber has received lecture and consultant fees from AstraZeneca, Daiichi Sankyo, Eli Lilly, Sanofi Aventis, Bristol Myers Squibb, Pfizer, Iroko, and The Medicines Company.

References1. Tantry US, et al. Consensus and update on the definition of on-treatment pla-

telet reactivity to adenosine diphosphate associated with ischaemia and bleed-ing. J Am Coll Cardiol 2013; 62: 2261–2273.

2. Siller-Matula JM, et al. Response Variability to P2Y12 Receptor Inhibitors: Ex-pectations and Reality. JACC Cardiovasc Interv 2013; 6: 1111–1128.

3. Sibbing D, et al. Platelet Reactivity After Clopidogrel Treatment Assessed With Point-of-Care Analysis and Early Drug-Eluting Stent Thrombosis. J Am Coll Cardiol 2009; 53: 849–856.

4. Geisler T, et al. Early but not late stent thrombosis is influenced by residual pla-telet aggregation in patients undergoing coronary interventions. Eur Heart J 2010; 31: 59–66.

5. Siller-Matula JM, et al. Multiple Electrode Aggregometry predicts stent throm-bosis better than the VASP assay. J Thromb Haemost 2010; 8: 351–359.

6. Buonamici P, et al. Impact of platelet reactivity after clopidogrel administration on drug-eluting stent thrombosis. J Am Coll Cardiol 2007; 49: 2312–2317.

7. Migliorini A, et al. High residual platelet reactivity after clopidogrel loading and long-term clinical outcome after drug-eluting stenting for unprotected left main coronary disease. Circulation 2009; 120: 2214–2221.

8. Gori AM, et al. Incidence and clinical impact of dual nonresponsiveness to as-pirin and clopidogrel in patients with drug-eluting stents. J Am Coll Cardiol 2008; 52: 734–739.

9. Cuisset T, et al. Predictive values of post-treatment adenosine diphosphate-in-duced aggregation and vasodilator-stimulated phosphoprotein index for stent

thrombosis after acute coronary syndrome in clopidogrel-treated patients. Am J Cardiol 2009; 104: 1078–1082.

10. Matetzky S, et al. Clopidogrel resistance is associated with increased risk of re-current atherothrombotic events in patients with acute myocardial infarction. Circulation 2004; 109: 3171–3175.

11. Gurbel PA, et al. Clopidogrel effect on platelet reactivity in patients with stent thrombosis: results of the CREST Study. J Am Coll Cardiol 2005; 46: 1827–1832.

12. Cuisset T, et al. High post-treatment platelet reactivity is associated with a high incidence of myonecrosis after stenting for non-ST elevation acute coronary syndromes. Thromb Haemost 2007; 97: 282–287.

13. Geisler T, et al. Genetic variation of platelet function and pharmacology: An up-date of current knowledge. Thromb Haemost 2013; 110: 876–887.

14. Gurbel PA, et al. Platelet reactivity to adenosine diphosphate and long-term is-chaemic event occurrence following percutaneous coronary intervention: a po-tential antiplatelet therapeutic target. Platelets 2008; 19: 595–604.

15. Siller-Matula JM, et al. Phenotyping vs. genotyping for prediction of clopidogrel efficacy and safety: the PEGASUS-PCI study. J Thromb Haemost 2012; 10: 529–542.

16. Geisler T, et al. Low response to clopidogrel is associated with cardiovascular outcome after coronary stent implantation. Eur Heart J 2006; 27: 2420–2425.

17. Hochholzer W, et al. Impact of the degree of peri-interventional platelet in-hibition after loading with clopidogrel on early clinical outcome of elective cor-onary stent placement. J Am Coll Cardiol 2006; 48: 1742–1750.

18. Bonello L, et al. High on-treatment platelet reactivity after prasugrel loading dose and cardiovascular events after percutaneous coronary intervention in acute coronary syndromes. J Am Coll Cardiol 2011; 58: 467–473.

19. Michelson AD, et al. Pharmacodynamic assessment of platelet inhibition by pra-sugrel vs. clopidogrel in the TRITON-TIMI 38 trial. Eur Heart J 2009; 30: 1753–1763.

20. Bonello L, et al. Relationship between post-treatment platelet reactivity and is-chaemic and bleeding events at one year follow-up in patients receiving prasu-grel. J Thromb Haemost 2012; 10: 1999–2005.

21. Alexopoulos D, et al. Prasugrel overcomes high on-clopidogrel platelet reactivity in chronic coronary artery disease patients more effectively than high dose (150 mg) clopidogrel. Am Heart J 2011; 162: 733–739.

22. Alexopoulos D, et al. Antiplatelet Effects of Prasugrel vs Double Clopidogrel in Patients on Hemodialysis and High On-Treatment Platelet Reactivity. J Thromb Haemost 2011; 9: 2379–2385.

23. Alexopoulos D, et al. randomised Assessment of Ticagrelor Versus Prasugrel Antiplatelet Effects in Patients with ST-Segment-Elevation Myocardial Infarc-tion. Circ Cardiovasc Interv 2012; 5: 797–804.

24. Parodi G, et al. Comparison of prasugrel and ticagrelor loading doses in ST-seg-ment elevation myocardial infarction patients: RAPID (Rapid Activity of Pla-telet Inhibitor Drugs) primary PCI study. J Am Coll Cardiol 2013; 61: 1601–1606.

25. Sibbing D, et al. Antiplatelet effects of clopidogrel and bleeding in patients undergoing coronary stent placement. J Thromb Haemost 2010; 8: 250–256.

26. Sibbing D, et al. Platelet aggregation and its association with stent thrombosis and bleeding in clopidogrel-treated patients: initial evidence of a therapeutic window. J Am Coll Cardiol 2010; 56: 317–318.

27. Campo G, et al. Prospective evaluation of on-clopidogrel platelet reactivity over time in patients treated with percutaneous coronary intervention relationship with gene polymorphisms and clinical outcome. J Am Coll Cardiol 2011; 57: 2474–2483.

28. Mokhtar OA, et al. Relationship between platelet reactivity inhibition and non-CABG related major bleeding in patients undergoing percutaneous coronary intervention. Thromb Res 2010; 126: e147–149.

29. Parodi G, et al. Residual Platelet Reactivity, Bleedings, and Adherence to Treat-ment in Patients Having Coronary Stent Implantation Treated With Prasugrel. Am J Cardiol 2012; 109: 214–218.

30. Cuisset T, et al. Clinical implications of very low on-treatment platelet reactivity in patients treated with thienopyridine: the POBA study (predictor of bleedings with antiplatelet drugs). JACC Cardiovasc Interv 2013; 6: 854–863.

31. Angiolillo DJ. Antiplatelet therapy in diabetes: efficacy and limitations of cur-rent treatment strategies and future directions. Diabetes Care 2009; 32: 531–540.

32. Geisler T, et al. The Residual Platelet Aggregation after Deployment of Intracor-onary Stent (PREDICT) score. J Thromb Haemost 2008; 6: 54–61.




50

33. Cayla G, et al. Clinical, angiographic, and genetic factors associated with early coronary stent thrombosis. J AmMed Assoc 2011; 306: 1765–1774.

34. Neubauer H, et al. Tailored antiplatelet therapy can overcome clopidogrel and aspirin resistance--the BOchum CLopidogrel and Aspirin Plan (BOCLA-Plan) to improve antiplatelet therapy. BMC Med 2011; 9: 3.

35. Htun P, et al. Low responsiveness to clopidogrel increases risk among CKD pa-tients undergoing coronary intervention. J Am Soc Nephrol 2011; 22: 627–633.

36. Muller K, et al. Impact of inflammatory markers on platelet inhibition and car-diovascular outcome including stent thrombosis in patients with symptomatic coronary artery disease. Atherosclerosis 2010; 213: 256–262.

37. Siller-Matula JM, et al. Calcium-channel blockers reduce the antiplatelet effect of clopidogrel. J Am Coll Cardiol 2008; 52: 1557–1563.

38. Harmsze AM, et al. The use of amlodipine, but not of P-glycoprotein inhibiting calcium channel blockers is associated with clopidogrel poor-response. Thromb Haemost 2010; 103: 920–925.

39. Hochholzer W, et al. Impact of cytochrome P450 2C19 loss-of-function poly-morphism and of major demographic characteristics on residual platelet func-tion after loading and maintenance treatment with clopidogrel in patients undergoing elective coronary stent placement. J Am Coll Cardiol 2010; 55: 2427–2434.

40. Harmsze AM, et al. Combined influence of proton-pump inhibitors, calcium-channel blockers and CYP2C19*2 on on-treatment platelet reactivity and on the occurrence of atherothrombotic events after percutaneous coronary interven-tion. J Thromb Haemost 2011; 9: 1892–1901.

41. Gilard M, et al. Influence of omeprazole on the antiplatelet action of clopidogrel associated with aspirin: the randomised, double-blind OCLA (Omeprazole CLopidogrel Aspirin) study. J Am Coll Cardiol 2008; 51: 256–260.

42. Cuisset T, et al. Comparison of omeprazole and pantoprazole influence on a high 150-mg clopidogrel maintenance dose the PACA (Proton Pump Inhibitors And Clopidogrel Association) prospective randomised study. J Am Coll Cardiol 2009; 54: 1149–1153.

43. Siller-Matula JM, et al. Effect of proton pump inhibitors on clinical outcome in patients treated with clopidogrel: a systematic review and meta-analysis. J Thromb Haemost 2010; 8: 2624–2641.

44. Siller-Matula JM, et al. Effects of pantoprazole and esomeprazole on platelet in-hibition by clopidogrel. Am Heart J 2009; 157: 148.e1-.e5.

45. Teng R. Pharmacokinetic, pharmacodynamic and pharmacogenetic profile of the oral antiplatelet agent ticagrelor. Clin Pharmacokinet 2012; 51: 305–318.

46. Siller-Matula JM, et al. Clinical implications of drug-drug interactions with P2Y12 receptor inhibitors. J Thromb Haemost 2014; 12: 2–13.

47. Hobl EL, et al. Morphine decreases clopidogrel concentrations and effects: a randomised, double-blind, placebo-controlled trial. J Am Coll Cardiol 2014; 63: 630–635.

48. Hulot JS, et al. CYP2C19 but not PON1 genetic variants influence clopidogrel pharmacokinetics, pharmacodynamics, and clinical efficacy in post-myocardial infarction patients. Circ Cardiovasc Interv 2011; 4: 422–428.

49. Giusti B, et al. Relation of cytochrome P450 2C19 loss-of-function polymor-phism to occurrence of drug-eluting coronary stent thrombosis. Am J Cardiol 2009; 103: 806–811.

50. Collet JP, et al. Cytochrome P450 2C19 polymorphism in young patients treated with clopidogrel after myocardial infarction: a cohort study. Lancet 2009; 373: 309–317.

51. Mega JL, et al. Cytochrome p-450 polymorphisms and response to clopidogrel. N Engl J Med 2009; 360: 354–362.

52. Shuldiner AR, et al. Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy. J Am Med Assoc 2009; 302: 849–857.

53. Bhatt DL, et al. The relationship between CYP2C19 polymorphisms and is-chaemic and bleeding outcomes in stable outpatients: the CHARISMA genetics study. Eur Heart J 2012: 33: 2143–2150.

54. Mega JL, et al. Dosing clopidogrel based on CYP2C19 genotype and the effect on platelet reactivity in patients with stable cardiovascular disease. J Am Med Assoc 2011; 306: 2221–2228.

55. Simon T, et al. Genetic determinants of response to clopidogrel and cardiovas-cular events. N Engl J Med 2009; 360: 363–375.

56. Harmsze AM, et al. CYP2C19*2 and CYP2C9*3 alleles are associated with stent thrombosis: a case-control study. Eur Heart J 2010; 31: 3046–3053.

57. Jeong YH, et al. Effect of CYP2C19*2 and *3 loss-of-function alleles on platelet reactivity and adverse clinical events in East Asian acute myocardial infarction

survivors treated with clopidogrel and aspirin. Circ Cardiovasc Interv 2011; 4: 585–594.

58. Wallentin L, et al. Effect of CYP2C19 and ABCB1 single nucleotide polymor-phisms on outcomes of treatment with ticagrelor versus clopidogrel for acute coronary syndromes: a genetic substudy of the PLATO trial. Lancet 2010; 376: 1320–1328.

59. Sibbing D, et al. Cytochrome 2C19*17 allelic variant, platelet aggregation, bleed-ing events, and stent thrombosis in clopidogrel-treated patients with coronary stent placement. Circulation 2010; 121: 512–518.

60. Frere C, et al. The CYP2C19*17 allele is associated with better platelet response to clopidogrel in patients admitted for non-ST acute coronary syndrome. J Thromb Haemost 2009; 7: 1409–1411.

61. Mega JL, 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.

62. Jaitner J, et al. No association of ABCB1 C3435T genotype with clopidogrel re-sponse or risk of stent thrombosis in patients undergoing coronary stenting. Circ Cardiovasc Interv 2012; 5: 82–88, S1–2.

63. Campo G, et al. Relationship between paraoxonase Q192R gene polymorphism and on-clopidogrel platelet reactivity over time in patients treated with percut-aneous coronary intervention. J Thromb Haemost 2011; 9: 2106–2108.

64. Fontana P, et al. Adenosine diphosphate-induced platelet aggregation is associ-ated with P2Y12 gene sequence variations in healthy subjects. Circulation 2003; 108: 989–995.

65. Mega JL, et al. Cytochrome P450 genetic polymorphisms and the response to prasugrel: relationship to pharmacokinetic, pharmacodynamic, and clinical out-comes. Circulation 2009; 119: 2553–2560.

66. von Beckerath N, et al. A double-blind, randomised study on platelet aggre-gation in patients treated with a daily dose of 150 or 75 mg of clopidogrel for 30 days. Eur Heart J 2007; 28: 1814–1819.

67. Angiolillo DJ, et al. Impact of platelet reactivity on cardiovascular outcomes in patients with type 2 diabetes mellitus and coronary artery disease. J Am Coll Cardiol 2007; 50: 1541–1547.

68. Angiolillo DJ, et al. Functional impact of high clopidogrel maintenance dosing in patients undergoing elective percutaneous coronary interventions. Results of a randomised study. Thromb Haemost 2008; 99: 161–168.

69. Bonello L, et al. Tailored clopidogrel loading dose according to platelet reactivity monitoring to prevent acute and subacute stent thrombosis. Am J Cardiol 2009; 103: 5–10.

70. Bonello L, et al. Adjusted clopidogrel loading doses according to vasodilator-stimulated phosphoprotein phosphorylation index decrease rate of major ad-verse cardiovascular events in patients with clopidogrel resistance: a multicenter randomised prospective study. J Am Coll Cardiol 2008; 51: 1404–1411.

71. Siller-Matula JM, et al. Personalised antiplatelet treatment after percutaneous coronary intervention: the MADONNA study. Int J Cardiol 2013; 167: 2018–2023.

72. Trenk D, et al. Antiplatelet response to the 150-mg maintenance dose of clopi-dogrel in patients with insufficient platelet inhibition after clopidogrel loading for elective coronary stent placement. EuroIntervention 2008; 4: 214–221.

73. Aleil B, et al. Clopidogrel 150 mg/day to overcome low responsiveness in pa-tients undergoing elective percutaneous coronary intervention: results from the VASP-02 (Vasodilator-Stimulated Phosphoprotein-02) randomised study. JACC Cardiovasc Interv 2008; 1: 631–638.

74. Jeong YH, et al. randomised comparison of adjunctive cilostazol versus high maintenance dose clopidogrel in patients with high post-treatment platelet reac-tivity: results of the ACCEL-RESISTANCE (Adjunctive Cilostazol Versus High Maintenance Dose Clopidogrel in Patients With Clopidogrel Resistance) rando-mised study. J Am Coll Cardiol 2009; 53: 1101–1109.

75. Collet JP, et al. High doses of clopidogrel to overcome genetic resistance: the randomised crossover CLOVIS-2 (Clopidogrel and Response Variability Inves-tigation Study 2). JACC Cardiovasc Interv 2011; 4: 392–402.

76. Valgimigli M, et al. Intensifying platelet inhibition with tirofiban in poor re-sponders to aspirin, clopidogrel, or both agents undergoing elective coronary intervention: results from the double-blind, prospective, randomised Tailoring Treatment with Tirofiban in Patients Showing Resistance to Aspirin and/or Re-sistance to Clopidogrel study. Circulation 2009; 119: 3215–3222.

77. Cuisset T, et al. Glycoprotein IIb/IIIa inhibitors improve outcome after coronary stenting in clopidogrel nonresponders: a prospective, randomised study. JACC Cardiovasc Interv 2008; 1: 649–653.




51

78. Price MJ, et al. Standard- vs high-dose clopidogrel based on platelet function testing after percutaneous coronary intervention: the GRAVITAS randomised trial. J Am Med Assoc 2011; 305: 1097–1105.

79. Trenk D, et al. A randomised trial of prasugrel versus clopidogrel in patients with high platelet reactivity on clopidogrel after elective percutaneous coronary intervention with implantation of drug-eluting stents: results of the TRIGGER-PCI (Testing Platelet Reactivity In Patients Undergoing Elective Stent Placement on Clopidogrel to Guide Alternative Therapy With Prasugrel) study. J Am Coll Cardiol 2012; 59: 2159–2164.

80. Gurbel PA, et al. Platelet function during extended prasugrel and clopidogrel therapy for patients with ACS treated without revascularisation: the TRILOGY ACS platelet function substudy. J Am Med Assoc 2012; 308: 1785–1794.

81. Aradi D, et al. Efficacy and safety of intensified antiplatelet therapy on the basis of platelet reactivity testing in patients after percutaneous coronary interven-tion: Systematic review and meta-analysis. Int J Cardiol 2013; 167: 2140–2148.

82. Collet JP, et al. Bedside Monitoring to Adjust Antiplatelet Therapy for Coronary Stenting. N Engl J Med 2012; 367: 2100–2109.

83. Stone G. A large-scale, prospective, multicenter registry examining the relation-ship between platelet responsiveness and stent thrombosis after des implan-tation. Results from the ADAPT-DES study. J Am Coll Cardiol 2011; 58 (Supplement B): Abstract LBCT.

84. Collet JP, et al. Bedside monitoring to adjust antiplatelet therapy for coronary stenting. N Engl J Med 2012; 367: 2100–2109.

85. Cattaneo M. Resistance to antiplatelet drugs: molecular mechanisms and lab-oratory detection. J Thromb Haemost 2007; 5 (Suppl 1): 230–237.

86. Sumaya W, et al. Hirudin anticoagulation allows more rapid determination of P2Y(1)(2) inhibition by the VerifyNow P2Y12 assay. Thromb Haemost 2013; 109: 550–555.

87. Schror K, et al. Functional testing methods for the antiplatelet effects of aspirin. Biomarkers Med 2011; 5: 31–42.

88. Weber AA, Schror K. Differential inhibition of adenosine diphosphate- versus thrombin receptor-activating peptide-stimulated platelet fibrinogen binding by abciximab due to different glycoprotein IIb/IIIa activation kinetics. Blood 2001; 98: 1619–1621.

89. Clopidogrel Genotyping for Antiplatelet Guidance in MI Stenting: Maybe Re-duced Ischaemic Risk. Medscape 2013; Nov. 6, 2013.

90. Gurbel PA, et al. The relation between CYP2C19 genotype and phenotype in stented patients on maintenance dual antiplatelet therapy. Am Heart J 2011; 161: 598–604.

91. Aradi D, et al. Optimizing P2Y12 receptor inhibition in patients with acute cor-onary syndrome on the basis of platelet function testing: impact of prasugrel and high-dose clopidogrel. J Am Coll Cardiol 2014; 63: 1061–1070.

92. Siller-Matula JM, Jilma B. Why have studies of tailored anti-platelet therapy failed so far? Thromb Haemost 2013; 110: 628–631.

93. Gurbel PA, et al. Platelet function monitoring in patients with coronary artery disease. J Am Coll Cardiol 2007; 50: 1822–1834.

94. Storey RF, et al. Lower Mortality Following Pulmonary Adverse Events and Sep-sis with Ticagrelor Compared to Clopidogrel in the PLATO Study. Platelets 2013; Epub ahead of print.

95. Kozinski M, et al. Diurnal variation in platelet inhibition by clopidogrel. Pla-telets 2011; 22: 579–587.

96. Kozinski M, et al. Increased morning ADP-dependent platelet aggregation per-sists despite dual antiplatelet therapy in patients with first ST-segment elevation myocardial infarction: Preliminary report. Cardiol J 2008; 15: 530–536.

97. Siller-Matula JM, et al. The effect of antiplatelet drugs clopidogrel and aspirin is less immediately after stent implantation. Thromb Res 2009; 123: 874–880.

98. De Caterina R, et al. Bedside monitoring of antiplatelet therapy for coronary stenting. N Engl J Med 2013; 368: 871.

99. Jneid H, et al. 2012 ACCF/AHA focused update of the guideline for the manage-ment of patients with unstable angina/non-ST-elevation myocardial infarction (updating the 2007 guideline and replacing the 2011 focused update): a report of the American College of Cardiology Foundation/American Heart Associ-ation Task Force on Practice Guidelines. J Am Coll Cardiol 2012; 60: 645–681.

100. Hamm CW, et al. ESC Guidelines for the management of acute coronary syn-dromes 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.

101. Levine GN, et al. 2011 ACCF/AHA/SCAI Guideline for Percutaneous Coron-ary Intervention. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions. J Am Coll Cardiol 2011; 58: e44–122.

102. Wallentin L, et al. Ticagrelor versus Clopidogrel in Patients with Acute Coron-ary Syndromes. N Engl J Med 2009; 361: 1045–1057.

103. Wiviott SD, et al. Prasugrel versus clopidogrel in patients with acute coronary syndromes. N Engl J Med 2007; 357: 2001–2015.

104. Steg PG, et al. ESC Guidelines for the management of acute myocardial infarc-tion in patients presenting with ST-segment elevation: The Task Force on the management of ST-segment elevation acute myocardial infarction of the Euro-pean Society of Cardiology (ESC). Eur Heart J 2012; 33: 2569–2619.

105. O’Gara PT, et al. 2013 ACCF/AHA guideline for the management of ST-elev-ation myocardial infarction: executive summary: a report of the American Col-lege of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines: developed in collaboration with the American College of Emergency Physicians and Society for Cardiovascular Angiography and Inter-ventions. Catheter Cardiovasc Interv 2013; 82: E1–27.

106. Huber K, Lip GY. Differences between ACC/AHA and ESC Guidelines on anti-platelet therapy in patients with acute coronary syndromes. Thromb Haemost 2013; 110: 11–13.

107. Siller-Matula J, et al. Thienopyridines in cardiovascular disease: focus on clopi-dogrel resistance. Thromb Haemost 2007; 97: 385–393.

108. Alexopoulos D, et al. Prevalence of contraindications and conditions for pre-caution for prasugrel administration in a real world acute coronary syndrome population. J Thromb Thrombolysis 2011; 32: 328–333.

109. Geisler T, et al. CYP2C19 and nongenetic factors predict poor responsiveness to clopidogrel loading dose after coronary stent implantation. Pharmacoge-nomics 2008; 9: 1251–1259.

110. Breet NJ, et al. Comparison of platelet function tests in predicting clinical out-come in patients undergoing coronary stent implantation. J Am Med Assoc 2010; 303: 754–762.

111. Freynhofer MK, et al. Multiple electrode aggregometry and vasodilator stimu-lated phosphoprotein-phosphorylation assay in clinical routine for prediction of postprocedural major adverse cardiovascular events. Thromb Haemost 2011; 106: 230–239.

112. Bonello L, et al. Vasodilator-stimulated phosphoprotein phosphorylation analysis prior to percutaneous coronary intervention for exclusion of postpro-cedural major adverse cardiovascular events. J Thromb Haemost 2007; 5: 1630–1636.

113. Bal Dit Sollier C, et al. Differential sensitivity and kinetics of response of differ-ent ex vivo tests monitoring functional variability of platelet response to clopi-dogrel. Thromb Haemost 2010; 104: 571–581.

114. Johnston LR, et al. Methodological considerations for the assessment of ADP induced platelet aggregation using the Multiplate(R) analyser. Platelets 2013; 24: 303–307.

115. Capranzano P, et al. Platelet function profiles in the elderly: Results of a phar-macodynamic study in patients on clopidogrel therapy and effects of switching to prasugrel 5 mg in patients with high platelet reactivity. Thromb Haemost 2011; 106: 1149–1157.

116. Ferreiro JL, et al. Impact of Adjunctive Cilostazol Therapy Versus High Main-tenance Dose of Clopidogrel in Suboptimal Responders With Diabetes Melli-tus. Rev Esp Cardiol 2011; 65: 105–106.

117. Kozinski M, et al. Prasugrel overcomes high on-clopidogrel platelet reactivity in the acute phase of acute coronary syndrome and maintains its antiplatelet potency at 30-day follow-up. Cardiol J 2014; Epub ahead of print.

118. Matetzky S, et al. Effectiveness of reloading to overcome clopidogrel nonre-sponsiveness in patients with acute myocardial infarction. Am J Cardiol 2008; 102: 524–529.

119. Gurbel PA, et al. The effect of elinogrel on high platelet reactivity during dual antiplatelet therapy and the relation to CYP2C19*2 genotype: first experience in patients. J Thromb Haemost 2010; 8: 43–53.

120. Gurbel PA, et al. Response to ticagrelor in clopidogrel nonresponders and re-sponders and effect of switching therapies: the RESPOND study. Circulation 2010; 121: 1188–1199.

121. Neubauer H, et al. How to optimise clopidogrel therapy? Reducing the low-re-sponse incidence by aggregometry-guided therapy modification. Thromb Hae-most 2008; 99: 357–362.




52

122. Roberts JD, et al. Point-of-care genetic testing for personalisation of antiplatelet treatment (RAPID GENE): a prospective, randomised, proof-of-concept trial. Lancet 2012; 379: 1705–1711.

123. Kim IS, et al. Platelet inhibition by adjunctive cilostazol versus high mainten-ance-dose clopidogrel in patients with acute myocardial infarction according to cytochrome P450 2C19 genotype. JACC Cardiovasc Interv 2011; 4: 381–391.

124. Hwang SJ, et al. Cytochrome 2C19 polymorphism and response to adjunctive cilostazol versus high maintenance-dose clopidogrel in patients undergoing percutaneous coronary intervention. Circ Cardiovasc Interv 2010; 3: 450–459.

125. Gurbel PA, et al. Clopidogrel for coronary stenting: response variability, drug resistance, and the effect of pretreatment platelet reactivity. Circulation 2003; 107: 2908–2913.

126. Bouman HJ, et al. Which platelet function test is suitable to monitor clopido-grel responsiveness? A pharmacokinetic analysis on the active metabolite of clopidogrel. J Thromb Haemost 2010; 8: 482–488.

127. Breet NJ, et al. High on-treatment platelet reactivity to both aspirin and clopi-dogrel is associated with the highest risk of adverse events following percut-aneous coronary intervention. Heart 2011; 97: 983–990.

128. Elsenberg EH, et al. The influence of clinical characteristics, laboratory and in-flammatory markers on ’high on-treatment platelet reactivity’ as measured with different platelet function tests. Thromb Haemost 2009; 102: 719–727.

129. Gurbel PA, et al. Assessment of clopidogrel responsiveness: measurements of maximum platelet aggregation, final platelet aggregation and their correlation with vasodilator-stimulated phosphoprotein in resistant patients. Thromb Res 2007; 121: 107–115.

130. Jakubowski JA, et al. A comparison of the antiplatelet effects of prasugrel and high-dose clopidogrel as assessed by VASP-phosphorylation and light trans-mission aggregometry. Thromb Haemost 2008; 99: 215–222.

131. Linnemann B, et al. Assessment of clopidogrel non-response by the PFA-100 system using the new test cartridge INNOVANCE PFA P2Y. Ann Hematol 2010; 89: 597–605.

132. Paniccia R, et al. Comparison of methods for monitoring residual platelet reac-tivity after clopidogrel by point-of-care tests on whole blood in high-risk pa-tients. Thromb Haemost 2010; 104: 287–292.

133. Sibbing D, et al. Assessment of ADP-induced platelet aggregation with light transmission aggregometry and multiple electrode platelet aggregometry be-fore and after clopidogrel treatment. Thromb Haemost 2008; 99: 121–126.

134. Li YG, et al. Inhibition of platelet aggregation with prasugrel and clopidogrel: an integrated analysis in 846 subjects. Platelets 2009; 20: 316–327.

135. Komosa A, et al. Comparison of the antiplatelet effect of two clopidogrel bisul-fate formulations: Plavix and generic-Egitromb. Platelets 2014; Epub ahead of print.

136. Siller-Matula JM, et al. Dual non-responsiveness to antiplatelet treatment is a stronger predictor of cardiac adverse events than isolated non-responsiveness to clopidogrel or aspirin. Int J Cardiol 2013; 167: 430–435.

137. Christ G, et al. Platelet Inhibition by Abciximab Bolus-Only Administration and Oral ADP Receptor Antagonist Loading in Acute Coronary Syndrome Pa-tients: The Blocking and Bridging Strategy. Thromb Res 2013; 132: e36-e41.

138. Spiel AO, et al. Effects of prasugrel on platelet inhibition during systemic en-dotoxaemia: a randomised controlled trial. Clin Sci 2012; 123: 591–600.

139. Siller-Matula JM, et al. ARC15105 is a potent antagonist of von Willebrand fac-tor mediated platelet activation and adhesion. Arterioscler Thromb Vasc Biol 2012; 32: 902–909.

140. Kasprzak M, et al. Pantoprazole may enhance antiplatelet effect of enteric-coated aspirin in patients with acute coronary syndrome. Cardiol J 2009; 16: 535–544.

141. Sibbing D, et al. Clopidogrel response status assessed with Multiplate point-of-care analysis and the incidence and timing of stent thrombosis over six months following coronary stenting. Thromb Haemost 2010; 103: 151–159.

142. Blindt R, et al. The significance of vasodilator-stimulated phosphoprotein for risk stratification of stent thrombosis. Thromb Haemost 2007; 98: 1329–1334.

143. Lev EI, et al. Aspirin and clopidogrel drug response in patients undergoing per-cutaneous coronary intervention: the role of dual drug resistance. J Am Coll Cardiol 2006; 47: 27–33.

144. Cuisset T, et al. Role of the T744C polymorphism of the P2Y12 gene on platelet response to a 600-mg loading dose of clopidogrel in 597 patients with non-ST-segment elevation acute coronary syndrome. Thromb Res 2007; 120: 893–899.

145. Frelinger AL, 3rd, et al. Intrinsic platelet reactivity before P2Y12 blockade con-tributes to residual platelet reactivity despite high-level P2Y12 blockade by pra-sugrel or high-dose clopidogrel. Results from PRINCIPLE-TIMI 44. Thromb Haemost 2011; 106: 219–226.

146. Cuisset T, et al. Relation of low response to clopidogrel assessed with point-of-care assay to periprocedural myonecrosis in patients undergoing elective cor-onary stenting for stable angina pectoris. Am J Cardiol 2008; 101: 1700–1703.

147. Jakubowski JA, et al. The use of the VerifyNow P2Y12 point-of-care device to monitor platelet function across a range of P2Y(12) inhibition levels following prasugrel and clopidogrel administration. Thromb Haemost 2008; 99: 409–415.

148. Price MJ, et al. Prognostic significance of post-clopidogrel platelet reactivity as-sessed by a point-of-care assay on thrombotic events after drug-eluting stent implantation. Eur Heart J 2008; 29: 992–1000.

149. Mayr FB, et al. The aptamer ARC1779 blocks von Willebrand factor-dependent platelet function in patients with thrombotic thrombocytopenic purpura ex vivo. Transfusion 2010; 50: 1079–1087.

150. Siller-Matula JM, et al. Cross validation of the Multiple Electrode Aggrego-metry. A prospective trial in healthy volunteers. Thromb Haemost 2009; 102: 397–403.

151. Panzer S, et al. Monitoring survival and function of transfused platelets in Bernard-Soulier syndrome by flow cytometry and a cone and plate(let) ana-lyzer (Impact-R). Transfusion 2007; 47: 103–106.

152. Spiel AO, et al. Single dose granulocyte colony-stimulating factor markedly en-hances shear-dependent platelet function in humans. Platelets 2010; 21: 464–469.

153. Lordkipanidze M, et al. A comparison of six major platelet function tests to de-termine the prevalence of aspirin resistance in patients with stable coronary ar-tery disease. Eur Heart J 2007; 28: 1702–1708.

154. Grove EL, et al. A comparison of platelet function tests and thromboxane metabolites to evaluate aspirin response in healthy individuals and patients with coronary artery disease. Thromb Haemost 2010; 103: 1245–1253.

155. Frelinger AL, 3rd, et al. Association of cyclooxygenase-1-dependent and -inde-pendent platelet function assays with adverse clinical outcomes in aspirin-treated patients presenting for cardiac catheterisation. Circulation 2009; 120: 2586–2596.

156. Gurbel PA, et al. Platelet reactivity in patients and recurrent events post-stent-ing: results of the PREPARE POST-STENTING Study. J Am Coll Cardiol 2005; 46: 1820–1826.

157. Bliden KP, et al. Increased risk in patients with high platelet aggregation receiv-ing chronic clopidogrel therapy undergoing percutaneous coronary interven-tion: is the current antiplatelet therapy adequate? J Am Coll Cardiol 2007; 49: 657–666.

158. Craft RM, et al. A novel modification of the Thrombelastograph assay, isolating platelet function, correlates with optical platelet aggregation. J Lab Clin Med 2004; 143: 301–309.

159. Scharbert G, et al. Evaluation of the Platelet Mapping Assay on rotational thromboelastometry ROTEM. Platelets 2009; 20: 125–130.

160. Mahla E, et al. Platelet function measurement-based strategy to reduce bleed-ing and waiting time in clopidogrel-treated patients undergoing coronary ar-tery bypass graft surgery: the timing based on platelet function strategy to re-duce clopidogrel-associated bleeding related to CABG (TARGET-CABG) study. Circ Cardiovasc Interv 2012; 5: 261–269.



how to improve the concept of individualised antiplatelet therapy with...

Documents