ISRN CardiologyVolume 2012 (2012), Article ID 692761, 8 pagesdoi:10.5402/2012/692761

Clinical Study

Impact of Dual Antiplatelet Therapy with Proton Pump Inhibitors on the Outcome of Patients with Acute Coronary Syndrome Undergoing Drug-Eluting Stent Implantation

Francesca Macaione, Carla Montaina, Salvatore Evola, Giuseppina Novo, and Salvatore Novo

Division of Cardiology and Post-Graduate School of Cardiology, Center for the Early Diagnosis of Preclinical and Multifocal Atherosclerosis and for the Secondary Prevention, University Hospital “P. Giaccone” of the University of Palermo, 127-90127 Palermo, Italy

Received 21 March 2012; Accepted 7 May 2012

Academic Editors: J. Mansourati and J. M. Perez-Pomares

Copyright © 2012 Francesca Macaione et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

This study aimed to assess if proton pump inhibitors (PPIs) may reduce the effectiveness of clopidogrel, than H2 antagonist (anti-H2) in order to determine rehospitalization for acute coronary syndrome (re-ACS), target vessel revascularization (TVR) and cardiac death. This case-control study included 176 patients with ACS undergoing angioplasty (PCI) with drug-eluting stent implantation. The population was divided into two groups: PPI group () consisting of patients receiving at discharge dual antiplatelet therapy (DAT) plus PPI and anti-H2 group (), consisting of patients receiving at discharge DAT + H2 receptor antagonist (H2RA). In a followup of 36 months the prevalence of ACS event (), TVR () was higher in the PPI group than in the anti-H2 group; instead there was no statistically significant difference between groups for death. The variables independently associated with ACS were the diabetes, omeprazole, and esomeprazole; instead the variables independently associated with TVR were only omeprazole. Our data shows that the use of omeprazole and esomeprazole, with clopidogrel, is associated with increased risk of adverse outcomes after PCI with drug-eluting stent implantation.

1. Introduction

The introduction of coronary stents into clinical practice has revolutionized the treatment of coronary artery disease. The use of dual antiplatelet therapy (DAT) with aspirin and clopidogrel, in the setting of percutaneous coronary intervention (PCI) with stent implantation, is the cornerstone of the pharmacological management to prevent adverse cardiovascular events.

In the era of drug-eluting stent prolonged antiplatelet therapy is mandatory because of the potential increased risk of late stent thrombosis [1]. Current guidelines recommend DAT for minimum of 12 months after DES implantation [2].

The obvious concern and serious complication with prolonged DAT is a bleeding of the gastrointestinal tract.

For this reason, a dual antiplatelet therapy, Clopidogrel + ASA, is commonly used with an antisecretory agent, such as proton pump inhibitors (PPIs) or H2 antagonist receptor (H2RA) [3, 4].

Intense debate is ongoing about if PPIs may reduce the efficacy and safety of clopidogrel; in fact many aspects in the current clinical practice are still under investigation.

Observational studies have showed inconsistency regarding whether concomitant clopidogrel and PPI use is [5–7], or not associated with adverse clinical outcomes [8–10].

Clopidogrel is a prodrug, belonging to the class of thienopyridines, administered orally.

About 85% of the prodrug is hydrolyzed by esterases in the blood, in an inactive carboxylic acid derivative, and only 15% of the prodrug is metabolized in the liver by cytochrome P450 with a mechanism of oxidation to generate an active metabolite. The active metabolite irreversibly inhibits platelet P2Y12 receptor for adenosine diphosphate (ADP) [11, 12]. The isoenzyme CYP2C19 plays an important role in the clopidogrel activation. Patients with reduced-function genetic polymorphisms have lower levels of the active metabolite of clopidogrel and they have an increased risk of cardiovascular events, as they have a reduced inhibition of ADP-induced platelet aggregation [13–15].

Several proton pump inhibitors (PPIs) are metabolized by CYP2C19 and thus may interact with clopidogrel metabolism [16]; therefore the use of concomitant PPIs could impede or prevent the metabolism of clopidogrel to its active metabolites through competition for the same substrate, resulting in decreased activation of clopidogrel which leads to an increased risk of adverse cardiovascular events [5, 17, 18].

The importance of this interaction arises from the large number of PCI performed annually, the increasing use of drug-eluting stent associated with long-term treatment, and the possibility of preventing an adverse interaction by avoiding coadministration of PPI.

The rationale of this study arose from the need to further investigation about the potential interaction between proton pump inhibitors and clopidogrel.

The aim of this study was to investigate the clinical impact of PPI on the outcome of patients with acute coronary syndrome who underwent percutaneous coronary intervention with drug-eluting stent implantation, evaluating, also, the differences across the various types of IPP on the outcome.

2. Methods

In our retrospective study we assessed a population of 234 consecutive patients with acute coronary syndrome (ACS), as documented by electrocardiographic criteria, levels of troponin, and other clinical evidence, undergoing percutaneous coronary intervention (PCI) with drug-eluting in our Division of Cardiology, General Hospital of Palermo “Paolo Giaccone.”

Interventional procedures were performed according to international guidelines. For all patients PCI of occluded or stenotic coronary was performed by the femoral approach and use of guiding catheters 6Fr.

All patients were pretreated with aspirin and clopidogrel. The use of glycoprotein IIb/IIIa during coronary intervention was based on the operators discretion and current guidelines.

Exclusion criteria were nonaccessibility to followup, a life expectancy of less than a year, allergy to thienopyridines, ticlopidine therapy with dual antiplatelet therapy, no gastroprotective therapy, tumors, oral anticoagulation therapy, balloon angioplasty without stenting.

In the study were included the patients remaining.

In this manner, a final sample size of 176 (75.21%) of 234 patients was enrolled. The demographic, clinical, therapeutic, and angiographic characteristics are summarized in Table 1.

Table 1: Population characteristics.

Total ()
PPI group ()
Anti-H2 group ()
value < 0.05

Demographics characteristics

    Age

0.203

    Male (%)
145 (82.38)
97 (80.16)
48 (87.27)
0.196

Clinical characteristics (%)

    Smoke
61 (34.65)
45 (37.19)
15 (27.27)
0.265

    Dyslipidemia
97 (55.11)
65 (53.71)
32 (58.18)
0.697

    Familiar history
63 (35.79)
42 (34.71)
21 (38.18)
0.782

    Hypertension
130 (73.86)
85 (70.24)
45 (81.81)
0.152

    Obesity (Kg/m²)
22 (12.50)
11 (9.09)
11 (20)
0.074

    Diabetes
78 (44.31)
50 (41.32)
33 (49.09)
0.43

    Previous CABG
11 (6.25)
11 (9.09)
0 (0)
0.048

    Previous AF
5 (2.84)
1 (0.82)
4 (7.27)
0.057

    Previous AMI
28 (15.90)
20 (16.52)
8 (14.54)
0.912

    Previous PCI
38 (21.59)
29 (23.96)
9 (16.36)
0.348

    Previous HF
4 (2.27)
3 (2.47)
1 (1.81)
0.784

    Renal failure
38 (21.59)
28 (23.14)
10 (18.18)
0.587

    Anemia (%)
62 (35.22)
50 (41.32)
12 (21.81)
0.019

Therapy at discharge (%)

    ACE inhibitors
106 (60.22)
75 (61.98)
30 (54.54)
0.443

    -blockers
137 (77.84)
94 (77.68)
43 (78.18)
0.903

    Statine
163 (92.61)
109 (90.08)
54 (98.18)
0.111

Angiographics data

    Multivessel disease (%)
64 (36.36)
44 (36.36)
20 (36.36)
0.865

    No. of stents
1.26 ± 0.56
1.24 ± 0.60
1.25 ± 0.55
0.916

CABG: coronary artery bypass graft surgery; AF: atrial fibrillation; HF: heart failure; AMI: acute myocardial infarction; PCI: percutaneous coronary intervention.

All patients included had a successful procedure, defined by the recovery of coronary flow TIMI 3 (Thrombolysis in Myocardial Infarction) with residual stenosis less than 50%. After procedure, all patients were prescribed dual antiplatelet therapy, aspirin (100 mg daily) indefinitely, plus clopidogrel (75 mg/day), to continue from 12 to 18 months, with a concomitant gastroprotective therapy, using PPI or H2RA.

All patients enrolled underwent an accurate anamnesis, clinical examination, laboratory analysis, and anthropometric measurements. The database contains data listed in Table 1.

Familiar history of coronary artery disease (CAD) was defined as coronary event occurring before 55 and 65 years, for first-degree male and female, respectively.

Hypertension was defined as a blood pressure >140/90 mmHg or as use antihypertensive drugs.

Diabetes mellitus was defined as a fasting glucose ≥126 mg/dL or as use hypoglycemic drugs [19].

Patients smokersif they were current smokers or had stopped smoking since less than a year.

Dyslipidemia was defined as plasma triglycerides >150 mg/dL and/or plasma LDL-C >130 mg/dL or plasma HDL-C <40 mg/dL in men and <50 mg/dL in women. Obesity was defined as a BMI (body mass index) ≥30 kg/m². Anemia was defined as hemoglobin level <12 g/dL in women and <13 g/dL in men [20].

Chronic renal failure was defined as an estimated glomerular filtration rate (eGFR) <60 mL/minute/1.73 m assessed by the MDRD equation [21].

Multivessel disease was defined as two or more lesions >50% in two or more epicardial coronary arteries. The clinical endpoints were new rehospitalization for acute coronary syndrome (re-ACS), target vessel revascularization (TVR), and cardiac death. TVR was defined as any percutaneous or surgical revascularization of any segment of the target vessel.

The target vessel is defined as the entire major coronary vessel proximal and distal to the target lesion, which includes upstream and downstream branches and the target lesion itself.

The diagnosis of ACS was based on the presence of at least two of these criteria: clinical symptoms suggestive of ACS [22], ischemic electrocardiographic changes (transitory or persistent ST segment deviation of the least 0.1 mV in at least two contiguous leads) [23], positive biomarkers of myocardial necrosis [24] (cardiac troponin, creatine kinase MB) in two consecutive determinations.

Followup of clinical end points was conducted for up to 36 months after PCI.

The clinical follow-up data were collected through telephone calls, outpatients cardiologic visit or further rehospitalization after the index procedure, and hospital records.

During follow-up periods, the patients who died for noncardiac causes were censored.

Statistical AnalysisContinuous variables are presented as mean ± standard deviation and were compared using Student’s unpaired test. Categorical variables are presented as counts and percentages and were compared with the “Chi-square” test when appropriate (expected frequency >5). Otherwise, the Fisher’s exact test was used.Multivariate analyses (logistic regression) were conducted to identify the possible variables independently correlated with ACS and TVR in the followup. Models were developed with stepwise techniques, and by consideration all variables at univariate analysis showed value ≤0.10. Results of this model were presented as odds ratio (OR) and 95% confidence intervals (95% CI) for OR. value equal or less than 0.05 was considered statistically significant.The statistical analysis was performed using MedCalc software version 11.3.0.0.

3. Results

The study population consisted of 176 patient with mean age of 64.31 ± 10.08 years most of the patients were male (82.38%).

The patient sample was divided up into two groups: patients treated with proton pump inhibitors, PPI group, and patients treated with H2RA, anti-H2 group.

The PPI group included a total of 121 (68.75%) patients with mean age 63.66 ± 10.56 years.

The anti-H2 group included a total of 55 (31.25%) patients with mean age 65.75 ± 8.85 years.

In the PPI group we included esomeprazole (, 11.57%), omeprazole (, 42.97%), lansoprazole (, 10.74%), and pantoprazole (, 34.71%) because they were the most prescribed as gastric protection in our Unit. The distribution of PPI use is shown in Figure 1.

Figure 1: Prevalence of proton pump inhibitors in the PPIs group.

The demographic, clinical, therapeutic, and angiographic characteristics of the population and of the groups are summarized in Table 1.

The patients of PPI group had significantly higher proportion of anemia () and previous CABG () compared with patients of anti-H2 group.

There were no significant differences for all other variables and two groups did not differ with regard to medications use.

At the end of three-year followup among the patients of PPI group, there were 38 (31.40%) re-ACSs, 25 (20.66%) TVRs, 2 (1.65%) cardiac deaths.

Instead among the patients of anti-H2 group, there were 7 (17.72%) re-ACSs, 3 (5.45%) TVRs, 0 cardiac deaths.

On data obtained from followup we applied a univariate analysis that showed a higher incidence of re-ACS events () and TVR () in the PPI group in comparison with anti-H2 group.

An overview of events between two groups is shown in Table 2.

Table 2: Statistical analysis cardiovascular events.

Total ( = 176)
PPI group ( = 121)
Anti-H2 group ( = 55)
value < 0.05

re-ACS (%)
45 (25.58)
38 (31.40)
7 (12.72)
0.014

TVR (%)
28 (15.90)
25 (20.66)
3 (5.45)
0.031

Cardiac Death (%)
2 (1.36)
2 (1.65)
0 (0)
0.84

re-ACS: rehospitalization for acute coronary syndrome; TVR: target vessel revascularization.

We also used univariate analysis to search for possible significant differences in baseline demographic, clinical, therapeutic, and angiographic parameters between the groups of patients with or without re-ACS (Table 3), with or without TVR (Table 4) and the clinical events registered in followup.

Table 3: Univariate analysis for re-ACS event.

Patients with re-ACS ()
value < 0.05
Patients without re-ACS ()

Age
66.8 ± 10.45
0.055
63.46 ± 9.85

Male (%)
37 (82.22)
0.846
108 (82.24)

Smoke
16 (35.55)
0.97
45 (0.34)

Dyslipidemia
21 (46.66)
0.25
76 (58.01)

Familiar history
14 (31.11)
0.562
49 (37.40)

Hypertension
33 (73.33)
0.918
97 (74.04)

Obesity ( Kg/m²)
1 (2.22)
0.03
21 (16.03)

Diabetes
27 (60)
0.022
51 (38.93)

Renal failure
9 (20)
0.92
29 (22.13)

Anemia (%)
18 (40)
0.55
44 (33.58)

Multivessel disease n (%)
15 (33.33)
0.756
49 (37.40)

No. Stents
1.24 ± 0.60
0.918
1.25 ± 0.55

Omeprazole
22 (48.88)
0.0019
30 (22.90)

Esomeprazole
8 (17.77)
0.012
6 (4.58)

Lansoprazole
5 (11.11)
0.43
8 (6.10)

Pantoprazole
3 (6.66)
0.0033
39 (29.77)

Anti-H2
7 (15.55)
0.0144
48 (36.64)

Table 4: Univariate analysis for TVR event.

Patients with TVR ()
value < 0.05
Patients without TVR ()

Age
64.92 ± 9.93
0.729
64.20 ± 10.13

Male (%)
23
0.815
122

Smoke
11
0.730
50

Dyslipidemia
15
0.977
82

Familiar history
9
0.822
54

Hypertension
21
0.932
109

Obesity ( Kg/m²)
2
0.525
20

Diabetes
18
0.034
60

Renal failure
6
0.819
32

Anemia (%)
16
0.015
46

Multivessel disease (%)
12
0.57
52

No. Stents
1.26 ± 0.56
0.870
1.24 ± 0.60

Omeprazole
14
0.018
38

Esomeprazole
5
0.083
9

Lansoprazole
2
0.73
11

Pantoprazole
6
0.93
36

Anti-H2
3
0.019
52

Particularly we evaluated the PPI individually such as omeprazole, esomeprazole, lansoprazole, and pantoprazole.

We found that patients with ACS presented a significant prevalence of obesity (), diabetes () and significant prevalence of treatment with omeprazole (), esomeprazole (), and pantoprazole (); in contrast, the patients without re-ACS were a significantly higher proportion of treatment with ranitidine ().

The patients with TVR presented a significant prevalence of anemia () and significant prevalence of treatment with omeprazole (); in contrast, the patients without TVR were a significantly higher proportion of treatment with ranitidine ().

An overview of re-ACS and TVR events correlated at the use of PPI individually and of anti-H2 is shown in Figure 2.

Figure 2: ACS and TVR events correlated at the use of PPI individually and of anti-H2. re-ACS: rehospitalization for acute coronary syndrome; TVR: target vessel revascularization.

In addition we used logistic regression analysis in order to identify the independent predictor for occurrence of re-ACS and TVR during followup.

Multivariate logistic regression analysis that was adjusted for all variables at univariate analysis showed P value ≤0.10, and we found that the omeprazole (, OR: 5, 95% CI: 2.26–11.10), esomeprazole (, OR: 7.09, 95% CI: 2.10–23.80), and diabetes (, OR: 2.37, 95% CI: 1.12–5.05) can be considered independent re-ACS predictors; instead only omeprazole (, OR: 2.89, 95% CI: 1.27–6.62) can be considered independent of TVR predictors (Table 5).

Table 5: Logistic regression analysis, independent correlates of acute coronary syndrome (ACS) and of target vessel revascularization (TVR).

Variability
Coefficient
Std. error
value
OR
95% CI

re-ACS

    Omeprazole
1.6113
0.4059
0.0001
5.0093
2.2606–11.1002

    Esomeprazole
1.9588
0.6198
0.0016
7.09
2.1042–23.8046

    Diabetes
0.8646
0.3851
0.0248
2.37
1.1159–5.0502

TVR

    Omeprazole
1.0629
0.4222
0.0118
2.8947
1.2654–6.6222

re-ACS: rehospitalization for acute coronary syndrome; TVR: target vessel revascularization.

4. Discussion

Dual antiplatelet therapy (DAT) with aspirin and clopidogrel is the cornerstone of the pharmacological management in patients with acute coronary syndromes or those undergoing percutaneous coronary intervention (PCI) [25–27]. Although beneficial in these settings, prolonged DAT might be associated with the risk of gastrointestinal bleeding, [28]. For this reason, proton pump inhibitors (PPIs) and H2 antagonist are often prescribed in patients with DAT.

Our study aims to better understand if the type of gastroprotective therapy could influence the outcome of patients, independently of some variables such as duration of treatment and the type of stent implanted. We analyzed only the patients who underwent DES implantation because in these patients the therapy with DAT after PCI is prolonged, and in this manner the patients are more exposed to treatment of gastric protection with DAT.

Our small, single center study shows that patients, discharged on clopidogrel and PPI after undergoing PCI with drug eluting stent implantation for ACS, were at a significantly higher risk of readmission for new cardiovascular adverse events. By multivariate analysis, we found that not the entire class of PPI must be incriminated but that among PPIs, omeprazole (, OR: 5, 95% CI: 2.26–11.10) and esomeprazole (, OR: 7.09, 95% CI: 2.10–23.80) were independent re-ACS predictors, while only omeprazole (, OR: 2.89, 95% CI: 1.27–6.62) was independent TVR predictor at 3-year followup.

Previously described biological mechanisms support the findings of our study. Clopidogrel is converted to its metabolite by sequential oxidative steps in the liver by CYP450 isoenzymes, primarily CYP2C19. PPIs are metabolized by the same hepatic cytochrome, CYP2C19; therefore the use of concomitant PPIs could impede or prevent the metabolism of clopidogrel to its active metabolites through competition for the same substrate [5, 17, 18].

Intense debate is ongoing about if PPIs may reduce the efficacy and safety of clopidogrel.

Studies, such as the study of O’Donoghue et al., the recent works of Simon et al. [8, 29] and data from two other trials, PRINCIPLE-TIMI 44 and TRITON-TIMI 38, seem to contradict that the association between clopidogrel and PPI increases risk of adverse outcomes [30, 31]. Especially the recent study of Rossini et al. [32] has showed that association of clopidogrel and PPIs after drug-eluting stent implantation seems safe.

Other studies, instead, suggest that PPIs decrease the effectiveness and safety of clopidogrel [5, 33, 34]. Ho et al. [5] found that the concomitant use of clopidogrel and PPIs was associated with a higher risk of death or rehospitalization for acute coronary syndrome. Gaglia et al. have examined the effect of PPI at discharge after PCI with DES on the incidence of major adverse events (MACEs) in patients with clopidogrel and with or without a PPI. Univariate survival analysis of the outcomes showed a greater rate of MACE () and overall mortality () in the PPI group. After multivariate analysis, the adjusted MACE hazard ratio for PPI at discharge was 1.8 (95% confidence interval 1.1 to 2.7, ) [35]. Gilard et al., using a novel surrogate marker (vasodilator-stimulated phosphoprotein platelet reactivity index or PRI) for cardiovascular events, have reported that there is higher PRI in patients taking clopidogrel plus PPI than in those taking clopidogrel without PPI [36].

The findings of our study show that the PPIs, especially esomeprazole and omeprazole, lessen the efficacy and safety of clopidogrel; in fact in our study, lansoprazole is not responsible, both with a univariate analysis and with multivariate analysis, for the events considered; instead the therapy with pantoprazole if univariate analysis was significant for ACS, in multivariate analysis pantoprazole is not an independent predictor for ACS.

Several randomized trials, in fact, showed that inhibition of CYP2C19 changes within the class of proton pump inhibitors. Juurlink et al. [6] found that current use of PPIs other than pantoprazole, among omeprazole, lansoprazole, and rabeprazole, in elderly patients on clopidogrel was associated with a significantly increased short-term risk of reinfarction after acute myocardial infarction. Angiolillo et al. in their study have shown that a “Drug-drug” interaction exists for clopidogrel and omeprazole but not for clopidogrel and pantoprazole [37]; other studies have shown that pantoprazole is less potent than omeprazole to inhibit CYP2C19 [38] and seems not to interfere in the pharmacodynamic of clopidogrel. Sibbing et al. [7] have shown that attenuating effects of concomitant PPI treatment on platelet response to clopidogrel were restricted to the use of omeprazole. No attenuating effects on platelet response to clopidogrel were observed for pantoprazole or esomeprazole. In vitro tests showed that, among PPIs, esomeprazole and omeprazole are the most potent inhibitors of CYP2C19; on the other hand in Europe, the European Medicines Agency (EMEA) also issued a statement that concomitant use of omeprazole and other CYP2C19 inhibitors, such as esomeprazole, should be avoided in patients treated with clopidogrel [39–41].

Despite these data, the current clinical evidence does not indicate that one PPI is clearly different from another, so merely switching PPIs cannot be viewed as sufficient to avoid any potential risk.

5. Study Limitation

Our study carries the inherent limitations of an observational study, including failure to account for all confounding variables that could have contributed to the observed findings. Other study limitations are the small study population, telephone followup, the possible reduced absorption of the intestinal mucosa, the presence of residual confounding in the association and especially the contribution of selection bias which may be due to the presence of subjects presenting a polymorphism of CYP2C19.

Different studies have already demonstrated that a CYP2C19 gene polymorphism is associated with a higher platelet aggregation and an increase in adverse cardiac events similar to the poor antiplatelet effects of omeprazole or esomeprazole [38] on clopidogrel. High platelet activity linked to inhibition of PPIs on clopidogrel and a no-response to clopidogrel linked to a polymorphism of cytochrome P450 are associated with an increased risk of adverse events after stent implantation [42, 43].

6. Conclusion

In conclusion, our findings suggest that omeprazole and esomeprazole, in combination with clopidogrel, have been associated with a lower efficacy of clopidogrel in patients with ACS undergoing coronary stenting with drug-eluting stent implantation. This has not been found with other PPIs.

Pending further evidence, we discourage the concomitant use of omeprazole or esomeprazole, as a routine prophylactic, how many times it is used, with the clopidogrel, and we suggest to use anti-H2 or another PPI as lansoprazole or pantoprazole, such as gastric protection, with DAT assessing the possible onset of gastric disorders. However the question of whether the efficacy of clopidogrel is influenced by concomitant use of PPI is open due to the fact that the studies conducted had conflicting results.

Research now in progress will almost certainly help clarify the picture.

References

I. Iakovou, T. Schmidt, E. Bonizzoni et al., “Incidence, predictors and outcome of thrombosis after succesful implantation of drug-eluting stents,” JAMA, vol. 293, no. 17, pp. 2126–2130, 2005.

C. L. Grines, R. O. Bonow, D. E. Casey et al., “Prevention of premature discontinuation of dual antiplatelet therapy in patients with coronary artery stents: a science advisory from the American Heart Association, American College of Cardiology, Society for Cardiovascular Angiography and Interventions, American College of Surgeons, and American Dental Association, with representation from the American College of Physicians,” Circulation, vol. 115, no. 6, pp. 813–818, 2007.

S. Yusuf, F. Zhao, S. R. Mehta, S. Chrolavicius, G. Tognoni, and K. K. Fox, “Effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes without ST-segment elevation,” The New England Journal of Medicine, vol. 345, no. 7, pp. 494–502, 2001.

F. K. L. Chan, J. Y. L. Ching, and L. C. T. Hung, “Clopidogrel versus aspirin and esomeprazole to prevent recurrent ucler bleeding,” The New England Journal of Medicine, vol. 352, no. 3, pp. 338–344, 2005.

P. M. Ho, T. M. Maddox, and L. Wang, “Risk of adverse outcomes associated with concomitant use of clopidogrel and proton pump inhibitors following acute coronary syndrome,” JAMA, vol. 301, no. 9, pp. 937–944, 2009.

D. N. Juurlink, T. Gomes, D. T. Ko et al., “A population-based study of the drug interaction between proton pump inhibitors and clopidogrel,” CMAJ, vol. 180, no. 7, pp. 713–718, 2009.

D. Sibbing, T. Morath, J. Stegherr et al., “Impact of proton pump inhibitors on the antiplatelet effects of clopidogrel,” Thrombosis and Haemostasis, vol. 101, no. 4, pp. 714–719, 2009.

M. L. O'Donoghue, E. Braunwald, E. M. Antman et al., “Pharmacodynamic effect and clinical efficacy of clopidogrel and prasugrel with or without a proton-pump inhibitor: an analysis of two randomised trials,” The Lancet, vol. 374, no. 9694, pp. 989–997, 2009.

V. E. Valkhoff, G. W. 'T Jong, E. M. Van Soest, E. J. Kuipers, and M. C. J. M. Sturkenboom, “Risk of recurrent myocardial infarction with the concomitant use of clopidogrel and proton pump inhibitors,” Alimentary Pharmacology and Therapeutics, vol. 33, no. 1, pp. 77–88, 2011.

S. Banerjee, R. A. Weideman, M. W. Weideman et al., “Effect of concomitant use of clopidogrel and proton pump inhibitors after percutaneous coronary intervention,” American Journal of Cardiology, vol. 107, no. 6, pp. 871–878, 2011.

D. J. Angiolillo, A. Fernandez-Ortiz, E. Bernardo et al., “Variability in individual responsiveness to clopidogrel,” Journal of the American College of Cardiology, vol. 49, no. 14, pp. 1505–1516, 2007.

J. Geiger, L. Teichmann, R. Grossmann et al., “Monitoring of clopidogrel action: comparison of methods,” Clinical Chemistry, vol. 51, no. 6, pp. 957–965, 2005.

J. T. Brandt, S. L. Close, S. J. Iturria et al., “Common polymorphisms of CYP2C19 and CYP2C9 affect the pharmacokinetic and pharmacodynamic response to clopidogrel but not prasugrel,” Journal of Thrombosis and Haemostasis, vol. 5, no. 12, pp. 2429–2436, 2007.

J. L. Mega, S. L. Close, S. D. Wiviott et al., “Cytochrome P-450 polymorphisms and response to clopidogrel,” The New England Journal of Medicine, vol. 360, no. 4, pp. 354–362, 2009.

B. L. Chen, W. Zhang, Q. Li et al., “Inhibition of ADP-induced platelet aggregation by clopidogrel is related to CYP2C19 genetic polymorphisms,” Clinical and Experimental Pharmacology and Physiology, vol. 35, no. 8, pp. 904–908, 2008.

N. S. Abraham, M. A. Hlatky, E. M. Antman et al., “ACCF/ACG/AHA 2010 expert consensus document on the concomitant use of proton pump inhibitors and thienopyridines: a focused update of the ACCF/ACG/AHA 2008 expert consensus document on reducing the gastrointestinal risks of antiplatelet therapy and NSAID use,” Journal of the American College of Cardiology, vol. 56, no. 24, pp. 2051–2066, 2010.

T. Simon, C. Verstuyft, M. Mary-Krause et al., “Genetic determinants of response to clopidogrel and cardiovascular events,” The New England Journal of Medicine, vol. 360, no. 4, pp. 363–375, 2009.

M. Gilard, B. Arnaud, G. Le Gal, J. F. Abgrall, and J. Boschat, “Influence of omeprazol on the antiplatelet action of clopidogrel associated to aspirin,” Journal of Thrombosis and Haemostasis, vol. 4, no. 11, pp. 2508–2509, 2006.

R. Kahn, “Report of the expert committee on the diagnosis and classification of diabetes mellitus,” Diabetes Care, vol. 20, no. 7, pp. 1183–1197, 1997.

World Health Organization, Nutrizional Anemia: Report of a WHO Scientific Group, World Health Organization, Geneva, Switzerland, 1968.

National Kidney Foundation, “K/DOQI: clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification,” American Journal of Kidney Diseases, vol. 39, pp. 1–237, 2002.

J. L. Anderson, C. D. Adams, E. M. Antman et al., “ACC/AHA 2007 guidelines for the management of patients with unstable angina/Non—ST-elevation myocardial infarction—executive summary: a report of the American College of Cardiology/American Heart Association Task Force on practice guidelines (Writing Committee to Revise the 2002 Guidelines for the Management of Patients With Unstable Angina/Non—ST-Elevation Myocardial Infarction) Developed in Collaboration with the American College of Emergency Physicians, the Society for Cardiovascular Angiography and Interventions, and the Society of Thoracic Surgeons endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation and the Society for Academic Emergency Medicine,” Journal of the American College of Cardiology, vol. 50, no. 7, pp. 652–726, 2007.

K. Thygesen, J. S. Alpert, H. D. White, et al., “On behalf of the joint ESC/ACCF/AHA/WHF Task Force for the redifition of myocardial infarction. Universal definition of myocardial infarction,” Circulation, vol. 116, pp. 2643–2653, 2007.

J. S. Hochman, J. E. Tamis, T. D. Thompson et al., “Sex, clinical presentation, and outcome in patients with acute coronary syndromes,” The New England Journal of Medicine, vol. 341, no. 4, pp. 226–232, 1999.

S. B. King III, S. C. Smith Jr., J. W. Hirshfeld Jr. et al., “2007 Focused update of the ACC/AHA/SCAI 2005 guideline update for percutaneous coronary intervention: A report of the American College of Cardiology/American Heart Association task force on practice guidelines,” Circulation, vol. 117, no. 2, pp. 261–295, 2008.

S. R. Mehta, S. Yusuf, R. J. G. Peters et al., “Effects of pretreatment with clopidogrel and aspirin followed by long-term therapy in patients undergoing percutaneous coronary intervention: the PCI-CURE study,” The Lancet, vol. 358, no. 9281, pp. 527–533, 2001.

S. R. Steinhubl, P. B. Berger, J. Tift Mann et al., “Early and sustained dual oral antiplatelet therapy following percutaneous coronary intervention: a randomized controlled trial,” JAMA, vol. 288, no. 19, pp. 2411–2420, 2002.

D. L. Bhatt, J. Scheiman, N. S. Abraham, et al., “ACCF/ACG/AHA 2008 expert consensus document on reducing the gastrointestinal risks of antiplatelet therapy and NSAID use: a report of the American College of Cardiology Foundation Task Force on clinical expert consensus documents,” Circulation, vol. 118, no. 18, pp. 1894–1909, 2008.

T. Simon, P. G. Steg, M. Gilard 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, vol. 123, no. 5, pp. 474–482, 2011.

S. D. Wiviott, D. Trenk, A. L. Frelinger et al., “Prasugrel compared with high loading- and maintenance-dose clopidogrel in patients with planned percutaneous coronary intervention: the prasugrel in comparison to clopidogrel for inhibition of platelet activation and aggregation-thrombolysis in myocardial infarction 44 trial,” Circulation, vol. 116, no. 25, pp. 2923–2932, 2007.

S. D. Wiviott, E. Braunwald, C. H. McCabe et al., “Intensive oral antiplatelet therapy for reduction of ischaemic events including stent thrombosis in patients with acute coronary syndromes treated with percutaneous coronary intervention and stenting in the TRITON-TIMI 38 trial: a subanalysis of a randomised trial,” The Lancet, vol. 371, no. 9621, pp. 1353–1363, 2008.

R. Rossini, D. Capodanno, G. Musumeci et al., “Safety of clopidogrel and proton pump inhibitors in patients undergoing drug-eluting stent implantation,” Coronary Artery Disease, vol. 22, no. 3, pp. 199–205, 2011.

R. E. Aubert, R. S. Epstein, J. R. Teagarden, et al., “Proton pump inhibitors effect on Clopidogrel effectiveness: the Clopidogrel Medco Outcomes Study,” Circulation, vol. 118, article S815, 2008.

I. Tentzeris, R. Jarai, S. Farhan et al., “Impact of concomitant treatment with proton pump inhibitors and clopidogrel on clinical outcome in patients after coronary stent implantation,” Thrombosis and Haemostasis, vol. 104, no. 6, pp. 1211–1218, 2010.

M. A. Gaglia, R. Torguson, N. Hanna et al., “Relation of proton pump inhibitor use after percutaneous coronary intervention with drug-eluting stents to outcomes,” American Journal of Cardiology, vol. 105, no. 6, pp. 833–838, 2010.

M. Gilard, B. Arnaud, J. C. Cornily et al., “Influence of omeprazole on the antiplatelet action of clopidogrel associated with aspirin: the randomized, double-blind OCLA (Omeprazole CLopidogrel Aspirin) study,” Journal of the American College of Cardiology, vol. 51, no. 3, pp. 256–260, 2008.

D. J. Angiolillo, C. M. Gibson, S. Cheng et al., “Differential effects of omeprazole and pantoprazole on the pharmacodynamics and pharmacokinetics of clopidogrel in healthy subjects: randomized, placebo-controlled, crossover comparison studies,” Clinical Pharmacology and Therapeutics, vol. 89, no. 1, pp. 65–74, 2011.

X. Q. Li, T. B. Andersson, M. Ahlström, and L. Weidolf, “Comparison of inhibitory effects of the proton pump-inhibiting drugs omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole on human cytochrome P450 activities,” Drug Metabolism and Disposition, vol. 32, no. 8, pp. 821–827, 2004.

T. Cuisset, C. Frere, J. Quilici 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 randomized study,” Journal of the American College of Cardiology, vol. 54, no. 13, pp. 1149–1153, 2009.

M. Lettino, “Inhibition of the antithrombotic effects of clopidogrel by proton pump inhibitors: facts or fancies?” European Journal of Internal Medicine, vol. 21, no. 6, pp. 484–489, 2010.

US Food and Drug Administration safety alert for human medicinal products clopidogrel (marketed as Plavix) and omeprazole (marketed as Prilosec)—drug interaction, http://www.emea.europa.eu/docs/en_GB/document_library/Public_statement/2010/03/WC500076346.pdf

P. Barragan, J. L. Bouvier, P. O. Roquebert et al., “Resistance to thienopyridines: clinical detection of coronary stent thrombosis by monitoring of vasodilator-stimulated phosphoprotein phosphorylation,” Catheterization and Cardiovascular Interventions, vol. 59, no. 3, pp. 295–302, 2003.

S. Matetzky, B. Shenkman, V. Guetta et al., “Clopidogrel resistance is associated with increased risk of recurrent atherothrombotic events in patients with acute myocardial infarction,” Circulation, vol. 109, no. 25, pp. 3171–3175, 2004.