Prevalence of poor biological response to clopidogrel

Carotid Endarterectomy on Antiplatelet Agents in the Era of Point-of-Care Testing

OBJECTIVE

The safety of carotid endarterectomy in patients with a response to antiplatelet agents (aspirin and clopidogrel) confirmed by point-of-care testing is unknown. Thus, we sought to determine whether using point-of-care assessment of platelet inhibition reveals risk factors for operative complications or predicts clinical outcomes.

METHODS

We reviewed records of carotid endarterectomy patients treated from March 2013 to July 2015 to extract demographics, lesion characteristics, laboratory data, procedural complications, and follow-up. Administration of aspirin, clopidogrel, or therapeutic anticoagulation within 5 days before surgery was recorded.

RESULTS

We analyzed 79 patients with 86 lesions (mean age 70.9 ± 10.0 years). More patients with a P2Y12 reaction unit (PRU) <170 had neck hematomas (4/10, 40.0%) than those with a PRU ≥170 (2/9, 22.2%) (P = 0.63). Estimated blood loss ≥100 mL was more frequent among patients with PRU <170 (9/10, 90.0%) than among those with PRU ≥170 (5/9, 55.6%) (P = 0.09). Clopidogrel use, regardless of response, independently predicted neck hematoma in a logistic regression model, with increased odds of 8.5. Mean postoperative modified Rankin Scale scores did not differ statistically between clopidogrel users and nonusers at a mean follow-up of 108.5 ± 146.3 days (P = 0.27).

CONCLUSIONS

Clopidogrel use within 5 days of carotid endarterectomy independently predicted postoperative neck hematomas, most of which were managed conservatively. Patients with PRU <170 were more likely to have estimated blood loss ≥100 mL during surgery and surgery lasting ≥3 hours.

Cigarette smoking might weaken the prognostic significance of cytochrome P450 2C19*2 polymorphism in acute myocardial infarction patients

Prognostic significance of cytochrome P450 2C19*2 polymorphism in acute myocardial infarction is still not well investigated. The aim of the study was to determine the relationship between the genetic polymorphism and the outcome of the acute myocardial infarction patients, and to further clarify the impact of smoking on such relationship. Six hundred acute myocardial infarction patients were enrolled. All of them provided blood samples and underwent clopidogrel treatment. The genetic polymorphism was determined by polymerase chain reaction–restriction fragment length polymorphism analysis, and the platelet function was assessed using conventional aggregometry. Of the included patients, 287 carried GG wild‐type genotypes, 225 carried GA genotypes and 88 carried AA genotypes. The platelet aggregation rate was significantly elevated in the AA genotype patients, mainly in the non‐smoking patients (P < 0.001) and the former‐smoking patients (P < 0.001). During 5‐year follow‐up period, after adjusted for multiple confounding factors, AA genotypes were associated with the increase in 5‐year mortalities in the non‐smoking patients [OR: 7.06, 95% confidence interval (CI): 2.16–11.49] and the former‐smoking patients (OR: 4.38, 95% CI: 1.05–9.40), but not in the current‐smoking patients (OR: 1.12, 95% CI: 0.60–2.31). In conclusion, the study suggested a potential role of P450 2C19*2 polymorphism as a prognostic indicator in acute myocardial infarction patients. We had also obtained some evidence that current smoking might weaken the prognostic significance of the genetic polymorphism in patients.

Repetitive stent thrombosis in a patient who had resistance to both clopidogrel and prasugrel

Clopidogrel resistance is associated with stent thrombosis. Prasugrel achieves greater platelet inhibition with less variability among patients than does clopidogrel. Thus, a patient who had stent thrombosis due to clopidogrel resistance may receive prasugrel to prevent repeated episodes of stent thrombosis. This case report describes a case of repetitive stent thrombosis in which resistance not only to clopidogrel, but also to prasugrel, was observed. <Learning objective: In the face of clopidogrel resistance, prescribing prasugrel may be an acceptable treatment option. However, cross-unresponsiveness may be observed between clopidogrel and prasugrel. Thus, platelet function assay should be performed in patients with stent thrombosis, even when clopidogrel is replaced with prasugrel.>.

Anti-platelet Therapy Resistance - Concept, Mechanisms and Platelet Function Tests in Intensive Care Facilities

It is well known that critically ill patients require special attention and additional consideration during their treatment and management. The multiple systems and organ dysfunctions, typical of the critical patient, often results in different patterns of enteral absorption in these patients. Anti-platelet drugs are the cornerstone in treating patients with coronary and cerebrovascular disease. Dual anti-platelet therapy with aspirin and clopidogrel is the treatment of choice in patients undergoing elective percutaneous coronary interventions and is still widely used in patients with acute coronary syndromes. However, despite the use of dual anti-platelet therapy, some patients continue to experience cardiovascular ischemic events. Recurrence of ischemic events is partly attributed to the fact that some patients have poor inhibition of platelet reactivity despite treatment. These patients are considered low- or non-responders to therapy. The underlying mechanisms leading to resistance are not yet fully elucidated and are probably multifactorial, cellular, genetic and clinical factors being implicated. Several methods have been developed to asses platelet function and can be used to identify patients with persistent platelet reactivity, which have an increased risk of thrombosis. In this paper, the concept of anti-platelet therapy resistance, the underlying mechanisms and the methods used to identify patients with low responsiveness to anti-platelet therapy will be highlighted with a focus on aspirin and clopidogrel therapy and addressing especially critically ill patients.

Increased platelet inhibition after switching from maintenance clopidogrel to prasugrel in Japanese patients with stable coronary artery disease

BACKGROUND

The pharmacodynamic effects of changing from standard-dose clopidogrel to low-dose (3.75 mg) prasugrel in Japanese patients are largely unknown.

METHODS AND RESULTS

A total of 53 consecutive Japanese patients with stable coronary artery disease (CAD) who received aspirin and clopidogrel were enrolled. Clopidogrel was switched to 3.75 mg prasugrel. At day 14, prasugrel was switched to 75 mg clopidogrel. Platelet reactivity was measured using the VerifyNow assay at baseline, day 14, and day 28. VerifyNow P2Y12 reaction units (PRU) >208 was defined as high on-treatment platelet reactivity (HPR). The prevalence of HPR (18.9% vs. 41.5% vs. 44.2%, P<0.001) and the PRU level (154.3±54.2 vs. 196.2±55.5 vs. 194.6±55.8, P<0.001) were significantly lower on prasugrel maintenance therapy compared with the clopidogrel therapy before and after switching. The CYP2C19 genotypes that account for the 3 phenotypes (ie, extensive metabolizer, intermediate metabolizer, and poor metabolizer) had a significant impact on platelet reactivity with clopidogrel (174.9±54.0 vs. 193.1±56.5 vs. 240.6±25.4 PRU, P<0.001) but not prasugrel (147.0±51.9 vs. 147.5±58.3 vs. 184.4±38.3 PRU, P=0.15).

CONCLUSIONS

Low-dose prasugrel achieves stronger platelet inhibition than clopidogrel in Japanese patients with stable CAD.

Effect of prasugrel in patients with asthma: results of PRINA, a randomized, double-blind, placebo-controlled, cross-over study

BACKGROUND

Although experimental studies have demonstrated that platelets are proinflammatory cells, no randomized studies have tested the anti-inflammatory effect of antiplatelet agents in humans. The platelet P2Y12 receptors mediated bronchial inflammation in a mouse model of asthma, suggesting that P2Y12 represents a pharmacologic target for asthma.

OBJECTIVES

In this proof-of concept, placebo-controlled, randomized, cross-over study, we tested the effects of the P2Y12 antagonist prasugrel on bronchial hyperreactivity of asthmatic patients.

PATIENTS/METHODS

Twenty-six asthmatic patients were randomly and blindly allocated to prasugrel (10 mg once daily) or placebo for 15 days. After a ≥ 15-day wash-out, patients were crossed over to the alternative treatment. Before and after each treatment, patients underwent a bronchial provocation test with mannitol and measurement of fractional exhaled nitric oxide (FeNO). Inhibition of P2Y12 -dependent platelet reactivity (platelet reactivity index [PRI]) was measured with the vasodilator-stimulated phosphoprotein phosphorylation assay.

RESULTS

The provocative dose of mannitol causing a 15% drop in forced expiratory volume in 1 s increased from 142 mg (95% confidence interval [CI] 82-202) to 187 mg (95% CI 113-262) after prasugrel treatment (P = 0.09), and did not change after placebo treatment (136 mg [95% CI 76-196] and 144 mg [95% CI 84-204], P = 0.65). FeNO did not change after either treatment. The PRI decreased from 80% (95% CI 77-83) to 23% (95% CI 7-29) after prasugrel treatment (P < 0.001) and remained unchanged after placebo.

CONCLUSIONS

Our proof-of-concept, randomized, controlled study is the first one to test in vivo the anti-inflammatory effects of platelet inhibition in human patients. The results suggest that pharmacologic inhibition of P2Y12 receptors may slightly reduce the bronchial inflammatory burden, and lay the groundwork for further studies, with clinical endpoints.

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

BACKGROUND AND OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Treatment options for patients with poor clopidogrel response

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

Cytochrome p450 gene variants, race, and mortality among clopidogrel-treated patients after acute myocardial infarction

BACKGROUND

Clopidogrel is recommended after acute myocardial infarction but has variable efficacy and safety, in part related to the effect of cytochrome P450 (CYP) polymorphisms on its metabolism. The effect of CYP polymorphisms on cardiovascular events among clopidogrel-treated patients after acute myocardial infarction remains controversial, and no studies to date have investigated the association of CYP variants with outcomes in black patients.

METHODS AND RESULTS

Subjects (2732: 2062 whites; 670 blacks) hospitalized with acute myocardial infarction enrolled in the prospective, multicenter TRIUMPH study were genotyped for CYP polymorphisms. The majority of whites (79%) and blacks (64.4%) were discharged on clopidogrel. Among whites, carriers of the loss-of-function CYP2C19*2 allele had significantly increased 1-year mortality (adjusted hazards ratio [HR]: 1.70; confidence interval [CI]: 1.01-2.86; P=0.046) and a trend toward increased rate of recurrent MI (adjusted HR: 2.10; CI: 0.95-4.63; P=0.066). Among blacks, increased 1-year mortality was associated with the gain-of-function CYP2C19*17 allele (adjusted HR for *1/*17 versus *1/*1: 2.02; CI: 0.92-4.44; *17/*17 versus *1/*1: 8.97; CI: 3.34-24.10; P<0.0001) and the CYP1A2*1C allele (adjusted HR for *1/*1C versus *1/*1: 1.89; CI: 0.85-4.22; *1C/*1C versus *1/*1: 4.96; CI: 1.69-14.56; P=0.014). Bleeding events were significantly more common among black carriers of CYP2C19*17 or CYP1A2*1C.

CONCLUSIONS

Both loss-of-function and gain-of-function CYP polymorphisms affecting clopidogrel metabolism are associated with increased mortality among clopidogrel-treated patients after acute myocardial infarction; the specific polymorphism and the putative mechanism vary according to race.

No effect of clopidogrel activity or cessation on vascular function or markers of inflammation

The platelet adenosine diphosphate (ADP)-receptor blocker clopidogrel is effective in reducing the rate of thrombosis in cardiovascular disease, but may also have nonplatelet activity. However, there is variability in the suppression of platelet function in individuals, leading to the concept of clopidogrel resistance, that is, reduced platelet-suppressing activity. We tested the hypothesis that some of the beneficial effect of clopidogrel may be due to the variable activity of this drug on the vascular system (assessed by plasma markers von Willebrand factor and soluble E-selectin, and functional arterial pulse wave velocity) and inflammation (C-reactive protein and interleukin-6) while 32 patients with coronary artery disease taking 75 mg clopidogrel daily, and again 2 weeks after cessation of clopidogrel therapy. Platelet responsiveness to clopidogrel was assessed by the phosphorylation of intracellular regulatory protein-vasodilator-stimulated phosphoprotein method and aggregometry to ADP. Response to aspirin was assessed using arachidonic acid (AA), and soluble P-selectin and PAC-1 were also measured. While on clopidogrel, there were no relationships between any vascular or inflammatory index and the response to clopidogrel. After stopping clopidogrel, there were no differences in platelet aggregation to AA, or the expression of P-selectin or PAC-1 at rest, or after stimulation by AA, but platelet responses to ADP all increased (p < 0.01). Although soluble P-selectin increased when clopidogrel was stopped (p = 0.006), there were no changes in plasma markers or vascular function. We conclude that 75 mg/day clopidogrel has no effect of markers of vascular function or inflammation.

Comparison of a new P2Y12 receptor specific platelet aggregation test with other laboratory methods in stroke patients on clopidogrel monotherapy

Background

Clinical studies suggest that 10-50% of patients are resistant to clopidogrel therapy. ADP induced platelet aggregation, a widely used test to monitor clopidogrel therapy, is affected by aspirin and is not specific for the P2Y12 receptor inhibited by clopidogrel.

Objectives

To develop a P2Y12-specific platelet aggregation test and to compare it with other methods used for monitoring clopidogrel therapy.

Patients/Methods

Study population included 111 patients with the history of ischemic stroke being on clopidogrel monotherapy and 140 controls. The effect of clopidogrel was tested by a newly developed ADP(PGE1) aggregation test in which prostaglandin E1 treated platelets are used. Results of conventional ADP induced platelet aggregation, VerifyNow P2Y12 assay and ADP(PGE1) aggregation were compared to those obtained by flow cytometric analysis of vasodilator stimulated phosphoprotein (VASP) phosphorylation. Reference intervals for all assays were determined according to the guidelines of Clinical Laboratory Standards Institute.

Results

The P2Y12-specificity of ADP(PGE1) test was proven by comparing it with ADP aggregation in the presence of P2Y1 antagonist, adenosine 3’, 5’-diphosphate. The method was not influenced by aspirin treatment. Approximately 50% of patients were clopidogrel resistant by conventional ADP aggregation and VerifyNow tests. The ADP(PGE1) method and the VASP phosphorylation assay identified 25.9% and 11.7% of patients as non-responders, respectively. ADP(PGE1) aggregation showed good correlation with VASP phosphorylation and had high diagnostic efficiency.

Conclusion

The new ADP(PGE1) method is a reliable test for monitoring P2Y12 receptor inhibition by platelet aggregation. As a subset of patients are non-responders, monitoring clopidogrel therapy by adequate methods is essential.

Tailored Thienopyridine therapy: no urgency for CYP2C19 genotyping

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

Influence of the paraoxonase-1 Q192R genetic variant on clopidogrel responsiveness and recurrent cardiovascular events: a systematic review and meta-analysis

BACKGROUND

A poor biological response to clopidogrel is associated with an increased risk of major cardiovascular ischemic events (MACE). Paraoxonase 1 (PON1) enzyme activity is modulated by the PON1-Q192R variant (rs662) and was recently suggested to be strongly involved in clopidogrel bioactivation, but the influence of the PON1-Q192R variant on the risk of MACE in clopidogrel-treated patients is controversial.

OBJECTIVES

To determine whether the PON1-Q192R variant influences clopidogrel biological responsiveness and the risk of MACE in patients treated with clopidogrel.

METHODS

Systematic review and meta-analysis of studies of the association between the PON1-Q192R polymorphism and the biological response to clopidogrel and/or the risk of MACE during clopidogrel administration.

RESULTS

Seventeen studies were included. In the 12 studies of the biological response to clopidogrel (n = 5302 patients), there was no significant difference between 192QQ and 192QR + 192RR subjects, whatever the laboratory method used (global mean standardized difference = 0.10 [-0.06; 0.25], P = 0.22). Eleven studies assessed the risk of MACE, four using a case-control design (n = 2739 patients) and seven a prospective design (n = 5353 patients). Overall, MACE occurred in 19% of patients in case-control studies and in 6% of patients in prospective cohort studies, with no significant difference between 192QQ and 192QR + 192RR patients (OR = 1.28 [0.97; 1.68], P = 0.08). Similar results were obtained when study design was taken into account. Heterogeneity was mainly driven by one publication.

CONCLUSIONS

This meta-analysis suggests that the PON1-Q192R polymorphism has no major impact on the risk of MACE and does not alter the biological response to clopidogrel in clopidogrel-treated patients.

Biological efficacy of a 600 mg loading dose of clopidogrel in ST-elevation myocardial infarction

Optimal platelet reactivity (PR) inhibition is critical to prevent thrombotic events in primary percutaneous coronary intervention (PCI). We aimed to determine the relationship between high on-treatment platelet reactivity (HTPR) and ST-elevation myocardial infarction (STEMI) following a 600 mg loading dose (LD) of clopidogrel. We performed a prospective monocentre study enrolling patients on clopidogrel undergoing PCI. The VASP index was used to assess PR inhibition after clopidogrel LD. HTPR was defined according to the consensus as a VASP index ≥50%. The present study included 833 patients undergoing PCI. Most patients had PCI for an acute coronary syndrome (58.7%). The mean VASP index was 50 ± 23% with a large inter-individual variability (range: 1-94%). Patients with a VASP index ≥50% were significantly older (p= 0.03), with a higher body mass index (BMI) (p<0.001), more often diabetic (p=0.03), taking omeprazole (p=0.03), admitted for an acute coronary syndrome (ACS) and with a high fibrinogen level compared to good responders (VASP <50%). In multivariate analysis BMI, omeprazole use, ACS and high fibrinogen level (p<0.001) remained significantly associated with HTPR. Of importance, in this analysis STEMI was independently associated with HTPR when compared with the other forms of ACS (NSTEMI and unstable angina) with an odd ratio of 2.14 (95% CI: 1.3 -3.5; p=0.003). In conclusion, STEMI is associated with high on-treatment platelet reactivity following 600 mg of clopidogrel. The present results suggest that 600 mg of clopidogrel may not be able to achieve an optimal PR inhibition in STEMI patients undergoing PCI and more potent drugs may be preferred.