Which platelet function test is suitable to monitor clopidogrel responsiveness? A pharmacokinetic analysis on the active metabolite of clopidogrel

Summary. Background: Multiple platelet function tests claim to be P2Y12‐pathway specific and capable of capturing the biological activity of clopidogrel. Objectives: The aim of the present study was to determine which platelet function test provides the best reflection of the in vivo plasma levels of the active metabolite of clopidogrel (AMC). Patients/methods: Clopidogrel‐naive patients scheduled for elective percutaneous coronary intervention (PCI) received a 600 mg loading dose of clopidogrel and 100 mg of aspirin. For pharmacokinetic analysis, blood was drawn at 0, 20, 40, 60, 90, 120, 180, 240 and 360 min after clopidogrel loading and peak plasma concentrations (C_max) of the AMC were quantified with liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Platelet function testing was performed at baseline and 360 min after the clopidogrel loading. Results: The VASP‐assay, the VerifyNow P2Y12‐assay and 20 μmol L^?1 adenosine diphosphate (ADP)‐induced light transmittance aggregometry (LTA) showed strong correlations with C_max of the AMC (VASP: R² = 0.56, P < 0.001; VerifyNow platelet reactivity units (PRU): R² = 0.48, P < 0.001; VerifyNow %inhibition: R² = 0.59, P < 0.001; 20 μmol L^?1 ADP‐induced LTA: R² = 0.47, P < 0.001). Agreement with C_max of the AMC was less evident for 5 μmol L^?1 ADP‐induced LTA or whole blood aggregometry (WBA), whereas the IMPACT‐R ADP test did not show any correlation with plasmalevels of the AMC. Conclusion: The flow cytometric VASP‐assay, the VerifyNow P2Y12 assay and, although to a lesser extent, 20 μmol L^?1 ADP‐induced LTA correlate best with the maximal plasma level of the AMC, suggesting these may be the preferred platelet function tests for monitoring the responsiveness to clopidogrel.     

Different methodologies for evaluating the effect of clopidogrel on platelet function in high-risk coronary artery disease patients

BACKGROUND: Two point-of-care (POC) systems have been recently proposed as rapid tools with which to evaluate residual platelet reactivity (RPR) in coronary artery disease (CAD) patients. OBJECTIVES AND METHODS: We compared Platelet Function Analyzer-100 (PFA-100) closure times (CTs) by collagen/adenosine 5'-diphosphate (ADP) (C/ADP CT) cartridge and the VerifyNow P2Y12 Assay (VerifyNow) with light transmission aggregation (LTA) induced by 2 and 10 micromol L(-1) ADP in 1267 CAD patients on dual antiplatelet therapy who underwent percutaneous coronary intervention. We also performed the vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay by cytofluorimetric analysis in a subgroup of 115 patients. RESULTS: Cut-off values for identifying RPR were: > or = 54% and > or = 66% for LTA induced by 2 and 10 micromol L(-1) ADP respectively, and > or = 264 P2Y12 Reaction Units (PRU) for VerifyNow. The cut-off for PFA-100 C/ADP CT was > or = 68 s. RPR was detected in 25.1% of patients by 2 mumol L(-1) ADP-induced LTA (ADP-LTA), in 23.2% by 10 micromol L(-1) ADP-LTA, in 24.4% by PFA-100, and in 24.7% by VerifyNow. PFA-100 results did not parallel those obtained with LTA. VerifyNow showed a significant correlation (rho = 0.62, P < 0.001) and significant agreement (k = 0.34, P < 0.001) with LTA induced by 2 micromol L(-1) ADP. The correlation was similar but the agreement was better between VerifyNow and 10 micromol L(-1) ADP-LTA (rho = 0.64, P < 0.0001; k = 0.43, P < 0.001). Significant relationships were found between VASP platelet reactivity index and both ADP-LTA and VerifyNow. PFA-100 C/ADP CT did not significantly correlate with any of the other assays. CONCLUSIONS: Our results show a significant correlation between LTA and VerifyNow but not the PFA-100 C/ADP assay. Clinical validation studies for POC systems are necessary.     

The effect of elinogrel on high platelet reactivity during dual antiplatelet therapy and the relation to cyp 2c19*2 genotype: first experience in patients

Summary.  To study the effect of a new direct acting reversible P2Y₁₂ inhibitor, elinogrel (PRT060128), and the relation to cytochrome P450 (CYP) polymorphisms in patients with high platelet reactivity (HPR) on standard dual antiplatelet therapy. Methods and Results : We studied the pharmacodynamic and pharmacokinetic effects of a single 60-mg oral dose of elinogrel in 20 of 45 previously stented stable patients with HPR. We also genotyped for CYP2C19*2,3,5,17 and CYP3A5*3. Platelet reactivity fell within 4 h of dosing, the earliest time point evaluated as measured by the following assays: maximum 5 and 10 μ m ADP LTA ( P  < 0.001 for both vs. predosing); maximum 20 μ m ADP LTA ( P  < 0.05); VerifyNow ( P  < 0.001); thrombelastography ( P  < 0.05); VASP phosphorylation ( P  < 0.01); and perfusion chamber assay ( P  < 0.05); this was reversible within 24 h in these same assays ( P  = ns vs. predosing for all assays). CYP2C19*2 was present in 44% of all patients but was more frequent in HPR patients (77% vs. 16%, P  = 0.0004). Conclusions:  HPR is reversibly overcome by a single 60-mg oral dose of elinogrel, a drug now being investigated in a phase 2 trial. CYP2C19*2 was associated with HPR during conventional dual antiplatelet therapy.     

Antiplatelet effects of prasugrel vs. double clopidogrel in patients on hemodialysis and with high on‐treatment platelet reactivity

Summary. Background: High on‐treatment platelet reactivity (HTPR) is frequent in patients on hemodialysis (HD) receiving clopidrogel. Objectives: The primary aim of this study was to determine the antiplatelet effects of prasugrel vs. high‐dose clopidogrel in patients on HD with HTPR. Patients/Methods: We performed a prospective, single‐center, single‐blind, investigator‐initiated, randomized, crossover study to compare platelet inhibition by prasugrel 10 mg day^?1 with that by high‐dose 150 mg day^?1 clopidogrel in 21 patients on chronic HD with HTPR. Platelet function was assessed with the VerifyNow assay, and genotyping was performed for CYP2C19*2 carriage. Results: The primary endpoint of platelet reactivity (PR, measured in P2Y12 reaction units [PRU]) was lower in patients receiving prasugrel (least squares [LS] estimate 156.6, 95% confidence interval [CI] 132.2–181.1) than in those receiving high‐dose clopidogrel (LS 279.9, 95% CI 255.4–304.3), P < 0.001). The LS mean differences between the two treatments were ? 113.4 PRU (95% CI ? 152.9 to ? 73.8, P < 0.001) and ? 163.8 PRU (95% CI ? 218.1 to ? 109.2, P < 0.001) in non‐carriers and carriers of at least one CYP2C19*2 allele, respectively. HTPR rates were lower for prasugrel than clopidogrel, in all patients (19% vs. 85.7%, P < 0.001) and in non‐carriers (25.7% vs. 80%, P = 0.003). All carriers continued to show HTPR while receiving high‐dose clopidogrel, but none showed it while receiving prasugrel. Conclusions: In HD patients exhibiting HTPR following standard clopidogrel treatment, prasugrel 10 mg day^–1 is significantly more efficient than doubling the clopidogrel dosage in achieving adequate platelet inhibition. Neither effect seems to be influenced by carriage of the loss‐of‐function CYP2C19*2 allele.     

Examining warfarin underutilization rates in patients with atrial fibrillation: Detailed chart review essential to capture contraindications to warfarin therapy

Background

To test the hypothesis that point-of-care assays of platelet reactivity would demonstrate reduced response to antiplatelet therapy in patients who experienced Drug Eluting Stent (DES) ST whilst on dual antiplatelet therapy compared to matched DES controls. Whilst the aetiology of stent thrombosis (ST) is multifactorial there is increasing evidence from laboratory-based assays that hyporesponsiveness to antiplatelet therapy is a factor in some cases.

Methods

From 3004 PCI patients, seven survivors of DES ST whilst on dual antiplatelet therapy were identified and each matched with two patients without ST. Analysis was performed using (a) short Thrombelastogram PlateletMapping? (TEG) and (b) VerifyNow Aspirin and P2Y12 assays. TEG analysis was performed using the Area Under the Curve at 15 minutes (AUC15) as previously described.

Results

There were no differences in responses to aspirin. There was significantly greater platelet reactivity on clopidogrel in the ST group using the Accumetrics P2Y12 assay (183 ± 51 vs. 108 ± 31, p = 0.02) and a trend towards greater reactivity using TEG AUC15 (910 ± 328 vs. 618 ± 129, p = 0.07). 57% of the ST group by TEG and 43% of the ST cases by Accumetrics PRU had results > two standard deviations above the expected mean in the control group.

Conclusion

This study demonstrates reduced platelet response to clopidogrel in some patients with DES ST compared to matched controls. The availability of point-of-care assays that can detect these responses raises the possibility of prospectively identifying DES patients at risk of ST and manipulating their subsequent risk.     

Determinants of high on-treatment platelet reactivity and agreement between VerifyNow and Multiplate assays

Dual antiplatelet therapy with clopidogrel is a regimen used before and after drug-eluting stent (DES) implantation. Point-of-care platelet reactivity assays are easy-to-use methods to determine adequate response to the drug. The aim of this study was a comparison of the two platelet reactivity assays: Multiplate^® and VerifyNow^® and an identification of factors potentially influencing the results of these tests, including common genetic polymorphisms. The study included 39 patients receiving 75?mg clopidogrel daily before angioplasty with DES implantation. Platelet reactivity was measured with Multiplate and P2Y₁₂ VerifyNow assays. Genetic polymorphisms of CYP2C19*2, ABCB1 3435C?>?T, and CYP3A4*1G were determined with PCR-RFLP method and CYP2C19*17 was determined by means of an allele-specific PCR. Agreement between Multiplate and VerifyNow assays was poor (Cohen’s κ?=?0.056, p?=?.273). Hematocrit significantly negatively correlated with VerifyNow assayed platelet reactivity (r?=??.487, p?=?.002). Female sex was significantly associated with higher VerifyNow assay results after adjustment to hematocrit (253.2?±?47.6 PRU vs. 195.9?±?56.9 PRU, p?=?.013) and the prevalence of high-on-treatment platelet reactivity (OR: 8.50; 95% CI 1.13–77.60, p?=?.024). Reactivity measured with Multiplate was lower in women (82.3 vs. 175.6?AU·min, p?=?.037) and in patients who received calcium channel blockers (74.7 vs. 191.7?AU·min, p?=?.002). None of the studied polymorphisms significantly influenced platelet aggregation measurements. In conclusion, different aspects modify between-patient variability of the Multiplate and VerifyNow assays and agreement between those two assays was poor.     

A case–control study on platelet reactivity in patients with coronary stent thrombosis

Summary. Background: The pathophysiology of stent thrombosis (ST) has evolved from the identification of single causative factors to a complex multifactorial model. Objectives: The aim of the present study was to investigate whether patients with a history of ST exhibit heightened platelet reactivity to clopidogrel and aspirin. Patients/methods: Pretreatment and on‐treatment platelet reactivity to clopidogrel and aspirin, as well as dual antiplatelet therapy resistance, was determined in 84 patients with a history of definite ST (cases: 41 early ST; 43 late ST) and in 103 control patients with a previously implanted coronary stent but no ST after the index procedure. Platelet function was evaluated with optical aggregometry, the VerifyNow P2Y12 and aspirin assays, the PFA‐100 Innovance P2Y* cartridge, the flow cytometric vasodilator‐stimulated phosphoprotein assay and urine 11‐dehydrothromboxane B₂ measurement before and after the administration of a 600‐mg loading dose of clopidogrel and 100 mg of aspirin. The study was registered at ClinicalTrials.gov, number NCT01012544. Results: Patients with a history of early ST clearly demonstrated higher on‐clopidogrel platelet reactivity than controls. Patients with both early and late ST exhibited heightened on‐aspirin platelet reactivity status, and dual antiplatelet therapy resistance was more frequent. Conclusions: Patients with a history of early ST exhibit a poor response to clopidogrel. Furthermore, both early and late ST are strongly and independently associated with heightened on‐aspirin platelet reactivity, and dual antiplatelet therapy resistance is more frequent.     

Assessing post-treatment platelet reactivity: a focus on patient selection and setting

Dual antiplatelet therapy is critical to inhibit platelet reactivity in order to prevent ischemic reccurences in stented patients. However, studies have observed a variable blockade of the P2Y12 adenosine diphosphate receptor between patients following clopidogrel intake. This interindividual variability in the biological response is not uncommon with clopidogrel (about 50%) and even prasugrel (20%). High on-treatment platelet reactivity (HTPR) is correlated with thrombotic events following percutaneous coronary intervention. Several studies suggested that tailoring of antiplatelet therapy based on platelet reactivity (PR) monitoring could safely reduce the rate of major adverse cardiovascular events in HTPR patients. In addition, low on-treatment PR was recently associated with bleeding events both in patients treated with prasugrel and clopidogrel. Of importance, bleedings are associated with a poor prognosis in stented patients. Overall, the potential of PR monitoring to individualize antiplatelet therapy might benefit stented patients by reducing both ischemic and bleeding risks. However, such strategies remain to be evaluated in adequately designed large-scale randomized clinical trials.     

Decreased platelet inhibition by P2Y12 receptor blockers in anaemia

Background

Anaemic patients undergoing angioplasty and stenting are at an increased risk of ischaemic events, which may be caused by an inadequate response to antiplatelet therapy with adenosine diphosphate (ADP) P2Y₁₂ inhibitors. In the current study, we investigated the associations between anaemia and on‐treatment platelet reactivity in clopidogrel‐treated (group 1, n = 306) and prasugrel‐/ticagrelor‐treated (group 2, n = 109) patients undergoing elective and acute angioplasty with stent implantation, respectively.

Materials and methods

Monocyte‐platelet aggregate (MPA) formation was determined by flow cytometry in both groups. On‐treatment residual platelet reactivity in response to ADP was assessed by light transmission aggregometry (LTA) in both groups, and by the VerifyNow P2Y₁₂ assay and the Impact‐R in group 1. P‐selectin expression was measured by flow cytometry in group 2.

Results

In both groups, anaemia was associated with significantly higher MPA formation in response to ADP (both P ≤ .02). Moreover, by LTA maximal aggregation in response to ADP was significantly higher in patients with anaemia in both groups (both P < .05), and anaemic patients in group 1 had a significantly higher on‐treatment platelet reactivity by the VerifyNow P2Y₁₂ assay and the Impact‐R than those without anaemia (both P < .001). In group 2, significantly higher platelet surface expression of P‐selectin was seen in anaemia after stimulation with ADP (P = .02).

Conclusion

Anaemia is associated with decreased platelet inhibition by ADP P2Y₁₂ receptor antagonists after elective and acute percutaneous interventions with stent implantation. However, due to inconsistencies between different platelet function tests additional data are needed to clarify the role of anaemia for platelet inhibition.     

The future of platelet function testing to guide therapy in clopidogrel low and enhanced responders

Dual oral antiplatelet therapy with aspirin and clopidogrel is the therapy of choice in patients with acute coronary syndromes and in patients undergoing coronary stent placement to lower the risk of thrombotic events. Responsiveness to aspirin and especially to clopidogrel is not uniform and is subject to considerable interindividual variability. Furthermore, there is a broad consensus that clopidogrel low response or so-called high on-treatment platelet reactivity is linked to the occurrence of ischemic events. On the other hand, evidence is accumulating that enhanced clopidogrel responders are at increased risk of bleeding. Newer antiplatelet drugs, such as prasugrel and ticagrelor, are more potent and produce more consistent inhibition of platelet aggregation via the P2Y(12) ADP platelet receptor. A variety of methods of platelet function testing are available for evaluating platelet inhibition in percutaneous coronary intervention-treated patients in order to help determine the individual risk for ischemic and bleeding complications. Although not yet routinely undertaken, platelet function testing offers the potential to tailor antiplatelet therapy for individual patients. Whether alteration of therapy based on platelet function testing improves patients' outcomes remains unclear and is currently under investigation. This article reviews the impact of antiplatelet drug responsiveness on clinical outcomes with a focus on P2Y(12) receptor inhibition as well as on current and future concepts for personalized antiplatelet strategies.     

Increased clopidogrel response is associated with ABCC3 expression: a pilot study

BackgroundThe aim of this study was investigate the relationship between ABCB1 and ABCC3 gene expressions in peripheral blood cells (PBC) and the response to clopidogrel in patients with coronary arterial disease (CAD).MethodsTwenty-six male CAD patients (50–70 years) under treatment with clopidogrel (75 mg/day) for at least 5 days were selected. Blood samples were obtained to evaluate platelet reactivity and ABCB1 and ABCC3 mRNA expression. Platelet reactivity was measured in P2Y12 Reaction Units (PRU) using VerifyNow. RNA was extracted from PBC and mRNA levels were measured by qPCR, using GAPD as a reference gene.ResultsPlatelet response to clopidogrel was categorized in to PRU quartiles. Individuals with PRU values within the first quartile (Q1, < 151 units) were considered good responders, while those who had PRU within the fourth quartile (Q4, PRU > 260) were considered non-responders. ABCC3 was 1.7 times more expressed in Q4 than in Q1 PRU group (p = 0.048). Moreover, CAD patients with low ABCC3 expression (Qe1, < 2.5 × 10^? 3) had higher probability to have a good response to clopidogrel (OR: 18.00, 95%CI: 1.90–169.99, p = 0.001). Univariate linear regression analysis demonstrated that low ABCC3 mRNA expression contributed with a reduction of 73 PRU in relation to the patients with expression value higher than 2.5 × 10^? 3 (p = 0.027). Neither ABCB1 mRNA levels nor clinical variables studied influenced PRU values.ConclusionsLow ABCC3 mRNA expression in peripheral blood cells is associated with increased clopidogrel response, but further studies are needed to describe the functional relationship of clopidogrel with the ABCC3.     

Gene polymorphisms of insulin secretion signaling pathway associated with clopidogrel resistance in Han Chinese population

BackgroundDue to the loss of responsiveness to insulin, diabetes mellitus (DM) patients develop increased platelet reactivity and reduced response to antiplatelet agents. Nevertheless, the relationship between the single‐nucleotide polymorphisms (SNP) of the signal pathway gene of insulin secretion and the effect of clopidogrel is elusive.MethodsBlood samples were collected from patients administered with dual‐antiplatelet therapy (clopidogrel, 75 mg, once daily and aspirin, 100 mg, once daily) after 5 days and completed test within 4 h. The VerifyNow P2Y12 assay was used to measure the platelet functions, and the results were expressed as a P2Y12 reaction unit (PRU). Notably, the selected SNPs were analyzed to demonstrate the functionality of genetic variants.ResultsAnalysis of the study population showed that old age, lower plasma albumin (ALB) level, higher creatinine (CREA) level, higher uric acid (UA) level, lower platelet (PLT) count, and lower plateletcrit (PCT) potentially increased the risk of clopidogrel resistance. In a single‐nucleotide polymorphism rs6056209 of the PCLB1 gene, the AG genotype was a risk factor for clopidogrel resistance (p < 0.05, OR = 1.574). Similarly, the CC and AG genotype in GNAS rs7121 and CCKAR rs1800857 were protective factors (p < 0.05, OR = 0.094; p <0.05, OR = 0.491). TT was a protective factor in rs10814274 of the CREB3 gene (p < 0.05, OR = 0.444). In the RAPGEF4 gene polymorphism rs17746510, TG was the protective genotype, and the TT genotype was a risk factor for clopidogrel resistance. GCG rs5645 was confirmed; there was a relationship between genotypes containing A or G and clopidogrel resistance.ConclusionSingle‐nucleotide polymorphisms of insulin secretion signaling pathway genes trigger clopidogrel resistance.     

Randomized double‐blind placebo‐controlled crossover study to determine the effects of esomeprazole on inhibition of platelet function by clopidogrel

Summary. Background: Pharmacokinetic studies suggest that clopidogrel and esomeprazole are metabolized by similar hepatic enzymes; however, previous studies have not identified a biochemical interaction. Objectives: To determine whether addition of esomeprazole to patients receiving aspirin and clopidogrel reduces the antiplatelet effects of clopidogrel. Patient/Methods: Patients with a history of an acute coronary syndrome who had previously received clopidogrel were recruited. Subjects were commenced on clopidogrel and randomized to one of two treatment arms (esomeprazole or placebo) for 6 weeks. Following a 2‐week washout period for study medications, patients were crossed over onto the alternative treatment arm for a further 6 weeks. Platelet function tests were undertaken at baseline, following the first treatment period, after washout and following the second treatment period. Results: Thirty‐one patients were enrolled. Significant attenuation of clopidogrel’s antiplatelet effects was seen with co‐administration of esomeprazole compared with placebo. Vasodilator stimulated phosphoprotein (VASP), platelet aggregometry (area under the curve (AUC)) and VerifyNow results were 54.7% ± 2.8 platelet reactivity index (PRI), 66.3 ± 2.6 AUC units and 213.1 ± 14.1 platelet reactivity units (PRU) with esomeprazole vs. 47% ± 2.7 PRI, 59.7 ± 3.7 AUC units and 181.4 ± 14.6 PRU with placebo (P < 0.01 esomeprazole vs. placebo for all measures). There was no significant difference in platelet aggregometry (maximal aggregation) between the esomeprazole group (68.9% ± 2.7 units) and placebo‐treated group (64.5% ± 4.1 units; P > 0.05). Conclusion: Esomeprazole when co‐administered with aspirin and clopidogrel results in a significant attenuation of clopidogrel’s antiplatelet effects.     

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 intervention

Summary. Background: The carriage of CYP2C19*2 and the use of proton‐pump inhibitors (PPIs) and calcium‐channel blockers (CCBs) has been associated with the diminished efficacy of clopidogrel. However, previous studies have only assessed the isolated impact of these risk factors for clopidogrel poor response. Objectives: The aim of the present study was to investigate the impact of the combined presence of three risk factors for clopidogrel poor response, that is, the use of CCBs, PPIs and the carriage of CYP2C19*2, on on‐treatment platelet reactivity and the occurrence of atherothrombotic events in 725 patients on dual antiplatelet therapy undergoing elective coronary stenting. Methods: In a prospective, follow‐up study, on‐treatment platelet reactivity was quantified using ADP‐induced light transmittance aggregometry (LTA) and the VerifyNow P2Y12 assay. The clinical study endpoint was the composite of all‐cause mortality, myocardial infarction, stent thrombosis and stroke at 1 year after stenting. Results: Patients with either one or more than one risk factor exhibited increased platelet reactivity (mean relative increase one risk factor: 11% and > 1 risk factor: 22%, respectively). Sixty‐four events occurred during follow‐up (8.8% of the study population). Patients with one risk factor for clopidogrel poor response did not have an increased risk of the composite endpoint. However, patients using both CCBs and PPIs and carriers of CYP2C19*2 who used CCBs had a statistically significant increased risk of the composite endpoint [hazard ratio(HR)_adj 2.2 95% CI, 1.0–5.3, P = 0.044 and HR_adj 3.3 95% CI, 1.1–9.8, P = 0.032, respectively]. Conclusions: The presence of more than one of the three investigated risk factors for clopidogrel poor response is associated with an increased risk of adverse cardiovascular events within 1 year after elective coronary stenting.     

Pharmacogenomic polygenic risk score for clopidogrel responsiveness among Caribbean Hispanics: A candidate gene approach

This multicenter clinical study was aimed at conducting a targeted pharmacogenomic association analysis of residual on‐clopidogrel platelet reactivity in 474 Caribbean Hispanic patients. Platelet reactivity was measured using the VerifyNow P2Y12 assay and clopidogrel resistance was defined as P2Y12 reaction units (PRUs) greater than or equal to 208. Genotyping was performed using the whole‐genome Infinium MEGA BeadChip array. An ancestry‐adjusted, weighted polygenic risk score (wPGxRS) was developed to account for the effect of multiple variants on PRU and compared between clopidogrel responders and nonresponders. The mean PRU across the study cohort was 173.8 ± 68.5 and 33.5% of patients were defined as clopidogrel resistant. Multivariate linear regression showed that 19% of PRU variability was attributed to nine independent predictors, with CYP2C19*2 (rs4244285) accounting for ~ 7% of observed PRU variation (p < 0.001). PON1 rs662, ABCB1/MDR1 rs2032582, PEAR1 rs12041331 carrier status, and the interaction between African ancestry and rs12041331 carriers also predicted PRU among the participants (p ≤ 0.05). A clear gene‐dose effect was detected between PRU and CYP2C19*2 genotype, consistent with previous studies in European patient populations, as well as rs12777823. Importantly, a significant positive correlation was detected between our novel wPGxRS (4 variants) and PRU among the Hispanic patient population (r _p = 0.35, p < 0.001). Moreover, the wPGxRS discriminated between nonresponders and responders (p = 0.003), indicating that this multigene‐based score is a useful predictor of clopidogrel resistance among Caribbean Hispanics. Taken together, these results help close the gap of knowledge on clopidogrel pharmacogenomics and its potential clinical implementation in this under‐represented population.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

CYP2C19*2 is significantly associated with an impaired response to clopidogrel in patients of mainly European ancestry, but this genetic variant accounts for only a small fraction of observed variability in clopidogrel resistance.

• WHAT QUESTION DID THIS STUDY ADDRESS?

This study answers the question of whether there is an association of relevant candidate pharmacogenes involved in clopidogrel absorption, metabolism, and pharmacodynamics with antiplatelet response among Caribbean Hispanics using a multigene‐based score approach.

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

This study closes the existing gap of knowledge about clopidogrel pharmacogenomics in Caribbean Hispanics by both confirming and identifying relevant genetic determinants of clopidogrel responsiveness in this underrepresented population after developing an ancestry‐based polygenic risk score model.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

By gaining a better understanding of underlying determinants of poor clopidogrel response among marginally represented groups, such as Caribbean Hispanics, worldwide efforts to translate such findings into a global precision medicine paradigm of true benefit for everyone can finally bring cardiovascular health equity to the population at large.     

Earlier recovery of platelet function after discontinuation of treatment with ticagrelor compared with clopidogrel in patients with high antiplatelet responses

Summary. Background: The rate of recovery of platelet function after discontinuation of P2Y₁₂ inhibitors depends on the reversibility of the antiplatelet effect and the extent of the on‐treatment response. P2Y₁₂ inhibition increases the bleeding risk in patients requiring surgery. Objectives: To evaluate recovery of platelet function after discontinuation of ticagrelor vs. clopidogrel in stable coronary artery disease (CAD) patients with high levels of platelet inhibition (HPI) during the ONSET/OFFSET study. Methods: Patients received aspirin 75–100 mg per day and either ticagrelor 90 mg twice‐daily or clopidogrel 75 mg daily for 6 weeks. This subanalysis included patients with HPI after the last dose of maintenance therapy, defined as: inhibition of platelet aggregation (IPA) > 75% 4 h post‐dose (ADP 20 μm , final extent); < 120 P2Y₁₂ reaction units 8 h post‐dose (VerifyNow P2Y₁₂ assay); or platelet reactivity index < 50% 8 h post‐dose (VASP‐P assay). Results: IPA > 75% was observed in 39 out of 47 ticagrelor‐treated and 17 out of 44 clopidogrel‐treated patients. The rate of offset of IPA over 4–72 h was greater with ticagrelor (IPA %/hour slope: ?1.11 vs. ?0.67 for clopidogrel; P < 0.0001). Mean IPA was significantly lower with ticagrelor than clopidogrel between 48 and 168 h post‐dose (P < 0.01). Similar findings were observed with the other assays. The average time for IPA to decline from 30% to 10% was 50.8 h with ticagrelor vs. 110.4 h with clopidogrel. Conclusions: In patients with HPI, recovery of platelet function was more rapid after discontinuation of ticagrelor than clopidogrel leading to significantly greater platelet reactivity by 48 h after the last dose in the ticagrelor group.     

Point-of-care Measurements of Platelet Inhibition After Clopidogrel Loading in Patients With Acute Coronary Syndrome: Comparison of Generic and Branded Clopidogrel Bisulfate

PurposePlatelet-function suppression with antiplatelet therapy is effective in preventing and treating cardiovascular disease. Clopidogrel is a thienopyridine derivative that blocks platelet activation by adenosine diphosphate receptor binding. This study demonstrates the effects of generic clopidogrel bisulfate in comparison to branded clopidogrel bisulfate in patients with acute coronary syndromes.MethodsThis prospective, 2-arm, single-center, open-label trial used 1:1 randomization to assign patients to receive generic or branded clopidogrel bisulfate. Patients with unstable angina or non–ST-segment elevation myocardial infarction and scheduled to undergo coronary angiography were enrolled. Platelet function was measured with a P2Y₁₂ assay and reported in P2Y₁₂ reaction units (PRU) and aspirin reaction units (ARU) after randomization. Platelet function was measured at 2, 4, 8, and 24 hours after 600-mg clopidogrel loading. The clinical outcome was checked at 1 month after coronary angiography.FindingsNinety-five patients were enrolled and randomized to the generic or branded group. Ninety patients (62 men [69%], 28 women [31%]; mean age, 58 years) completed the study protocol. The clinical characteristics were similar between the 2 groups. The difference in the baseline PRU measurements between the generic and branded groups was not significant (274.8 [59.7] vs 285.4 [62.4], respectively; P = 0.414). There were significant differences in 2-hour PRU (231.1 [71.3] vs 266.9 [67.4]; P = 0.017) and 4-hour PRU (227.3 [80.4] vs 265.7 [71.0]; P = 0.020); however, 24-hour PRU (200.5 [82.1] vs 220.6 [75.8]; P = 0.253) was similar. No death, myocardial infarction, target lesion revascularization, stent thrombosis, or Thrombolysis in Myocardial Infarction–defined major bleeding complications were reported during in-hospital stay or 1-month follow-up.ImplicationIn patients with ACS, loading of generic clopidogrel bisulfate was associated with an antiplatelet effect comparable to that of branded clopidogrel bisulfate. ClinicalTrials.gov identifier: NCT02060786.     

Effect of preanalytical time-delay on platelet function as measured by multiplate,PFA-100 and VerifyNow

Background and aims: Platelet function testing may help to identify poor responders to antiplatelet drugs. The aim of this study was to compare three commonly used platelet function tests with special focus on the pre-analytical influence of time-delay on the tested parameters.

Methods: We assessed ADP-induced platelet function by the Multiplate, Platelet Function Analyzer-100 (PFA-100) and VerifyNow in nine healthy volunteers and 36 patients receiving clopidogrel or prasugrel 1 and 3?hours after sampling. Results: The PFA-100 demonstrated non-closure time in 23 patients. A more graded response could be detected with the two other devices. Aggregation in whole blood (Multiplate) decreased after 3?hours compared to 1?hour in all subjects (p?p?Conclusion: Responses to ADP are time-dependent after blood sampling for the Multiplate in all subjects and for the VerifyNow in patients on antiplatelet drugs. For both devices, platelet aggregation was reduced 3?hours after sampling which may affect data interpretation and clinical consequences.     

Small bowel ulcer bleeding due to suspected clopidogrel use in a patient with clopidogrel resistance: A case report

BACKGROUNDClopidogrel is a platelet aggregation inhibitor used for the management of cardiovascular disease. While antiplatelet therapy decreases cardiovascular events after successful coronary drug-eluting stenting, it increases the risk of gastrointestinal (GI) bleeding. About 20% of the patients who take clopidogrel exhibit resistance to the drug.CASE SUMMARYWe report the first case of a small bowel bleeding ulcer in an 86-year-old man with clopidogrel resistance. He had a history of taking clopidogrel due to unstable angina. There was no evidence of bleeding in the stomach, duodenum, or colon through upper and lower GI endoscopies. The abdominal computed tomography showed the extravasation of radiocontrast media at the ileum. Because of unstable vital signs, emergency surgery was performed. Multiple ulcers with inflammation were found in the ileum. The pathologic findings revealed simple inflammation. The VerifyNow P2Y12 test showed clopidogrel resistance. One year after changing to aspirin, capsule endoscopy was performed and the small bowel ulcers were improved.CONCLUSIONSmall bowel ulcers and bleeding due to clopidogrel are not very common, but the prevalence is expected to increase in older age patients with risk factors despite clopidogrel resistance.     

Aspirin withdrawal in patients treated with ticagrelor presenting with non‐ST elevation myocardial infarction

Essentials

• Strong P2Y₁₂ blockade may cause platelet inhibition that is only minimally enhanced by aspirin.
• We evaluated aspirin withdrawal on platelet reactivity in ticagrelor treated patients.
• Aspirin withdrawal resulted in increased platelet reactivity to arachidonic acid.
• Aspirin withdrawal caused little difference in adenosine diphosphate‐induced platelet aggregation.

Summary

Background

Recent studies have shown that the thromboxane A₂‐dependent pathway is dependent on the ADP–P2Y₁₂ pathway, and that strong P2Y₁₂ receptor blockade alone causes inhibition of platelet aggregation that is minimally enhanced by aspirin. Data from the PLATO trial suggested that, among ticagrelor‐treated patients, high‐dose versus low‐dose (< 100 mg day^?1) aspirin is associated with an increased risk fof ischemic events.

Objectives

To evaluate the impact of aspirin withdrawal on platelet reactivity in acute coronary syndrome (ACS) patients treated with a potent P2Y₁₂ blocker.

Patients/Methods

This was a current prospective, randomized, placebo‐controlled, double‐blind, cross‐over study. The study population comprised 22 consecutive ACS patients who underwent percutaneous coronary intervention and were treated with aspirin (100 mg day^?1) and ticagrelor. Thirty days post‐ACS, open‐label aspirin was stopped, and patients were randomized to either blinded aspirin or placebo for 2 weeks, with each patient crossing over to the other arm for an additional 2 weeks. Platelet reactivity to arachidonic acid and ADP determined with light‐transmission aggregometry (LTA) and VerifyNow was evaluated at baseline, and 2 weeks and 4 weeks later.

Results

Aspirin withdrawal resulted in an increase in arachidonic‐acid induced platelet reactivity as determined with both LTA (77.0% ± 11.3% versus 20.8% ± 4.4%) and VerifyNow (607.7 ± 10.6 aspirin reaction units [ARU] versus 408.5 ± 14.4 ARU). Platelet response to ADP, as determined with both LTA and VerifyNow, did not differ with either aspirin or placebo (32.9% ± 2.6% versus 35.8% ± 3.6%, and 33.5 ± 6.4 P2Y₁₂ reaction units (PRU) versus 29.6 ± 5.7 PRU, respectively).

Conclusions

Aspirin withdrawal early post‐ACS results in increased platelet reactivity in response to arachidonic acid, despite concomitant treatment with the potent P2Y₁₂ blocker ticagrelor.