Decrease in high on-treatment platelet reactivity (HPR) prevalence on switching from clopidogrel to prasugrel: Insights from the switching anti-platelet (SWAP) study

Advances in the Pharmacogenomics of Antiplatelet Therapy

BACKGROUND

Acute coronary syndrome (ACS) is a highly thrombotic state, and a sustained antiplatelet effect is vital to the prevention of thrombotic complications. Clopidogrel, the most widely used oral P2Y12 receptor antagonist in ACS, has attracted considerable attention because of significant variability in antiplatelet effect depending on the presence of CYP2C19 allele. Other P2Y12 receptor antagonists offer sustained and more predictable antiplatelet effects than clopidogrel albeit at an increased cost. Several studies have demonstrated the promising application of pharmacogenetics in choosing personalized antiplatelet therapy using the point-of-care genotype assays.

AREAS OF UNCERTAINTY

Guidelines regarding the genotype-guided approach to the selection of antiplatelet therapy have been conflicting, and studies evaluating the effect of pharmacogenetic-guided selection of antiplatelet therapy on the outcomes have demonstrated mixed results.

DATA SOURCES

A literature search was conducted using MEDLINE and EMBASE for studies reporting the association of pharmacogenetic-guided selection of antiplatelet therapy and the outcomes in patients with ACS until December 2018.

RESULTS

Presence of specific CYP2C19 allele significantly influences clopidogrel metabolism and associated outcomes in patients with ACS. Thrombotic and bleeding complications are more common in patients with loss-of-function (LOF) and gain-of-function (GOF) alleles, respectively. Although the pharmacogenetic-guided approach to the selection of antiplatelet therapy appears promising in ACS, studies have shown conflicting results, and direct randomized evidence linking this approach with the better outcomes is lacking.

CONCLUSIONS

Genotype-guided selection of antiplatelet therapy is expected to be useful in patients undergoing percutaneous coronary intervention (PCI) with a high risk of adverse outcomes. The patient-physician discussion should be an essential part of this decision-making process. Large-scale multicenter randomized controlled trials using the point-of-care genotype assay are needed to investigate this approach further before its use can be recommended in all comers.

Switching P2Y12 Receptor Inhibiting Therapies

Antiplatelet therapy with aspirin and a P2Y₁₂ receptor inhibitor is the cornerstone of treatment of patients with atherothrombotic disease manifestations. Switching between P2Y₁₂ inhibitors occurs commonly in clinical practice for a variety of reasons, including safety, efficacy, adherence, and economic considerations. There are concerns about the optimal approach for switching because of potential drug interactions, which may lead to ineffective platelet inhibition and thrombotic complications, or potential overdosing due to overlap in drug therapy, which might cause excessive platelet inhibition and increased bleeding. This review provides practical considerations of switching based on pharmacodynamic and clinical data available from the literature.

Effects of switching ticagrelor to clopidogrel on cardiovascular outcomes in patients with acute coronary syndrome

Present study was to evaluate whether switching ticagrelor to clopidogrel would impact platelet reactivity and cardiovascular outcomes in acute coronary syndrome (ACS) patients after percutaneous coronary intervention (PCI).A total of 202 ACS patients after PCI were enrolled and prescribed ticagrelor. Before discharge, 138 (68%) patients were switched to clopidogrel. Peripheral blood was obtained before switching and at 48 hours after switching to measure platelet reactivity. Patients were followed for 30 days to evaluate cardiovascular events.Compared to ticagrelor group, patients in clopidogrel group were more likely to be male (69.6% vs 65.6%), smokers (34.1% vs 31.3%) and had higher prevalence of hypertension (75.4% vs 71.9%). The frequency of right coronary artery lesion was significantly higher in ticagrelor group (34.4% vs 30.4%). There were no significant differences in baseline platelet reactivity (37.6 ± 5.2% vs 38.4 ± 4.9%). Forty-eight hours after switching to clopidogrel, platelet reactivity in clopidogrel group was significantly higher (46.3 ± 5.6% vs 38.1 ± 5.0%, P <.05). Patients in clopidogrel group had significantly higher incidence of cardiovascular events (3.6% vs 1.6%, P <.05). However, after further adjusted for platelet reactivity at 48 hours of switching, clopidogrel switching was not significantly associated with composite outcomes, with hazard ratio 1.08 (95% confidence interval 0.98-1.21, P = .063), indicating that platelet reactivity was a critical mediator between antiplatelet drug switching and cardiovascular outcomes.ACS patients after PCI treatment, early switching ticagrelor to clopidogrel results in increased platelet reactivity and higher incidence of short-term cardiovascular events.

Transferring from clopidogrel loading dose to prasugrel loading dose in acute coronary syndrome patients

High on-treatment platelet reactivity (HPR) has been identified as an independent risk factor for ischaemic events. The randomised, doubleblind, TRIPLET trial included a pre-defined comparison of HPR in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI) following a placebo/600-mg clopidogrel loading dose (LD) immediately before a subsequent prasugrel 60-mg or 30-mg LD. Platelet reactivity was assessed using the VerifyNow® P2Y12 assay (P2Y12 Reaction Units, PRU) within 24 hours (h) following the placebo/clopidogrel LD (immediately prior to prasugrel LD), and at 2, 6, 24, 72 h following prasugrel LDs. The impact of CYP2C19 predicted metaboliser phenotype (extensive metaboliser [EM] and reduced metabolisers [RM]) on HPR status was also assessed. HPR (PRU ≥240) following the clopidogrel LD (prior to the prasugrel LD) was 58.5% in the combined clopidogrel LD groups. No significant difference was noted when stratified by time between the clopidogrel and prasugrel LDs (≤6 hs vs >6 h). At 6 h following the 2nd loading dose in the combined prasugrel LD groups, HPR was 7.1%, with 0% HPR by 72 h. There was no significant effect of CYP2C19 genotype on pharmacodynamic (PD) response following either prasugrel LD treatments at any time point, regardless of whether it was preceded by a clopidogrel 600-mg LD. In conclusion, in this study, patients with ACS intended for PCI showed a high prevalence of HPR after clopidogrel 600-mg LD regardless of metaboliser status. When prasugrel LD was added, HPR decreased substantially by 6 h, and was not seen by 72 h.

Why have studies of tailored anti-platelet therapy failed so far?

Published data linking clopidogrel non-responsiveness to adverse ischaemic events lead to the suggestion that the magnitude of platelet inhibition by clopidogrel can be monitored and individually adjusted. This has been tested in randomised clinical trials (ARCTIC, GRAVITAS and TRIGGER-PCI), but despite reducing platelet reactivity, a strategy of therapy adjustment based on platelet function monitoring did not reduce the incidence of cardiac ischaemic events. Several critical issues regarding the design of these trials, which might in part have led to negative results, are discussed in this article.

Antiplatelet Therapy for Non-ST-Segment Elevation Myocardial Infarction in Complex "Real" Clinical Scenarios: A Consensus Document of the "Campania NSTEMI Study Group"

The incidence of ST-segment elevation myocardial infarction (STEMI) has significantly decreased. Conversely, the rate of non-STEMI (NSTEMI) has increased. Patients with NSTEMI have lower short-term mortality compared to patients with STEMI, whereas at long-term follow-up, the mortality becomes comparable. This might be due to the differences in baseline characteristics, including older age and a greater prevalence of comorbidities in the NSTEMI population. Although antithrombotic strategies used in patients with NSTEMI have been well studied in clinical trials and updated guidelines are available, patterns of use and outcomes in clinical practice are less well described. Thus, a panel of Italian cardiology experts assembled under the auspices of the "Campania NSTEMI Study Group" for comprehensive discussion and consensus development to provide practical recommendations, for both clinical and interventional cardiologists, regarding optimal management of antithrombotic therapy in patients with NSTEMI. This position article presents and discusses various clinical scenarios in patients with NSTEMI or unstable angina, including special subsets (eg, patients aged ≥85 years, patients with chronic renal disease or previous cerebrovascular events, and patients requiring triple therapy or long-term antithrombotic therapy), with the panel recommendations being provided for each scenario.

Clinical pathways and management of antithrombotic therapy in patients with acute coronary syndrome (ACS): a Consensus Document from the Italian Association of Hospital Cardiologists (ANMCO), Italian Society of Cardiology (SIC), Italian Society of Emergency Medicine (SIMEU) and Italian Society of Interventional Cardiology (SICI-GISE)

Antiplatelet therapy is the cornerstone of the pharmacologic management of patients with acute coronary syndrome (ACS). Over the last years, several studies have evaluated old and new oral or intravenous antiplatelet agents in ACS patients. In particular, research was focused on assessing superiority of two novel platelet ADP P2Y12 receptor antagonists (i.e., prasugrel and ticagrelor) over clopidogrel. Several large randomized controlled trials have been undertaken in this setting and a wide variety of prespecified and post-hoc analyses are available that evaluated the potential benefits of novel antiplatelet therapies in different subsets of patients with ACS. The aim of this document is to review recent data on the use of current antiplatelet agents for in-hospital treatment of ACS patients. In addition, in order to overcome increasing clinical challenges and implement effective therapeutic interventions, this document identifies all potential specific care pathway for ACS patients and accordingly proposes individualized therapeutic options.

Morphine interaction with prasugrel: a double-blind, cross-over trial in healthy volunteers

Background

Morphine decreases the concentrations and effects of clopidogrel, which could lead to treatment failure in myocardial infarction.

Objectives

To clarify whether more potent P2Y₁₂-inhibitors may provide an effective alternative, we examined drug–drug interactions between morphine and prasugrel.

Methods

Twelve healthy volunteers received 60 mg prasugrel with placebo or 5 mg morphine intravenously in a randomized, double-blind, placebo-controlled, cross-over trial. Pharmacokinetics were determined by liquid chromatography tandem mass spectrometry, and prasugrel effects were measured by platelet function tests.

Results

Morphine neither diminished total drug exposure (AUC), which was the primary endpoint, nor significantly delayed drug absorption of prasugrel. However, morphine reduced maximal plasma concentrations (C_max) of prasugrel active metabolite by 31 % (p = 0.019). Morphine slightly, but not significantly, delayed the onset of maximal inhibition of platelet plug formation under high shear rates (30 vs. 20 min). Whole blood aggregation was not influenced.

Conclusions

Although morphine significantly decreases the maximal plasma concentrations of prasugrel active metabolite, it does not diminish its effects on platelets to a clinically relevant degree in healthy volunteers. However, it should be considered that the observed decrease in C_max of prasugrel active metabolite caused by morphine co-administration may gain relevance in STEMI patients.

Clinical Trial Registration: NCT01369186, EUDRA-CT#: 2010-023761-22.

Genetically Determined Platelet Reactivity and Related Clinical Implications

Many drugs are nowadays available to inhibit platelet activation and aggregation, especially in patients with acute coronary syndromes and undergoing percutaneous coronary intervention with stent implantation. Primary targets are represented by enzymes or receptors involved in platelet activation. Genetic mutations in these targets contribute to the inter-individual variability in platelet responses therefore weakening the efficacy of antiplatelet agents. High on treatment platelet reactivity is a condition characterized by low levels of platelet inhibition despite the use of antiplatelet drugs. This could be responsible for re-infarction, stent-thrombosis and strokes, affecting short and long-term prognosis after coronary revascularization. So far, to test antiplatelet resistance either the assessment of platelet function or the identification of genetic carriers of poly morphisms have been pursued. Although several methods are now available to test platelet reactivity, it is still debated whether its routine assessment gives real benefits in clinical practice. The present review aims at examining current evidences on genetic polymorphisms affecting optimal platelet inhibition.

A prospective randomized evaluation of a pharmacogenomic approach to antiplatelet therapy among patients with ST-elevation myocardial infarction: the RAPID STEMI study

Treatment of carriers of the CYP2C19*2 allele and ABCB1 TT genotype with clopidogrel is associated with increased ischemic complications after percutaneous coronary intervention (PCI). We sought to evaluate a pharmacogenomic strategy among patients undergoing PCI for ST-elevation myocardial infarction (STEMI), by performing a randomized trial, enrolling 102 patients. Point-of-care genetic testing for CYP2C19*2, ABCB1 TT and CYP2C19*17 was performed with carriers of either the CYP2C19*2 allele or ABCB1 TT genotype randomly assigned to a strategy of prasugrel 10 mg daily or an augmented dosing strategy of clopidogrel (150 mg daily for 6 days then 75 mg daily). The primary end point was the proportion of at-risk carriers exhibiting high on-treatment platelet reactivity (HPR), a marker associated with increased adverse cardiovascular events, after 1 month. Fifty-nine subjects (57.8%) were identified as carriers of at least one at-risk variant. Treatment with prasugrel significantly reduced HPR compared with clopidogrel by P2Y12 reaction unit (PRU) thresholds of >234 (0 vs 24.1%, P=0.0046) and PRU>208 (3.3 vs 34.5%, P=0.0025). The sensitivity of point-of-care testing was 100% (95% CI 88.0-100), 100% (86.3-100) and 96.9% (82.0-99.8) and specificity was 97.0% (88.5-99.5), 97.1% (89.0-99.5) and 98.5% (90.9-99.9) for identifying CYP2C19*2, ABCB1 TT and CYP2C19*17, respectively. Logistic regression confirmed carriers as a strong predictor of HPR (OR=6.58, 95% CI 1.24-34.92; P=0.03). We confirmed that concurrent identification of three separate genetic variants in patients with STEMI receiving PCI is feasible at the bedside. Among carriers of at-risk genotypes, treatment with prasugrel was superior to an augmented dosing strategy of clopidogrel in reducing HPR.

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.

Pharmacodynamic evaluation of switching from ticagrelor to prasugrel in patients with stable coronary artery disease: Results of the SWAP-2 Study (Switching Anti Platelet-2)

OBJECTIVES

The goal of this study was to evaluate the pharmacodynamic effects of switching patients from ticagrelor to prasugrel.

BACKGROUND

Clinicians may need to switch between more potent P2Y12 inhibitors because of adverse effects or switch to the use of a once-daily dosing regimen due to compliance issues.

METHODS

After a 3- to 5-day run-in phase with a ticagrelor 180-mg loading dose (LD) followed by a ticagrelor 90-mg twice-daily maintenance dose (MD), aspirin-treated patients (N = 110) with stable coronary artery disease were randomized to continue ticagrelor or switch to prasugrel 10-mg once-daily MD, with or without a 60-mg LD. Pharmacodynamic assessments were defined according to P2Y12 reaction unit (PRU) (P2Y12 assay) and platelet reactivity index (vasodilator-stimulated phosphoprotein phosphorylation assay) at baseline (before and after the run-in phase) and 2, 4, 24, and 48 h and 7 days after randomization.

RESULTS

Platelet reactivity was significantly greater at 24 and 48 h after switching to prasugrel versus continued therapy with ticagrelor, although to a lesser extent in those receiving an LD. Mean PRU remained significantly higher in the combined prasugrel groups versus the ticagrelor group (least-squares mean difference: 46 [95% confidence interval 25 to 67]) and did not meet the primary noninferiority endpoint (upper limit of the confidence interval ≤45), although PRU in the prasugrel cohort was lower at 7 days than at 24 or 48 h. Accordingly, rates of high on-treatment platelet reactivity were higher at 24 and 48 h in both prasugrel groups. At 7 days, there was no difference in high on-treatment platelet reactivity rate between the combined prasugrel and ticagrelor groups.

CONCLUSIONS

Compared with continued ticagrelor therapy, switching from ticagrelor to prasugrel therapy was associated with an increase in platelet reactivity that was partially mitigated by the administration of an LD.