Kevin P. Bliden

Clopidogrel for Coronary Stenting Response Variability, Drug Resistance, and the Effect of Pretreatment Platelet Reactivity

Background Clopidogrel is administered to prevent stent thrombosis; however, the uniformity of platelet inhibition after treatment and the influence of pretreatment reactivity on drug response have not been described. Methods and Results Platelet aggregation (5 and 20 μmol/L ADP), the activation of glycoprotein IIb/IIIa (PAC‐1 antibody), and the expression of P‐selectin were measured in patients undergoing elective coronary stenting (n=96) at baseline and at 2 hours, 24 hours, 5 days, and 30 days after stenting. All patients received aspirin (325 mg). Clopidogrel (300 mg) was administered in the catheterization laboratory and followed by 75 mg daily. There was marked interindividual variability in drug response as measured by all markers that showed a normal distribution. Resistance, defined as baseline aggregation (%) minus posttreatment aggregation (%) ≤10% by 5 μmol/L ADP, was present in 31% and 15% of patients at 5 and 30 days, respectively. Patients with the highest pretreatment platelet reactivity remained the most reactive at 24 hours after treatment (P<0.0001). Conclusions Interindividual variability in the platelet inhibitory response from clopidogrel occurs in patients undergoing elective coronary stenting. Patients with high pretreatment reactivity are least protected. Alternative pharmacological strategies and the association of adverse ischemic events should be investigated in these patients. (Circulation. 2003; 107:2908‐2913.)

Association of Cytochrome P450 2C19 Genotype With the Antiplatelet Effect and Clinical Efficacy of Clopidogrel Therapy

CONTEXT Clopidogrel therapy improves cardiovascular outcomes in patients with acute coronary syndromes and following percutaneous coronary intervention by inhibiting adenosine diphosphate (ADP)-dependent platelet activation. However, nonresponsiveness is widely recognized and is related to recurrent ischemic events. OBJECTIVE To identify gene variants that influence clopidogrel response. DESIGN, SETTING, AND PARTICIPANTS In the Pharmacogenomics of Antiplatelet Intervention (PAPI) Study (2006-2008), we administered clopidogrel for 7 days to 429 healthy Amish persons and measured response by ex vivo platelet aggregometry. A genome-wide association study was performed followed by genotyping the loss-of-function cytochrome P450 (CYP) 2C19*2 variant (rs4244285). Findings in the PAPI Study were extended by examining the relation of CYP2C19*2 genotype to platelet function and cardiovascular outcomes in an independent sample of 227 patients undergoing percutaneous coronary intervention. MAIN OUTCOME MEASURE ADP-stimulated platelet aggregation in response to clopidogrel treatment and cardiovascular events. RESULTS Platelet response to clopidogrel was highly heritable (h(2) = 0.73; P < .001). Thirteen single-nucleotide polymorphisms on chromosome 10q24 within the CYP2C18-CYP2C19-CYP2C9-CYP2C8 cluster were associated with diminished clopidogrel response, with a high degree of statistical significance (P = 1.5 x 10(-13) for rs12777823, additive model). The rs12777823 polymorphism was in strong linkage disequilibrium with the CYP2C19*2 variant, and was associated with diminished clopidogrel response, accounting for 12% of the variation in platelet aggregation to ADP (P = 4.3 x 10(-11)). The relation between CYP2C19*2 genotype and platelet aggregation was replicated in clopidogrel-treated patients undergoing coronary intervention (P = .02). Furthermore, patients with the CYP2C19*2 variant were more likely (20.9% vs 10.0%) to have a cardiovascular ischemic event or death during 1 year of follow-up (hazard ratio, 2.42; 95% confidence interval, 1.18-4.99; P = .02). CONCLUSION CYP2C19*2 genotype was associated with diminished platelet response to clopidogrel treatment and poorer cardiovascular outcomes.

Randomized Double-Blind Assessment of the ONSET and OFFSET of the Antiplatelet Effects of Ticagrelor Versus Clopidogrel in Patients With Stable Coronary Artery Disease The ONSET/OFFSET Study

Background— Ticagrelor is the first reversibly binding oral P2Y12 receptor antagonist. This is the first study to compare the onset and offset of platelet inhibition (IPA) with ticagrelor using the PLATO (PLATelet inhibition and patient Outcomes) trial loading dose (180 mg) with a high loading dose (600 mg) of clopidogrel. Methods and Results— In a multicenter, randomized, double-blind study, 123 patients with stable coronary artery disease who were taking aspirin therapy (75 to 100 mg/d) received ticagrelor (180-mg load, 90-mg BID maintenance dose [n=57]), clopidogrel (600-mg load, 75-mg/d maintenance dose [n=54]), or placebo (n=12) for 6 weeks. Greater IPA (20 &mgr;mol/L ADP, final extent) occurred with ticagrelor than with clopidogrel at 0.5, 1, 2, 4, 8, and 24 hours after loading and at 6 weeks (P<0.0001 for all); by 2 hours after loading, a greater proportion of patients achieved >50% IPA (98% versus 31%, P<0.0001) and >70% IPA (90% versus 16%, P<0.0001) in the ticagrelor group than in the clopidogrel group, respectively. A faster offset occurred with ticagrelor than with clopidogrel (4-to-72–hour slope [% IPA/h] −1.04 versus −0.48, P<0.0001). At 24 hours after the last dose, mean IPA was 58% for ticagrelor versus 52% for clopidogrel (P=NS). IPA for ticagrelor on day 3 after the last dose was comparable to clopidogrel at day 5; IPA on day 5 for ticagrelor was similar to clopidogrel on day 7 and did not differ from placebo (P=NS). Conclusions— Ticagrelor achieved more rapid and greater platelet inhibition than high-loading-dose clopidogrel; this was sustained during the maintenance phase and was faster in offset after drug discontinuation. Clinical Trial Registration Information— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00528411.

Reduced-Function CYP2C19 Genotype and Risk of Adverse Clinical Outcomes Among Patients Treated With Clopidogrel Predominantly for PCI: A Meta-Analysis

CONTENT Clopidogrel, one of the most commonly prescribed medications, is a prodrug requiring CYP450 biotransformation. Data suggest its pharmacologic effect varies based on CYP2C19 genotype, but there is uncertainty regarding the clinical risk imparted by specific genotypes. OBJECTIVE To define the risk of major adverse cardiovascular outcomes among carriers of 1 (≈ 26% prevalence in whites) and carriers of 2 (≈ 2% prevalence in whites) reduced-function CYP2C19 genetic variants in patients treated with clopidogrel. DATA SOURCES AND STUDY SELECTION A literature search was conducted (January 2000-August 2010) in MEDLINE, Cochrane Database of Systematic Reviews, and EMBASE. Genetic studies were included in which clopidogrel was initiated in predominantly invasively managed patients in a manner consistent with the current guideline recommendations and in which clinical outcomes were ascertained. DATA EXTRACTION Investigators from 9 studies evaluating CYP2C19 genotype and clinical outcomes in patients treated with clopidogrel contributed the relevant hazard ratios (HRs) and 95% confidence intervals (CIs) for specific cardiovascular outcomes by genotype. RESULTS Among 9685 patients (91.3% who underwent percutaneous coronary intervention and 54.5% who had an acute coronary syndrome), 863 experienced the composite end point of cardiovascular death, myocardial infarction, or stroke; and 84 patients had stent thrombosis among the 5894 evaluated for such. Overall, 71.5% were noncarriers, 26.3% had 1 reduced-function CYP2C19 allele, and 2.2% had 2 reduced-function CYP2C19 alleles. A significantly increased risk of the composite end point was evident in both carriers of 1 (HR, 1.55; 95% CI, 1.11-2.17; P = .01) and 2 (HR, 1.76; 95% CI, 1.24-2.50; P = .002) reduced-function CYP2C19 alleles, as compared with noncarriers. Similarly, there was a significantly increased risk of stent thrombosis in both carriers of 1 (HR, 2.67; 95% CI, 1.69-4.22; P < .0001) and 2 (HR, 3.97; 95% CI, 1.75-9.02; P = .001) CYP2C19 reduced-function alleles, as compared with noncarriers. CONCLUSION Among patients treated with clopidogrel for percutaneous coronary intervention, carriage of even 1 reduced-function CYP2C19 allele appears to be associated with a significantly increased risk of major adverse cardiovascular events, particularly stent thrombosis.

Randomized Double-Blind Assessment of the ONSET and OFFSET of the Antiplatelet Effects of Ticagrelor Versus Clopidogrel in Patients With Stable Coronary Artery Disease Randomized Double-Blind Assessment of the ONSET and OFFSET of the Antiplatelet Effects of Ticagrelor Versus Clopidogrel in Patients With Stable Cornonary Disease: The ONSET/OFFSET Study

Background— Ticagrelor is the first reversibly binding oral P2Y12 receptor antagonist. This is the first study to compare the onset and offset of platelet inhibition (IPA) with ticagrelor using the PLATO (PLATelet inhibition and patient Outcomes) trial loading dose (180 mg) with a high loading dose (600 mg) of clopidogrel. Methods and Results— In a multicenter, randomized, double-blind study, 123 patients with stable coronary artery disease who were taking aspirin therapy (75 to 100 mg/d) received ticagrelor (180-mg load, 90-mg BID maintenance dose [n=57]), clopidogrel (600-mg load, 75-mg/d maintenance dose [n=54]), or placebo (n=12) for 6 weeks. Greater IPA (20 &mgr;mol/L ADP, final extent) occurred with ticagrelor than with clopidogrel at 0.5, 1, 2, 4, 8, and 24 hours after loading and at 6 weeks (P<0.0001 for all); by 2 hours after loading, a greater proportion of patients achieved >50% IPA (98% versus 31%, P<0.0001) and >70% IPA (90% versus 16%, P<0.0001) in the ticagrelor group than in the clopidogrel group, respectively. A faster offset occurred with ticagrelor than with clopidogrel (4-to-72–hour slope [% IPA/h] −1.04 versus −0.48, P<0.0001). At 24 hours after the last dose, mean IPA was 58% for ticagrelor versus 52% for clopidogrel (P=NS). IPA for ticagrelor on day 3 after the last dose was comparable to clopidogrel at day 5; IPA on day 5 for ticagrelor was similar to clopidogrel on day 7 and did not differ from placebo (P=NS). Conclusions— Ticagrelor achieved more rapid and greater platelet inhibition than high-loading-dose clopidogrel; this was sustained during the maintenance phase and was faster in offset after drug discontinuation. Clinical Trial Registration Information— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00528411.

Clopidogrel Loading With Eptifibatide to Arrest the Reactivity of Platelets. Results of the Clopidogrel Loading With Eptifibatide to Arrest the Reactivity of Platelets (CLEAR PLATELETS) Study

Background—Pretreatment is not the most common strategy practiced for clopidogrel administration in elective coronary stenting. Moreover, limited information is available on the antiplatelet pharmacodynamics of a 300-mg versus a 600-mg clopidogrel loading dose, and the comparative effect of eptifibatide with these regimens is unknown. Methods and Results—Patients undergoing elective stenting (n=120) were enrolled in a 2×2 factorial study (300 mg clopidogrel with or without eptifibatide; 600 mg clopidogrel with or without eptifibatide) (Clopidogrel Loading With Eptifibatide to Arrest the Reactivity of Platelets [CLEAR PLATELETS] Study). Clopidogrel was administered immediately after stenting. Aggregometry and flow cytometry were used to assess platelet reactivity. Eptifibatide added a ≥2-fold increase in platelet inhibition to 600 mg clopidogrel alone at 3, 8, and 18 to 24 hours after stenting as measured by 5 &mgr;mol/L ADP–induced aggregation (P<0.001). Without eptifibatide, 600 mg clopidogrel produced better inhibition than 300 mg clopidogrel at all time points (P<0.001). Glycoprotein IIb/IIIa (GPIIb/IIIa) blockade was associated with lower cardiac marker release. Active GPIIb/IIIa expression was inhibited most in the groups treated with eptifibatide (P<0.05). Conclusions—In elective stenting without clopidogrel pretreatment, use of a GPIIb/IIIa inhibitor produces superior platelet inhibition and lower myocardial necrosis compared with high-dose (600 mg) or standard-dose (300 mg) clopidogrel loading alone. In the absence of a GPIIb/IIIa inhibitor, 600 mg clopidogrel provides better platelet inhibition than the standard 300-mg dose. These results require confirmation in a large-scale clinical trial.

Response to Ticagrelor in Clopidogrel Nonresponders and Responders and Effect of Switching Therapies. The RESPOND Study

Background— The antiplatelet effects of the Platelet Inhibition and Patient Outcomes (PLATO) trial dose of ticagrelor in patients nonresponsive to clopidogrel and after they switch agents are unknown. Methods and Results— Patients with stable coronary artery disease on aspirin therapy received a 300-mg clopidogrel load; nonresponders were identified by light transmittance aggregometry. In a 2-way crossover design, nonresponders (n=41) and responders (n=57) randomly received clopidogrel (600 mg/75 mg once daily) or ticagrelor (180 mg/90 mg twice daily) for 14 days during period 1. In period 2, all nonresponders switched treatment; half of the responders continued the same treatment, whereas the others switched treatment. Inhibition of platelet aggregation was higher in nonresponders treated with ticagrelor compared with clopidogrel (P<0.05). Treatment with ticagrelor among nonresponders resulted in a >10%, >30%, and >50% decrease in platelet aggregation from baseline in 100%, 75%, and 13% of patients, respectively. Platelet aggregation fell from 59±9% to 35±11% in patients switched from clopidogrel to ticagrelor and increased from 36±14% to 56±9% in patients switched from ticagrelor to clopidogrel (P<0.0001 for both). Platelet reactivity was below the cut points previously associated with ischemic risk measured by light transmittance aggregometry, VerifyNow P2Y12 assay, and vasodilator-stimulated phosphoprotein phosphorylation in 98% to 100% of patients after ticagrelor therapy versus 44% to 76% of patients after clopidogrel therapy. Conclusions— Ticagrelor therapy overcomes nonresponsiveness to clopidogrel, and its antiplatelet effect is the same in responders and nonresponders. Nearly all clopidogrel nonresponders and responders treated with ticagrelor will have platelet reactivity below the cut points associated with ischemic risk. Clinical Trial Registration— http://www.clinicaltrials.gov. Unique Identifier: NCT00642811.

Evaluation of Dose-Related Effects of Aspirin on Platelet Function Results From the Aspirin-Induced Platelet Effect (ASPECT) Study

Background— The antiplatelet effect of aspirin is attributed to platelet cyclooxygenase-1 inhibition. Controversy exists on the prevalence of platelet resistance to aspirin in patients with coronary artery disease and effects of aspirin dose on inhibition. Our primary aim was to determine the degree of platelet aspirin responsiveness in patients, as measured by commonly used methods, and to study the relation of aspirin dose to platelet inhibition. Methods and Results— We prospectively studied the effect of aspirin dosing on platelet function in 125 stable outpatients with coronary artery disease randomized in a double-blind, double-crossover investigation (81, 162, and 325 mg/d for 4 weeks each over a 12-week period). At all doses of aspirin, platelet function was low as indicated by arachidonic acid (AA)-induced light transmittance aggregation, thrombelastography, and VerifyNow at any 1 dose. Resistance to aspirin was 0% to 6% in the overall group when AA was used as the agonist, whereas it was 1% to 27% by other methods [collagen and ADP-induced light transmittance aggregation, platelet function analyzer (PFA-100)]. Platelet response to aspirin as measured by collagen-induced light transmittance aggregation, ADP-induced light transmittance aggregation, PFA-100 (81 mg versus 162 mg, P≤0.05), and urinary 11-dehydrothromboxane B2 was dose-related (81 mg versus 325 mg, P=0.003). No carryover effects were observed. Conclusions— The assessment of aspirin resistance is highly assay-dependent; aspirin is an effective blocker of AA-induced platelet function at all doses, whereas higher estimates of resistance were observed with methods that do not use AA as the stimulus. The observation of dose-dependent effects despite nearly complete inhibition of AA-induced aggregation suggests that aspirin may exert antiplatelet properties through non–cyclooxygenase-1 pathways and deserves further investigation.

The Association of Cigarette Smoking With Enhanced Platelet Inhibition by Clopidogrel

OBJECTIVES The purpose of this study was to examine the effect of cigarette smoking on the platelet response to clopidogrel. BACKGROUND Response variability to clopidogrel therapy has been demonstrated. Clopidogrel is metabolically activated by several hepatic cytochrome P450 (CYP) isoenzymes, including CYP1A2. Cigarette smoking induces CYP1A2 and may, therefore, enhance the conversion of clopidogrel to its active metabolite. METHODS Among 259 consecutive patients undergoing elective coronary stenting; 120 were on chronic clopidogrel therapy and were not loaded; and 139 were clopidogrel naïve and were loaded with 600 mg. There were 104 current smokers (CS) and 155 nonsmokers (NS). The adenosine diphosphate (ADP)-stimulated platelet aggregation (PA) was assessed by conventional aggregometry. The ADP-stimulated total and active glycoprotein (GP) IIb/IIIa expression were assessed with flow cytometry. Low PA was defined as the lowest quartile of 5 micromol/l ADP-induced post-treatment PA. RESULTS Current smokers on chronic clopidogrel therapy displayed significantly lower PA and ADP-stimulated active GP IIb/IIIa expression compared with NS (p < or = 0.0008 for both). Similarly, CS treated with 600 mg of clopidogrel displayed greater platelet inhibition and lower active GP IIb/IIIa expression compared with NS (p < or = 0.05). In a multivariate Cox regression analysis, current smoking was an independent predictor of low PA (p = 0.0001). CONCLUSION Clopidogrel therapy in CS is associated with increased platelet inhibition and lower aggregation as compared with NS. The mechanism of the smoking effect deserves further study and may be an important cause of response variability to clopidogrel therapy.

The effect of aspirin dosing on platelet function in diabetic and nondiabetic patients: an analysis from the aspirin-induced platelet effect (ASPECT) study.

OBJECTIVE— Diabetic patients may have a higher prevalence of platelet aspirin resistance than nondiabetic patients. Our goal was to analyze platelet aspirin responsiveness to various aspirin doses in diabetic and nondiabetic patients. RESEARCH DESIGN AND METHODS— We examined the effect of aspirin (81, 162, and 325 mg/day for 4 weeks each) on platelet aspirin responsiveness in 120 stable outpatients (30 diabetic patients and 90 nondiabetic patients) with coronary artery disease (CAD) using light transmittance aggregometry (LTA), VerifyNow, platelet function analyzer (PFA)-100, and levels of urinary 11-dehydro-thromboxane B2 (11-dh-TxB2). RESULTS— In the total group, a low prevalence (0–2%) of aspirin resistance was observed with all aspirin doses as determined by arachidonic acid–induced LTA. Aspirin resistance was higher at the 81-mg dose in diabetic versus nondiabetic patients using collagen-induced LTA (27 vs. 4%, P = 0.001), VerifyNow (13 vs. 3%, P = 0.05), and urinary 11-dh-TxB2 (37 vs. 17%, P = 0.03). Diabetic patients treated with 81 mg exhibited higher platelet function measured by VerifyNow, collagen- and ADP-induced LTA, and 11-dh-TxB2 levels (P ≤ 0.02 for all comparisons). Higher aspirin doses significantly inhibited platelet function and decreased aspirin resistance in diabetic patients (P < 0.05). CONCLUSIONS— Diabetic patients with CAD treated with 81 mg aspirin exhibit a higher prevalence of aspirin resistance and have significantly higher ADP- and collagen-induced platelet aggregation, 11-dh-TxB2 levels, and aspirin reaction units measured by VerifyNow than nondiabetic patients. Increased aspirin dosing resulted in similar rates of resistance and platelet function levels between groups. These findings indicate that diabetic patients exhibit a global high platelet reactivity phenotype that may be partially overcome by higher aspirin doses.