PAR-1 genotype influences platelet aggregation and procoagulant responses in patients with coronary artery disease prior to and during clopidogrel therapy

Genetic variations of the protease-activated receptor-1 (PAR-1) have been associated with platelet receptor density and linked to thrombin receptor-activating peptide (TRAP)-induced phenotypes of platelet aggregation and P-selectin expression. We investigated whether the PAR-1 intervening sequence-14 A>T dimorphism influences platelet procoagulant activity. We also determined whether the P2Y12 antagonist clopidogrel could offset any observed functional polymorphism of the PAR-1 receptor by inhibiting P2Y12-mediated amplification of TRAP-induced responses. We studied 54 patients listed for elective percutaneous coronary intervention assessing TRAP-induced platelet aggregation and markers of procoagulant activity. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. Each patient was genotyped for the PAR-1 intervening sequence-14 A/T dimorphism. Increased platelet aggregation and procoagulant responses were observed with PAR-1 A allele homozygotes. Clopidogrel significantly inhibited these platelet responses regardless of PAR-1 genotype, but did not offset the hyper-reactivity associated with the A/A homozygotes. We conclude that a common sequence variation within the PAR-1 gene influences TRAP-induced platelet procoagulant activity as well as aggregation. Higher platelet reactivity associated with PAR-1 IVSn-14 A allele homozygotes persists despite clopidogrel therapy. These individuals may be at higher risk of thromboembolic events and may require additional anti-platelet medication.     

PAR-1 genotype influences platelet aggregation and procoagulant responses in patients with coronary artery disease prior to and during clopidogrel therapy

Genetic variations of the protease-activated receptor-1 (PAR-1) have been associated with platelet receptor density and linked to thrombin receptor-activating peptide (TRAP)-induced phenotypes of platelet aggregation and P-selectin expression. We investigated whether the PAR-1 intervening sequence-14 A?>?T dimorphism influences platelet procoagulant activity. We also determined whether the P2Y₁₂ antagonist clopidogrel could offset any observed functional polymorphism of the PAR-1 receptor by inhibiting P2Y₁₂-mediated amplification of TRAP-induced responses. We studied 54 patients listed for elective percutaneous coronary intervention assessing TRAP-induced platelet aggregation and markers of procoagulant activity. Platelet responses were measured at baseline, 4?h post clopidogrel 300?mg, and 10 and 28 days following clopidogrel 75?mg daily. Each patient was genotyped for the PAR-1 intervening sequence-14 A/T dimorphism. Increased platelet aggregation and procoagulant responses were observed with PAR-1 A allele homozygotes. Clopidogrel significantly inhibited these platelet responses regardless of PAR-1 genotype, but did not offset the hyper-reactivity associated with the A/A homozygotes. We conclude that a common sequence variation within the PAR-1 gene influences TRAP-induced platelet procoagulant activity as well as aggregation. Higher platelet reactivity associated with PAR-1 IVSn–14 A allele homozygotes persists despite clopidogrel therapy. These individuals may be at higher risk of thromboembolic events and may require additional anti-platelet medication.     

High clopidogrel loading dose during coronary stenting: effects on drug response and interindividual variability.

AIM: To assess platelet inhibitory effects, interindividual variability in platelet inhibition as well as response to a 600 mg, compared to a standard 300 mg, clopidogrel loading dose (LD) after coronary stenting METHODS AND RESULTS: Platelet function profiles were assessed in 50 patients undergoing coronary stenting receiving either a 300 mg (n=27) or 600 mg clopidogrel LD. ADP (6 microM) and collagen (6 microg/mL) induced platelet aggregation, as well as ADP (2 microM) induced glycoprotein (GP) IIb/IIIa activation and P-selectin expression were assessed at baseline and 4, 24, and 48 h following clopidogrel front-loading. A more intense and rapid inhibition of platelet activation (both GP IIb/IIIa activation and P-selectin expression) were achieved using a 600 mg, compared to a 300 mg, LD throughout the entire 48 hours (p<0.001). Although there were no differences in platelet aggregation, overall a 600 mg LD increased the number of clopidogrel responders and this was also achieved earlier compared to a 300 mg LD. A 600 mg LD did not reduce interindividual variability of platelet response. CONCLUSION: The use of a 600 mg clopidogrel LD in patients undergoing coronary stenting optimises platelet inhibitory effects early after intervention and may provide a more effective protection against early thrombotic complications.     

Effect of clopidogrel with and without eptifibatide on tumor necrosis factor-alpha and C-reactive protein release after elective stenting: results from the CLEAR PLATELETS 1b study.

OBJECTIVES: This study was performed to compare the effects of antiplatelet regimens on early inflammation and cardiac marker release after elective stenting. BACKGROUND: Few data exist regarding the comparative effects of specific antiplatelet regimens on early inflammation marker release after stenting. METHODS: In a 2 x 2 factorial randomized investigation, patients undergoing stenting were treated with either clopidogrel alone (300 mg or 600 mg; n = 60) or clopidogrel with eptifibatide (n = 60). Platelet aggregation (5 and 20 muM adenosine diphosphate [ADP]), ADP-stimulated expression of active glycoprotein (GP) IIb/IIIa, and platelet-bound P-selectin, tumor necrosis factor (TNF)-alpha, C-reactive protein (CRP), and cardiac markers were measured. RESULTS: Compared with a strategy of clopidogrel alone, clopidogrel + eptifibatide reduced the release of cardiac markers. A marked reduction in platelet aggregation and active GP IIb/IIIa expression (p < or = 0.001) with clopidogrel + eptifibatide was associated with a decrease in CRP and TNF-alpha release (p < or = 0.001). CONCLUSIONS: A strategy of clopidogrel with GP IIb/IIIa blockade resulted in superior inhibition of inflammation and cardiac marker release, which was accompanied by superior platelet inhibition immediately after percutaneous coronary intervention compared with a strategy of clopidogrel alone. The mechanistic and clinical implications of attenuated periprocedural inflammation and myocardial necrosis with a strategy of GP IIb/IIIa inhibition warrant further investigation.     

Effect of 150-mg vs 300-mg loading doses of clopidogrel on platelet function in Japanese patients undergoing coronary stent placement

BACKGROUND: The loading dose of ticlopidine is 500 mg in both the US and Europe and 200 mg in Japan. A lower loading dose of clopidogrel might achieve adequate platelet inhibition in Japanese patients. METHODS AND RESULTS: Platelet aggregation was serially measured at baseline, and 2, 4, 6, and 8 h after 150-mg (n=20) and 300-mg (n=20) clopidogrel loading. Platelets were stimulated with 5 and 20 micromol/L adenosine diphosphate (ADP) and aggregation was assessed by optical aggregometry. Pretreatment ADP-induced platelet aggregation in the 150-mg clopidogrel group did not differ from that of the 300-mg group. The administration of 300-mg clopidogrel loading dose resulted in lower platelet aggregation 2 h after the administration (5 micromol/L ADP: 53+/-9% vs 61+/-12%, p<0.05 and 20 micromol/L ADP: 61+/-10% vs 68+/-9%, p<0.05). A lower platelet aggregation induced with 20 micromol/L ADP was still observed 4 h after the 300-mg clopidogrel loading (58+/-10% vs 65+/-9%, p<0.05). CONCLUSIONS: The 150-mg clopidogrel loading does not achieve rapid platelet inhibition. The 300-mg loading dose should be used to suppress platelet function rapidly even in Japanese patients undergoing coronary stent placement.     

Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy

The efficacy of the platelet P2Y12 receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y12 gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G > A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4 h post clopidogrel 600 mg. Patients were genotyped for P2Y12 haplotype and the CYP3A5 6986G > A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y12 and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.     

The platelet hyporesponsiveness to clopidogrel in acute coronary syndrome patients treated with 75 mg/day clopidogrel may be overcome within 1 month of treatment

Platelets are involved in thrombus formation and inflammation following vascular injury, while clopidogrel exerts antithrombotic and anti-inflammatory actions. We investigated various platelet-derived prothrombotic and proinflammatory mediators as well as the platelet aggregatory response in patients with acute coronary syndromes (ACS) receiving clopidogrel, as a function of the patient responsiveness to drug treatment. Blood samples were obtained from 40 patients with recent (<24?h) ACS before clopidogrel loading 600?mg (followed by a maintenance dose of 75?mg/day) as well as 5-days and 30-days afterwards. Twelve patients exhibited platelet reactivity index (PRI) values higher than 50% evaluated by the Vasodilator Stimulated Phosphoprotein (VASP) test at 5 days and were characterized as nonresponders. The platelet response to adenosine diphosphate (ADP) and thrombin receptor agonist peptide-14 (TRAP) was studied by flow cytometry and light transmission aggregometry. A maximum reduction of ADP- or TRAP-induced platelet aggregation in 28 clopidogrel responding patients was observed at 5 days postclopidogrel loading, whereas in nonresponders, it was achieved at 30-days along with a significant decrease in the PRI values. Similar results were obtained for the membrane expression of CD40L and the production of platelet-derived microparticles. By contrast, the maximum inhibition of P-selectin expression and platelet-leukocyte conjugate formation was observed at 30-days in both patient groups. A maintenance dose of 75?mg clopidogrel differentially affects the platelet aggregation and platelet-derived prothrombotic and proinflammatory mediators in ACS patients within the first month of the treatment, a phenomenon that is highly influenced by the drug response variability. Since these factors may be involved in the major adverse cardiovascular events in ACS patients, especially in those undergoing percutaneous coronary intervention, the above findings may be clinically important.     

High glucose levels enhance platelet activation: involvement of multiple mechanisms

Diabetes mellitus (DM) and hyperglycaemia are associated with platelet activation. The present study was designed to investigate how high glucose levels influence platelet function. Fasting human blood was incubated with different concentrations of D-glucose (5, 15 and 30 mmol/l) and other sugars without or with in vitro stimuli. Platelet activation was monitored by whole blood flow cytometry. High glucose levels enhanced adenosine diphosphate (ADP)- and thrombin receptor-activating peptide (TRAP)-induced platelet P-selectin expression, and TRAP-induced platelet fibrinogen binding. Similar effects were seen with 30 mmol/l L-glucose, sucrose and galactose. Hyperglycaemia also increased TRAP-induced platelet-leucocyte aggregation. Protein kinase C (PKC) blockade did not counteract the enhancement of platelet P-selectin expression, but abolished the enhancement of TRAP-induced platelet fibrinogen binding by hyperglycaemia. Superoxide anion scavenging by superoxide dismutase (SOD) attenuated the hyperglycaemic enhancement of platelet P-selectin expression, but did not counteract the enhancement of TRAP-induced platelet fibrinogen binding. Hyperglycaemia did not alter platelet intracellular calcium responses to agonist stimulation. Blockade of cyclo-oxygenase (COX), phosphotidylinositol-3 (PI3) kinase, or nitric oxide synthase, or the addition of insulin did not influence the effect of hyperglycaemia. In conclusion, high glucose levels enhanced platelet reactivity to agonist stimulation through elevated osmolality. This occurred via superoxide anion production, which enhanced platelet P-selectin expression (secretion), and PKC signalling, which enhanced TRAP-induced fibrinogen binding (aggregablity).     

Effects of triple antiplatelet therapy (aspirin, clopidogrel, and cilostazol) on platelet aggregation and P-selectin expression in patients undergoing coronary artery stent implantation

The purpose of this study was to determine the effect of the addition of cilostazol to aspirin plus clopidogrel on platelet aggregation after intracoronary stent implantation. Twenty patients who underwent coronary stent placement were randomly assigned to therapy with aspirin plus clopidogrel (dual-therapy group, n = 10) or aspirin plus clopidogrel plus cilostazol (triple-therapy group, n = 10). A loading dose of clopidogrel (300 mg) and cilostazol (200 mg) was administered immediately after stent placement, and clopidogrel (75 mg/day) and cilostazol (100 mg twice daily) were given for 1 month. Platelet aggregation in response to adenosine diphosphate (ADP; 5 and 20 micromol/L) or collagen and P-selectin (CD-62P) expression was assayed at baseline, 2 hours, 24 hours, 1 week, and 1 month after stent placement. Inhibition of ADP-induced platelet aggregation was significantly higher in patients receiving triple therapy than those receiving dual therapy from 24 hours after stent placement, and inhibition of collagen-induced platelet aggregation was significantly higher in the triple-therapy group beginning 1 week after stent placement. P-Selectin expression was significantly lower in the triple-therapy than dual-therapy group at 1 week and 30 days. In conclusion, compared with dual antiplatelet therapy, triple therapy after coronary stent placement resulted in more potent inhibition of platelet aggregation induced by ADP and collagen. These findings suggest that triple therapy may be used clinically to prevent thrombotic complications after coronary stent placement.     

Effect of 450-mg loading dose of clopidogrel on platelet function in Japanese patients undergoing coronary stent placement

Usefulness of higher (>300 mg) loading doses of clopidogrel has been demonstrated in studies from the United States and Europe. The present study evaluated platelet aggregation after the administration of a 450-mg loading dose of clopidogrel in Japanese patients undergoing coronary stenting. Platelet aggregation was serially measured at baseline, and 2, 4, 6, and 8 h after 450-mg clopidogrel loading in 25 patients undergoing coronary stenting. Platelets were stimulated with 5 and 20 μmol/l adenosine diphosphate (ADP) and aggregation was assessed by optical aggregometry. Platelet aggregation (5 μmol/l ADP 42.8% ± 13.5% and 20 μmol/l ADP 51.2% ± 11.6%) was significantly suppressed ≤4 h after 450-mg clopidogrel loading. There were no adverse events except one minor nasal bleed. The present study shows that platelet inhibition is achieved ≤4 h after the administration of a 450-mg clopidogrel loading dose in Japanese patients.     

瑞舒伐他汀和阿托伐他汀对氯吡格雷抗血小板活性的影响

目的观察瑞舒伐他汀和阿托伐他汀对氯吡格雷抗血小板活性的影响。方法选择60例冠心病患者接受阿司匹林100mg/d、氯吡格雷75 mg/d及低分子肝素5000 U/12 h治疗,5 d后随机分为阿托伐他汀20mg/d(阿托伐他汀组,30例)和瑞舒伐他汀10 mg/d(瑞舒伐他汀组,30例)。在服用氯吡格雷之前(基线值)、加用他汀类药物之前及服用他汀类药物3d后,用全血阻抗法分别测定不同浓度二磷酸腺苷(5、10、20μmol/L)诱导的血小板聚集率。结果与基线值比较,服用氯吡格雷5 d后和加服他汀类药物治疗3 d后,2组患者血小板聚集率明显降低,差异有统计学意义(P<0.05);与治疗前比较,阿托伐他汀组患者血小板聚集率有所升高,而瑞舒伐他汀组患者血小板聚集率有所下降,但差异无统计学意义(P>0.05)。结论经细胞色素3A4途径代谢的阿托伐他汀及不经细胞色素3A4代谢的瑞舒伐他汀,短期内对氯吡格雷抗血小板活性无影响。     

Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy

The efficacy of the platelet P2Y₁₂ receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y₁₂ gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G?>?A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4?h post clopidogrel 300?mg, and 10 and 28 days following clopidogrel 75?mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4?h post clopidogrel 600?mg. Patients were genotyped for P2Y₁₂ haplotype and the CYP3A5 6986G?>?A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y₁₂ and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.     

The inhibitory potency of clopidogrel on ADP-induced platelet activation is not attenuated when it is co-administered with atorvastatin (20 mg/day) for 5 weeks in patients with acute coronary syndromes

The antiplatelet potency of clopidogrel may be attenuated by short-term co-administration of lipophilic statins metabolized through the cytochrome P-450, isoform 3A4. We investigated whether the co-administration of atorvastatin (20?mg/day) for 5 weeks, in patients with acute coronary syndromes (ACS) could affect the antiplatelet activity of clopidogrel. Fifty-one patients with the first episode of an ACS were included in the study. All patients underwent percutaneous coronary intervention (PCI) and received a loading dose of 375 mg of clopidogrel, followed by 75 mg/day for at least 3 months. Twenty-six of them presented with low density lipoprotein (LDL) cholesterol levels >100?mg/dl (2.6 mmol/l) (measured within 24 h from the onset of symptoms) and received daily 20 mg/day of atorvastatin. The ADP- or TRAP-induced platelet aggregation, as well as P-selectin and CD40L surface expression, were studied at baseline (within 30 min after admission) and 5 weeks afterwards. Atorvastatin did not influence either the clopidogrel-induced inhibition of platelet aggregation initiated by 5 or 10 microM ADP or the clopidogrel-induced reduction of the membrane expression of P-selectin and CD40L induced by ADP. In conclusion, atorvastatin, even at a dose of 20 mg/day does not affect the antiplatelet efficacy of clopidogrel when co-administered for 5 weeks in ACS patients.     

Inhibitory effects of P2Y12 receptor antagonists on TRAP-induced platelet aggregation, procoagulant activity, microparticle formation and intracellular calcium responses in patients with acute coronary syndromes

Thrombin induces platelet aggregation and membrane rearrangements leading to enhanced procoagulant activity and microparticle production, all of which are thought to contribute to thrombus formation in patients with acute coronary syndromes (ACS). Clopidogrel, an adenosine diphosphate (ADP) receptor antagonist acting at the P2Y(12) receptor, has been shown to provide clinical benefit in ACS. We aimed to investigate the effects of clopidogrel ex vivo and another ADP-antagonist, AR-C69931MX in vitro on thrombin receptor activating peptide (TRAP)-induced platelet aggregation, procoagulant activity, microparticle formation and [Ca(2+)]i responses in patients with ACS. Measurements were performed in platelet-rich plasma using aggregometry and flow cytometry (n = 12). Clopidogrel (300 mg loading dose plus 75 mg daily) significantly inhibited TRAP-induced aggregation, procoagulant activity (annexin V binding) and microparticle production (all P < 0.05) but not as extensively as AR-C69931MX (400 nmol/l). [Ca(2+)]i responses induced by a combination of TRAP and ADP designed to mimic the physiological effects of released ADP showed that clopidogrel partially and AR-C69931MX completely removed the ADP component of the [Ca(2+)]i responses (n = 6). The results provide new information on the mechanisms involved in the beneficial effects of P2Y(12) antagonists in patients with ACS.     

Comparison of the pharmacodynamic effects of the platelet ADP receptor antagonists clopidogrel and AR-C69931MX in patients with ischaemic heart disease

We compared the antiplatelet effects of clopidogrel and the intravenous platelet P2Y 12 receptor antagonist AR-C69931MX, which acts on the same receptor as clopidogrel by a different and reversible mechanism and, unlike clopidogrel, is active in vitro . Thirteen patients with acute coronary syndromes entered into a phase II study of intravenous AR-C69931MX (Group 1) and eight patients undergoing intracoronary stent implantation and treated with clopidogrel (Group 2) were studied using a whole blood single-platelet counting aggregation assay. Group 2 patients were also studied using turbidimetry with ADP and TRAP as agonists and whole blood [ 14 C]5HT release to study dense granule secretion in response to ADP, collagen and TRAP. In Group 2 studies, a therapeutic concentration of AR-C69931MX was added in vitro before and after clopidogrel administration. AR-C69931MX in Group 1 achieved greater inhibition of ADP-induced platelet aggregation than clopidogrel in Group 2 and AR-C69931MX in vitro added to the effects of clopidogrel on ADP-induced aggregation. AR-C69931MX but not clopidogrel inhibited TRAP-induced aggregation and granule secretion and AR-C69931MX had a more consistent inhibitory effect on collagen-induced responses. In conclusion, therapeutic administration of clopidogrel moderately inhibits platelet P2Y 12 receptor activation and substantially greater P2Y 12 receptor blockade can be achieved with AR-C69931MX.     

Impact of the degree of peri-interventional platelet inhibition after loading with clopidogrel on early clinical outcome of elective coronary stent placement.

OBJECTIVES: Our prospective study tested the hypothesis that the 30-day clinical outcome of elective percutaneous catheter intervention (PCI) differs between strata defined by quartiles of platelet aggregation after loading with 600 mg clopidogrel. BACKGROUND: Platelet responses after loading with clopidogrel are highly variable. The impact of this variability on the peri-interventional risk of patients undergoing PCI has not been investigated prospectively. METHODS: Our study included 802 consecutive patients undergoing elective coronary stent placement. Before PCI, patients received a loading dose of 600 mg clopidogrel followed by 75 mg daily. Primary end point was the 30-day composite of death, myocardial infarction, and target lesion revascularization (major adverse cardiac events [MACE]). Platelet aggregation was assessed immediately before PCI by optical aggregometry (5 micromol/l adenosine diphosphate). RESULTS: During 30-day follow-up, 15 patients (1.9%) incurred MACE (3 deaths, 8 myocardial infarctions, 8 target lesion revascularizations). Quartiles of platelet aggregation were <4%, 4% to 14%, 15% to 32%, and >32%. Thirty-day MACE differed significantly (p = 0.034) between quartiles of platelet aggregation. It was 0.5% in the first quartile, 0.5% in the second, 3.1% in the third, and 3.5% in the fourth. Platelet aggregation above the median carried a 6.7-fold risk (95% confidence interval 1.52 to 29.41; p = 0.003) of 30-day MACE. Multivariable logistic regression analysis, including pertinent covariables, confirmed platelet aggregation as a significant independent predictor of 30-day MACE (adjusted odds ratio per 10% increase in platelet aggregation 1.32, 95% confidence interval 1.04 to 1.61; p = 0.026). CONCLUSIONS: The level of platelet aggregation immediately before elective coronary stenting in patients pre-treated with a high loading dose of clopidogrel is correlated with early outcome after the procedure.     

Platelet function in clopidogrel-treated patients with acute coronary syndrome.

Percutaneous coronary intervention (PCI) in patients presenting with acute coronary syndrome (ACS) is associated with increased risk of thrombotic complications. ACS enhances platelet activation; whether pretreatment with clopidogrel is sufficient to suppress platelet function in patients with ACS is not known. This study assessed platelet function in patients with and without ACS prior to PCI and after pretreatment with a single dose of 600 mg clopidogrel. Blood samples of 402 patients prior to PCI with (n = 119) or without (n = 283) ACS were collected at least 2 h after 600 mg clopidogrel administration. Maximal platelet aggregation in response to ADP (5 and 20 micromol/l), collagen (4 microg/ml) and TRAP (25 micromol/l) was measured with optical aggregometry. Surface expression of glycoprotein IIb/IIIa and P-selectin was assessed with flow cytometry at baseline and after stimulation with 5 and 20 micromol/l ADP. Agonist-induced platelet aggregation did not differ significantly between patients with and without ACS (P > or = 0.15). Parameters of platelet activation (glycoprotein IIb/IIIa and P-selectin surface expression) were significantly higher in ACS patients at baseline and after 5 and 20 micromol/l ADP stimulation (P < 0.0001). Patients with ACS continue to exhibit increased platelet activation after pretreatment with 600 mg clopidogrel. This finding supports the need for additional platelet function inhibition during PCI in patients with ACS.     

Aspirin and clopidogrel drug response in patients undergoing percutaneous coronary intervention: the role of dual drug resistance.

We evaluated the response to clopidogrel among aspirin-resistant versus aspirin-sensitive patients undergoing elective coronary stenting. Patients (n = 150) treated with aspirin but not clopidogrel had blood samples drawn at baseline and 24 h after clopidogrel loading. Depending on the definition used, 9% to 15% were resistant to aspirin and 24% to clopidogrel. About half of the aspirin-resistant patients were also resistant to clopidogrel. As a group, aspirin-resistant patients had lower response to clopidogrel (assessed by platelet aggregation and activation markers) than aspirin-sensitive patients. Both aspirin- and clopidogrel-resistant patients had higher incidence of creatine kinase-MB elevation than the respective sensitive patients. OBJECTIVES: We sought to evaluate the response to clopidogrel among aspirin-resistant versus aspirin-sensitive patients undergoing percutaneous coronary intervention (PCI). BACKGROUND: Wide variability has been reported in response to aspirin and clopidogrel. There are limited data on the simultaneous responses to both drugs. METHODS: Elective PCI patients (n = 150) who received aspirin for > or = 1 week but not clopidogrel were included. All patients received bivalirudin during PCI. Blood samples were drawn at baseline and 20 to 24 h after a 300-mg clopidogrel dose. Aspirin resistance was defined by > or = 2 of 3 criteria: rapid platelet function analyzer-ASA score > or = 550, 5 micromol/l adenosine diphosphate (ADP)-induced aggregation > or = 70%, and 0.5 mg/ml arachidonic acid-induced aggregation > or = 20%. Clopidogrel resistance was defined as baseline minus post-treatment aggregation < or = 10% in response to 5 and 20 micromol/l ADP. RESULTS: Nineteen (12.7%) patients were resistant to aspirin and 36 (24%) to clopidogrel. Nine (47.4%) of the aspirin-resistant patients were also clopidogrel resistant. Aspirin-resistant patients were more likely to be women and have diabetes than were aspirin-sensitive patients. They also had lower response to clopidogrel, assessed by platelet aggregation and activation markers (flow cytometry-determined PAC-1 binding and P-selectin expression). Elevation of creatine kinase-myocardial band after stenting occurred more frequently in aspirin-resistant versus aspirin-sensitive patients (38.9% vs. 18.3%; p = 0.04) and in clopidogrel-resistant versus clopidogrel-sensitive patients (32.4% vs. 17.3%; p = 0.06). CONCLUSIONS: Aspirin-resistant patients as a group have reduced response to clopidogrel. Furthermore, we have identified a unique group of dual drug-resistant patients who may be at increased risk for thrombotic complications after PCI.     

Comparison of the pharmacodynamic effects of the platelet ADP receptor antagonists clopidogrel and AR-C69931MX in patients with ischaemic heart disease

We compared the antiplatelet effects of clopidogrel and the intravenous platelet P2Y(12) receptor antagonist AR-C69931MX, which acts on the same receptor as clopidogrel by a different and reversible mechanism and, unlike clopidogrel, is active in vitro. Thirteen patients with acute coronary syndromes entered into a phase II study of intravenous AR-C69931MX (Group 1) and eight patients undergoing intracoronary stent implantation and treated with clopidogrel (Group 2) were studied using a whole blood single-platelet counting aggregation assay. Group 2 patients were also studied using turbidimetry with ADP and TRAP as agonists and whole blood [(14)C]5HT release to study dense granule secretion in response to ADP, collagen and TRAP. In Group 2 studies, a therapeutic concentration of AR-C69931MX was added in vitro before and after clopidogrel administration. AR-C69931MX in Group 1 achieved greater inhibition of ADP-induced platelet aggregation than clopidogrel in Group 2 and AR-C69931MX in vitro added to the effects of clopidogrel on ADP-induced aggregation. AR-C69931MX but not clopidogrel inhibited TRAP-induced aggregation and granule secretion and AR-C69931MX had a more consistent inhibitory effect on collagen-induced responses. In conclusion, therapeutic administration of clopidogrel moderately inhibits platelet P2Y(12) receptor activation and substantially greater P2Y(12) receptor blockade can be achieved with AR-C69931MX.     

Clopidogrel anti-platelet effect: an evaluation by optical aggregometry, impedance aggregometry, and the platelet function analyzer (PFA-100)

Platelet aggregation inhibition by clopidogrel may be suboptimal in 4-30% of patients. Traditionally, optical aggregometry is used to assess clopidogrel's anti-platelet effects by inhibition of ADP-induced aggregation in platelet rich plasma. Red blood cells are an important source of ADP and, thus, are known to modulate platelet function. Because the whole blood aggregation by impedance method assesses platelet function in a physiological milieu, we compared clopidogrel response by this method with the optical method in platelet rich plasma (PRP) and the Platelet Function Analyzer (PFA-100). Platelet function studies were performed in 17 healthy subjects at baseline and after 10 days of clopidogrel intake (75 mg/day). Optical and impedance aggregometry were performed after addition of ADP (10 and 20 microM) and collagen (1 and 2 microg/mL). For PFA-100 analysis, whole blood closure time was measured in collagen-coated cartridges with ADP and epinephrine. All subjects except one showed a decrease in ADP-induced aggregation using both aggregation methods. However, ADP-induced platelet aggregation was significantly inhibited when assessed in whole blood as compared to the optical method (71+/- 34% vs. 34.2+/- 23%, p = 0.0002); this suggests that whole blood aggregometry is more sensitive in the detection of clopidogrel effect in the presence of red cells, which are known to modulate platelet function. The PFA-100 ADP closure time was slightly prolonged above the reference interval in only 5/17 (29%) subjects, suggesting that this instrument is not able to detect clopidogrel effect. We conclude that whole blood aggregation appears to be more sensitive in detecting clopidogrel effect compared with the platelet rich plasma method; the PFA-100 was unable to detect clopidogrel effect in the majority of the subjects.