Increased risk in patients with high platelet aggregation receiving chronic clopidogrel therapy undergoing percutaneous coronary intervention: is the current antiplatelet therapy adequate?

OBJECTIVES: We sought to determine whether patients receiving chronic clopidogrel therapy undergoing nonemergent stenting who display high on-treatment preprocedural platelet aggregation measured by standard light transmittance aggregometry and thrombelastography (TEG) will be at increased risk for poststenting ischemic events. BACKGROUND: Patients exhibiting heightened platelet reactivity to adenosine diphosphate (ADP) might be at increased risk for recurrent ischemic events after coronary stenting. METHODS: A total of 100 consecutive patients receiving chronic antiplatelet therapy consisting of aspirin (325 mg qd) and clopidogrel (75 mg qd) were studied before undergoing nonemergent stenting. Patients were followed for 1 year after coronary stenting for the occurrence of death, myocardial infarction, stent thrombosis, stroke, or ischemia requiring a hospital stay. RESULTS: All patients were aspirin responsive. Patients with ischemic events (23 of 100, 23%) within 1 year had greater on-treatment prestent ADP-induced platelet aggregation than patients without ischemic events by aggregometry and TEG (p < 0.001 for both measurements). Of patients with an ischemic event, 70% and 87% displayed high on-treatment platelet reactivity at baseline by aggregometry and TEG, respectively. High on-treatment platelet reactivity as measured by aggregometry and TEG were the only variables significantly related to ischemic events (p < 0.001 for both assays). The administration of eptifibatide reduced periprocedural elevation in platelet reactivity, with no significant differences in bleeding events. CONCLUSIONS: Patients receiving chronic clopidogrel therapy undergoing nonemergent percutaneous coronary intervention who exhibit high on-treatment ADP-induced platelet aggregation are at increased risk for postprocedural ischemic events. These findings might have implications for the alteration in clopidogrel maintenance dose and use of glycoprotein IIb/IIIa inhibitors in selected patients.     

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.     

Underlying mechanism and specific prevention of hemolysis-induced platelet activation

Thromboembolic complications significantly impair the outcome of hemolytic disorders. We hypothesized that red cell adenosine diphosphate (ADP) release results in significant platelet activation in hemolysis and that this prothrombotic state can be prevented by inhibition of the ADP P2Y₁₂ receptor. In the current study, we therefore sought to investigate the mechanism and inhibition of hemolysis-induced platelet activation. The expression of activated integrin αIIbß3 was determined by flow cytometry, and platelet aggregation was assessed by multiple electrode platelet aggregometry. We demonstrate platelet activation and increased platelet aggregation by adding hemolytic blood (lysates) to whole blood, similarly to that achieved by the platelet agonist ADP. Enhanced platelet activation and reactivity in the presence of hemolytic blood were significantly abolished by apyrase, which catalyzes ADP degradation, and inhibited by blockade of the platelet ADP P2Y₁₂ receptor with cangrelor. Platelets from patients treated with the ADP P2Y₁₂ receptor antagonist clopidogrel showed a reduced response to lysates compared to platelets from healthy controls without antiplatelet treatment. Further, in vitro blood group ABO incompatibility induced hemolysis and led to increased platelet activation. Finally, “spontaneous” platelet aggregation seen in patients with cold agglutinin disease was completely abolished by cangrelor. In conclusion, hemolysis is associated with increased platelet activation and aggregation due to red cell derived ADP, which can be prevented by ADP receptor blockade.     

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?µM) and collagen (1 and 2?µg/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.     

Doubling the clopidogrel dose in patients with reduced responsiveness to the standard dose is associated with a limited effectiveness as evaluated by impedance aggregometry

BackgroundDifferent methods are available for quantifying platelet function inhibition. Measuring vasodilator-stimulated phosphoprotein (VASP) phosphorylation is currently the most specific method for assessing the clopidogrel effect. The aim of our study was to compare different tests in view of a clinically applicable bedside test. Further, we examined whether doubling the clopidogrel dose to 150 mg/d in clopidogrel low-responder would lead to a reduction in platelet reactivity.Methods and resultsADP-, ADP Hs-, and TRAP-induced platelet aggregation were measured by impedance aggregometry in 100 patients with CAD and 18 healthy controls. Moreover, platelet aggregation was assessed by flow cytometrical detection of VASP-phosphorylation and surface P-selectin in a subgroup of 34 patients and in healthy controls. Another 10 patients with CAD, identified as low-responder, were treated with a clopidogrel dose of 150 mg/d. Thereafter, ADP-induced platelet aggregation was assessed by impedance aggregometry. Significant correlations were observed between ADP-induced platelet aggregation assessed by VASP-phosphorylation and by impedance aggregometry. Doubling the dose of clopidogrel to 150 mg/d was associated with a reduction of ADP-induced platelet aggregation in only 60% of the patients.ConclusionsImpedance aggregometry is a valuable bedside test to assess platelet function inhibition. Doubling the clopidogrel dose is not effective to reduce high on-treatment platelet reactivity in almost half of these patients, pointing to the need of a more powerful platelet inhibitor.     

血栓弹力图评价患者颅内外动脉狭窄支架置入术后抗血小板聚集药物的疗效

目的采用血栓弹力图（TEG）仪检测颅内外动脉支架置入术（PTAS）后,服用阿司匹林和氯吡格雷患者的血小板抑制情况,以指导PTAS术后抗血小板聚集药物的个体化调整。方法回顾性分析从南京卒中注册系统中纳入的65例脑梗死或者短暂性脑缺血发作患者的临床资料。在PTAS治疗术后第3天抽取静脉血,采用TEG仪检测花生四烯酸（AA）途径诱导的血小板抑制率和腺苷二磷酸（ADP）受体途径诱导的血小板抑制率,比较患者经两种途径诱导的血小板抑制率以及患者对阿司匹林和氯吡格雷治疗反应的差异。结果①阿司匹林对AA途径的抑制率为（80±28）%,显著高于氯吡格雷对ADP受体途径的抑制率（53±31）%,差异有统计学意义,（P〈0.01）。②65例患者中,对阿司匹林组治疗效果良好、有效、反应低、无效者分别为45（69.2%）、8（12.3%）、7（10.8%）、5例（7.7%）,氯吡格雷分别为19（29.2%）、14（21.5%）、23（35.4%）、9例（13.8%）。对阿司匹林反应良好的患者,3例对氯吡格雷无反应,14例反应低下;对氯吡格雷反应良好的患者,均对阿司匹林反应良好或有效。对氯吡格雷反应低下者,4例对阿司匹林反应低,5例对阿司匹林有效,14例效果良好。两种疗效有一定关联性（χ2=33.311,P〈0.01）。③对阿司匹林反应良好＋有效者为53例,反应低＋无效者为12例;而对氯吡格雷反应良好＋有效者为33例;反应低＋无效者为32例,两种药物疗效差异有统计学意义（χ2m=15.042,P〈0.01）。结论采用TEG仪检测PTAS患者的血小板聚集的抑制率,有利于指导临床制定个体化的抗血小板聚集治疗方案。阿司匹林对PTAS患者血小板聚集的抑制作用强于氯吡格雷。患者对阿司匹林和氯吡格雷治疗的反应有差异性,部分对氯吡格雷反应低下者,可能对阿司匹林反应良好或有效。     

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.     

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.     

Multiple antiplatelet effects of clopidogrel are not modulated by statin type in patients undergoing percutaneous coronary intervention

We investigated whether statin type or dose influenced the inhibition of platelet function induced by clopidogrel in a prospective, open, parallel group study in patients undergoing elective percutaneous coronary intervention. Patients were taking CYP3A4 metabolised atorvastatin (n = 20) or simvastatin (n = 21), non-CYP3A4 metabolised pravastatin (n = 11) or fluvastatin (n = 2), or no statin therapy (n = 5). ADP and TRAP-induced platelet aggregation were measured using optical aggregometry, whole-blood single-platelet counting, and the Ultegra and Plateletworks point-of-care systems. Platelet pro-coagulant activity (annexin V binding and microparticle formation), P-selectin expression and platelet-leukocyte conjugate formation were assessed by flow cytometry. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and after 10 and 28 days with clopidogrel 75 mg daily. Clopidogrel significantly inhibited both ADP and TRAP-induced platelet responses over time, with steady state inhibition achieved by day 10. This was demonstrated by all techniques used. There was no significant effect of statin type or dose on platelet responses by any method at any time-point. In conclusion, statins do not influence the inhibitory effects of clopidogrel on multiple platelet responses, including aggregation, P-selectin expression, platelet-leucocyte conjugate formation and pro-coagulant responses, in patients undergoing elective PCI.     

Effects of aspirin and clopidogrel in healthy men measured by platelet aggregation and PFA-100

There are no generally accepted definitions for low-response (frequently called resistance) to the platelet inhibitors, aspirin and clopidogrel. Low-response may increase the risk of cardiovascular events in atherosclerotic patients. We aimed to define the normal drug responses in healthy men. Platelet function was measured in 20 healthy men during 11 days of aspirin or clopidogrel intake, using light transmission aggregometry (LTA) and the Platelet Function Analyzer 100 (PFA-100). The lower limits for LTA at baseline were 64% and 61%, using arachidonic acid and ADP as agonists, respectively. During aspirin intake the LTA results were stable from day to day, and an upper limit of 9% arachidonic acid stimulated aggregation was found. Clopidogrel intake was best shown by ADP induced aggregation. However, two out of 20 individuals exhibited low-response to clopidogrel. In the remaining 18 volunteers an upper limit of 48% aggregation was found. We found an upper limit for collagen-epinephrine stimulated PFA-100 results of 166 s at baseline. During aspirin intake, these results varied considerably from day to day in nine out of 20 men, resulting in an overlap between the reference ranges at baseline and during therapy. In conclusion, platelet inhibition by aspirin and clopidogrel assessed by aggregometry was stable during 11 days of treatment and reference ranges were established. The PFA-100 results varied greatly and low-response was not precisely defined by this method.     

Inhibition of platelet aggregation by AZD6140, a reversible oral P2Y12 receptor antagonist, compared with clopidogrel in patients with acute coronary syndromes.

OBJECTIVES: In a substudy of DISPERSE (Dose confIrmation Study assessing anti-Platelet Effects of AZD6140 vs. clopidogRel in non-ST-segment Elevation myocardial infarction)-2, we compared the antiplatelet effects of AZD6140 and clopidogrel and assessed the effects of AZD6140 in clopidogrel-pretreated patients. BACKGROUND: Clopidogrel, in combination with aspirin, reduces cardiovascular events in patients with acute coronary syndromes (ACS). However, patients with poor inhibition of platelet aggregation with clopidogrel may be less well protected. AZD6140 is a reversible oral P2Y(12) receptor antagonist that has been studied in ACS patients in comparison with clopidogrel (DISPERSE-2 study). METHODS: Patients were randomized to receive either AZD6140 90 mg twice a day, AZD6140 180 mg twice a day, or clopidogrel 75 mg once a day for up to 12 weeks in a double-blind, double-dummy design. One-half the patients allocated AZD6140 received a 270-mg loading dose. Patients randomized to receive clopidogrel were given a 300-mg loading dose unless they had already been treated with clopidogrel. Adenosine diphosphate-induced platelet aggregation was assessed by optical aggregometry on day 1 and at 4-week intervals. RESULTS: AZD6140 inhibited platelet aggregation in a dose-dependent fashion and both doses achieved greater levels of inhibition than clopidogrel (e.g., 4 weeks, 4-h postdose [mean (+/-SD)]: clopidogrel 64% [+/-22%], AZD6140 90 mg 79% [+/-22%], AZD6140 180 mg 95% [+/-8%]. AZD6140 also produced further suppression of platelet aggregation in patients previously treated with clopidogrel. CONCLUSIONS: AZD6140 exhibited greater mean inhibition of platelet aggregation than a standard regimen of clopidogrel in ACS patients. In addition, AZD6140 further suppressed platelet aggregation in clopidogrel pretreated patients.     

Platelet responsiveness to clopidogrel in patients with coronary syndrome. Comparison of platelet aggregation induced by ADP and flow cytometric analysis of intraplatelet VASP phosphorylation

Although antiplatelet therapy with ASA-clopidogrel reduces the risk of cardiovascular episodes after PCI, a substantial number of events occur during follow-up. Sustained platelet reactivity under dual antiplatelet therapy was recently associated with increased risk of recurrent atherothrombotic events after PCI. Whereas it appears significant to determine clopidogrel responsiveness, the accurate platelet function assay is still under investigation. OBJECTIVES: (i) to determine the proportion of "low-responders" or "resistants" patients during coronary syndrome (ii) to identify determinants of interindividual variability response to clopidogrel (iii) to compare aggregometry and VASP phosphorylation measured by flow cytometry. Patients were treated by clopidogrel (300 mg loading dose and 75 mg maintenance dose) and ASA (160 mg) (N=27). Additional treatment by GPIIbIIIa antagonists was given to high-risk patients (N=9). Platelet function was monitored by ADP aggregometry (5, 10, 20 microM) and VASP phosphorylation before any treatment by clopidogrel (d0) and at least five days after (d5). The platelet reactivity index (PRI), expressed as percentage, is the difference in VASP fluorescence intensity between resting (+ PGE1) and activated (ADP) platelets. At d5, low responsiveness to clopidogrel was defined by either (i) a PRI > 67.3% corresponding to the mean value -2SD measured in untreated patients (dO) (ii) or an absolute change (delta d0-d5) in aggregation (ADP 10 microM) < to 30%. RESULTS: PRI, platelet aggregometry to ADP was significantly reduced following clopidogrel treatment (P < 0.01). A wide inter-individual variability to clopidogrel was observed at d5 (PRI from 11 to 83%). Whatever the platelet function used, a large proportion of patients were detected as "low-responders" (37% by VASP, 44% by ADP aggregometry). Absolute change in ADP aggregation was correlated to the variation of PRI (R = 0.559; P = 0.02). Contrary to ADP aggregometry, PRI was not influenced by GPIIbIIIa antagonists or prior administration of ASA. However, the conformity of the two methods to evaluate clopidogrel responsiveness was only 66%. No differences in platelet aggregometry could be observed at d5 between "low" and "good-responders" defined by VASP analysis. At d5, a higher PRI value could be detected in male and patients with history of dyslipemia. CONCLUSION: During coronary syndrome, impaired platelet responsiveness to clopidogrel was observed in a large proportion of patients whatever the platelet function assay used. VASP analysis was found insensitive to GPIIbIIIa or aspirin administration. Possible mechanisms linking clopidogrel "resistance" measured by VASP assay and enhanced thrombogenicity remain to be characterized. Indeed, clopidogrel "resistance" defined by VASP analysis was not associated with higher platelet aggregation.     

Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides

The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.     

Direct evidence for the interaction of the nucleotide affinity analog 5'-p-fluorosulfonylbenzoyl adenosine with a platelet ADP receptor

Previous reports have indicated that the nucleotide affinity analog 5'- p-fluorosulfonylbenzoyl adenosine (FSBA) at concentrations between 40 and 100 mumol/L and at times greater than 20 minutes covalently modifies a single protein component on the external platelet membrane surface and that adenosine diphosphate (ADP) protects against this reaction. That this protein is an ADP receptor linked to platelet activation is shown by FSBA inhibition of ADP-mediated platelet shape change, aggregation, and fibrinogen receptor exposure. In this report, further evidence for the interaction of FSBA with the ADP receptor on platelets is provided by the observation that FSBA at high concentrations (100 to 500 mumol/L) behaves as a weak agonist to produce platelet shape change within one minute as detected by spectroscopic assay and scanning electron microscopy with concomitant phosphorylation of the light chain of platelet myosin. The specificity of FSBA as an agonist is demonstrated by inhibition of FSBA-induced shape change by ATP and the covalent incorporation of SBA as well as the failure of 5'-fluorosulfonylbenozoyl guanosine (FSBG) to cause shape change. In contrast, incubation of platelets with low concentrations of [3H]-FSBA (40 mol/L) is not associated with stimulation of platelet shape change or myosin light chain phosphorylation.     

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.     

Prasugrel loading dose in diabetic patients with acute STEMI – Always sufficiently effective? Observation in two cases and review of current knowledge

The activation and subsequent platelet aggregation play a key role in the formation of arterial thrombosis and therefore is the key therapeutic target in the treatment of acute coronary syndromes. Dual antiplatelet therapy containing aspirin and P2Y12 ADP receptor antagonist forms currently the basis in acute ST – elevation myocardial infarction (STEMI) pharmacological treatment. Nevertheless, there is a wide variability in pharmacodynamic response to administration of clopidogrel, the most frequently used P2Y12 ADP receptor antagonist. High platelet reactivity after clopidogrel administration is associated with increased risk of stent thrombosis and points to the suitability of laboratory monitoring of antiplatelet therapy efficacy in clinical practice. Laboratory monitoring of antiplatelet therapy by ex vivo platelet function tests may help to identify individuals with poor antiplatlet response. Recently, there is a growing number of data reporting a failure in antiplatelet response following clopidogrel administration, which is specifically associated with insulin resistance and diabetes mellitus. Prasugrel, a new, potent P2Y12 ADP receptor antagonist, provides faster and more consistent inhibition of platelet function compared with clopidogrel. Prasugrel therapy was repeatedly described as an effective method to overcome clopidogrel resistance and prasugrel resistance has not yet been reliably described. We report two cases of patients with diabetes mellitus type 2 at the stage of organ complications, in whom a prasugrel loading dose of 60 mg did not reach adequate antiplatelet response in 60 min after prasugrel administration. The antiplatelet response was measured by light transmission aggregometry and by VASP protein phosphorylation assessment.     

The Retention Index Test Homburg (RTH-II): Response to clopidogrel and comparison with aggregometry and CD62P-expression

The Retention Index Test Homburg (RTH-II) is quoted to detect effects of shear stress on platelets, which involve ADP receptor signaling. RTH-II might be a tool for monitoring antiplatelet therapy for compounds that interfere with ADP induced platelet activation and secretion. In a series of investigations, we used an ADP (2 microM) triggered RTH-II in parallel with light-transmittance aggregometry and flow cytometry in subjects before and after clopidogrel. A loading dose of 225 mg clopidogrel leads to a significant reduction (p < 0.01) in the ADP-stimulated retention index (RI) from 69 +/- 15 to 48 +/- 21%, in the aggregation response to 5 microM ADP (from 50 +/- 20 to 29 +/- 21%) and the expression of CD62P (from 64 +/- 11 to 41 +/- 17%). Correlation analysis showed that the RI corresponds significantly to CD62P-expression (p < 0.01) but not to aggregation. We also found a strong correlation (p < 0.01) between the ADP-stimulated RI and the expression of CD62P after stimulation with 2 microM ADP, whereas no correlation was seen for RI vs. binding of PAC-1 or aggregation. Platelets not retained in the filter had lower CD62P expression than measured in the sample before the filter passage (54 vs. 35%). A direct interaction of CD62P with platelet ligands might lead to enhanced retention in RTH and explain the correlation of RI with CD62P expression. The RTH-II might be a simple and easy to handle platelet function assay for monitoring effects on P2Y(12)-inhibitors on platelet degranulation, perhaps in addition to aggregometry.     

Disaggregation Following Agonist-Induced Platelet Activation in Patients on Dual Antiplatelet Therapy

Disaggregation as the difference between maximal and final platelet aggregation by light transmission aggregometry indicates the stability of platelet aggregates. We evaluated the extent of disaggregation after platelet stimulation with adenosine diphosphate (ADP), arachidonic acid (AA), collagen, epinephrine, and thrombin receptor-activating peptide (TRAP)-6 in 323 patients on dual antiplatelet therapy with daily aspirin and clopidogrel (group 1), prasugrel (group 2), or ticagrelor (group 3) therapy. All patients in group 1 underwent elective angioplasty and stenting, whereas all patients included in groups 2 and 3 suffered from acute coronary syndromes (STEMI or NSTEMI) and underwent urgent PCI. Significant differences between maximal and final platelet aggregation were observed with all agonists throughout the groups (all p<0.001). Disaggregation was highest using AA (clopidogrel 36.5%; prasugrel/ticagrelor 100%) and ADP (clopidogrel 21.7%; prasugrel/ticagrelor 100%). In contrast, low disaggregation was observed after platelet stimulation with collagen and TRAP-6 in clopidogrel-treated patients, and after platelet stimulation with collagen and epinephrine in prasugrel- and ticagrelor-treated patients. In conclusion, pathways of platelet activation that are not inhibited by standard antiplatelet therapy allow persisting platelet aggregation and may at least in part be responsible for adverse ischemic events.     

Diurnal variation in platelet inhibition by clopidogrel

Morning increase in the occurrence of myocardial infarction, stroke and sudden cardiac death is a well-recognized phenomenon, which is in line with a morning enhancement of platelet aggregation. We investigated whether platelet inhibition during clopidogrel and aspirin therapy varies during the day. Fifty-nine consecutive patients (45 men and 14 women) with first ST-segment elevation myocardial infarction (STEMI) treated with primary percutaneous coronary interventions (pPCI) on dual antiplatelet therapy were prospectively enrolled into the study. Blood samples were collected 4 days after start of clopidogrel treatment at 6.00?a.m., 10.00?a.m., 2.00?p.m. and 7.00?p.m. Arachidonic acid and adenosine diphosphate (ADP)-induced platelet aggregation were assessed by impedance aggregometry. Platelet inhibition by clopidogrel was lowest in the midmorning: median ADP-induced platelet aggregation was 55%, 17% and 27% higher at 10.00?a.m. compared to 6.00?a.m., 2.00?p.m. and 7.00?p.m., respectively (p?相似文献   

Clopidogrel inhibits platelet aggregation in patients on aspirin with stable chronic angina pectoris

Ten patients with chronic stable angina pectoris and ten aged-matched healthy controls were investigated. Aspirin was given as 160 mg/day and clopidogrel as 300 mg loading dose followed by 75 mg/day. Whole blood aggregometry was performed at baseline and after 10 days with collagen or ADP as stimulator. ADP as well as collagen-induced platelet aggregation was each reduced (P<0.02) both in healthy volunteers and in patients with stable angina pectoris with combination therapy compared with aspirin only. In conclusion, treatment with clopidogrel and aspirin provides significantly greater inhibition of platelet activity than aspirin alone in patients with stable angina pectoris and in healthy control subjects.