Platelet P2Y12 blockers confer direct postconditioning-like protection in reperfused rabbit hearts.

BACKGROUND: Blockade of platelet activation during primary percutaneous intervention for acute myocardial infarction is standard care to minimize stent thrombosis. To determine whether antiplatelet agents offer any direct cardioprotective effect, we tested whether they could modify infarction in a rabbit model of ischemia/reperfusion caused by reversible ligation of a coronary artery. METHODS AND RESULTS: The P2Y12 (adenosine diphosphate) receptor blocker cangrelor administered shortly before reperfusion in rabbits undergoing 30-minute regional ischemia/3-hour reperfusion reduced infarction from 38% of ischemic zone in control hearts to only 19%. Protection was dose dependent and correlated with the degree of inhibition of platelet aggregation. Protection was comparable to that seen with ischemic postconditioning (IPOC). Cangrelor protection, but not its inhibition of platelet aggregation, was abolished by the same signaling inhibitors that block protection from IPOC suggesting protection resulted from protective signaling rather than anticoagulation. As with IPOC, protection was lost when cangrelor administration was delayed until 10 minutes after reperfusion and no added protection was seen when cangrelor and IPOC were combined. These findings suggest both IPOC and cangrelor may protect by the same mechanism. No protection was seen when cangrelor was used in crystalloid-perfused isolated hearts indicating some component in whole blood is required for protection. Clopidogrel had a very slow onset of action requiring 2 days of treatment before platelets were inhibited, and only then the hearts were protected. Signaling inhibitors given just prior to reperfusion blocked clopidogrel's protection. Neither aspirin nor heparin was protective. CONCLUSIONS: Clopidogrel and cangrelor protected rabbit hearts against infarction. The mechanism appears to involve signal transduction during reperfusion rather than inhibition of intravascular coagulation. We hypothesize that both drugs protect by activating IPOC's protective signaling to prevent reperfusion injury. If true, patients receiving P2Y12 inhibitors before percutaneous intervention may already be postconditioned thus explaining failure of recent clinical trials of postconditioning drugs.

Influence of omeprazole and famotidine on the antiplatelet effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes: a prospective, randomized, multicenter study.

BACKGROUND: It remains unclear whether concomitant use of omeprazole attenuates platelet function as compared with that of famotidine in patients with acute coronary syndromes (ACS) who receive clopidogrel. METHODS AND RESULTS: In this prospective study, 130 ACS patients treated with aspirin and clopidogrel who underwent stent implantation were randomly assigned to receive a Japanese standard dose of omeprazole 10mg daily or famotidine 20mg daily for at least 4 weeks. Between 14 and 28 days after enrollment, there was no significant difference in the platelet reactivity index (PRI) measured with vasodilator-stimulated phosphoprotein phosphorylation assay between the omeprazole group (n=65) and famotidine group (n=65) (55±17% vs. 51±19%; P=0.26). The cumulative rate of adverse cardiovascular events at 12 months was similar in the groups (13% vs. 17%; P=0.81). The PRI was similar (54.9±17.9% vs. 54.0±17.8%; P=0.83) in the omeprazole group (n=33) and the famotidine group (n=39) among patients with ST-elevation myocardial infarction (STEMI). However, there was a trend toward a higher PRI (55.2±15.9% vs. 46.4±19.4%; P=0.06) in the omeprazole group (n=32) as compared with the famotidine group (n=26) among patients without persistent ST-segment elevation ACS. CONCLUSIONS: As compared with famotidine, concomitant use of low-dose omeprazole does not significantly attenuate the antiplatelet effects of clopidogrel in patients with ACS, especially in those with STEMI.

Pharmacodynamic effects of cangrelor and clopidogrel: the platelet function substudy from the cangrelor versus standard therapy to achieve optimal management of platelet inhibition (CHAMPION) trials.

Cangrelor is an intravenous antagonist of the P2Y(12) receptor characterized by rapid, potent, predictable, and reversible platelet inhibition. However, cangrelor was not superior to clopidogrel in reducing the incidence of ischemic events in the cangrelor versus standard therapy to achieve optimal management of platelet inhibition (CHAMPION) trials. A prospectively designed platelet function substudy was performed in a selected cohort of patients to provide insight into the pharmacodynamic effects of cangrelor, particularly in regard to whether cangrelor therapy may interfere with the inhibitory effects of clopidogrel. This pre-defined substudy was conducted in a subset of patients from the CHAMPION-PCI trial (n = 230) comparing cangrelor with 600 mg of clopidogrel administered before percutaneous coronary intervention (PCI) and from the CHAMPION-PLATFORM trial (n = 4) comparing cangrelor at the time of PCI and 600 mg clopidogrel given after the PCI. Pharmacodynamic measures included P2Y12 reaction units (PRU) assessed by VerifyNow P2Y12 testing (primary endpoint marker), platelet aggregation by light transmittance aggregometry following 5 and 20 µmol/L adenosine diphosphate stimuli, and markers of platelet activation determined by flow cytometry. The primary endpoint was the percentage of patients who achieved <20 % change in PRU between baseline and >10 h after PCI. The main trial was stopped early limiting enrollment in the platelet substudy. A total of 167 patients had valid pharmacodynamic assessments for the primary endpoint. The percent of individuals achieving <20 % change in PRU between baseline and >10 h after PCI was higher with cangrelor + clopidogrel (32/84, 38.1 %) compared with placebo + clopidogrel (21/83, 25.3 %), but this was not statistically significant (difference:12.79 %, 95 % CI: -1.18 %, 26.77 %;p = 0.076). All pharmacodynamic markers as well as the prevalence of patients with high on-treatment platelet reactivity were significantly lower in patients treated with cangrelor. A rapid platelet inhibitory effect was achieved during cangrelor infusion and a rapid offset of action after treatment discontinuation. This CHAMPION platelet function substudy represents the largest pharmacodynamic experience with cangrelor, demonstrating its potent P2Y(12) receptor inhibitory effects, and rapid onset/offset of action. Although there was no significant pharmacodynamic interaction when transitioning to clopidogrel therapy, further studies are warranted given that enrollment in this study was limited due to premature interruption of the main trial.

A meta-analysis of impact of proton pump inhibitors on antiplatelet effect of clopidogrel.

Previous mechanistic studies have suggested a possible interaction between proton pump inhibitor (PPIs) and clopidogrel. However, the results of clinical trials about the effects of PPIs on safety and efficacy of clopidogrel are controversial. The study sought to estimate the impact of PPIs on antiplatelet effect of clopidogrel. The study performed a meta-analysis of comparative concomitant use of clopidogrel with PPIs versus clopidogrel without PPIs studies published or presented to October 2010. Cardiovascular death, readmission for myocardial infarction/readmission for acute coronary syndrome, and nonfatal stroke were set as clinical endpoints. In randomized control trials (RCTs), the clinical endpoints risk ratio for clopidogrel with PPIs versus clopidogrel without PPIs was 1.20 (P= 0.34) in the random-effects model and 1.03 (P= 0.63) in the fixed-effects model. In observational studies, the risk ratio for the clinical endpoints for clopidogrel with PPI versus clopidogrel without PPI was 1.40 (P < 0.001) in the random-effects model and 1.49 (P < 0.001) in the fixed-effects model. Different assay methods showed that coadministration of clopidogrel with PPIs was associated with attenuation of clopidogrel's antiplatelet effect in vitro. This meta-analysis indicated an obvious discrepancy between RCTs and observational studies with respect to the interaction between PPIs and clopidogrel.

Inhibitory interaction between calcium channel blocker and clopidogrel. -Efficacy of cilostazol to overcome it-.

BACKGROUND: The clinical effect of, and additive measures to overcome the possible inhibitory calcium channel blocker (CCB)-clopidogrel interaction in Asian patients undergoing percutaneous coronary intervention is unknown. METHODS AND RESULTS: A total of 900 Korean patients enrolled for the multicenter, prospective, randomized Influence of CILostazol-based triple antiplatelet therapy ON ischemic complication after drug-eluting stenT implantation (CILON-T) trial were divided into 4 groups depending on CCB prescription and type of anti-platelet therapy (dual [DAT] vs. triple [TAT; addition of cilostazol to DAT]) in a 2 × 2 factorial manner. The primary endpoint was a composite of cardiac death, non-fatal myocardial infarction and ischemic stroke at 6 months after PCI. On-treatment platelet reactivity (OPR) was assessed on VerifyNow P2Y12 assay. Concomitant CCB use increased OPR in the DAT group (mean ± SEM: 251.2 ± 7.6 vs. 225.6 ± 5.1; P=0.008), but not in the TAT group (214.5±9.1 vs. 203.4 ± 5.6; P=0.294). Primary endpoint increased by use of CCB in patients with DAT (4.9% vs. 0.9%, P=0.016), but not in those with TAT (0% vs. 1.8%, P=0.346). Addition of cilostazol to DAT reduced OPR and clinical events in patients taking CCB (P=0.007 for P2Y12 reaction units; P=0.027 for thrombotic events). CCB without concomitant cilostazol use was a significant predictor of total thrombotic events. CONCLUSIONS: Concomitant use of CCB may weaken the anti-platelet effect of clopidogrel and increase subsequent thrombotic events in Asian subjects. This hazardous CCB-clopidogrel interaction may be overcome by addition of cilostazol.

Oral anticoagulation with coumarin derivatives and antiplatelet effects of clopidogrel.

AIMS: A relevant proportion of patients receiving aspirin and clopidogrel after percutaneous coronary intervention (PCI) also require oral anticoagulation with a coumarin derivative such as phenprocoumon. Both clopidogrel and phenprocoumon are metabolized by the hepatic cytochrome P450 system and a drug-drug interaction may exist at this level. The aim of this study was to investigate the impact of phenprocoumon on the antiplatelet effects of clopidogrel in patients with coronary artery disease. METHODS AND RESULTS: Patients (n = 1223) eligible for this study were under dual maintenance antiplatelet treatment with aspirin and clopidogrel. Adenosine diphosphate-induced platelet aggregation (in AU*min) was measured with multiple electrode platelet aggregometry on a Multiplate analyzer (Dynabyte, Munich, Germany). From the entire study population, 124 (10.1%) patients were under concomitant phenprocoumon treatment at the time point of platelet function testing. Platelet aggregation (median [interquartile range]) was significantly higher in patients with (n = 124) concomitant phenprocoumon treatment compared with patients without (n = 1099) phenprocoumon treatment (308 [190-493] AU*min vs. 224 [145-390] AU*min; P = 0.0001, adjusted P = 0.002). CONCLUSION: Phenprocoumon significantly attenuates the antiplatelet effects of clopidogrel. The impact of this interaction on the risk of thrombotic and bleeding events after PCI requires further investigations.

Emergency reversal of antiplatelet agents in patients presenting with an intracranial hemorrhage: a clinical review.

OBJECTIVE: Prehospital use of antiplatelet agents has been associated with an increased risk for intracranial hemorrhage (ICH) as well as a secondary increase in ICH volume after the initial hemorrhage. Strategies to reestablish platelet aggregation are used in clinical practice, but without any established guidelines or recommendations. This article serves to evaluate the literature regarding "reversal" of antiplatelet agents in neurosurgical populations. METHODS: PubMed and MEDLINE databases were searched for publications from 1966 to 2009 relating to intracranial hemorrhage and antiplatelet agents. The reference sections of recent articles, guidelines, and reviews were reviewed and pertinent articles identified. Studies were classified by two broad subsets: those describing intracranial hemorrhage relatable to a traumatic mechanism and those with a spontaneous intracranial hemorrhage. Two independent auditors recorded and analyzed study design and the reported outcome measures. RESULTS: For the spontaneous intracranial hemorrhage group, nine reports assessing antiplatelet effects on various outcome measures were identified. Eleven studies evaluating the use of prehospital antiplatelets before a traumatic intracranial hemorrhage were examined. CONCLUSION: The data assessing the relationship between outcome and prehospital antiplatelet agents in the setting of ICH is conflicting in both the trauma and the stroke literature. Only one retrospective review specifically addressed outcomes after attempted reversal with platelet transfusion. Further study is needed to determine whether platelet transfusion ameliorates hematoma enlargement and/or improves outcome in the setting of acute ICH.

Influence of omeprazole on the antiplatelet action of clopidogrel associated with aspirin: the randomized, double-blind OCLA (Omeprazole CLopidogrel Aspirin) study.

OBJECTIVES: This trial sought to assess the influence of omeprazole on clopidogrel efficacy. BACKGROUND: Clopidogrel has proved its benefit in the treatment of atherothrombotic diseases. In a previous observational study, we found clopidogrel activity on platelets, tested by vasodilator-stimulated phosphoprotein (VASP) phosphorylation, to be diminished in patients receiving proton pump inhibitor (PPI) treatment. METHODS: In this double-blind placebo-controlled trial, all consecutive patients undergoing coronary artery stent implantation received aspirin (75 mg/day) and clopidogrel (loading dose, followed by 75 mg/day) and were randomized to receive either associated omeprazole (20 mg/day) or placebo for 7 days. Clopidogrel effect was tested on days 1 and 7 in both groups by measuring platelet phosphorylated-VASP expressed as a platelet reactivity index (PRI). Our main end point compared PRI value at the 7-day treatment period in the 2 groups. RESULTS: Data for 124 patients were analyzed. On day 1, mean PRI was 83.2% (standard deviation [SD] 5.6) and 83.9% (SD 4.6), respectively, in the placebo and omeprazole groups (p = NS), and on day 7, 39.8% (SD 15.4) and 51.4% (SD 16.4), respectively (p < 0.0001). RESULTS: Omeprazole significantly decreased clopidogrel inhibitory effect on platelet P2Y12 as assessed by VASP phosphorylation test. Aspirin-clopidogrel antiplatelet dual therapy is widely prescribed worldwide, with PPIs frequently associated to prevent gastrointestinal bleeding. The clinical impact of these results remains uncertain but merits further investigation.

Polimorfismo del receptor P2Y12 de ADP plaquetario en pacientes con enfermedad coronaria y variabilidad en agregación plaquetaria: resultados preliminares / Platelet P2Y12 ADP receptor polymorphism in patients with coronary artery disease and varying degrees of platelet

Introducción: Uno de los mecanismos que explicaría la variabilidad en la agregación plaquetaria observada en la respuesta inhibitoria a clopidogrel es el polimorfismo del receptor P2Y12 de ADP plaquetario, específicamente, el haplotipo H2 y H1/H2. No se ha descrito la prevalencia del haplotipo H1/H2 del receptor plaquetario en pacientes con enfermedad coronaria. Objetivo: Evaluar la presencia del haplotipo H1/H2 del receptor P2Y12 en un grupo de pacientes con enfermedad coronaria Métodos: Estudio prospectivo en pacientes sometidos en forma electiva a angioplastía coronaria con stent. Todos recibieron aspirina y una dosis de carga de clopidogrel de 600 mg, seguido de dosis de mantención de 75 mg/día. En todos se midió agregación plaquetaria previo a la dosis de carga de clopidogrel (día 0) y luego entre 6º y 8º día det ratamiento. La agregación plaquetaria se expresó de acuerdo al porcentaje de cambio respecto del valor basal. Se utilizó test t student pareado para evaluar el porcentaje de cambio. Se amplificó el segmento de interés del ADN de los pacientes mediante PCR y se determinó la presencia del haplotipo H1/H2 usando enzimas de restricción. Resultados: Se enrolaron 40 pacientes, 34 (85 por ciento) hombres, edad promedio 61 +/-12 años. El promedio de agregación plaquetaria, previo y durante terapia con clopidogrel fue de 64 +/-10 por ciento y 41 +/-14 por ciento, respectivamente (p<0.0001) frente a ADP 8 µM. La respuesta de agregación a clopidogrel presentó una distribución normal según el test de Kolmogorov-Smirnov (p=0.58). Los pacientes se estratificaron de acuerdo al porcentaje de cambio en cuartiles y el cuartil de menor cambio representó una diferencia menor a 10 por ciento. De estos pacientes, 30 por ciento (3 pacientes) tenían el haplotipo H1/H2. En total, se demostró la presencia del haplotipo H1/H2 en 4 (10 por ciento) pacientes...

Background: One factor influencing the variability in the anti aggregation effect of clopidogrel is the polymorphism of the platelet P2Y12 ADP receptor, specifically the H2 and H1/H2 haplotypes. The prevalence of the H1/H2 haplotype has not been described in patients with coronary artery disease. Aim: To evaluate the presence of H1/H2 haplotype of P2Y12 receptor in patients with coronary artery disease. Methods: A prospective study was conducted in patients undergoing elective PTCA with stenting. All received aspirin followed by a loading dose of clopidogrel 600 mg and a maintenance dose of 75 mg daily. Platelet aggregation was measured prior to the loading clopidogrel dose and at 6 and 8 days post treatment. Platelet aggregation was indicated as the percent change over the basal value. The Student’s t test was used to evaluate the response. The DNA segment involved was amplified by PCR and the H1/H2 haplotype was determined using restriction enzymes. Results: Fourty patients (85 percent males) with mean age 61 years (SD 12) were studied. Mean platelet aggregation changed from a basal value of 64+/-10 to a post clopidogrel value of 41 +/-14 percent (p<0.0001) with an ADP level of 8 µM. The platelet aggregation response was normal according to Kolmogorov-Smirnov. The lowest quartile of platelet aggregation showed a <10 percent change. Three patients in this group (30 percent) had the H1/H2 haplotype. The overall incidence of this haplotype was 10 percent (4 patients). Conclusion: Clopidogrel does not induce a significant decreased platelet aggregation in 25 percent of patients subjected to coronary angioplasty. A third of this patients exhibited the H1/H2 haplotype for the P2Y12 receptor. This group of patients might be at increased risk from subsequent cardiovascular events.

Can N-acetylcysteine reverse the antiplatelet effects of clopidogrel? An in vivo and vitro study.

BACKGROUND: The active metabolite of clopidogrel binds the P2Y12 ADP receptor on the platelet surface via a disulfide bond. N-Acetylcysteine (NAC) is able to reduce disulfide bonds. We postulated that NAC might reverse clopidogrel's effect on platelets. METHODS: Two groups of patients were investigated. Group 1 included 11 patients with stable coronary disease who, after discontinuation of aspirin, received 14 days of clopidogrel, 75 mg/day. Bleeding time and whole-blood platelet aggregometry (with 5 micromol/L ADP) were compared before and after the 14 days. Patients were then treated with 6 g of NAC orally, followed by repeat measurement of bleeding time and aggregometry. In group 2, 14 patients were treated with clopidogrel (300 mg) and aspirin before a percutaneous coronary intervention. Blood was drawn 22 +/- 3 hours later and divided into 2 samples. One was sent immediately for platelet-rich plasma aggregometry (using 5 and 2 micromol/L ADP, collagen, and arachidonic acid as agonists), thromboelastography, and aggregometry using the Plateletworks assay (Helena Laboratories, Beaumont, Tex). The other sample was treated with NAC (500 mg/L), after which these same platelet function tests were performed. RESULTS: In group 1, NAC therapy did not significantly change the bleeding time or results of aggregometry. In group 2, neither aggregometry nor the Plateletworks assay suggested reversal of inhibition by NAC. CONCLUSIONS: These studies reveal that a large dose of NAC does not reduce inhibition of platelet aggregation by clopidogrel in vitro or in vivo.

Aprotinin decreases postoperative bleeding and number of transfusions in patients on clopidogrel undergoing coronary artery bypass graft surgery: a double-blind, placebo-controlled, randomized clinical trial.

BACKGROUND: Clopidogrel, an irreversible platelet inhibitor, is used to treat patients with unstable angina. These patients often present for coronary artery bypass graft surgery (CABG) and are at increased risk for perioperative bleeding. The current investigation evaluates the impact of aprotinin on bleeding and transfusion requirements in clopidogrel-treated patients undergoing CABG. METHODS AND RESULTS: Seventy-five consecutive patients with unstable angina, administered clopidogrel <5 days before CABG, were randomized. Using a double-blind design, patients received full-dose aprotinin (n =37) or saline (n =38). Elapsed times between the last dose of clopidogrel and start of the operation were similar between the 2 groups [aprotinin, 58+/-28 hour (mean+/- SD); control, 54+/-27 hour; P=0.86], as were age (aprotinin, 66.4+/-10 years; control, 68.3+/-10 years; P=0.51), number of distal anastomoses (aprotinin, 3.6+/-1.0; control, 3.7+/-1.0; P=0.79), operative times (aprotinin, 192+/-48 minutes; control, 200+/-53 minutes; P=0.55), and lowest intraoperative hemoglobin level (aprotinin, 87+/-14 g/L; control, 88+/-14 g/L; P=0.60). Postoperative bleeding was 760+/-350 mL in aprotinin-treated patients versus 1200+/-570 mL (P<0.001) in control. During the hospital stay, patients in the aprotinin group received 1.2+/-1.5 and 0.1+/-0.4 U of erythrocytes and platelets, respectively, versus 2.8+/-3.2 (P=0.02) and 0.9+/-1.4 (P=0.002) units in the control. In the aprotinin group, 53% of patients received transfusions, whereas 79% of controls were exposed to blood products (P=0.02). CONCLUSIONS: Intraoperative aprotinin decreases postoperative bleeding and the number of transfusions in patients undergoing CABG and treated with clopidogrel <5 days before surgery.

Achieved platelet aggregation inhibition after different antiplatelet regimens during percutaneous coronary intervention for ST-segment elevation myocardial infarction.

OBJECTIVES: To evaluate the extent of platelet aggregation inhibition in patients with ST-segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI), treated with different antiplatelet agents and dosages. BACKGROUND: The extent of platelet aggregation inhibition is an independent predictor of major cardiac events after elective PCI. In STEMI patients undergoing PCI, routine dose of antiplatelet agents may be associated with less effective platelet aggregation inhibition. METHODS: Patients were treated with clopidogrel before angiography and randomized to abciximab, tirofiban, high-dose tirofiban, or no glycoprotein (GP) IIb/IIIa inhibitor; GP IIb/IIIa inhibitor bolus, followed by maintenance infusion, was administered after angiography, but before PCI. Platelet aggregation inhibition was assessed before angiography, immediately after PCI, and 1 and 6 h afterwards. RESULTS: The total study population consisted of 112 patients. Platelet aggregation inhibition was variable for individuals and suboptimal for all agents, particularly in the periprocedural period. Only with high-dose tirofiban, mean periprocedural platelet aggregation inhibition exceeded 80%. Angiographic parameters after PCI were not different between the groups. No relationship was found between the level of platelet aggregation and parameters of PCI success (Thrombolysis In Myocardial Infarction frame count and myocardial blush grade), after combining the data from all four groups studied. CONCLUSIONS: Platelet aggregation inhibition in STEMI patients undergoing PCI, treated with antiplatelet agents, is variable and suboptimal for all agents and dosages studied. Only with high-dose tirofiban, mean periprocedural platelet aggregation inhibition exceeded 80%. However, no relationship of platelet aggregation inhibition and angiographic outcome was found in this patient cohort.

Atorvastatin does not affect the antiplatelet potency of clopidogrel when it is administered concomitantly for 5 weeks in patients with acute coronary syndromes.

BACKGROUND: The antiplatelet effect of clopidogrel may be attenuated by short-term coadministration of lipophilic statins. We investigated whether the coadministration of atorvastatin for 5 weeks in patients with acute coronary syndromes (ACS) could affect the antiplatelet potency of clopidogrel. METHODS AND RESULTS: Forty-five hypercholesterolemic patients with the first episode of an ACS were included in the study. Patients were randomized to receive daily either 10 mg of atorvastatin (n=21) or 40 mg of pravastatin (n=24). Thirty patients who underwent percutaneous coronary intervention (PCI) received a loading dose of 375 mg of clopidogrel, followed by 75 mg/d for at least 3 months. In the remaining 15 patients who refused to undergo PCI, clopidogrel therapy was not administered. Eight normolipidemic patients with the first episode of an ACS were also included and received only clopidogrel. The serum levels of soluble CD40L and the adenosine 5'-diphosphate- or thrombin receptor activating peptide-14-induced platelet aggregation, as well as P-selectin and CD40L surface expression, were studied at baseline (within 30 minutes after admission) and 5 weeks later. Neither atorvastatin nor pravastatin significantly influenced the clopidogrel-induced inhibition of platelet activation, nor did clopidogrel influence the therapeutic efficacy of atorvastatin. CONCLUSIONS: Atorvastatin does not affect the antiplatelet potency of clopidogrel when coadministered for 5 weeks in ACS patients.