Increased Platelet Inhibition Research Articles

Comparative effects of fentanyl versus morphine on platelet inhibition induced by ticagrelor in patients with ST-segment elevation myocardial infarction: Full results of the PERSEUS randomized trial.

BackgroundMorphine reduces absorption and delays action onset of potent oral P2Y12 receptor inhibitors in patients with ST-segment elevation myocardial infarction (STEMI). We sought to determine the differential effects of fentanyl compared to morphine on the pharmacodynamics and pharmacokinetics of ticagrelor in STEMI patients undergoing primary percutaneous coronary intervention (PCI).MethodsPERSEUS (NCT02531165) was a prospective, single-center, open-label, randomized controlled study. Patients with STEMI who required analgesia were randomly assigned in a 1:1 ratio to treatment with intravenous fentanyl or morphine after ticagrelor loading dose (LD) administration. The primary endpoint was platelet reactivity at 2 hours after ticagrelor LD assessed by P2Y12 reaction units (PRU).ResultsThe study was prematurely stopped in June 2017 after enrolment of 38 out of 56 planned patients. PRU at 2 hours following ticagrelor LD was 173.3 ± 89.7 in the fentanyl group and 210.3 ± 76.4 in the morphine group (p = 0.179). At 4 hours, PRU was significantly lower among patients treated with fentanyl as compared to those treated with morphine (90.1 ± 97.4 vs. 168.0 ± 72.2; p = 0.011). Maximal plasma concentrations of ticagrelor and its active metabolite AR-C124910XX tended to be delayed and numerically lower among patients treated with morphine compared to fentanyl. Total exposures to ticagrelor and AR-C124910XX within 6 hours after ticagrelor LD were numerically greater among patients treated with fentanyl compared to those treated with morphine.ConclusionsIn patients with STEMI undergoing primary PCI, fentanyl did not improve platelet inhibition at 2 hours after ticagrelor pre-treatment compared with morphine. Fentanyl may, however, accelerate ticagrelor absorption and increase platelet inhibition at 4 hours compared to morphine.

Clinical efficacy and safety of tirofiban combined with conventional dual antiplatelet therapy in ACS patients undergoing PCI

Challenges remain for clinicians over balancing the efficacy of active antithrombotic therapy and simultaneous bleeding reduction in patients. The clinical data of 347 patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI) were retrospectively analyzed. On the basis of the given tirofiban, the patients were assigned into three different dose groups: high dose group (group H), medium dose group (group M), and low dose group (group L). The tirofiban efficacy was evaluated in terms of major adverse cardiovascular event (MACE) parameters and lab endpoints, including platelet count and function. The tirofiban safety was assessed by the occurrence of bleeding events. The patients were followed up for 1 month after the PCI. No significant difference in MACE events was evident among these groups (p > 0.05). Groups H and M reported an obvious reduction in platelet count (p < 0.05 for both) and an increased platelet inhibition rate (p < 0.05 for both). Group H showed a higher rate of total bleeding events than the other groups (Group H vs. Group M: 34.4% vs. 16.5%; Group H vs. Group L: 34.4% vs. 10.3%; p < 0.05 for both). A proper administration of a low dose of tirofiban may be a superior alternative in treating ACS patients, which can produce a similar favorable clinical outcome and a decrease in bleeding complication.

Study on Novel Nanoparticle Slow-Release Drugs for Moyamoya Disease.

Spontaneous basilar artery occlusive disease is a disease characterized by thickening of the intima of the bilateral internal carotid artery and the anterior and middle cerebral arteries, gradually narrowing the arterial diameter, and compensatory dilatation of the perforating artery at the base of the brain. Aspirin (acetylsalicylic acid), as a classic non-steroidal anti-inflammatory drug, has been proven to have antiplatelet, anti-inflammatory, and immune-regulating effects. But how to achieve long-term sustained release of aspirin and achieve anti-platelet aggregation remains to be studied. This study intends to build a microsphere sustained-release system to achieve long-term stable and slow release of aspirin drug, thereby achieving a more ideal anti-platelet aggregation effect. The therapeutic effects of three groups of nanoparticle sustained-release drug regimens on platelet aggregation were compared. The results showed that the platelet inhibition rate and NIHSS scores before treatment were compared between the three groups; compared with the other groups, the PLGA group had higher AA and ADP pathway-induced platelet inhibition rates after treatment and lower plasma Lp-PLA2 and NIHSS scores. This shows that aspirin nanoparticle slow-release drugs can effectively increase platelet inhibition rate and improve the antiplatelet ability of patients with spontaneous basilar artery occlusive disease, which is beneficial to promoting prognosis recovery.

Combination of Panax notoginseng saponins and aspirin potentiates platelet inhibition with alleviated gastric injury via modulating arachidonic acid metabolism

High platelet reactivity and gastric mucosal injury after aspirin (ASA) treatment are associated with poor compliance and an increased risk of cardiovascular events. Panax notoginseng saponins (PNS) have been widely used for the treatment of coronary heart disease (CHD) in addition to antiplatelet drugs in China; however, the joint effect and possible mechanism of PNS in addition to ASA on platelet activation and gastric injury remain unclear. This study was designed to investigate the combinational effects of PNS with ASA, and to explore the underlying mechanism via arachidonic acid (AA) metabolism pathway using lipidomic analysis. In a randomized, assessor-blinded trial, 42 patients with stable coronary heart disease (SCHD) and chronic gastritis were randomly assigned to receive ASA (n = 21) or PNS + ASA (n = 21) for 2 months. Compared with ASA alone, PNS + ASA further inhibited CD62p expression, GPIIb-IIIa activation and platelet aggregation and led to increased platelet inhibition rate. PNS + ASA suppressed the activity of platelet cyclooxygenase (COX)-1, and decreased the production of TXB2, PGD2, PGE2, 11-HETE, the downstream oxylipids of AA/COX-1 pathway in platelets, compared with ASA alone. The severity of dyspepsia assessment (SODA) results showed that patients in PNS + ASA group exhibited relieved dyspeptic symptoms as compared with those in ASA group, which might be associated with enhanced secretion of gastrin and motilin. In vivo study of myocardial infarction rats demonstrated that PNS attenuated ASA-induced gastric mucosal injury, which was related to markedly boosted gastric level of 6,15-diketo-13,14-dihydro-prostaglandin (PG)F1α, 13,14-dihydro-15-keto-PGE2 and PGE2 from AA/PG pathway in response to PNS + ASA compared with ASA alone. In summary, our study demonstrated that the combination of PNS and ASA potentiated the antiplatelet effect of ASA via AA/COX-1/TXB2 pathway in platelets, and mitigated ASA-related gastric injury via AA/PG pathway in gastric mucosa.

Platelet Inhibition With IV Glycoprotein IIb/IIIa Inhibitor to Prevent Thrombosis in Pediatric Patients Undergoing Aortopulmonary Shunting.

Shunt thrombosis, a potential complication of aortopulmonary shunting, is associated with high mortality. Commonly used oral antiplatelet drugs such as aspirin demonstrate variable absorption and inconsistent antiplatelet effect in critically ill patients early after surgery. IV glycoprotein IIb/IIIa inhibitors are antiplatelet agents with rapid and reproducible effect that may be beneficial as a bridge to oral therapy. Retrospective review of pediatric patients undergoing treatment with IV tirofiban. Discarded blood samples were used to determine pharmacokinetic parameters. Pediatric cardiac ICU at a single institution. Fifty-two pediatric patients (< 18 yr) undergoing surgical aortopulmonary shunt procedure who received tirofiban infusion as a bridge to oral aspirin. None. Primary outcome measures were shunt thrombosis and bleeding events, whereas secondary outcomes included measurement of platelet inhibition by thromboelastography with platelet mapping and pharmacokinetic analysis (performed in a subset of 15 patients). Shunt thrombosis occurred in two of 52 patients (3.9%) after prophylaxis treatment with tirofiban; both thrombosis events occurred after discontinuation of the drug. One patient (1.9%) experienced bleeding complication during the infusion. A tirofiban bolus of 10 µg/kg and infusion of 0.15 µg/kg/min resulted in significantly increased platelet inhibition via adenosine diphosphate pathway (median 66% [43-96] pre-tirofiban compared with 97% [92-99%] at 2 hr; p < 0.05). Half-life of tirofiban in plasma was 142 ± 1.5 minutes, and the average steady-state concentration was 112 ± 62 ng/mL. Age and serum creatinine were significant covariates associated with systemic clearance. Dosing simulations were generated based upon one compartment model. IV glycoprotein IIb/IIIa inhibitor as a bridge to oral antiplatelet therapy is safe in pediatric patients after aortopulmonary shunting. Dosing considerations should include both age and renal function. Randomized trials are warranted to establish efficacy compared with current anticoagulation practices.

Increased platelet inhibition after switching from prasugrel to low-dose ticagrelor in Japanese patients with prior myocardial infarction

BackgroundTicagrelor and prasugrel are novel and potent P2Y12 inhibitors. Ticagrelor 90mg or 60mg twice daily is known to reduce ischemic events but be associated with an increased risk of bleeding in patients with prior myocardial infarction in Western countries. Although ticagrelor 90mg twice daily was tested in a randomized clinical trial in East Asia, the clinical significance of ticagrelor 60mg twice daily is unclear. This study aimed to evaluate platelet inhibition of low-dose ticagrelor compared to prasugrel in Japanese patients. MethodsA total of 33 patients with prior myocardial infarction (>3 months) who received aspirin and prasugrel 3.75mg once daily were enrolled. Prasugrel was switched to ticagrelor 60mg twice daily. Platelet inhibition was assessed by VerifyNow assay (Accumetrics, San Diego, CA, USA) at baseline and 14 days after switching to ticagrelor. P2Y12 reaction unit (PRU) ≤95 was defined as low on-treatment platelet reactivity (LPR) and PRU≥262 as high on-treatment platelet reactivity. ResultsTicagrelor treatment resulted in significantly lower PRU [10 (7–39) vs. 143 (102–201), p<0.001] and a higher rate of LPR (94% vs. 24%, p<0.001), compared to prasugrel treatment. Neither patients treated with ticagrelor nor prasugrel had high on-treatment platelet reactivity. During 2-week follow-up on ticagrelor therapy, no major bleeding occurred in both groups, while four minor bleeding events were observed. ConclusionIn Japanese patients with prior myocardial infarction, significantly lower PRU and a higher rate of LPR were observed on ticagrelor 60mg twice daily compared to prasugrel 3.75mg once daily.

The effect of smoking on residual platelet reactivity to clopidogrel: a systematic review and meta-analysis

Cigarette smoking is an important cardiovascular risk factor, causing morbidity and mortality. There are many original studies on the impact of smoking, but its influence on platelet ADP-P2Y12 receptor inhibitors lack consistency. Thus, we conducted a systematic review and meta-analysis of already existing data/studies to further explore this issue. PubMed, Web of science, EMBASE, Clinical Trials, and the Cochrane Library were searched from inception to March 2018. Studies investigating the residual platelet reactivity categorized by smoking status and patients treated with platelet ADP-P2Y12 receptor inhibitors qualified the inclusion criteria. The primary outcome was P2Y12 reaction unit (PRU) value measured by VerifyNow P2Y12 assay, compared with different smoking status in ADP-P2Y12 receptor inhibitors treatment groups. Secondary outcome was post-treatment with 5 μmol/L ADP-inhibition of platelet aggregation (ADP-IPA) measured by light transmittance aggregometry (LTA). Of the 4954 citations retrieved, 12 studies involving 16 296 patients with acute coronary syndrome and/or stent deployment using platelet ADP-P2Y12 receptor inhibitors were included for meta-analysis. Pooled analysis revealed that PRU values of current smokers were 25.70 lower than nonsmokers (95% CI −38.81 to −12.60, p = 0.0001), getting better effects of antiplatelet treatment. In the smoking extent subgroup analysis, patients smoking >10 cigarettes/day shown about 46.49 lower of PRU values than patients smoking <10 cigarettes/day (p < 0.00001). Racial subgroup analyses found that smokers had increased platelet inhibition in the Caucasian population. Further, pooled analysis of ADP-IPA values for 1658 patients from five studies showed a significantly lower residual platelet reactivity in current smokers compared to that in nonsmokers (MD = −4.19; 95% CI −6.55 to −1.83; p = 0.0005). This systematic review and meta-analysis suggested that smokers have increased platelet inhibition and lower aggregation in response to clopidogrel than nonsmokers. These residual platelet reactivity observations may help to explain differential clinical outcomes in smokers vs. nonsmokers in large scale clinical trials.

Efficacy and safety of double-dosage Clopidogrel in elderly patients with Clopidogrel resistance after percutaneous coronary intervention

Objective To evaluate the efficacy and safety of double-dosage Clopidogrel in elderly patients with Clopidogrel resistance after percutaneous coronary intervention(PCI). Methods The randomized control trials design was used in this study.108 senile ACS patients with Clopidogrel resistance(platelet inhibition rate<30%)were randomized into control group(Clopidogrel 75 mg/d, n=54)and experimental group(Clopidogrel 150 mg/d, n=54). Blood platelet inhibition rate of ADP, major adverse cardiovascular events and main side effects were observed before and 7 d, 30 d, 90 d and 180 d after intervention. Results Compared with control group, the experimental group was associated with significantly increased platelet inhibition rate on 7 d(22.4±4.5)% vs.(37.6±4.5)%, 30 d(22.6±4.3)% vs.(38.8±4.7)%, 90 d(22.7±4.6)% vs.(38.5±4.5)%, and 180 d(23.7±4.3)% vs.(38.9±4.6)% after treatment(all P<0.05). Furthermore, the incidence of main adverse cardiovascular events was also significantly lower in the experimental group(3.7% vs.35.1%, χ2=15.133, P<0.001). Meanwhile, the incidence of bleeding and dyspnea were higher in experimental group, but there was no significant difference between the two groups. Conclusions Compared with general dosage, double-dosage of Clopidogrel offers better curative effect and good safety in elderly ACS patients with Clopidogrel resistance after PCI. Key words: Acute coronary syndrome; Angioplasty; Platelet aggregation inhibitors; Thrombelastography

TCT-182 One-year Outcomes With Prasugrel (Pre-)Treatment in Routine Practice: Early Results from the Dutch, Multicenter and Observational Rijnmond Collective Cardiology Research (CCR) Study

Increased platelet inhibition by prasugrel has been shown to result in reduced ischemic events along with greater bleeding hazards in patients with acute coronary syndromes (ACS) treated with percutaneous coronary intervention (PCI). Yet, there is limited experience with the use of prasugrel in

Efficacy of cilostazol on platelet reactivity and cardiovascular outcomes in patients undergoing percutaneous coronary intervention: insights from a meta-analysis of randomised trials

BackgroundCilostazol overcomes high on-treatment platelet reactivity (HTPR) and reduces adverse cardiovascular (CV) outcomes after percutaneous coronary intervention (PCI). However, the role for triple antiplatelet therapy (TAPT) with cilostazol in addition...

Water soluble polymer films for intravascular drug delivery of antithrombotic biomolecules

Over the past 10years, the number of percutaneous coronary intervention (PCI) procedures performed in the United States has increased by 33%; however, restenosis, which inhibits complete functional recovery of the vessel wall, remains a complication of this procedure. To traverse the complications associated with PCI, the investigation of therapeutic delivery has become an integral topic in modern research. One such therapeutic, a mimic of the proteoglycan decorin, termed DS-SILY, can mask exposed collagen and thereby effectively decrease platelet activation, has recently been developed by our lab. Drawing inspiration from coating technologies developed by the pharmaceutical industry, a fast-dissolving polymer film has been developed to deliver active therapeutic agents from a balloon catheter during PCI. This research investigates the release of DS-SILY from fast-dissolving polymer films composed of poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG). Thin, uniform polymer films were produced via spin coating technique. The dissolution speed of the polymer films was found to be dependent on the concentration of polymer solution, where at least 65% of the films were shown to dissolve into nanometer sized polymer fragments within 2min. DS-SILY, up to 6.26μg/cm2, was loaded into the films and functional release of the mimic was demonstrated by its successful binding to collagen upon release. Furthermore, DS-SILY released from films resulted in increased platelet inhibition. These results indicate that use of fast-dissolving polymer films allow for the successful release of biomolecules and further investigation of their use for localized drug delivery during PCI procedures is warranted.

Review of ticagrelor in the management of acute coronary syndromes

Introduction: Ticagrelor, an oral P2Y12 receptor antagonist used as part of dual antiplatelet therapy in the treatment of acute coronary syndromes (ACS), has many favorable characteristics when compared with the more frequently used P2Y12 receptor antagonist clopidogrel. Ticagrelor binds reversibly, with a rapid onset and offset of action, and produces high levels of platelet inhibition without variation secondary to genetic polymorphism. Ticagrelor produces increased platelet inhibition and an overall reduction in adverse cardiac events compared with clopidogrel. Clinically relevant side effects include an increase in non-CABG-related bleeding events as well as off-target adverse effects including ventricular pauses and dyspnea.Areas covered: This article details ticagrelor's pharmacokinetic and pharmacodynamic characteristics, development and chemical properties. The authors review relevant clinical trials looking at the efficiency and safety of ticagrelor focusing predominantly on the management of patients with ACS. Finally, the review article concludes with discussion of ticagrelor's current role and future integration into clinical practice.Expert opinion: Ticagrelor is a promising P2Y12 receptor antagonist with characteristics that offer advantages for patients beyond those currently demonstrated by other P2Y12 receptor antagonists. The challenge for prescribers is to identify those most likely to benefit from ticagrelor treatment while minimizing unnecessary bleeding events for ‘real-world' ACS patients.

Prasugrel and bivalirudin for primary angioplasty: Early results on stent thrombosis and bleeding

Optimal treatment of STEMI relies on early mechanical reperfusion with PPCI [1]. Successful revascularisation requires effective adjunctive pharmacology, ideally with agents that provide rapid and reliable anti-platelet and anti-thrombotic effects. A delicate balance exists between effective inhibition of thrombosis and treatment-related bleeding. Incomplete suppression of platelet and thrombin activity may result in stent thrombosis. Advances in anti-thrombotic pharmacology have facilitated a reduction in bleeding risk. The HORIZONS-AMI randomised controlled trial compared bivalirudin with heparin plus GPIIb/IIIa antagonists. In both groups aspirin and the P2Y12 inhibitor clopidogrel were administered. The trial demonstrated a reduced rate of net clinical events and major bleeding with bivalirudin over the previous gold standard treatment with unfractionated heparin and GPIIb/IIIa antagonists [2]. Additionally bivalirudin demonstrated a reduced 30 day mortality. Despite the overall superiority of bivalirudin, an excess of acute stent thromboses (with the majority of events occurring within 5 h of the PCI) was observed in the bivalirudin (2.6%) compared to the heparin+GPIIb/IIIa group (0.9%). Interestingly, the lack of pre-randomization heparin was one of the independent predictors of acute stent thrombosis [3]. Bivalirudin reversibly binds to thrombin, and has a half-life of 25 min. Upon cessation of the infusion, plasma levels rapidly fall to below that demonstrated to reduce ischemic events in PCI. In a highly prothrombotic setting such as STEMI, it may be important to assure peri-procedural thrombin inhibition with an extended infusion. Variabilityof response to clopidogrel andconcerns regardingspeedof onset of ADP-receptor inhibition has led to the adoption of newer generation P2Y12 inhibitors with faster onset of action, greater consistency of effect and increased platelet inhibition. Prasugrel, an irreversible P2Y12-receptor inhibitor demonstrates improved clinical outcomes compared to clopidogrel [4–6]. It has been speculated that combining prasugrel with bivalirudin may negate the risk of early stent thrombosis observed in HORIZONS-AMI through more rapid and consistent platelet inhibition. However, the trial testing this hypothesis (BRAVE-4 trial, ClinTrial.gov NCT00976092) will not publish results before 2013.

The Effect of St John's Wort on the Pharmacodynamic Response of Clopidogrel in Hyporesponsive Volunteers and Patients: Increased Platelet Inhibition by Enhancement of CYP3A4 Metabolic Activity

Clopidogrel is metabolically activated by cytochrome P450 (CYP) isoenzymes. We evaluated whether St. John's wort (SJW), a CYP2C19 and CYP3A4 inducer, enhances the pharmacodynamic response of clopidogrel. Volunteers (n = 45) were screened for clopidogrel hyporesponsiveness after a 300-mg load. After a 7-day washout, hyporesponders (n = 10) received 14 days of SJW (300 mg 3 times a day) followed by a second 300-mg clopidogrel. Platelet aggregation was measured at 0, 2, 4, and 6 hours postloading; hepatic CYP3A4 activity was simultaneously determined at 0 and 4 hours by the erythromycin breath test. A prospective, randomized, double-blind pilot study was conducted in postcoronary stent patients (n = 85) on clopidogrel 75 mg/d screened for clopidogrel hyporesponsiveness. Hyporesponders (n = 20) were randomized to SJW (n = 10) or placebo (n = 10); platelet aggregation was measured before and after 14 days of therapy. In volunteers, SJW decreased platelet aggregation (59% ± 14% vs. 40% ± 15% at 2 hours, P = 0.02; 56% ± 10% vs. 44% ± 13% at 4 hours, P < 0.03; and 55% ± 14% vs. 37% ± 14% at 6 hours, P = 0.01) and increased CYP3A4 activity (2.1% ± 0.4% CO2 exhaled per hour before vs. 2.9% ± 0.6% CO2 exhaled per hour after SJW, P = 0.002). In patients, SJW decreased platelet reactivity (226 ± 39 vs. 185 ± 49 P2Y12 reactivity units, P = 0.0002) and increased platelet inhibition (23% ± 11% vs. 41% ± 16%, P = 0.002). SJW may be a future therapeutic option to increase CYP metabolic activity and antiplatelet effect of clopidogrel in hyporesponders.

Clinical Impact of Enhanced Inhibition of P2Y12-Mediated Platelet Aggregation in Patients with ST-Segment Elevation Myocardial Infarction Undergoing Percutaneous Coronary Intervention

The combination of aspirin and clopidogrel at a loading dose of 300 mg followed by a maintenance dose of 75 mg daily is a well-established antiplatelet therapy for the secondary prevention of thrombotic complications in the settings of acute coronary syndrome and/or percutaneous coronary intervention (PCI). Despite the demonstrated clinical benefits associated with this antiplatelet therapy, there is accumulating evidence that a consistent proportion of patients persist in having high levels of platelet aggregation following standard clopidogrel dose. Importantly, the high platelet reactivity after clopidogrel treatment has been associated with higher risk for cardiovascular ischemic events, including stent thrombosis. This has warranted the need for alternative oral antiplatelet regimens that achieve a higher degree of platelet inhibition. Several functional studies have shown that a higher clopidogrel loading dose (600 mg) compared with standard dose, and novel oral adenosine diphosphate platelet receptor (P2Y12) antagonists compared with clopidogrel achieve a faster onset of action, increased platelet inhibition, and a more predictable drug response. These more favorable pharmacodynamic characteristics are of particular interest in the setting of primary PCI for ST-segment elevation myocardial infarction (STEMI), in which rapid and consistent inhibition of platelet activation and aggregation is desirable for therapeutic success. The present article reviews data on the clinical impact of enhanced P2Y12 inhibition with either higher clopidogrel dosing or new oral antiplatelet agents, including prasugrel and ticagrelor, in the setting of STEMI, focusing on results in the setting of primary PCI.

Increased Platelet Inhibition After Switching From Maintenance Clopidogrel to Prasugrel in Patients With Acute Coronary Syndromes: Results of the SWAP (SWitching Anti Platelet) Study

The objective was to evaluate the pharmacodynamic response of switching patients on maintenance phase clopidogrel therapy after an acute coronary syndrome (ACS) to prasugrel. Prasugrel P2Y(12) receptor blockade is associated with greater pharmacodynamic platelet inhibition and reduction of ischemic complications compared with that of clopidogrel in ACS patients undergoing percutaneous coronary intervention. The pharmacodynamic effects of switching patients during maintenance phase clopidogrel therapy after an ACS event to prasugrel are unknown. The SWAP (SWitching Anti Platelet) study was a phase 2, multicenter, randomized, double-blind, double-dummy, active-control trial. After a run-in of daily open-label clopidogrel 75 mg with aspirin therapy for 10 to 14 days, patients were randomly assigned to 1 of the following 3 treatments: placebo loading dose (LD)/clopidogrel 75 mg maintenance dose (MD), placebo LD/prasugrel 10 mg MD, or prasugrel 60 mg LD/10 mg MD. Platelet function was evaluated at 2 h, 24 h, 7 days, and 14 days using light transmittance aggregometry, VerifyNow P2Y(12) assay, and vasodilator-stimulated phosphoprotein phosphorylation. A total of 139 patients were randomized, of whom 100 were eligible for analysis. Maximum adenosine diphosphate-induced platelet aggregation (20 μM) by light transmittance aggregometry at 1 week (primary end point) was lower after prasugrel MD compared with clopidogrel MD (41.1% vs. 55.0%, p < 0.0001), and was also lower in the prasugrel LD+MD group compared with clopidogrel MD (41.0% vs. 55.0%, p < 0.0001). At 2 h, a prasugrel LD resulted in higher platelet inhibition compared with the other regimens. Similar results were found using light transmittance aggregometry with 5 μM adenosine diphosphate, VerifyNow P2Y(12), and vasodilator-stimulated phosphoprotein phosphorylation assays. For patients receiving maintenance clopidogrel therapy after an ACS event, switching from clopidogrel to prasugrel is associated with a further reduction in platelet function by 1 week using prasugrel MD or within 2 h with the administration of a prasugrel LD. (A Pharmacodynamic Comparison of Prasugrel [LY640315] Versus Clopidogrel in Subjects With Acute Coronary Syndrome Who Are Receiving Clopidogrel [SWAP]; NCT00356135).

Intra-individual variability in clopidogrel responsiveness in coronary artery disease patients under long term therapy

Clopidogrel responsiveness (CR) following a loading dose (LD) predicts thrombotic events after percutaneous coronary interventions (PCI). Some of the mechanisms involved in large inter-individual variability in CR may be varied. We therefore postulated that there may be an intra-individual variability in CR. Two hundred and one patients receiving long-term therapy with aspirin and clopidogrel after drug-eluting stents PCI were prospectively included in this monocentre study along with any patient re-admitted within 12 months post-PCI. Platelet reactivity (PR) inhibition was assessed by the vasodilator phosphoprotein (VASP) index following a 600 mg loading dose of clopidogrel on each admission to determine CR (VASP 1 during the first admission and VASP 2 during re-admission). DeltaVASP = VASP 2 –VASP 1 was used to study intra-individual variability in CR. We observed that the response to a 600 mg LD of clopidogrel was poorly correlated within an individual (kappa = 0.33; p < 0.001 (n = 201)). Although most patients had increased platelet inhibition at the time of readmission, 35.3% of patients exhibited a decreased platelet inhibition despite chronic clopidogrel therapy and a 600 mg reload. Quartiles analysis of DeltaVASP demonstrated that insulin-treated diabetes was associated with decreased CR over time (p = 0.03). In addition to the large inter-individual variability in clopidogrel responsiveness, there is large intra-individual variability. Decreased clopidogrel responsiveness despite long-term clopidogrel therapy could be a trigger for recurrent thrombotic events.

Combination Antithrombotic Therapies

Atherothrombosis is the major pathophysiological process responsible for the occurrence of severe ischemic events in patients with cardiovascular diseases. In the United States, atherothrombosis strongly influenced mortality in 2004: One in 2.8 deaths was due to CVD, 1 in 5 deaths to coronary heart disease, and 1 in 17 deaths to stroke.1 Because cardiovascular disease is a progressive and systemic disease, long-term antithrombotic therapies that effectively target the entire arterial vasculature and modulate the key components responsible for thrombus generation are essential to improve patient outcomes. Because platelet activation is determined by multiple receptor-mediated signaling pathways, clinical studies have evaluated the efficacy of multidrug administration in the prevention of atherothrombotic complications.2,3 The major concern with these therapies is the critical balance between anti-ischemic effect and bleeding risk. This review summarizes our understanding of the role of combination antiplatelet therapies in the treatment and prevention of atherothrombosis. Platelet activation and aggregation play a pivotal role in the generation of occlusive thrombus at the site of coronary arterial plaque rupture. In addition, platelets influence various endothelial and inflammatory responses during the initiation and progression of atherosclerosis. Under normal conditions, anucleate circulating platelets are in a quiescent state. Healthy vascular endothelium prevents adhesion and activation of platelets by producing antithrombotic factors such as CD39 (ectoADPase), prostaglandin I2, nitric oxide, heparin, matrix metalloproteinase-9, protein S, and thrombomodulin.3,4 Endothelial activation and denudation and frank atherosclerotic plaque rupture expose the subendothelial matrix and release prothrombotic factors during acute coronary syndromes (ACS) and percutaneous interventions. These processes result in localized platelet adhesion and platelet activation. After adhesion to the exposed subendothelial matrix, platelets are activated by shear and the soluble agonists thromboxane A2 (TxA2), ADP, and thrombin. TxA2 is produced from arachidonic acid, which originates from membrane phospholipids and …

The Association of Cigarette Smoking With Enhanced Platelet Inhibition by Clopidogrel

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

Abstract 3473: The Effect of Cigarette Smoking on the Antiplatelet Effect of Clopidogrel: The Smokers Paradox

Background: Wide response variability to clopidogrel therapy has been reported. Clopidogrel is a prodrug that requires metabolic activation by hepatic cytochromes (CYP). Cigarette smoking is an inducer of CYP1A2 and may, therefore, enhance the metabolism of clopidogrel. We sought to examine the effect of cigarette smoking on the platelet response to clopidogrel. Methods: Three hundred thirteen consecutive patients undergoing elective coronary stenting were studied. Platelet aggregation (PA) was assessed by light transmittance aggregometry (LTA) stimulated by 5 and 20μ M adenosine diphosphate. One hundred fourteen patients were on chronic clopidogrel therapy, were not reloaded, and had pre-stenting PA measurements. Pre-and post-stenting PA was measured in 199 patients: 60 were loaded with 300mg and 139 were loaded with 600mg. There were 120 current smokers (smoking within 2 weeks of PCI) and 193 non-smokers (no prior history of smoking). Low PA was defined as the lowest two quartiles of 5μM ADP-induced platelet aggregation (≤ 40%). Results: PA was significantly lower (p ≤ 0.008) in smokers on long term chronic clopidogrel treatment (Table ). Relative platelet inhibition (RPI) was higher in smokers treated with either 300mg or 600mg clopidogrel measured by 5 and 20μM ADP-induced PA. In a multivariate analysis, cigarette smoking was an independent predictor of low PA in patients on chronic clopidogrel therapy and in patients loaded with clopidogrel (r=0.3, p=0.0001). Conclusion: Clopidogrel therapy in smokers is associated with increased platelet inhibition and lower aggregation as compared to non-smokers. The mechanism of the smoking effect deserves further study and may be another cause of response variability to clopidogrel. RPI = 100 x ((baseline aggregation-post-treatment aggregation)/(baseline aggregation))