Rosemary Ecob

Inhibitory Effects of Ticagrelor Compared With Clopidogrel on Platelet Function in Patients With Acute Coronary Syndromes The PLATO (PLATelet inhibition and patient Outcomes) PLATELET Substudy

OBJECTIVES The PLATO (PLATelet inhibition and patient Outcomes) PLATELET substudy aimed to compare the antiplatelet effects of clopidogrel and ticagrelor in patients with acute coronary syndromes. BACKGROUND The PLATO study demonstrated superiority of ticagrelor over clopidogrel in the prevention of ischemic events in patients with acute coronary syndromes. METHODS Patients were randomized to receive either clopidogrel (300- to 600-mg loading dose [LD], 75 mg/day) or ticagrelor (180-mg LD, 90 mg twice daily). The effects of maintenance therapy were studied in 69 patients pre- and 2 to 4 h post-dose after at least 28 days. The LD effect was studied in 24 clopidogrel-naive patients. Light transmittance aggregometry (adenosine diphosphate 5 to 20 μM), VerifyNow P2Y12, and VASP phosphorylation assays were performed. RESULTS During maintenance therapy, ticagrelor achieved greater suppression of platelet reactivity compared with clopidogrel. The mean maximum light transmittance aggregometry responses (adenosine diphosphate 20 μM) post-maintenance dose were 44±15% for clopidogrel and 28±10% for ticagrelor (p<0.001). High platelet reactivity was seen more frequently in the clopidogrel group. Proton pump inhibitor use was associated with higher platelet reactivity with clopidogrel but not ticagrelor. The ticagrelor LD also achieved greater inhibition of platelet aggregation compared with the clopidogrel LD. CONCLUSIONS Ticagrelor achieves greater antiplatelet effect than clopidogrel in patients with acute coronary syndromes, both in the first hours of treatment and during maintenance therapy.

Clinical ResearchAntiplatelet TherapyInhibitory Effects of Ticagrelor Compared With Clopidogrel on Platelet Function in Patients With Acute Coronary Syndromes: The PLATO (PLATelet inhibition and patient Outcomes) PLATELET Substudy

OBJECTIVES The PLATO (PLATelet inhibition and patient Outcomes) PLATELET substudy aimed to compare the antiplatelet effects of clopidogrel and ticagrelor in patients with acute coronary syndromes. BACKGROUND The PLATO study demonstrated superiority of ticagrelor over clopidogrel in the prevention of ischemic events in patients with acute coronary syndromes. METHODS Patients were randomized to receive either clopidogrel (300- to 600-mg loading dose [LD], 75 mg/day) or ticagrelor (180-mg LD, 90 mg twice daily). The effects of maintenance therapy were studied in 69 patients pre- and 2 to 4 h post-dose after at least 28 days. The LD effect was studied in 24 clopidogrel-naive patients. Light transmittance aggregometry (adenosine diphosphate 5 to 20 μM), VerifyNow P2Y12, and VASP phosphorylation assays were performed. RESULTS During maintenance therapy, ticagrelor achieved greater suppression of platelet reactivity compared with clopidogrel. The mean maximum light transmittance aggregometry responses (adenosine diphosphate 20 μM) post-maintenance dose were 44±15% for clopidogrel and 28±10% for ticagrelor (p<0.001). High platelet reactivity was seen more frequently in the clopidogrel group. Proton pump inhibitor use was associated with higher platelet reactivity with clopidogrel but not ticagrelor. The ticagrelor LD also achieved greater inhibition of platelet aggregation compared with the clopidogrel LD. CONCLUSIONS Ticagrelor achieves greater antiplatelet effect than clopidogrel in patients with acute coronary syndromes, both in the first hours of treatment and during maintenance therapy.

Incidence of dyspnea and assessment of cardiac and pulmonary function in patients with stable coronary artery disease receiving ticagrelor, clopidogrel, or placebo in the ONSET/OFFSET study

OBJECTIVES We prospectively assessed cardiac and pulmonary function in patients with stable coronary artery disease (CAD) treated with ticagrelor, clopidogrel, or placebo in the ONSET/OFFSET (A Multi-Centre Randomised, Double-Blind, Double-Dummy Parallel Group Study of the Onset and Offset of Antiplatelet Effects of AZD6140 Compared With Clopidogrel and Placebo With Aspirin as Background Therapy in Patients With Stable Coronary Artery Disease) study. BACKGROUND Ticagrelor reduces cardiovascular events more effectively than clopidogrel in patients with acute coronary syndromes. Dyspnea develops in some patients treated with ticagrelor, and it is not known whether this is associated with changes in cardiac or pulmonary function. METHODS In all, 123 stable aspirin-treated CAD patients randomly received either ticagrelor (180 mg load, then 90 mg twice daily; n=57), clopidogrel (600 mg load, then 75 mg daily; n=54), or placebo (n=12) for 6 weeks in a double-blind, double-dummy design. Electrocardiography, echocardiography, serum N-terminal pro-brain natriuretic peptide, and pulmonary function tests were performed before (baseline) and 6 weeks after drug administration and/or after development of dyspnea. RESULTS After drug administration, dyspnea was reported by 38.6%, 9.3%, and 8.3% of patients in the ticagrelor, clopidogrel, and placebo groups, respectively (p<0.001). Most instances were mild and/or lasted<24 h, although 3 patients discontinued ticagrelor because of dyspnea. Eight of 22 and 17 of 22 ticagrelor-treated patients experiencing dyspnea did so within 24 h and 1 week, respectively, after drug administration. In all treatment groups, and in ticagrelor-treated patients with dyspnea, there were no significant changes between baseline and 6 weeks in any of the cardiac or pulmonary function parameters. CONCLUSIONS Dyspnea is commonly associated with ticagrelor therapy, but was not associated in this study with any adverse change in cardiac or pulmonary function. (A Multi-Centre Randomised, Double-Blind, Double-Dummy Parallel Group Study of the Onset and Offset of Antiplatelet Effects of AZD6140 Compared With Clopidogrel and Placebo With Aspirin as Background Therapy in Patients With Stable Coronary Artery Disease [ONSET/OFFSET]; NCT00528411).

Earlier recovery of platelet function after discontinuation of treatment with ticagrelor compared with clopidogrel in patients with high antiplatelet responses

Summary.  Background: The rate of recovery of platelet function after discontinuation of P2Y12 inhibitors depends on the reversibility of the antiplatelet effect and the extent of the on‐treatment response. P2Y12 inhibition increases the bleeding risk in patients requiring surgery. Objectives: To evaluate recovery of platelet function after discontinuation of ticagrelor vs. clopidogrel in stable coronary artery disease (CAD) patients with high levels of platelet inhibition (HPI) during the ONSET/OFFSET study. Methods: Patients received aspirin 75–100 mg per day and either ticagrelor 90 mg twice‐daily or clopidogrel 75 mg daily for 6 weeks. This subanalysis included patients with HPI after the last dose of maintenance therapy, defined as: inhibition of platelet aggregation (IPA) > 75% 4 h post‐dose (ADP 20 μm, final extent); < 120 P2Y12 reaction units 8 h post‐dose (VerifyNow P2Y12 assay); or platelet reactivity index < 50% 8 h post‐dose (VASP‐P assay). Results: IPA > 75% was observed in 39 out of 47 ticagrelor‐treated and 17 out of 44 clopidogrel‐treated patients. The rate of offset of IPA over 4–72 h was greater with ticagrelor (IPA %/hour slope: −1.11 vs. −0.67 for clopidogrel; P < 0.0001). Mean IPA was significantly lower with ticagrelor than clopidogrel between 48 and 168 h post‐dose (P < 0.01). Similar findings were observed with the other assays. The average time for IPA to decline from 30% to 10% was 50.8 h with ticagrelor vs. 110.4 h with clopidogrel. Conclusions: In patients with HPI, recovery of platelet function was more rapid after discontinuation of ticagrelor than clopidogrel leading to significantly greater platelet reactivity by 48 h after the last dose in the ticagrelor group.

Platelet P2Y12 Inhibitors Reduce Systemic Inflammation and Its Prothrombotic Effects in an Experimental Human Model

Objective—Clinical studies suggest that platelet P2Y12 inhibitors reduce mortality from sepsis, although the underlying mechanisms have not been clearly defined in vivo. We hypothesized that P2Y12 inhibitors may improve survival from sepsis by suppressing systemic inflammation and its prothrombotic effects. We therefore determined whether clopidogrel and the novel, more potent P2Y12 inhibitor, ticagrelor, modify these responses in an experimental human model. Approach and Results—We randomized 30 healthy volunteers to ticagrelor (n=10), clopidogrel (n=10), or no antiplatelet medication (controls; n=10). We examined the effect of P2Y12 inhibition on systemic inflammation, which was induced by intravenous injection of Escherichia coli endotoxin. Both P2Y12 inhibitors significantly reduced platelet–monocyte aggregate formation and peak levels of major proinflammatory cytokines, including tumor necrosis factor &agr;, interleukin-6, and chemokine (C–C motif) ligand 2. In contrast to clopidogrel, ticagrelor also significantly reduced peak levels of IL-8 and growth colony-stimulating factor and increased peak levels of the anti-inflammatory cytokine IL-10. In addition, ticagrelor altered leukocyte trafficking. Both P2Y12 inhibitors suppressed D-dimer generation and scanning electron microscopy revealed that ticagrelor also suppressed prothrombotic changes in fibrin clot ultrastructure. Conclusions—Potent inhibition of multiple inflammatory and prothrombotic mechanisms by P2Y12 inhibitors demonstrates critical importance of platelets as central orchestrators of systemic inflammation induced by bacterial endotoxin. This provides novel mechanistic insight into the lower mortality associated with P2Y12 inhibitors in patients with sepsis in clinical studies.

PAR1 antagonists inhibit thrombin-induced platelet activation whilst leaving the PAR4-mediated response intact

Abstract Thrombin-induced platelet activation is initiated by PAR1 and PAR4 receptors. Vorapaxar, a PAR1 antagonist, has been assessed in patients with acute coronary syndromes (ACS) and stable atherosclerotic disease in addition to standard-of-care treatment. In clinical trials, vorapaxar has been observed to reduce the frequency of ischaemic events in some subgroups though in others has increased the frequency of bleeding events. Among patients undergoing CABG surgery, which is associated with excess thrombin generation, bleeding was not increased. The aim of these studies was to investigate the effects of selective PAR1 antagonism on thrombin-induced platelet activation in patients receiving vorapaxar or placebo in the TRACER trial and to explore the roles of PAR1 and PAR4 in thrombin-induced platelet activation in healthy volunteers. ACS patients receiving vorapaxar or placebo in the TRACER trial were studied at baseline and 4 hours, 1 and 4 months during drug administration. Thrombin-induced calcium mobilisation in platelet-rich plasma was assessed by flow cytometry. In vitro studies were performed in healthy volunteers using the PAR1 antagonist SCH79797 or PAR4 receptor desensitisation. Vorapaxar treatment significantly inhibited thrombin-induced calcium mobilisation, leaving a residual, delayed response. These findings were consistent with calcium mobilisation mediated via the PAR4 receptor and were reproduced in vitro using SCH79797. PAR4 receptor desensitization, in combination with SCH79797, completely inhibited thrombin-induced calcium mobilisation confirming that the residual calcium mobilisation was mediated via PAR4. In conclusion vorapaxar selectively antagonises the PAR1-mediated component of thrombin-induced platelet activation, leaving the PAR4-mediated response intact, which may explain why vorapaxar is well tolerated in patients undergoing CABG surgery since higher thrombin levels in this setting may override the effects of PAR1 antagonism through PAR4 activation, thus preserving haemostasis. Further assessment may be warranted.

Hirudin anticoagulation allows more rapid determination of P2Y₁₂ inhibition by the VerifyNow P2Y12 assay

VerifyNow (VN) P2Y12 is a point-of-care assay used to assess response to P2Y12 inhibitors. Sodium citrate (citrate) is the standard anticoagulant used for this assay but requires a pre-incubation period. Hirudin is an alternative anticoagulant for platelet function studies that maintains physiological divalent cation levels. We investigated whether hirudin anticoagulation might allow more rapid testing of P2Y₁₂ inhibition at the time of percutaneous coronary intervention (PCI). Blood was collected from the arterial sheath of aspirin-treated patients undergoing elective, urgent or emergency coronary angiography±PCI and aliquots were anticoagulated with either citrate or hirudin. For each anticoagulant, VN P2Y12 was performed both immediately and after 20 minutes. A total of 98 patients were included in this study following pre-treatment with clopidogrel (n=88), prasugrel (n=6) or no P2Y₁₂ inhibitor (n=4). PRU with hirudin immediately (PRU_H_Imm) and PRU with citrate 20 minutes post sampling (PRU_C_20) were very strongly correlated (R=0.95) though PRU_H_Imm tended to be lower than PRU_C_20 so that optimal correlation was estimated by the equation PRU_H_Imm=0.95xPRU_C_20 (p<0.001). Bland-Altman plots showed good agreement between PRU_H_Imm and (0.95xPRU_C_20). Platelet reactivity was more stable over the studied time course with hirudin as compared to citrate. We therefore conclude that VN P2Y12 with hirudin anticoagulation can be performed more rapidly and results are strongly correlated with delayed citrate measurements. Further studies are warranted to assess the utility of this method for improving clinical outcomes in patients undergoing PCI.

Evolving pattern of platelet P2Y12 inhibition in patients with acute coronary syndromes

Abstract Dual antiplatelet therapy consisting of clopidogrel in addition to aspirin has previously been the standard of care for patients with acute coronary syndromes (ACS) but international guidelines have been evolving over the last 4 years with the introduction of prasugrel and ticagrelor. In October 2009, prasugrel was approved in the UK by the National Institute of Health and Clinical Excellence (NICE) for use in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI), diabetic patients with non-ST-elevation (NSTE) ACS undergoing PCI and patients with stent thrombosis while other ACS patients were to continue receiving clopidogrel. Ticagrelor was approved in October 2011 by NICE for use in patients with moderate-to-high risk NSTE ACS and STEMI undergoing primary PCI and was recommended in preference to clopidogrel in European guidelines. These recommendations were adopted in our region, constituting a population of 1.8 million. We studied the effect of changing patterns of P2Y12 inhibitor usage on levels of platelet inhibition during maintenance therapy. Patients admitted to Northern General Hospital, Sheffield, with NSTE ACS or STEMI managed with primary PCI were enrolled over two periods of time: May 2010 to November 2011 (T1); and October 2012 to February 2013 (T2). Venous blood samples were obtained at 1 month after the onset of ACS. Light transmittance aggregometry (LTA) was performed and maximum aggregation response to ADP 20 μM was determined. A total of 116 patients were enrolled in T1 of whom 82 were receiving clopidogrel and 34 were receiving prasugrel. Twenty-nine patients were enrolled in T2, all of whom were receiving ticagrelor. Mean LTA results according to treatment with clopidogrel, prasugrel and ticagrelor were 57 ± 18%, 41 ± 20%, and 31 ± 12%, respectively. Prasugrel was associated with significantly lower platelet aggregation responses than clopidogrel (p < 0.001) and ticagrelor was associated with significantly lower platelet aggregation responses than both prasugrel (p = 0.015) and clopidogrel (p < 0.001). We conclude that international guidelines and NICE approval have led to increasing levels of P2Y12 inhibition in ACS patients in this UK centre between May 2010 and February 2013. Ticagrelor was associated with significantly greater P2Y12 inhibition than both clopidogrel and prasugrel during maintenance therapy.

Stability of VerifyNow P2Y12 assay results with citrate anticoagulation as compared to hirudin anticoagulation over 20-min period

Antiplatelet therapy plays a central role in the management of ischaemic heart disease [1]. While poor inhibition of P2Y12 receptor has been linked to higher incidence of ischaemic events, enhanced inhibition has been associated with increased risk of bleeding events [2]. Platelet function testing has been suggested as a way to individualise therapy in order to minimize the risk of both bleeding and ischaemic events [3]. The VerifyNow analyser (VN) (Accumetrics, San Diego, CA) is a point-of-care device that provides rapid assessment of P2Y12 inhibition and results obtained with VN are reported as P2Y12 reaction units (PRU) [4]. Traditionally, trisodium citrate (‘‘citrate’’) has been used with the VN and measurements with citrate require an incubation period of at least 10 minutes and can be performed up to 4 hours post sampling, as per manufacturer’s instruction. Recently, we have demonstrated the possibility for the test to be performed immediately post sampling with hirudin anticoagulation and showed that measurements with hirudin were stable over 20 minutes whereas PRU results obtained with citrate immediately were significantly lower than those obtained after 20 minutes incubation [5]. In this study, we assessed the stability of PRU results obtained with citrate between the recommended minimum incubation time of 10 minutes compared to 20 minutes post sampling as well as compared to measurements with hirudin performed immediately or 20 minutes post sampling. Ten patients with stable coronary artery disease undergoing elective percutaneous angioplasty provided informed consent according to a protocol approved by the local ethics committee. All patients had been pretreated with aspirin and either 600 mg clopidogrel at least 2 hours pre-sampling (n1⁄4 6) or 75 mg daily for at least 5 days (n1⁄4 4). All blood samples for VN testing were obtained by venipuncture using a syringe and a needle. The first 2 mls were discarded and blood was added gently, avoiding turbulence, to uncapped anticoagulant tubes without the use of vacuum. Blood tubes were then capped and inverted gently to mix the blood with the anticoagulant. We used two tubes containing 3.2% citrate (Vacuette, Greiner BioOne, Kremsmünster, Austria) and two tubes containing415 mg/ml hirudin (Double-wall hirudin blood tube, Verum Diagnostica, Munich, Germany) for every patient. The VN P2Y12 test was performed at two time points for each anticoagulant: immediately and at 20 min post sampling with hirudin and at 10 minutes and 20 minutes post sampling with citrate. All statistical analyses were performed using PASW statistic version 19 (IBM SPSS Inc., New York, NY). Data are presented as mean SD and analysis was carried out using paired samples t-test for continuous variables. Measurements with hirudin provided more consistent results over the studied period as compared to measurements with citrate where PRU values tended to be significantly lower at 10 minutes (187 40) versus at 20 minutes (205 38; p1⁄4 0.009) (Table I, Figure 1). Measurements with hirudin as compared to measurements with citrate at 20 min further confirmed our previous study where optimum correlation between both measurements was estimated by the equation PRU_H_Imm1⁄4 0.95 X PRU_C_20. Base PRU (BASE) results representing platelet aggregation in response to thrombin receptor activating peptide (TRAP) were stable over the studied time with each anticoagulant, however measurements with hirudin were significantly different to measurements with citrate. These results are consistent with the results shown in our previous study [5]. The consistency in PRU results obtained with hirudin over the studied time might be explained by the mechanism of action of hirudin, which directly inhibits thrombin without affecting divalent cation levels [6] and this might help provide a stable medium for homeostasis over a 20-min period. Other studies assessing the use of hirudin with Multiple Electrode Aggregometry (MEA) demonstrated stability in results obtained with hirudin up to 12 hours post sampling [7, 8]. Citrate, on the other hand, appears to transiently blunt platelet reactivity, possibly due to the sudden shift in extracellular ionized cations affecting receptor activity and/or intracellular signalling. The limitations of this study are small sample size (although the results are consistent with our previous larger study) and assessment of only a 20-minute window since our primary focus related to rapid testing of P2Y12 inhibition in the clinical setting. We did not assess other assays, such as the VN aspirin assay since this is not currently recommended in clinical practice [9], and Keywords