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.     

Switching directly to prasugrel from clopidogrel results in greater inhibition of platelet aggregation in aspirin-treated subjects

Prasugrel, a novel P2Y₁₂ antagonist, achieves faster onset and greater inhibition of platelet aggregation than clopidogrel 300 and 600 mg loading doses (LD). We studied the safety, time course, and level of platelet inhibition when switching directly from clopidogrel 75 mg maintenance dose (MD) to a prasugrel 60 mg LD/10 mg MD or 10 mg MD regimen. Healthy subjects (n?=?39) on aspirin (81 mg/d) received a clopidogrel 600 mg LD followed by 10 days of clopidogrel MD (75 mg/d). Subjects were then randomized without a washout period to prasugrel 60 mg LD (n?=?16) followed by 10 days of prasugrel MD (10 mg/d) or to prasugrel MD (10 mg/d, n?=?19) for 11 days. Maximal platelet aggregation (MPA) to 20 µM ADP was measured by turbidimetric aggregometry. In subjects on clopidogrel 75 mg MD, mean MPA decreased from 39 to 12% by 30 minutes, and to 5% by 1 hour after a prasugrel 60 mg LD (p?<?0.001 for both) and from 37 to 28% (p?<?0.001) by 1 hour after a prasugrel 10 mg MD. During prasugrel MD, a new pharmacodynamic steady state MPA of ～24% (p?<?0.01 vs. clopidogrel MD) occurred within four to five days of switching from clopidogrel. Changing from clopidogrel to prasugrel did not increase bleeding episodes or other adverse events. Switching directly from clopidogrel MD to either prasugrel LD or MD was well tolerated and resulted in significantly greater levels of platelet inhibition than a clopidogrel 75 mg MD.     

Antagonism of P2Y₁₂ reduces physiological thromboxane levels

Antiplatelet therapy for the management of patients with cardiovascular risks often includes a combination therapy of aspirin and clopidogrel, acting through inhibition of thromboxane generation and blockade of G(i)-coupled P2Y?? receptor, respectively. We hypothesized that ADP acting through P2Y?? regulates physiological thromboxane levels. The serum thromboxane levels in mice (n?=?3) dosed with clopidogrel and prasugrel were decreased by 83.1?±?5.3% and 94.26?±?1.75% respectively compared to untreated mice. Pre-treatment of human blood (n?=?3) ex vivo with active metabolites of clopidogrel or prasugrel led to a reduction in thromboxane levels to 16.3?±?3.2% and 4.9?±?0.8% respectively, compared to untreated human serum. We also evaluated serum thromboxane levels in P2Y receptor null mice (n?=?4). Whereas serum thromboxane levels in P2Y? null mice were similar to those in wild type littermates, those in the P2Y?? null mice were inhibited by 83.15?±?3.8%. Finally, in a pilot study, serum thromboxane levels were reduced by 76.05?±?8.41% in healthy human volunteers (n?=?6) upon dosing with clopidogrel, compared to the levels before dosing. In conclusion, P2Y?? antagonism alone can decrease physiological thromboxane levels. Thus, this study could pave way the for newer/modified treatment regimens for the management of patients with thrombotic complications who are allergic or non-responsive to aspirin.     

Cangrelor inhibits the binding of the active metabolites of clopidogrel and prasugrel to P2Y12 receptors in vitro

Cangrelor is a rapid-acting, direct-binding, and reversible P2Y₁₂ antagonist which has been studied for use during percutaneous coronary intervention (PCI) in patients with or without pretreatment with an oral P2Y₁₂ antagonist. As cangrelor is administered intravenously, it is necessary to switch to an oral P2Y₁₂ antagonist following PCI, such as the thienopyridines clopidogrel, and prasugrel or the non-pyridine ticagrelor. Previous studies have suggested a negative pharmacodynamic interaction between cangrelor and thienopyridines. This in vitro study evaluated the receptor-level interaction between cangrelor and the active metabolite (AM) of clopidogrel or prasugrel by assessing functional P2Y₁₂ receptor number using a ³³P-2MeSADP binding assay. All P2Y₁₂ antagonists studied resulted in strong P2Y₁₂ receptor blockade (cangrelor: 93.6%; clopidogrel AM: 93.0%; prasugrel AM: 97.9%). Adding a thienopyridine AM in the presence of cangrelor strongly reduces P2Y₁₂ receptor blockade by the AM (clopidogrel AM: 7%, prasugrel AM: 3.2%). The thienopyridine AMs had limited ability to compete with cangrelor for binding to P2Y₁₂ (% P2Y₁₂ receptor blockade after co-incubation with cangrelor 1000?nmol/L: 11.7% for clopidogrel AM 3?µmol/L; 34.1% for prasugrel AM 3?µmol/L). In conclusion, in vitro cangrelor strongly inhibits the binding of clopidogrel and prasugrel AMs to the P2Y₁₂ receptor, consistent with the previous observation of a negative pharmacodynamic interaction. Care may need to be taken to not overlap exposure to thienopyridine AMs and cangrelor in order to reduce the risk of thrombotic complications following PCI.     

Association of plasma miR-223 and platelet reactivity in patients with coronary artery disease on dual antiplatelet therapy: A preliminary report

Decreased plasma levels of microRNA-223 (miR-223), predominantly of platelet origin, were proposed as a surrogate marker of efficacy of antiplatelet therapy. However, higher on-treatment platelet reactivity was associated with lower plasma miR-223 in patients with coronary artery disease (CAD) on dual antiplatelet therapy (DAPT) including clopidogrel and aspirin. Our aim was to compare plasma miR-223 and platelet reactivity in CAD patients on DAPT with newer P2Y₁₂ antagonists vs. clopidogrel. We studied 21 men with CAD admitted to our centre owing to a non-ST-elevation acute coronary syndrome, and with an uncomplicated hospital course. From the day of admission, the patients were receiving either clopidogrel (n?=?11) or prasugrel/ticagrelor (n?=?10) in addition to aspirin. Before discharge, miR-223 expression in plasma was estimated by quantitative polymerase chain reaction using the comparative Ct method relative to miR-16 as an endogenous control. Multiple electrode aggregometry was used to assess platelet aggregation in response to adenosine diphosphate (ADP). ADP-induced platelet reactivity was decreased in the patients treated with prasugrel or ticagrelor compared with those on clopidogrel (mean?±?SD: 139?±?71 vs. 313?±?162 arbitrary units [AU]*min, p?=?0.006), due to a more potent antiplatelet activity of the novel P2Y₁₂ antagonists. Consequently, six out of seven patients in the lower tertile of the ADP-induced platelet aggregation were treated with the newer P2Y₁₂ blockers, whereas six out of seven patients in the upper tertile were on clopidogrel. Plasma miR-223 was elevated with decreasing platelet reactivity (Spearman’s rho?=?–0.52; p?=?0.015 for trend), being significantly higher in the lower tertile of the ADP-induced platelet aggregation (median [range]: 1.06 [0.25–2.31]) vs. the upper tertile (0.20 [0.13–2.30]) (p?=?0.04). In conclusion, our preliminary results argue against the notion of low plasma miR-223 as a marker of platelet responsiveness to DAPT. On the contrary, more potent platelet inhibition associated mainly with newer P2Y₁₂ antagonists appears to coincide with higher miR-223 relative to the subjects with attenuated responsiveness to DAPT.     

Variation in thromboxane B2 concentrations in serum and plasma in patients taking regular aspirin before and after clopidogrel therapy

Dual antiplatelet therapy with aspirin and a P2Y₁₂ antagonist is widely prescribed for the prevention of thrombotic events in patients with an acute coronary syndrome or undergoing percutaneous coronary intervention (PCI). It is recognised that there is inter-individual variation in the antiplatelet effects of both drugs. Recent data also suggest that P2Y₁₂ antagonists can affect the response to aspirin. A direct indicator of the effect of aspirin on platelets is their ability to generate thromboxane, which if measured as the difference between the level of thromboxane B₂ in serum and plasma ([TxB2]_S-P) avoids the confounding effect of endogenous TxB2 production from other cells. We therefore analysed [TxB2]_S-P as a measure of aspirin response in a group of 123 patients undergoing elective PCI before and after the introduction of clopidogrel. In a subgroup of 40 patients taking aspirin alone, we compared [TxB2]_S-P and VerifyNow Aspirin for the assessment of aspirin response. There was a wide variation in plasma and serum TxB2 concentrations both before and after clopidogrel therapy but only 3.5% of patients had residual serum concentration of TxB2 > 10?ng/ml. There was a strong correlation between the pre and post clopidogrel levels of TxB2 (r?≥?0.78; p?=?0.001) and no significant difference in [TxB2]_S-P. There was no correlation between the magnitude of response to clopidogrel response and the generation of thromboxane B2. Correlation between [TxB2]_S-P and VerifyNow Aspirin was poor. We conclude that the use of a P2Y₁₂ antagonist does not influence the effect of aspirin on the ability of platelets to generate thromboxane. Therefore, measurement of TxB2 levels in serum, after subtracting the contribution from plasma, provides a measure of the response to aspirin in patients taking dual antiplatelet therapy.     

Angiographic and platelet reactivity outcomes with prasugrel 60?mg pretreatment and clopidogrel 600?mg pretreatment in primary percutaneous coronary intervention

Pretreatment with 60?mg of prasugrel is more effective than 300?mg of clopidogrel in reducing thrombotic complications with primary percutaneous coronary intervention (PCI). We compared angiographic outcomes and platelet reactivity between treatment with 60?mg of prasugrel and 600?mg of clopidogrel administered before primary PCI. In this single centre non-randomized study, 65 consecutive Asian patients with ST-elevation myocardial infarction (STEMI) received 60?mg of prasugrel before primary PCI. The pre- and post-PCI corrected thrombolysis in myocardial infarction frame count (CTFC) and the 8-h post-treatment platelet vasodilator-stimulated phosphoprotein (VASP) index was compared with a matched historical Asian STEMI cohort (n?=?65) receiving 600?mg of clopidogrel pretreatment. Comparing the prasugrel and clopidogrel groups, the mean age was 54.1?±?10.2 versus 55.5?±?11.8?years, P?=?0.238, and the mean body mass index was 24.6?±?2.0 versus 24.7?±?2.8?kg?m^?2, P?=?0.393. The mean pre-PCI CTFC was 82.1?±?30.2 versus 86.1?±?27.6, P?=?0.045, and the mean post-PCI CTFC was 21.1?±?13.9 versus 20.1?±?9.2, P?=?0.309. Pre-PCI coronary thrombi were visualised in 6.3 versus 18.1?%, P?=?0.038. The median VASP index was 22.2?±?24.5 versus 70.5?±?17.5?%, P?<?0.001, and high on-treatment platelet reactivity (VASP index?>?50?%) was observed in 13.8 versus 84.3?%, P?=?0.001. Rescue intracoronary glycoprotein inhibitors were administered to 29.7 versus 51.0?%, P?=?0.018, respectively. Treatment with 60?mg of prasugrel before primary PCI was associated with lower platelet reactivity, a modest trend towards better pre-PCI angiographic outcomes, less pre-PCI coronary thrombi and less rescue glycoprotein inhibitor use compared with 600?mg of clopidogrel. The very high frequency of high on-clopidogrel platelet reactivity with 600?mg of clopidogrel in this Asian STEMI cohort deserves further study.     

Effects on platelet function of an EP3 receptor antagonist used alone and in combination with a P2Y12 antagonist both in-vitro and ex-vivo in human volunteers

EP3 receptor antagonists may provide a new approach to the treatment of atherothrombotic disease by blocking the ability of prostaglandin E₂ (PGE₂) to promote platelet function acting via EP3 receptors. DG-041 is an EP3 antagonist in the early stage of clinical development. Here, we quantitated effects on platelet function of DG-041 in-vitro and ex-vivo after administration to man when given alone and concomitantly with clopidogrel or clopidogrel and aspirin. With its unique mechanism of action, it was anticipated that DG-041 would potentiate inhibition of platelet function when given in combination with clopidogrel without materially increasing bleeding time. Initially, in-vitro studies were performed to determine inhibitory effects of DG-041 (3?µM) used alone or in combination with the P2Y₁₂ antagonist cangrelor (1?µM), both without and with aspirin (100?µM). Platelet aggregation and P-selectin expression were measured in whole blood (n?=?10) following stimulation with the thromboxane A₂ (TXA₂) mimetic U46619 (0.3 or 1?µM) in combination with either the EP3 agonist sulprostone (0.1?µM), or PGE₂ (1?µM). DG-041 alone partially inhibited platelet function in-vitro, as did cangrelor. Addition of both DG-041 and cangrelor in combination provided significantly greater inhibition. An ex-vivo study was then performed using the same experimental approaches. This clinical study was a prospective, randomised, blinded (for DG-041/matching placebo), blocked, crossover study designed to compare the effects of DG-041, clopidogrel, or the combination of DG-041 with either clopidogrel or clopidogrel and aspirin. Healthy volunteers (n?=?42) were randomly assigned to receive no background treatment, clopidogrel (300?mg loading dose plus 75?mg daily) or clopidogrel and aspirin (75?mg daily) for 10 days alongside DG-041 (200?mg twice daily) or placebo for 5 days, crossed over to placebo or DG-041 for the next 5 days. Platelet effects and bleeding time were measured at baseline, days 5 and 10. DG-041 partially inhibited platelet function ex-vivo, as did clopidogrel, while administration of both DG-041 and clopidogrel provided significantly greater inhibition. Administration of DG-041 alone did not increase bleeding time, and did not significantly affect the increased bleeding time seen with clopidogrel or clopidogrel with aspirin. Using these experimental approaches, the antiplatelet effects of DG-041 and a P2Y₁₂ antagonist used alone and in combination can be determined both in-vitro and ex-vivo. Results show inhibitory effects of DG-041 on platelet function acting via EP3 receptor blockade, confirmed to be additional to those brought about by P2Y₁₂ blockade. In both in-vitro and ex-vivo studies, aspirin neither promoted nor negated the effects of the other drugs.     

Influence of cytochrome P450 polymorphisms on the antiplatelet effects of prasugrel in patients with non-cardioembolic stroke previously treated with clopidogrel

This randomized double-blind crossover study aimed to investigate the influence of cytochrome P450 (CYP) 2C19 polymorphisms on the antiplatelet effects of prasugrel in patients with non-cardioembolic stroke treated with clopidogrel. Patients received clopidogrel 75 mg/day for >?4 weeks. Subsequently, patients received prasugrel 3.75 mg/day (group A; n?=?64) or 2.5 mg/day (group B; n?=?65) for 4 weeks followed by a 4 week switched-dose regimen. To assess the influence of CYP2C19 polymorphisms, patients were classified as extensive metabolizers (EMs), intermediate metabolizers (IMs), and poor metabolizers (PMs). The primary endpoint was P2Y₁₂ reaction units (PRU) at the end of each 4 week treatment. A significant reduction in PRU was noted after treatment with prasugrel 3.75 mg/day compared with the pre-dose value (after treatment with clopidogrel) (p?<?0.0001). By CYP2C19 phenotypes, a significant reduction in PRU was noted in IMs and PMs after treatment with prasugrel 3.75 mg/day and in PMs after treatment with prasugrel 2.5 mg/day, as compared with the pre-dose value (p?<?0.0001). The plasma concentration of the active metabolite of clopidogrel was relatively low in PMs compared to EMs and IMs; prasugrel was similar across all CYP2C19 phenotypes. No major or clinically significant hemorrhagic adverse events occurred. By CYP2C19 phenotype, the antiplatelet effects of prasugrel were greater with 3.75 mg/day in IMs and PMs, and with 2.5 mg/day in PMs compared with clopidogrel 75 mg/day, without safety concerns. CYP2C19 polymorphisms did not affect the plasma concentration of the active metabolite of prasugrel or its antiplatelet effects. (JapicCTI-101044).     

Comparison of aspirin and indobufen in healthy volunteers

The aim of this study is to quantify the extent and recovery of platelet inhibition after administration of indobufen and aspirin in healthy volunteers. Indobufen inhibits platelet aggregation by reversibly inhibiting the platelet cyclooxygenase enzyme, thereby suppressing thromboxane synthesis. Twenty healthy volunteers completed the study and received aspirin (200?mg/day for 2 weeks) followed by a 4-week washout period and then indobufen (200?mg twice a day for 2 weeks). The percent (%) inhibition of platelet aggregation (IPA) was assessed using arachidonic acid (0.5?mg/ml) and adenosine diphosphate (5?µM) at 4, 12, 24 and 48 hours after last dose of each drug. IPA assessed using arachidonic acid as the agonist was similar at 4 hours after the last dose of indobufen (81.07?±?9.36%) and aspirin (96.99?±?0.29%, p?=?0.10), but significantly lower at 12 hours (74.04?±?9.55% vs. 97.94?±?0.28%, p?=?0.02), 24 hours (33.39?±?11.13% vs. 97.48?±?0.32%, p?p?p?=?0.002). Indobufen (200?mg twice a day) caused equivalent initial inhibition of platelet aggregation to aspirin (200?mg daily), and the anti-aggregation effect diminished faster than after aspirin.     

A platelet P-selectin test predicts adverse cardiovascular events in patients with acute coronary syndromes treated with aspirin and clopidogrel

Abstract

There is wide variation in response to antiplatelet therapy and high on-treatment platelet reactivity is associated with adverse cardiovascular events. The objective here was to determine whether the results of a novel strategy for assessing platelet reactivity (based on P-selectin measurement) are associated with clinical outcomes in patients with acute coronary syndromes (ACS). This was a prospective cohort study of 100 ACS patients taking aspirin and clopidogrel. P-selectin tests designed to assess response to P2Y₁₂ antagonists or aspirin were performed alongside light transmission aggregometry. For the P2Y₁₂ P-selectin test, an optimal cutoff for high platelet reactivity was determined by receiver operating characteristic (ROC) curve analysis. Patients were divided into two cohorts based on this value: patients with (n?=?42) or without (n?=?58) high platelet reactivity. The primary endpoint was defined as the composite of cardiovascular death, myocardial infarction and stent thrombosis. After 12 months, the primary endpoint occurred in 12 patients. ROC curve analysis determined that the P2Y₁₂ P-selectin test results were predictive of the primary endpoint (area under curve?=?0.69, p?=?0.046). The primary endpoint occurred more frequently in patients with high on-treatment platelet reactivity compared to those without (21.4% vs. 5.2%; hazard ratio (HR) 4.14; p?=?0.026). The P2Y₁₂ P-selectin test results correlated with light transmission aggregometry (Spearman p?<?0.0001). Using the Aspirin P-selectin test, only two patients demonstrated high on-treatment platelet reactivity. This study suggests that a P2Y₁₂ P-selectin test is capable of detecting high on-treatment platelet reactivity, which is associated with subsequent cardiovascular events.     

Platelet reactivity after administration of third generation P2Y<Subscript>12</Subscript>-antagonists does not depend on body weight in contrast to clopidogrel

The current standard of antiplatelet therapy for patients with myocardial infarction (MI) includes the P2Y₁₂-receptor antagonist clopidogrel, prasugrel or ticagrelor. While it has been shown that platelet reactivity after clopidogrel administration depends on factors such as body weight, it is not known if these factors have an effect on the activity of prasugrel or ticagrelor. Thus, this study aimed to analyse factors associated with high residual platelet reactivity after administration of third generation P2Y₁₂-antagonists compared to clopidogrel. In a single centre registry the antiplatelet effect of clopidogrel, prasugrel or ticagrelor was investigated by aggregometry in patients after MI. To assess the overall capacity of platelet aggregation whole blood was induced with thrombin receptor activating peptide (TRAP; 32 µM). To specifically quantify the effect of P2Y₁₂-antagonists, blood was stimulated with 6.4 µM adenosine diphophosphate (ADP). Relative ADP induced aggregation (r-ADP-agg) was defined as the ADP-TRAP-ratio to reflect an individual degree of P2Y₁₂-dependent platelet inhibition. Platelet function of 238 patients was analysed [clopidogrel (n = 58), prasugrel (n = 65), ticagrelor (n = 115)]. It was found that the r-ADP-agg correlated significantly with body weight in patients after clopidogrel administration (r = 0.423; p < 0.001). In contrast, this association was not present in patients after prasugrel (r = ?0.117; p = 0.354) or ticagrelor (r = ?0.082; p = 0.382) administration. Comparison of the correlation coefficients showed a significant difference (p = 0.003). In contrast to clopidogrel, platelet reactivity after administration of prasugrel or ticagrelor does not depend on body weight in patients after MI. Hence, our mechanistic data support the results of large clinical trials indicating that patients with high body weight do not need to be treated with increased doses of third generation P2Y₁₂-antagonists to achieve sufficient platelet inhibition (registry for patients after myocardial infarction treated with antiplatelet agents; DRKS00003146).     

Combination antiplatelet treatment in coronary artery disease patients: A necessary evil or an overzealous practice?

In seeking to improve care in coronary artery disease patients, further platelet inhibition has been occasionally applied beyond that provided by aspirin and a P2Y₁₂ receptor antagonist. This review aims to offer insights about the rationale, the efficacy and safety of combination antiplatelet therapy, involving three or more agents. Overall, the use of glycoprotein (GP) IIb/IIIa inhibitors did not significantly modify the treatment effect of different antiplatelet strategies, including double vs standard clopidogrel, prasugrel vs clopidogrel, ticagrelor vs clopidogrel, cangrelor vs clopidogrel, and vorapaxar vs placebo. With the caveat that the use of GP IIb/IIIa inhibitor was not randomized, adding such an agent to aspirin and a P2Y₁₂ receptor antagonist appears to carry a significantly increased bleeding potential. Moreover, adding vorapaxar to aspirin- and clopidogrel-treated patients is associated with more bleeding events, while the bleeding potential is further exacerbated in cases of quadruplicate antiplatelet treatment including aspirin, clopidogrel, vorapaxar, and a GP IIb/IIIa inhibitor. In ST-segment elevation, myocardial infarction patients’ administration of an intravenous antiplatelet agent (GP IIb/IIIa inhibitor or cangrelor), in addition to aspirin and a P2Y₁₂ receptor antagonist, efficiently bridges the pharmacodynamic gap of oral agents. Cilostazol on top of aspirin and clopidogrel appears to be safe, although of questionable clinical benefit. In conclusion, combination antiplatelet therapy should be reserved only for selected cases and following thoughtful consideration of the associated risk/benefit ratio.     

Sulfonylureas and on-clopidogrel platelet reactivity in type 2 diabetes mellitus patients

Clopidogrel is a prodrug that needs to be converted in vivo by several cytochrome (CYP) P450 iso-enzymes to become active. Both clopidogrel and the oral hypoglycemic drug class sulfonylureas are metabolized by the iso-enzyme CYP2C9. The objective of the study was to evaluate the relationship of sulfonylureas and on-clopidogrel platelet reactivity in type 2 diabetes mellitus patients undergoing elective coronary stent implantation. In this prospective, observational study, on-clopidogrel platelet reactivity was quantified using adenosine diphosphate (ADP)-induced light transmittance aggregometry in 139 type 2 diabetes mellitus patients undergoing elective coronary stent implantation treated with clopidogrel and aspirin. High on-clopidogrel platelet reactivity was defined as >70.7% platelet reactivity to 20?µmol/L ADP. A total of 53 patients (38.1%) were on concomitant treatment with sulfonylureas. The remaining 86 patients were on other hypoglycemic drugs. On-clopidogrel platelet reactivity was significantly higher in patients with concomitant sulfonylurea treatment as compared to patients without concomitant sulfonylurea treatment (for 5?µmol/L ADP: 46.0%?±?11.8 vs. 40.6%?±?16.0; p?=?0.035, adjusted p?=?0.032 and for 20?µmol/L ADP: 64.6%?±?10.8 vs. 58.7%?±?15.5; p?=?0.019, adjusted p?=?0.017). The concomitant use of sulfonylureas was associated with a 2.2-fold increased risk of high on-clopidogrel platelet reactivity (OR 2.2, 95% CI 1.1–4.7, p?=?0.039 and after adjustment for confounders: OR_adj 2.0, 95% CI 1.0–5.7, p?=?0.048). Concomitant treatment with sulfonylureas might be associated with decreased platelet inhibition by clopidogrel in type 2 diabetes mellitus patients on dual antiplatelet therapy undergoing elective coronary stent implantation.     

Predictors of antiplatelet response to prasugrel during maintenance treatment

Insufficient P2Y12 receptor inhibition is associated with a higher risk of thrombotic events after percutaneous coronary intervention (PCI). The third generation thienopyridine prasugrel achieves stronger platelet inhibition as compared to its predecessor clopidogrel. Little is known about predictors of prasugrel drug responsiveness. The aim of this study was to explore predictors of prasugrel responsiveness in patients with a recent PCI on prasugrel maintenance dose (MD) treatment. In a registry of PCI-treated patients (n?=?163, recruited between August 2009 and March 2012) on prasugrel MD treatment, the ADP-induced platelet aggregation (PA) was assessed on a Multiplate analyzer. The mean (interquartile range (IQR)) ADP-induced PA on prasugrel MD treatment was 206 (138–331) AU?×?min. Obese (defined by a body mass index (BMI)?≥?30) patients (n?=?42) (303 [192–467] vs. 187 [117–305] AU?×?min, p?=?0.0001), patients (n?=?70) with a history of clopidogrel low responsiveness (278 [161–409] vs. 192 [126–282] AU?×?min, p?=?0.002) and patients (n?=?18) on a low (5?mg) prasugrel MD (483 [252–798] vs. 198 [133–313] AU?×?min; p?=?0.0001) showed higher PA values on prasugrel MD as compared to the remaining patients. In a multivariable linear regression model, the latter three variables were independently associated with higher PA values on prasugrel MD treatment. In summary response variability is observed in patients on prasugrel MD treatment. Obesity, a history of clopidogrel low responsiveness and a reduced prasugrel MD of 5?mg are independent predictors of an attenuated response to prasugrel treatment. Further studies are needed to explore clinical implications of this observation.     

Comparison of half- and standard-dose ticagrelor in Chinese patients with NSTE-ACS

Ticagrelor is a novel direct-acting P2Y₁₂ receptor antagonist used for preventing atherothrombotic events in patients with acute coronary syndromes (ACS). The current recommended dose is 90 mg bid, but a low dose of ticagrelor has not been previously studied in Chinese ACS patients. Therefore, we performed this study to observe the different effects of half- and standard-dose ticagrelor on platelet aggregation in Chinese patients with NSTE-ACS. Sixty-two NSTE-ACS subjects were assigned to half-dose ticagrelor (n = 20), standard-dose ticagrelor (n = 22) and clopidogrel (n = 20) groups. Five days after drug administration, VerifyNow P2Y₁₂ assay was performed to test P2Y₁₂ reaction units (PRU) and inhibition of platelet aggregation (IPA). High-platelet reactivity (HPR) was defined as a PRU > 208. The adverse events, including bleeding events and dyspnoea, were monitored throughout the study. PRU values in the half-dose (44.55 ± 32.88) and standard-dose (39.10 ± 40.02) ticagrelor were dramatically lower than those in the clopidogrel group (189.20 ± 65.22; P < 0.0001). The half-dose (84% ± 10%) and standard-dose (86% ± 13%) ticagrelor both showed greater IPA than clopidogrel (33% ± 20%; P < 0.0001). There were no significant differences in PRU and IPA between the two ticagrelor groups (P = 0.3085 and 0.4028, respectively). HPR rates were significantly lower in the two ticagrelor groups (0% for both) than those in the clopidogrel group (35%). In conclusion, half-dose ticagrelor had a similar inhibitory effect on platelet aggregation as standard-dose ticagrelor in Chinese patients with NSTE-ACS, which was significantly stronger than that of clopidogrel.     

Antiplatelet efficacy of P2Y<Subscript>12</Subscript> inhibitors (prasugrel,ticagrelor, clopidogrel) in patients treated with mild therapeutic hypothermia after cardiac arrest due to acute myocardial infarction

Survivors after cardiac arrest (CA) due to AMI undergo PCI and then receive dual antiplatelet therapy. Mild therapeutic hypothermia (MTH) is recommended for unconscious patients after CA to improve neurological outcomes. MTH can attenuate the effectiveness of P2Y₁₂ inhibitors by reducing gastrointestinal absorption and metabolic activation. The combined effect of these conditions on the efficacy of P2Y₁₂ inhibitors is unknown. We compared the antiplatelet efficacies of new P2Y₁₂ inhibitors in AMI patients after CA treated with MTH. Forty patients after CA for AMI treated with MTH and received one P2Y₁₂ inhibitor (clopidogrel, prasugrel or ticagrelor) were enrolled in a prospective observational single-center study. Platelet inhibition was measured by VASP (PRI) on days 1, 2, and 3 after drug administration. In-hospital clinical data and 1-year survival data were obtained. The proportion of patients with ineffective platelet inhibition (PRI > 50 %, high on-treatment platelet reactivity) for clopidogrel, prasugrel, and ticagrelor was 77 vs. 19 vs. 1 % on day 1; 77 vs. 17 vs. 0 % on day 2; and 85 vs. 6 vs. 0 % on day 3 (P < 0.001). The platelet inhibition was significantly worse in clopidogrel group than in prasugrel or ticagrelor group. Prasugrel and ticagrelor are very effective for platelet inhibition in patients treated with MTH after CA due to AMI, but clopidogrel is not. Using prasugrel or ticagrelor seems to be a more suitable option in this high-risk group of acute patients.     

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?µM) 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?µM 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?µM 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 P2Y₁₂-inhibitors on platelet degranulation, perhaps in addition to aggregometry.     

Very-low-dose twice-daily aspirin maintains platelet inhibition and improves haemostasis during dual-antiplatelet therapy for acute coronary syndrome

Higher aspirin doses may be inferior in ticagrelor-treated acute coronary syndrome (ACS) patients and reducing bleeding risk whilst maintaining antithrombotic benefits could improve outcomes. We characterized the pharmacodynamics of a novel dual-antiplatelet-therapy regimen consisting of very-low-dose twice-daily (BD) aspirin with standard-dose ticagrelor. A total of 20 ticagrelor-treated ACS patients entered a randomized crossover to take aspirin 20 mg BD (12-hourly) during one 14-day period and 75 mg once-daily (OD) in the other. After 14 days of treatment, serum thromboxane (TX)B₂ and light-transmittance aggregometry were assessed pre- and 2 h post-morning-dose, bleeding time was measured post-dose, and TXA₂ and prostacyclin stable metabolites were measured in urine collected 2 h post-morning-dose. Data are expressed as mean ± SD. After 14 days treatment, serum TXB₂ levels were significantly greater 2 h post-dosing with aspirin 20 mg BD vs. 75 mg OD (3.0 ± 3.6 ng/mL vs. 0.8 ± 1.9 ng/mL; p = 0.018) whereas pre-dosing levels were not significantly different (3.5 ± 4.1 ng/mL vs. 2.5 ± 3.1 ng/mL, p = 0.23). 1-mmol/L arachidonic acid-induced platelet aggregation was similarly inhibited by both regimens pre-dose (8.5 ± 14.3% vs. 5.1 ± 3.6%, p = 0.24) and post-dose (8.7 ± 14.2% vs. 6.6 ± 5.3%; p = 0.41). Post-dose bleeding time was shorter with 20 mg BD (680 ± 306 s vs. 834 ± 386 s, p = 0.02). Urinary prostacyclin and TX metabolite excretion were not significantly different. In conclusion, compared to aspirin 75 mg OD, aspirin 20 mg BD provided consistent inhibition of platelet TXA₂ release and aggregation, and improved post-dose hemostasis, in ticagrelor-treated ACS patients. Further studies are warranted to assess whether this regimen improves the balance of clinical efficacy and safety.     

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

Thrombin induces platelet aggregation and membrane rearrangements leading to enhanced procoagulant activity and microparticle production, all of which are thought to contribute to thrombus formation in patients with acute coronary syndromes (ACS). Clopidogrel, an adenosine diphosphate (ADP) receptor antagonist acting at the P2Y₁₂ receptor, has been shown to provide clinical benefit in ACS. We aimed to investigate the effects of clopidogrel ex vivo and another ADP-antagonist, AR-C69931MX in vitro on thrombin receptor activating peptide (TRAP)-induced platelet aggregation, procoagulant activity, microparticle formation and [Ca²⁺]_i responses in patients with ACS. Measurements were performed in platelet-rich plasma using aggregometry and flow cytometry (n?=?12). Clopidogrel (300?mg loading dose plus 75?mg daily) significantly inhibited TRAP-induced aggregation, procoagulant activity (annexin V binding) and microparticle production (all P?<?0.05) but not as extensively as AR-C69931MX (400?nmol/l). [Ca²⁺]_i responses induced by a combination of TRAP and ADP designed to mimic the physiological effects of released ADP showed that clopidogrel partially and AR-C69931MX completely removed the ADP component of the [Ca²⁺]_i responses (n?=?6). The results provide new information on the mechanisms involved in the beneficial effects of P2Y₁₂ antagonists in patients with ACS.