A thienopyridine, CB-20, exerts diuretic activity by inhibiting urea transporters.

Urea transporters (UTs) are transmembrane proteins selectively permeable to urea and play an important role in urine concentration. UT-knockout mice exhibit the urea-selective urine-concentrating defect, without affecting electrolyte balance, suggesting that UT-B inhibitors have the potential to be developed as novel diuretics. In this study, we characterized a novel compound 5-ethyl-2-methyl-3-amino-6-methylthieno[2,3-b]pyridine-2,5-dicarboxylate (CB-20) with UT inhibitory activity as novel diuretics with excellent pharmacological properties. This compound was discovered based on high-throughput virtual screening combined with the erythrocyte osmotic lysis assay. Selectivity of UT inhibitors was assayed using transwell chambers. Diuretic activity of the compound was examined in rats and mice using metabolic cages. Pharmacokinetic parameters were detected in rats using LC-MS/MS. Molecular docking was employed to predict the potential binding modes for the CB-20 with human UT-B. This compound dose-dependently inhibited UT-facilitated urea transport with IC50 values at low micromolar levels. It exhibited nearly equal inhibitory activity on both UT-A1 and UT-B. After subcutaneous administration of CB-20, the animals showed polyuria, without electrolyte imbalance and abnormal metabolism. CB-20 possessed a good absorption and rapid clearance in rat plasma. Administration of CB-20 for 5 days did not cause significant morphological abnormality in kidney or liver tissues of rats. Molecular docking showed that CB-20 was positioned near several residues in human UT-B, including Leu364, Val367, and so on. This study provides proof of evidence for the prominent diuretic activity of CB-20 by specifically inhibiting UTs. CB-20 or thienopyridine analogs may be developed as novel diuretics.

Benefit and Risk of Prolonged DAPT After Coronary Stenting in Women.

BACKGROUND: Women may derive differential benefit from prolonged DAPT (dual antiplatelet therapy) after coronary stenting than men. We assessed whether the risks/benefits of prolonged DAPT differ between women and men. METHODS AND RESULTS: The DAPT study was a randomized double-blind, placebo-controlled trial comparing continued thienopyridine versus placebo beyond 12 months after coronary stenting. We compared rates of myocardial infarction, stent thrombosis, major adverse cardiovascular and cerebrovascular events, and bleeding by sex and randomized treatment. Of 11 648 patients, women (N=2925) were older, with higher prevalence of diabetes mellitus and lower rates of acute coronary syndrome than men. At 12 to 30 months, women had similar adjusted ischemic and bleeding events as men. The effects of continued thienopyridine therapy did not differ significantly by sex for stent thrombosis (women: hazard ratio [HR], 0.54; 95% confidence interval [CI], 0.22-1.36; men: HR, 0.26; 95% CI, 0.15-0.44; interaction P=0.17), myocardial infarction (women: HR, 0.75; 95% CI, 0.50-1.14; men: HR, 0.46; 95% CI, 0.36-0.60; interaction P=0.052), major adverse cardiovascular and cerebrovascular events (women: HR, 0.87; 95% CI, 0.62-1.22; men: HR, 0.70; 95% CI, 0.58-0.85; interaction P=0.26), and bleeding (women: HR, 1.45; 95% CI, 0.88-2.40; men: HR, 1.78; 95% CI, 1.28-2.49; interaction P=0.50). CONCLUSIONS: Women had similar late risks of ischemia and bleeding as men after coronary stent procedures. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifier: NCT00977938.

Manejo perioperatorio de pacientes usuarios de antiagregantes plaquetarios / Perioperative management of patients using antiplatelet agents

Resumen El uso de fármacos antiagregantes plaquetarios para prevención primaria y secundaria de eventos cardiovasculares es una práctica común en clínica. La terapia antiagregante plaquetaria disminuye significativamente la incidencia de eventos cardiovasculares, incluyendo infarto agudo al miocardio y accidente cerebro-vascular. Cada vez es más frecuente enfrentarse a pacientes en terapia antiagregante plaquetaria que serán sometidos a algún procedimiento quirúrgico, por tanto es fundamental conocer el manejo perioperatorio de estos fármacos, para disminuir los riesgos y complicaciones asociados a la suspensión o mantención de estas drogas en el período perioperatorio. Los antiagregantes plaquetarios de mayor uso en Chile son la aspirina y las tienopiridinas, siendo el clopidogrel el fármaco más utilizado en este grupo. El enfrentamiento perioperatorio de estos fármacos está supeditado al riesgo trombótico individual de cada paciente y al riesgo hemorrágico de cada cirugía. En cirugías no cardiacas, se sugiere mantener la aspirina, excepto en pacientes con bajo-moderado riesgo trombótico que serán sometidos a cirugías con alto riesgo de sangrado, en los cuales se recomienda suspenderla 5-7 días previo a la intervención quirúrgica. El clopidogrel se sugiere suspenderlo 5 días antes de la cirugía, excepto en pacientes con alto riesgo trombótico que se someterán a procedimientos quirúrgicos con riesgo hemorrágico bajo-moderado. En cirugías de revascularización miocárdica, se recomienda mantener aspirina y suspender clopidogrel 5 días antes del procedimiento. En relación al reinicio postquirúrgico de estos fármacos, se sugiere reanudar aspirina 6 h posterior a la cirugía y clopidogrel durante las primeras 24 h postoperatorias, asegurando previamente una adecuada hemostasia quirúrgica.

The use of antiplatelet drugs for primary and secondary prevention of cardiovascular disease events is a common clinical practice. Antiplatelet therapy significantly decreases the incidence of cardiovascular disease events, including acute myocardial infarction and cerebrovascular accident. It is increasingly common to face patients on antiplatelet therapy who will undergo some surgical procedure, so it is essential to know the perioperative management of these drugs, to reduce the risks and complications associated with the suspension or maintenance of these therapies in the perioperative period. The most common antiplatelet agents used in Chile are acetylsalicylic acid and thienopyridines, of which clopidogrel is the most frequent one. The perioperative management of these drugs has to be based on the individual thrombotic risk of each patient and the risk of hemorrhage of each surgery. In noncardiac surgeries, it is suggested to maintain acetylsalicylic acid, except in patients with low to moderate thrombotic risk who will undergo surgeries with a high risk of bleeding, in which case it is recommended to suspend it 5 to 7 days before surgery. Clopidogrel is suggested to be discontinued 5 days before surgery, except in patients with high thrombotic risk who will undergo surgical procedures with low to moderate risk of hemorrhage. In myocardial revascularization surgeries, it is recommended to maintain acetylsalicylic acid and to suspend clopidogrel 5 days before the procedure. Once assuring adequate surgical hemostasis, it is suggested to reinitiate acetylsalicylic acid 6 hours after surgery and to reinitiate clopidogrel during the first 24 postoperative hours.

Newly Formed Reticulated Platelets Undermine Pharmacokinetically Short-Lived Antiplatelet Therapies.

OBJECTIVE: Aspirin together with thienopyridine P2Y12 inhibitors, commonly clopidogrel, is a cornerstone of antiplatelet therapy. However, many patients receiving this therapy display high on-treatment platelet reactivity, which is a major therapeutic hurdle to the prevention of recurrent thrombotic events. The emergence of uninhibited platelets after thrombopoiesis has been proposed as a contributing factor to high on-treatment platelet reactivity. Here, we investigate the influences of platelet turnover on platelet aggregation in the face of different dual-antiplatelet therapy strategies. APPROACH AND RESULTS: Traditional light transmission aggregometry, cytometry, advanced flow cytometric imaging, and confocal microscopy were used to follow the interactions of populations of platelets from healthy volunteers and patients with stable cardiovascular disease. Newly formed, reticulated platelets overproportionately contributed to, and clustered at, the core of forming aggregates. This phenomenon was particularly observed in samples from patients treated with aspirin plus a thienopyridine, but was absent in samples taken from patients treated with aspirin plus ticagrelor. CONCLUSIONS: Reticulated platelets are more reactive than older platelets and act as seeds for the formation of platelet aggregates even in the presence of antiplatelet therapy. This is coherent with the emergence of an uninhibited subpopulation of reticulated platelets during treatment with aspirin plus thienopyridine, explained by the short pharmacokinetic half-lives of these drugs. This phenomenon is absent during treatment with ticagrelor, because of its longer half-life and ability to act as a circulating inhibitor. These data highlight the important influences of pharmacokinetics on antiplatelet drug efficacies, especially in diseases associated with increased platelet turnover.

Cancer Event Rate and Mortality with Thienopyridines: A Systematic Review and Meta-Analysis.

INTRODUCTION: Thienopyridines are a class of antiplatelet drugs widely used in cardiovascular disease prevention and treatment. A recent concern has come to light regarding the safety of thienopyridines because of the possible risk of malignancy. We therefore performed a systematic review and meta-analysis to evaluate the association between thienopyridine exposure and malignancy. METHODS: We searched the MEDLINE and EMBASE databases in March 2016 for studies that evaluated incident cancer and cancer mortality with and without exposure to thienopyridines. Relevant studies were identified, and data were extracted and analysed using random-effects meta-analysis. RESULTS: A total of nine studies (six randomised controlled trials and three cohort studies) that included 282,084 participants were included. The cancer event rate with clopidogrel and prasugrel was 3.25% and 1.58% respectively. When compared with standard aspirin or placebo, thienopyridines are not significantly associated with cancer mortality and event rate (odds ratio [OR] 1.12, 95% confidence interval [CI] 0.80-1.56, n = 3; and OR 0.92, 95% CI 0.52-1.64, n = 2, respectively. Further analyses examining clopidogrel showed no significant association with cancer event rate or malignancy-related death. When comparing prasugrel with clopidogrel, no significant association was noted for cancer event rate (OR 1.10, 95% CI 0.89-1.37, n = 2]. Subanalyses according to cancer location showed that thienopyridines are not significantly associated with malignancy mortality and/or incidence. CONCLUSIONS: Our results suggest that there is currently insufficient evidence to suggest that thienopyridine exposure is associated with an increased risk of cancer event rate or mortality.

The role of P2Y12 receptor and activated platelets during inflammation.

Platelets play an important role not only during thrombosis, but also in modulating immune responses through their interaction with immune cells and by releasing inflammatory mediators upon activation. The P2Y12 receptor is a Gi-coupled receptor that not only regulates ADP-induced aggregation but can also dramatically potentiate secretion, when platelets are activated by other stimuli. Considering the importance of P2Y12 receptor in platelet function, a class of antiplatelet drugs, thienopyridines, have been designed and successfully used to prevent thrombosis. This review will focus on the role of activated platelets in inflammation and the effects that P2Y12 antagonism exerts on the inflammatory process. A change in platelet functions was noted in patients treated with thienopyridines during inflammatory conditions, suggesting that platelets may modulate the inflammatory response. Further experiments in a variety of animal models of diseases, such as sepsis, rheumatoid arthritis, myocardial infarction, pancreatitis and pulmonary inflammation have also demonstrated that activated platelets influence the inflammatory state. Platelets can secrete inflammatory modulators in a P2Y12-dependent manner, and, as a result, directly alter the inflammatory response. P2Y12 receptor may also be expressed in other cells of the immune system, indicating that thienopyridines could directly influence the immune system rather than only through platelets. Overall the results obtained to date strongly support the notion that activated platelets significantly contribute to the inflammatory process and that antagonizing P2Y12 receptor can influence the immune response.

Pharmacogenetics in the Community Pharmacy: Thienopyridine Selection Post-Coronary Artery Stent Placement.

INTRODUCTION: Although antiplatelet therapy is a mainstay of post-percutaneous coronary intervention therapy, pharmacogenetic (PGt) considerations of therapy are often ignored despite related Food and Drug Administration warnings. Pharmacists are well situated to provide PGt guidance, and the community pharmacy is one setting where PGt testing, interpretation, and recommendations can take place to ensure optimal therapeutic outcomes. CASE REPORT: A 65-year-old man who had a myocardial infarction that was treated with PCI and stent placement was determined by a community pharmacist to be a candidate for PGt testing to ensure optimal antiplatelet therapy. The patient was seen in the pharmacy as a part of a medication therapy management encounter and underwent genetic testing. Results of the genetic testing indicated the need for modification of therapy. The community pharmacist interpreted the results and made the appropriate recommendation to the cardiologist who in turn modified antiplatelet therapy appropriately. CONCLUSION: This case describes the potential for collaboration between pharmacists and physicians to optimize antiplatelet therapy through PGt testing. Points of consideration for others looking to implement related PGt services are also discussed.

Thienopyridines resistance and recovery of platelet function after discontinuation of thienopyridines in cardiac surgery patients.

OBJECTIVES: Patients who undergo cardiac operations under the effects of thienopyridines have a greater risk of major postoperative bleeding, transfusions and surgical revision due to bleeding. Discontinuation of thienopyridine is suggested but an adequate recovery period following discontinuation is still under debate, with opinions ranging from 3 to 7 days. The aim of this study was to assess the rate of recovery of thienopyridine-resistant patients and the time taken for resumption of platelet function after discontinuation of thienopyridine, in the setting of patients scheduled for cardiac operations. METHODS: This was a retrospective study, based on 344 patients screened for platelet aggregation before cardiac operations. All the patients received thienopyridines within 7 days prior to the test. Multiple electrode aggregometry adenosine diphosphate test was used to assess platelet aggregation before the operation. RESULTS: Thienopyridine resistance rate was 28%. Patients receiving clopidogrel had a significantly higher rate (32%) of resistance, compared with those receiving ticlopidine (14%) and thienopyridine resistance was significantly associated with platelet count (P = 0.006). The time taken to recover platelet function after thienopyridine discontinuation was variable between individuals; the only factor associated with a faster recovery time was the serum bilirubin value (P = 0.002). Platelet aggregation values high enough to avoid major bleeding were reached 3 days after discontinuation (95% confidence interval: 2-4 days); however, a complete recovery of platelet function was reached only after 8 days (95% confidence interval: 7-9 days). CONCLUSIONS: Patient-specific factors determine the effectiveness of thienopyridine treatment and platelet function recovery rate. Among these, platelet count (for thienopyridine resistance) and serum bilirubin values (for platelet function recovery rate) should be considered.

Bleeding risk with triple antithrombotic therapy in patients with atrial fibrillation and drug-eluting stents.

In the era of drug-eluting stents (DES), a long-term dual antiplatelet therapy is required to prevent late stent thrombosis. However, in patients with atrial fibrillation (AF), there is a concern that combining warfarin with dual antiplatelet therapy may increase the risk of bleeding. We analyzed 1274 consecutive patients with coronary artery disease who were treated with coronary intervention from January 2006 through January 2009. Of these, we enrolled 74 AF patients treated with DES and dual antiplatelet therapy as well as warfarin. The primary endpoint was the incidence of major bleeding within 3 years; the predictive factor of major bleeding was also analyzed. To evaluate the efficacy of anticoagulant therapy, time in therapeutic range (TTR) was also measured. The 3-year incidence of major bleeding was 12.2 % (nine of 74 patients). The average observation period was 25.7 ± 20.2 months. Mean TTR value was 44.6 ± 33.0 % and was maintained at a relatively low level. Multivariate analysis revealed that a higher CHADS2 score (2-point more) was an independent predictor of increased risk of major bleeding. Major bleeding in the patients with triple antithrombotic therapy including warfarin occurred at a relatively high rate. Although the higher CHADS2-score indicates a high risk of thrombotic events, it was strongly associated with bleeding complications.

[Oral antiplatelet agents can still be used along with proton pump inhibitors in spite of drug interactions]. / Orale trombocythæmmere kan fortsat anvendes med protonpupehæmmere trods farmakologiske interaktioner.

Acetylsalicylic acid and P2Y12-receptor antagonists are antiplatelet agents widely used in the treatment and secondary prevention of cardiovascular disease. Since upper gastrointestinal bleeding is common during antiplatelet treatment, many patients are also treated with a proton pump inhibitor. In recent years it has been heavily discussed if proton pump inhibitors may attenuate the cardiovascular protection achieved with oral antiplatelet agents. Pharmacodynamic studies have suggested important drug interactions, but clinical studies have failed to confirm any clinical impact.

Preparation of the thienopyridine derivatives loaded liposomes and study on the effect of compound-lipid interaction on release behavior.

The article describes characterization of two liposome formulations containing thienopyridine derivatives, namely TP-58 and TP-67. By preparing the liposomes, the concentration of the two compounds in ultrapure water was increased up to three orders of magnitude. After i.v. administration of the liposomes in rats, the initial compound plasma concentrations were enhanced more than fifty times relative to that after i.g. administration of the compound suspensions. It was found out that the release rate of TP-67 from the liposome both in vitro and in vivo was not significantly different from that of TP-58. TP-58 was more lipophilic than TP-67 according to partition coefficiency, and TP-67 had greater polarity than TP-58 based on polar surface area (PSA). With DSC, it was found out that the interaction magnitude between TP-67 and the lipid bilayer was not significantly different from that between TP-58 and the lipid bilayer, which accounted for the similarity of the two compounds in release rate both in vitro and in vivo. It indicated liposome can be used as a potential carrier for broading the application of TP-58 and TP-67. Interaction between the thienopyridine derivatives and the lipid bilayer is probably the decisive factor for compound release from the liposomes.

Mechanisms of platelet activation in acute coronary syndromes.

Platelets are known to play a fundamental role in acute coronary syndromes. After atherosclerotic plaque rupture, platelets can form pathogenic, occlusive thrombi leading to acute ischemic events. Today there are promising results from recently developed antiplatelet agents. However, morbidity and mortality from acute coronary syndromes remain significant despite the administration of combination therapies (aspirin, thienopyridines). Sharing similar mechanisms, platelets may also form a thin monolayer in areas of damaged endothelium contributing to primary hemostasis. For this reason, administration of antiplatelet drugs is often associated with increased bleeding risk. As a result, currently available antiplatelet therapy cannot be characterized as optimal. The precise mechanisms of platelet activation in acute coronary syndromes are still under investigation. The study of basic mechanisms of platelet adhesion, activation and aggregation after atherosclerotic plaque rupture may help to define new targets for their inhibition. In the future, newer antiplatelet agents may offer more comprehensive platelet inhibition without interfering with primary hemostasis, thus offering greater protection with lower hemorrhagic risk.

Bridging antiplatelet therapy with cangrelor in patients undergoing cardiac surgery: a randomized controlled trial.

CONTEXT: Thienopyridines are among the most widely prescribed medications, but their use can be complicated by the unanticipated need for surgery. Despite increased risk of thrombosis, guidelines recommend discontinuing thienopyridines 5 to 7 days prior to surgery to minimize bleeding. OBJECTIVE: To evaluate the use of cangrelor, an intravenous, reversible P2Y(12) platelet inhibitor for bridging thienopyridine-treated patients to coronary artery bypass grafting (CABG) surgery. DESIGN, SETTING, AND PATIENTS: Prospective, randomized, double-blind, placebo-controlled, multicenter trial, involving 210 patients with an acute coronary syndrome (ACS) or treated with a coronary stent and receiving a thienopyridine awaiting CABG surgery to receive either cangrelor or placebo after an initial open-label, dose-finding phase (n = 11) conducted between January 2009 and April 2011. Interventions Thienopyridines were stopped and patients were administered cangrelor or placebo for at least 48 hours, which was discontinued 1 to 6 hours before CABG surgery. MAIN OUTCOME MEASURES: The primary efficacy end point was platelet reactivity (measured in P2Y(12) reaction units [PRUs]), assessed daily. The main safety end point was excessive CABG surgery-related bleeding. RESULTS: The dose of cangrelor determined in 10 patients in the open-label stage was 0.75 µg/kg per minute. In the randomized phase, a greater proportion of patients treated with cangrelor had low levels of platelet reactivity throughout the entire treatment period compared with placebo (primary end point, PRU <240; 98.8% (83 of 84) vs 19.0% (16 of 84); relative risk [RR], 5.2 [95% CI, 3.3-8.1] P < .001). Excessive CABG surgery-related bleeding occurred in 11.8% (12 of 102) vs 10.4% (10 of 96) in the cangrelor and placebo groups, respectively (RR, 1.1 [95% CI, 0.5-2.5] P = .763). There were no significant differences in major bleeding prior to CABG surgery, although minor bleeding episodes were numerically higher with cangrelor. CONCLUSIONS: Among patients who discontinue thienopyridine therapy prior to cardiac surgery, the use of cangrelor compared with placebo resulted in a higher rate of maintenance of platelet inhibition. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00767507.

Clinical effects and outcomes with new P2Y12 inhibitors in ACS.

Thienopyridines have become the cornerstone of treatment for percutaneous coronary intervention although no survival benefit has ever been shown with clopidogrel despite increasing loading doses. Newly developed P2Y12 inhibitors are more potent, more predictable, and have a faster onset of action than clopidogrel, characteristics that make them particularly attractive for high-risk percutaneous coronary intervention (PCI). Four new P2Y12 inhibitors have been tested each of them having particular individual properties. Prasugrel is an oral pro-drug leading to irreversible blockade of the P2Y12 receptor and is approved worldwide for ACS PCI. Ticagrelor is a direct-acting and reversible inhibitor of the P2Y12 receptor with potentially more pleiotropic effects. Cangrelor is an intravenous direct and reversible inhibitor of the P2Y12 receptor providing the highest level of inhibition, and elinogrel is an intravenous and oral P2Y12 antagonist with a direct and reversible action. Both prasugrel and ticagrelor, opposed to clopidogrel, have shown that stronger P2Y12 inhibition led respectively to significant 19 and 16% relative risk reduction of a similar primary end point combining cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke. Both drugs showed a significant 0.6% absolute excess of TIMI major bleeding not related to CABG surgery. Because in clinical trials, patients perceived to be at higher risk of bleeding usually are excluded, the risk of major and even fatal bleeding might even be higher in a 'real-world' setting, i.e. in the elderly patient with comorbidities. On the other hand, these newly developed P2Y12 inhibitors decrease mortality after PCI compared with clopidogrel. The risk/benefit ratio is particularly favorable in PCI for patients with STEMI.

Impact of concomitant use of proton-pump inhibitors and thienopyridine derivatives on the antiplatelet effects.

BACKGROUND: Although there has been an intense debate whether concomitant use of proton-pump inhibitors (PPIs) attenuates the antiplatelet effects of thienopyridine derivatives, the drug-drug interaction remains unclear in Japanese patients with coronary artery disease. METHODS AND RESULTS: Platelet function test was performed in 461 patients who were scheduled for or had undergone stent implantation, treated with 100mg/day of aspirin and a thienopyridine (200mg/day of ticlopidine or 75 mg/day of clopidogrel) for at least 14 days. Adenosine diphosphate-induced platelet aggregation was evaluated with screen filtration pressure method, and the upper quartile of high platelet reactivity was defined as high on-treatment platelet reactivity (HPR). PPI use was at physician's discretion. Patients taking a thienopyridine plus a PPI (n=166) were older and had a higher incidence of acute coronary syndromes on admission compared with patients taking a thienopyridine without a PPI (n=295). The rate of HPR was higher in patients taking a thienopyridine plus a PPI than in patients taking a thienopyridine without a PPI (31% vs 21%, p=0.01). On multivariate logistic regression analysis, independent predictors of HPR were concomitant PPI use [odds ratio (OR): 1.66, 95% confidence interval (CI): 1.03-2.68], diabetes mellitus (OR: 1.76, CI: 1.11-2.81), and calcium channel blockers use (OR: 1.93, CI: 1.18-3.18). However, there was no significant difference in the rate of extremely high platelet reactivity [58 patients (12.5%) with PATI<4.0 µM] between patients treated with a thienopyridine plus a PPI and those without a PPI (14% vs 11%, NS). CONCLUSION: HPR was frequently observed in Japanese patients treated with thienopyridines plus PPIs compared to those without PPIs. Further prospective studies are needed to estimate the risk of adverse cardiovascular events associated with concomitant use of PPIs and thienopyridines.

Thienopyridines, but not elinogrel, result in off-target effects at the vessel wall that contribute to bleeding.

Clinical studies with clopidogrel or prasugrel show that although increased inhibition of P2Y(12) and platelet function improves efficacy, bleeding is also increased. Other preclinical and clinical studies have suggested a greater therapeutic index (TI) with reversible inhibitors and disproportionate effects of thienopyridines on bleeding at high doses. We used multiple in vivo (FeCl(3)-induced arterial thrombosis in mesenteric arteries, blood loss after tail transsection, and platelet deposition and wound closure time in a micropuncture model in mesenteric veins) and ex vivo (light transmittance aggregometry, prothrombin time, and activated partial thromboplastin time) mouse models to 1) compare the TI of clopidogrel, prasugrel, and elinogrel, a reversible, competitive antagonist, with that in P2Y(12)(-/-) mice and 2) determine whether the bleeding consequences of the thienopyridines are attributed only to the inhibition of P2Y(12). Data indicated greater (elinogrel) and decreased (thienopyridines) TI compared with that in P2Y(12)(-/-) mice. The impaired TI associated with the thienopyridines was not attributed to non-P2Y(12) activities on platelet function or coagulation but was related to a direct effect at the vessel wall (inhibition of vascular tone). Further analysis showed that the prasugrel off-target effect was dose- and time-dependent and of a reversible nature. In conclusion, the TI of thienopyridines in the mouse may be decreased by P2Y(12)-independent off-target effects at the vessel wall, whereas that of elinogrel may be enhanced by the reversible, competitive nature of the antiplatelet agent.