Prasugrel: a novel thienopyridine antiplatelet agent. A review of preclinical and clinical studies and the mechanistic basis for its distinct antiplatelet profile

Prasugrel (CS-747, LY640315) is a novel member of the thienopyridine class of oral antiplatelet agents that includes ticlopidine and clopidogrel. Like other thienopyridines, prasugrel is a prodrug that is inactive in vitro. Prasugrel's distinct chemical structure permits efficient conversion to its active metabolite with a less rigorous dependence on specific cytochrome P-450 enzymes. Prasugrel is rapidly converted in vivo to an active metabolite (R-138727) that binds specifically and irreversibly to the platelet P2Y 12 purinergic receptor inhibiting ADP-mediated platelet activation and aggregation. Preclinical studies indicated that prasugrel is approximately 10- and 100-fold more potent at inhibiting ex vivo platelet aggregation and in vivo thrombus formation than clopidogrel and ticlopidine, respectively. Early clinical data in healthy subjects confirmed the greater platelet inhibition and consistency with prasugrel compared to clopidogrel. While the active metabolites of prasugrel and clopidogrel resulted in similar levels of platelet inhibition in vitro, the amount of each active metabolite generated in vivo was quite different-prasugrel (60 mg) resulting in an approximately 12-fold greater exposure to its active metabolite compared with clopidogrel (300 mg). This observation provides a mechanistic basis for the faster, greater, and more consistent inhibition of platelet aggregation observed with prasugrel. Clinical studies in patients with cardiovascular disease confirmed the potent antiplatelet effect of prasugrel compared with clopidogrel. Collectively, these phase 1/1b studies and a phase 2 study (JUMBO-TIMI 26) aided in dose selection for the recently completed phase 3 trial (TRITON-TIMI 38) in patients with acute coronary syndrome undergoing percutaneous coronary intervention.     

Prasugrel: a novel platelet ADP P2Y12 receptor antagonist. A review on its mechanism of action and clinical development

Antiplatelet therapy is the cornerstone of treatment for patients who present with acute coronary syndrome (ACS) or undergo percutaneous coronary intervention (PCI). Clopidogrel, in combination with aspirin, is associated with improvement in long-term clinical outcomes in these patients and is currently the antiplatelet therapy of choice. However, a significant number of patients experience recurrent ischemic events, which have been in part attributed to variability in individual response profiles to currently recommended treatment regimens. The presence of variable degrees of responsiveness, thus inadequate platelet inhibition in some patients, underscores the need for novel agents with more potency and less variable platelet inhibitory effects. Prasugrel (CS-747; LY640315), a novel third-generation oral thienopyridine, is a specific, irreversible antagonist of the platelet adenosine diphosphate (ADP) P2Y₁₂ receptor. Pre-clinical and early phase clinical studies have shown prasugrel to be characterized by more potent antiplatelet effects, lower interindividual variability in platelet response, and faster onset of activity compared with clopidogrel. Recent findings from large-scale Phase III testing showed prasugrel to be more efficacious in preventing ischemic events in ACS patients undergoing PCI; however, this is achieved at the expense of an increased risk of bleeding. This article reviews the currently available data regarding the efficacy and safety of prasugrel.     

Prasugrel: a novel platelet ADP P2Y12 receptor antagonist. A review on its mechanism of action and clinical development

Antiplatelet therapy is the cornerstone of treatment for patients who present with acute coronary syndrome (ACS) or undergo percutaneous coronary intervention (PCI). Clopidogrel, in combination with aspirin, is associated with improvement in long-term clinical outcomes in these patients and is currently the antiplatelet therapy of choice. However, a significant number of patients experience recurrent ischemic events, which have been in part attributed to variability in individual response profiles to currently recommended treatment regimens. The presence of variable degrees of responsiveness, thus inadequate platelet inhibition in some patients, underscores the need for novel agents with more potency and less variable platelet inhibitory effects. Prasugrel (CS-747; LY640315), a novel third-generation oral thienopyridine, is a specific, irreversible antagonist of the platelet adenosine diphosphate (ADP) P2Y(12) receptor. Pre-clinical and early phase clinical studies have shown prasugrel to be characterized by more potent antiplatelet effects, lower interindividual variability in platelet response, and faster onset of activity compared with clopidogrel. Recent findings from large-scale Phase III testing showed prasugrel to be more efficacious in preventing ischemic events in ACS patients undergoing PCI; however, this is achieved at the expense of an increased risk of bleeding. This article reviews the currently available data regarding the efficacy and safety of prasugrel.     

Thienopyridines and Other ADP-Receptor Antagonists

Platelet P2Y12 receptor inhibition plays a pivotal role in preventing thrombotic vascular events in patients with ACS and in patients undergoing percutaneous coronary intervention (PCI). Among the P2Y12 receptor inhibitors, the group of thienopyridines include ticlopidine, clopidogrel and prasugrel, all of which are orally administered prodrugs leading to irreversible P2Y12 receptor inhibition. Non-thienopyridine derivatives including ticagrelor, cangrelor and elinogrel do not require metabolic activation and lead to a reversible P2Y12 receptor inhibition in contrast to thienopyridines. The extend of platelet inhibition is subject to the administered antiplatelet agent and influenced by individual genetic and clinical factors. Insufficient platelet inhibition, termed high platelet reactivity (HPR) is associated with an increased risk for ischemic events after PCI whereas exceeding platelet inhibition results in an increased bleeding risk. Pharmacologic properties and clinical outcome data differ substantially between the existing P2Y12 receptor inhibitors. Whether individualized antiplatelet treatment incorporating different P2Y12 receptor inhibitors improves patients' clinical outcomes warrants further investigation.     

The role of antiplatelet therapy in the management of acute coronary syndromes

The benefit of aspirin use in the emergent care of acute coronary syndromes (ACS) has been well-established. Recent studies have further demonstrated the importance of antiplatelet therapy in the acute setting, primarily with the use of intravenous glycoprotein IIb/IIIa receptor inhibitors. Aspirin and the thienopyridines (ticlopidine and clopidogrel) are oral antiplatelet agents that interfere with platelet activation in complementary, but separate pathways. Combination therapy of aspirin with other antiplatelet agents has demonstrated a benefit for the management of ACS. This article reviews the pathophysiology of platelet activation in ACS, landmark trials regarding antiplatelet agents, and the current recommendations for the use of both intravenous and oral antiplatelet agents in the management of patients with ACS.     

Review of clopidogrel dose escalation in the current era of potent P2Y12 inhibitors

Dual anti-platelet therapy with aspirin and a P2Y12 inhibitor is the standard of care for patients with acute coronary syndromes (ACS) and for patients undergoing percutaneous coronary intervention (PCI). Clopidogrel is associated with increased risk of high on-treatment platelet reactivity (HTPR) compared to ticagrelor and prasugrel. Investigators have therefore sought to “escalate” clopidogrel dosing to overcome HTPR to reduce ischemic/thrombotic events. In this review, we will summarize the evidence for dose escalation in the context of genetic determinants of resistance and platelet function data. We will review contemporary clinical trials that have sought to improve delivery of dual antiplatelet therapy to patients with coronary artery disease and discuss the potential of clopidogrel dose escalation in specific populations.     

The role of antiplatelet therapy in the management of acute coronary syndromes

The benefit of aspirin use in the emergent care of acute coronary syndromes (ACS) has been well-established. Recent studies have further demonstrated the importance of antiplatelet therapy in the acute setting, primarily with the use of intravenous glycoprotein IIb/IIIa receptor inhibitors. Aspirin and the thienopyridines (ticlopidine and clopidogrel) are oral antiplatelet agents that interfere with platelet activation in complementary, but separate pathways. Combination therapy of aspirin with other antiplatelet agents has demonstrated a benefit for the management of ACS. This article reviews the pathophysiology of platelet activation in ACS, landmark trials regarding antiplatelet agents, and the current recommendations for the use of both intravenous and oral antiplatelet agents in the management of patients with ACS.     

Platelet hyperreactivity and stent thrombosis in patients undergoing coronary stenting

Stent thrombosis (ST) is a rare but very serious event complicating percutaneous coronary intervention (PCI) procedures. Both procedure- and patient-related factors, including inadequate platelet inhibition are well known predictors of ST. According to the present guidelines, a dual antiplatelet treatment regimen consisting of aspirin and a P2Y12 receptor inhibitor such as clopidogrel, prasugrel or ticagrelor is routinely administered to ACS patients and to patients undergoing PCI in order to prevent thrombotic vessel occlusions. In recent years, evidence has grown that patients showing high on-treatment platelet reactivity (HPR) under clopidogrel intake exhibit a higher risk for the occurrence of ischemic events including ST. For assessing HPR, different platelet function assays are currently available and have already found their way into routine clinical practice in several centers. Along with this development, more potent P2Y12 receptor inhibitors like prasugrel and ticagrelor are substitutes for clopidogrel in specific circumstances such as in ACS patients or in patients who do not adequately respond to standard clopidogrel treatment. Utilizing platelet function monitoring, patients showing HPR can be identified and an optimized antiplatelet treatment regime can be tailored for these patients. This review paper aims to summarize the important facts in relation to ST and antiplatelet therapy with a particular focus on P2Y12 receptor inhibition and its ex vivo assessment in patients undergoing coronary stent placement.     

Importance of potent P2Y(12) receptor blockade in acute myocardial infarction: focus on prasugrel

INTRODUCTION: Prasugrel therapy is recommended in patients with acute coronary syndromes (ACS) undergoing percutaneous coronary intervention (PCI). AREAS COVERED: This article reviews the efficacy and safety profile of prasugrel, cost considerations, and its role in clinical practice based on published data. The authors searched PubMed and Ovid databases for English language clinical trial articles involving the use of prasugrel in human subjects and patients, published through June 2012. The keyword "prasugrel" was used. The review focuses on clinical trials, but other articles including Food and Drug Administration documents are also reviewed. EXPERT OPINION: Prasugrel has a more rapid and greater pharmacodynamic (PD) effect than clopidogrel. No significant drug - drug interactions have been reported. In a large-scale randomized clinical trial, prasugrel was associated with better protection against ischemic event occurrence compared to clopidogrel, but more bleeding in ACS patients undergoing PCI. Adverse outcomes outweighed the benefit of prasugrel in certain subgroups, including patients over the age of 75, those weighing less than 60 kg, and patients with a prior history of stroke or transient ischemic attack. In subsequent PD studies, prasugrel therapy showed suboptimal platelet inhibition in selected patients. In addition, "hyper-responsiveness" to prasugrel may increase the risk of serious bleeding in high-risk patients. More detailed studies are warranted to explore antiplatelet regimens tailored to optimally limit ischemic and bleeding event occurrences. A Phase-III TRILOGY trial (NCT00699998) will indicate the clinical efficacy and safety of prasugrel in patients with non-ST-segment elevation ACS, who are medically managed without coronary revascularization.     

Role of platelet function testing in clinical practice: current concepts and future perspectives

Oral antiplatelet therapy is routinely administered to ACS patients as well as to patients undergoing percutaneous coronary intervention (PCI) with the primary aim of inhibiting platelet-mediated thrombus formation and subsequent abrupt vessel occlusion. Individual platelet response to aspirin and especially to clopidogrel is highly variable and evidence has grown in recent years linking an attenuated response to therapy with the occurrence of ischemic events. At present, the antiplatelet therapy landscape is changing with the emergence of prasugrel and ticagrelor as alternative and more potent treatment options. In addition, tests for near-patient monitoring of platelet function in clinical practice are available and are being increasingly employed for the optimization of antiplatelet treatment. It is hypothesized that platelet function testing may prove useful for achieving an optimized balance of proven platelet inhibition at a cost of moderate bleeding risk. This is also why first centers have already included testing in day-to-day routine. Extensive clinical evaluations with a range of currently-available assays for platelet function testing are ongoing and the current and future role of platelet function testing in clinical practice is a topic of much debate. Widespread adoption of this practice and its incorporation into clinical guidelines awaits the results of ongoing trials where treatment is changed based on platelet function testing data. This review paper summarizes the key characteristics of platelet function tests available, presents an overview of relevant studies and examines the present role of platelet function testing in clinical practice with a focus on antiplatelet therapy in patients undergoing coronary stent placement.     

Clopidogrel

Dual antiplatelet therapy with acetylsalicylic acid (aspirin) and clopidogrel is a guideline-recommended standard of care for patients with acute coronary syndromes (ACS) and those who undergo percutaneous coronary intervention (PCI). Despite a large body of clinical evidence obtained from randomized clinical trials and patient registries supporting the efficacy and safety of aspirin plus clopidogrel therapy in these patients, questions concerning the optimal use of dual antiplatelet therapy remain. Widely debated topics pertaining to dual antiplatelet therapy in patients with ACS or undergoing PCI include (i) the appropriate clopidogrel loading dose; (ii) the optimal time to initiate the clopidogrel loading dose; (iii) the optimal duration of dual antiplatelet therapy following ACS or PCI; (iv) impact of variability of platelet response on patient outcomes; and (v) the role of other recommended and emerging P2Y₁₂ antagonists. This review discusses these ongoing controversies regarding the optimal use of dual antiplatelet therapy with aspirin and clopidogrel in patients with ACS or those undergoing PCI.     

On-treatment platelet reactivity: State of the art and perspectives

High on-clopidogrel platelet reactivity (HcPR) during dual-antiplatelet therapy is a marker of vascular risk, in particular stent thrombosis, in patients with acute coronary syndromes (ACS). Genetic determinants (CYP2C19*2 polymorphism), advanced age, female gender, diabetes and reduced ventricular function are related to a higher risk to develop HcPR. In addition, inflammation and increased platelet turnover, as revealed by the elevated percentage of reticulated platelets in patients’ blood, that characterize the acute phase of acute coronary syndromes, are associated with HcPR. To overcome the limitation of clopidogrel, new antiplatelet agents (prasugrel and ticagrelor) were developed and the demonstration of their superiority over clopidogrel was obtained in the two randomized trials, TRITON TIMI 38 and PLATO. Emerging evidence is accumulating on the role of high-on aspirin platelet reactivity (HaPR), especially in the clinical context of diabetes. Finally, the presence of new, potent antiplatelet drugs has shifted the focus from thrombotic to bleeding risk. Recent data document that low on-treatment platelet reactivity (LPR) is associated with a significantly higher bleeding risk. Due to the current possibility to choose between multiple antiplatelet strategies, the future perspective is to include in the management of ACS, in addition to clinical data and classical risk factors, the definition of platelet function during treatment in order to set a tailored therapy.     

Treating acute coronary syndromes with new antiplatelet drugs: the mortality issue with prasugrel and ticagrelor

Acute coronary syndromes (ACS) are the leading cause of mortality in Western countries. Until a few years ago, the antiplatelet drug to be administered in association with aspirin was indisputably clopidogrel. Recent data from randomized trials conducted in ACS patients have shown that the new oral antiplatelet regimens, prasugrel and ticagrelor, are associated with a significant reduction in cardiovascular events, as compared to clopidogrel. Moreover ticagrelor reduced both all-cause and cardiovascular mortality as compared to clopidogrel in the PLATO trial. However, there are intrinsic differences between the trials design and among the enrolled ACS populations, that make complex the generalization of the mortality results in the whole spectrum of ACS patients. We aimed to provide further insights into the unresolved mortality issues raised in the PLATO and TRITON-TIMI 38 trials, by analysing the effects of ticagrelor and prasugrel in the ACS populations included in the respective trials.     

Treating acute coronary syndromes with new antiplatelet drugs: the mortality issue with prasugrel and ticagrelor

Abstract

Acute coronary syndromes (ACS) are the leading cause of mortality in Western countries. Until a few years ago, the antiplatelet drug to be administered in association with aspirin was indisputably clopidogrel. Recent data from randomized trials conducted in ACS patients have shown that the new oral antiplatelet regimens, prasugrel and ticagrelor, are associated with a significant reduction in cardiovascular events, as compared to clopidogrel. Moreover ticagrelor reduced both all-cause and cardiovascular mortality as compared to clopidogrel in the PLATO trial. However, there are intrinsic differences between the trials design and among the enrolled ACS populations, that make complex the generalization of the mortality results in the whole spectrum of ACS patients. We aimed to provide further insights into the unresolved mortality issues raised in the PLATO and TRITON–TIMI 38 trials, by analysing the effects of ticagrelor and prasugrel in the ACS populations included in the respective trials.     

A comprehensive comparative review of adenosine diphosphate receptor antagonists

INTRODUCTION: Thrombosis risk necessitates dual antiplatelet therapy with aspirin and an adenosine diphosphate (ADP) receptor antagonist, in patients who have acute coronary syndrome. Current guidelines emphasize the critical role of dual antiplatelet therapy in both medical management and invasive strategy, especially in patients undergoing percutaneous coronary intervention. With the availability of multiple ADP-receptor antagonists, it is crucial to select the most appropriate agent for each patient. AREAS COVERED: The pertinent trials were identified through a MEDLINE search, in addition to a manual search from the articles retrieved. This review examines the differences between clopidogrel, prasugrel and ticagrelor in terms of their pharmacological/pharmacokinetic properties, clinical efficacy, drug interactions and safety parameters. EXPERT OPINION: Prasugrel and ticagrelor exhibit greater platelet inhibition and superior efficacy compared with clopidogrel, at the expense of higher bleeding risk. Prasugrel and ticagrelor should be preferred over clopidogrel in patients who are at a high risk of thrombotic events with low risk of bleeding. Additionally, these two agents may offer advantage over clopidogrel in those patients who might have risk for drug resistance due to CYP2C19 polymorphism. In selecting the ideal agent for patients, clinicians should tailor the antiplatelet regimen by considering individual risk factors and medication characteristics.     

Novel Antiplatelet Therapy in Acute Coronary Syndromes: What is New in the Pipeline?

Acute coronary syndromes (ACS) are triggered by enhanced platelet activation and aggregation. Hence, a cornerstone of successful secondary prevention in ACS is an effective platelet inhibition. Additionally, coronary interventions (PCI) lead to even increased artherothrombotic risks, another challenge in preventing recurrent events including stent thrombosis. Promising platelet targets were characterized and novel molecules were developed that are currently under investigation. Intensified antiplatelet therapy includes the risk of major bleeding which itself increases the mortality rate. Previous strategies of antiplatelet therapy were based on an "one-size fits all" concept. However, there has been evidence that variability of drug response exists and represents a clinically relevant issue. This observation is in line with results of randomized clinical trials that standard-of-care antiplatelet therapy is not sufficient to reduce cardiovascular (CV) risk in certain subgroups of ACS patients. In the last years, novel antiplatelet substances have entered the clinical arena and others are currently under investigation in phase II and III clinical trials. These include 3rd generation thienopyridine (prasugrel, elinogrel), ATP analogs (Ticagrelor, cangrelor), and non-ADP-receptor blocking antiplatelet substances like thrombin receptor antagonists. These agents have shown promising results in pilot studies and recent randomized trials. As the prevention of atherothrombotic risk is at the expense of bleeding risk, it will be a future task to clearly define patients' groups and subsets of ACS for the best net clinical benefit. This article focuses on the role of novel antiplatelet substances to reduce CV risk in ACS, discuss clinical implications and their potential future role.     

The role of the cytochrome P450 polymorphisms in clopidogrel efficacy and clinical utility

Clopidogrel, an antiplatelet agent, prevents platelet aggregation by inhibiting the adenosine disphosphate (ADP) P2Y12 receptor, which is located on the platelet surface. Although dual antiplatelet therapy appears to be efficient, a considerable number of patients continue to experience adverse cardiovascular events, such as stent thrombosis. The percentage of low response to antiplatelet therapy varies from 4% to 30% of patients depending on the cut-off values. In addition, several factors such as poor absorption, drug-to-drug interactions, inadequate dosing, elevated body mass index, insulin resistance and the nature of acute coronary syndromes have been implicated in low clopidogrel response. Recently, studies have focused on the role of genetic polymorphisms encoding enzymes that participate in clopidogrel hepatic metabolism or receptors involved in intestinal absorption and ADP induced platelet aggregation, which may affect the percentage of platelet inhibition after clopidogrel administration. The management of clopidogrel resistance remains a controversial issue and additional studies are required to evaluate the safety and efficacy of increased loading of clopidogrel or replacement with other new antiplatelet agents such as prasugrel.     

Prasugrel

Clinical trials have demonstrated the superior clinical efficacy of dual antiplatelet therapy with a thienopyridine (a P2Y(12) receptor blocker) and aspirin (COX-1 inhibitor) in patients undergoing stenting as well as patients with acute coronary syndromes. However, clopidogrel treatment is associated with a wide response variability and non-responsiveness in selected patients. The latter phenomenon is linked to the occurrence of recurrent ischaemic events including stent thrombosis in the recent studies. Prasugrel is a new thienopyridine derivative that produces more potent platelet inhibition and a rapid onset of action that is associated with irreversible P2Y(12) receptor blockade. The latter properties of prasugrel may provide a superior alternative to clopidogrel, with less response variability and a decreased prevalence of non-responsiveness.     

Repeat oral dosing of prasugrel, a novel P2Y12 receptor inhibitor, results in cumulative and potent antiplatelet and antithrombotic activity in several animal species

Antiplatelet and antithrombotic activity of multiple oral dosing of prasugrel were evaluated in several animal species. Prasugrel's active metabolite concentration-relatedly inhibited in vitro ADP-induced aggregation of rat, rabbit, dog, monkey and human platelets. Oral administration of prasugrel to dogs (0.03-0.3 mg/kg/day) and monkeys (0.1 and 0.3 mg/kg/day) once a day for 14 days resulted in potent, dose-related and cumulative inhibition of ADP-induced platelet aggregation. The inhibitory effects reached a plateau on days 3 to 5 and thereafter were maintained during dosing. Inhibition decreased gradually after cessation of dosing with near full recovery by 7 days after last dose. Antiplatelet and antithrombotic activity of prasugrel and clopidogrel were further examined in rats. Multiple oral dosing of prasugrel (0.3-3 mg/kg/day) to rats resulted in more potent inhibition of platelet aggregation compared to clopidogrel (3-30 mg/kg/day) and ticlopidine (30-300 mg/kg/day). Separate experiments confirmed that platelet inhibition was associated with inhibition of [(3)H]-2-methylthio-ADP binding to rat platelets. In a rat model of electrically-induced arterial thrombosis, prasugrel (0.1-1 mg/kg/day, p.o.) significantly prolonged the time to arterial occlusion and increased the duration of arterial patency. The inhibition of platelet aggregation of prasugrel was about 10 and 300 times more potent than clopidogrel and ticlopidine, respectively. Overall these results show that in several species multiple oral administration of prasugrel results in more potent inhibition of platelet aggregation and thrombus formation than clopidogrel and ticlopidine, and that these effects are mediated by inhibition of platelet ADP receptors.     

优化冠心病抗血小板治疗的策略

阿司匹林联合氯吡格雷是目前治疗急性冠状动脉综合征和接受了经皮冠状动脉介入术后抗血小板方案中最佳的组合。然而,出血和部分病人出现不敏感或对抗,促使寻找更理想的抗血小板药物或更优化的治疗方案。高剂量氯吡格雷给药策略虽然轻度增加大出血风险,但有助于更强地抑制血小板功能、改善临床结果。更新、更有效的抗血小板药物,如普拉格雷和替卡格雷,在急性冠状动脉综合征和接受了经皮冠状动脉介入术病人中有更好的短期和长期收益。本文就有关研究进展作简要的综述。