Prasugrel for the treatment of coronary thrombosis: a review of pharmacological properties, indications for use and future development

Phase 2 study of TAK-442, an oral factor Xa inhibitor, in patients following acute coronary syndrome

TAK-442 is an oral direct factor Xa inhibitor. We sought to determine the dose-dependent effect of TAK-442 on major bleeding when added to standard treatment in stabilised patients with acute coronary syndrome (ACS). In this phase II double-blind study, 2,753 ACS patients were randomised to TAK-442 or placebo in addition to usual care using a three-stage adaptive design. Patients were randomised to placebo in all stages, but doses of TAK-442 escalated from 10 mg BID, 20 mg twice-daily (BID), or 40 mg once-daily (QD) in stage 1; to 40 mg BID, 80 mg QD, or 80 mg BID in stage 2; and to 160 mg QD or 120 mg BID in stage 3. Study drug was started 36 hours after emergent treatment of ACS and within seven days of admission, and continued for 24 weeks. The primary endpoint was incidence of TIMI (thrombolysis in myocardial infarction) major bleeding. TIMI major bleeding incidence was low, but higher with the pooled TAK-442 doses than with placebo (17 [0.9%] vs 4 [0.5%]; p=0.47), although the difference was neither significant nor dose-dependent. However, a dose response was evident when using the modified ISTH scale. The incidence of cardiovascular events was similar among TAK-442 dose groups and placebo. When administered over a wide range of doses after an ACS event, TAK-442 treatment did not result in a dose-dependent increase in TIMI major bleeding, but increased bleeding was observed when a more sensitive bleeding scale was used. There was no evidence for efficacy.

[New antiplatelet drugs in coronary artery disease]

The dual antiplatelet therapy with acetylsalicylic acid and clopidogrel has been the mainstay of both acute and chronic phase coronary artery disease, reducing importantly the risk of adverse events. Despite a correct compliance, a non-negligible rate of adverse events still happens. New compounds, with improved properties, are now clinically available (such as prasugrel or ticagrelor) or under advanced development. The aim of the present review is the description of these new compounds, particularly prasugrel and ticagrelor.

A brief review of 50 years of perioperative thrombosis and hemostasis management

Perioperative thrombosis and hemostasis management has changed dramatically over the past 50 years. From two anticoagulants and one anti-aggregant, the number of currently available drugs has recently increased several-fold, leaving clinicians with the problem of choosing the optimal agent. Individualized preoperative assessment of bleeding risk based on bleeding history and testing limited to high-risk patients is an emerging concept. Based on the identification of risk factors for venous thromboembolism (VTE), pharmacologic and non-pharmacologic strategies for perioperative VTE prophylaxis have had a major impact on patient outcome. For patients undergoing surgery who are treated with anticoagulants and anti-aggregants, "bridging" strategies have been proposed. Bleeding management strategies have shifted focus from replacing lost blood volume to new approaches aimed at preventing blood loss, reducing the potential complications of blood loss, and preventing the transfusion of blood products. For some areas of perioperative thrombosis and hemostasis management, randomized controlled trial (RCT) data are emerging, but the database remains insufficient to date. Clearly, more RCTs need to be published for perioperative thrombosis and hemostasis management to become an evidence-based approach.

Atopaxar: a review of its mechanism of action and role in patients with coronary artery disease

Platelet activation and aggregation is a complex and key process in thrombus formation after the rupture of an atherosclerotic plaque, which can lead to an acute coronary syndrome. Aspirin, an irreversible inhibitor of thromboxane A2 synthesis, in combination with an inhibitor of P2Y12 ADP platelet receptors (clopidogrel, prasugrel or ticagrelor), represents the current standard of care of antiplatelet therapy for patients with acute coronary syndrome and in those patients undergoing percutaneous coronary intervention. Despite the benefit of these agents, the risk of thrombotic events and bleeding complications may still occur while on such antiplatelet treatment regimens, thus representing an important limitation. Thrombin is one of the most important platelet activators. The inhibition of thrombin-mediated platelet activation by means of protease-activated receptor-1 inhibitors represents an attractive therapeutic option for patients with atherothrombotic disease processes. This article provides an overview on atopaxar (E5555), an orally active protease-activated receptor-1 antagonist that has recently completed Phase II clinical investigation.

P2 receptors and platelet function

Following vessel wall injury, platelets adhere to the exposed subendothelium, become activated and release mediators such as TXA(2) and nucleotides stored at very high concentration in the so-called dense granules. Released nucleotides and other soluble agents act in a positive feedback mechanism to cause further platelet activation and amplify platelet responses induced by agents such as thrombin or collagen. Adenine nucleotides act on platelets through three distinct P2 receptors: two are G protein-coupled ADP receptors, namely the P2Y(1) and P2Y(12) receptor subtypes, while the P2X(1) receptor ligand-gated cation channel is activated by ATP. The P2Y(1) receptor initiates platelet aggregation but is not sufficient for a full platelet aggregation in response to ADP, while the P2Y(12) receptor is responsible for completion of the aggregation to ADP. The latter receptor, the molecular target of the antithrombotic drugs clopidogrel, prasugrel and ticagrelor, is responsible for most of the potentiating effects of ADP when platelets are stimulated by agents such as thrombin, collagen or immune complexes. The P2X(1) receptor is involved in platelet shape change and in activation by collagen under shear conditions. Each of these receptors is coupled to specific signal transduction pathways in response to ADP or ATP and is differentially involved in all the sequential events involved in platelet function and haemostasis. As such, they represent potential targets for antithrombotic drugs.

Historical perspective and future directions in platelet research

Platelets are a remarkable mammalian adaptation that are required for human survival by virtue of their ability to prevent and arrest bleeding. Ironically, however, in the past century, the platelets' hemostatic activity became maladaptive for the increasingly large percentage of individuals who develop age-dependent progressive atherosclerosis. As a result, platelets also make a major contribution to ischemic thrombotic vascular disease, the leading cause of death worldwide. In this brief review, I provide historical descriptions of a highly selected group of topics to provide a framework for understanding our current knowledge and the trends that are likely to continue into the future of platelet research. For convenience, I separate the eras of platelet research into the "Descriptive Period" extending from ~1880-1960 and the "Mechanistic Period" encompassing the past ~50 years since 1960. We currently are reaching yet another inflection point, as there is a major shift from a focus on traditional biochemistry and cell and molecular biology to an era of single molecule biophysics, single cell biology, single cell molecular biology, structural biology, computational simulations, and the high-throughput, data-dense techniques collectively named with the "omics postfix". Given the progress made in understanding, diagnosing, and treating many rare and common platelet disorders during the past 50 years, I think it appropriate to consider it a Golden Age of Platelet Research and to recognize all of the investigators who have made important contributions to this remarkable achievement..

Antiplatelet drug therapy: role of pharmacodynamic and genetic testing

Antiplatelet therapy represents the cornerstone of treatment for the short- and long-term prevention of atherothrombotic disease processes, in particular in high-risk settings such as in patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. Currently, dual antiplatelet therapy with aspirin and clopidogrel represents the most commonly used treatment regimen in these settings. However, a considerable number of patients continue to experience adverse outcomes, including both bleeding and recurrent ischemic events. Numerous investigations have demonstrated that this phenomenon may be, in part, attributed to the broad variability in individual response profiles to this standard antiplatelet treatment regimen, as identified by various assays of platelet function testing. In addition, recent studies have demonstrated that genetic polymorphisms may also have an important role in determining levels of platelet inhibition and may be considered as a tool to identify patients at risk of adverse events. This article provides an overview on antiplatelet drug response variability, an update on definitions, including the role of pharmacodynamic testing, underlying mechanisms – with emphasis on recent understandings on pharmacogenetics and drug–drug interactions – and current and future perspectives on individualized antiplatelet therapy.