Incidence and clinical course of thrombotic thrombocytopenic purpura due to ticlopidine following coronary stenting. EPISTENT Investigators. Evaluation of Platelet IIb/IIIa Inhibitor for Stenting

Current and Future Insights for Optimizing Antithrombotic Therapy to Reduce the Burden of Cardiovascular Ischemic Events in Patients with Acute Coronary Syndrome

The pharmacological treatment strategies for acute coronary syndrome (ACS) in recent years are constantly evolving to develop more potent antithrombotic agents, as reflected by the introduction of more novel P2Y₁₂ receptor inhibitors and anticoagulants to reduce the ischemic risk among ACS patients. Despite the substantial improvements in the current antithrombotic regimen, a noticeable number of ACS patients continue to experience ischemic events. Providing effective ischemic risk reduction while balancing bleeding risk remains a clinical challenge. This updated review discusses the currently approved and widely used antithrombotic agents and explores newer antithrombotic treatment strategies under development for the initial phase of ACS.

Antiplatelet agents for chronic kidney disease

BACKGROUND

Antiplatelet agents are widely used to prevent cardiovascular events. The risks and benefits of antiplatelet agents may be different in people with chronic kidney disease (CKD) for whom occlusive atherosclerotic events are less prevalent, and bleeding hazards might be increased. This is an update of a review first published in 2013.

OBJECTIVES

To evaluate the benefits and harms of antiplatelet agents in people with any form of CKD, including those with CKD not receiving renal replacement therapy, patients receiving any form of dialysis, and kidney transplant recipients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 13 July 2021 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We selected randomised controlled trials of any antiplatelet agents versus placebo or no treatment, or direct head-to-head antiplatelet agent studies in people with CKD. Studies were included if they enrolled participants with CKD, or included people in broader at-risk populations in which data for subgroups with CKD could be disaggregated.

DATA COLLECTION AND ANALYSIS

Four authors independently extracted data from primary study reports and any available supplementary information for study population, interventions, outcomes, and risks of bias. Risk ratios (RR) and 95% confidence intervals (CI) were calculated from numbers of events and numbers of participants at risk which were extracted from each included study. The reported RRs were extracted where crude event rates were not provided. Data were pooled using the random-effects model. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

We included 113 studies, enrolling 51,959 participants; 90 studies (40,597 CKD participants) compared an antiplatelet agent with placebo or no treatment, and 29 studies (11,805 CKD participants) directly compared one antiplatelet agent with another. Fifty-six new studies were added to this 2021 update. Seven studies originally excluded from the 2013 review were included, although they had a follow-up lower than two months. Random sequence generation and allocation concealment were at low risk of bias in 16 and 22 studies, respectively. Sixty-four studies reported low-risk methods for blinding of participants and investigators; outcome assessment was blinded in 41 studies. Forty-one studies were at low risk of attrition bias, 50 studies were at low risk of selective reporting bias, and 57 studies were at low risk of other potential sources of bias. Compared to placebo or no treatment, antiplatelet agents probably reduces myocardial infarction (18 studies, 15,289 participants: RR 0.88, 95% CI 0.79 to 0.99, I² = 0%; moderate certainty). Antiplatelet agents has uncertain effects on fatal or nonfatal stroke (12 studies, 10.382 participants: RR 1.01, 95% CI 0.64 to 1.59, I² = 37%; very low certainty) and may have little or no effect on death from any cause (35 studies, 18,241 participants: RR 0.94, 95 % CI 0.84 to 1.06, I² = 14%; low certainty). Antiplatelet therapy probably increases major bleeding in people with CKD and those treated with haemodialysis (HD) (29 studies, 16,194 participants: RR 1.35, 95% CI 1.10 to 1.65, I² = 12%; moderate certainty). In addition, antiplatelet therapy may increase minor bleeding in people with CKD and those treated with HD (21 studies, 13,218 participants: RR 1.55, 95% CI 1.27 to 1.90, I² = 58%; low certainty). Antiplatelet treatment may reduce early dialysis vascular access thrombosis (8 studies, 1525 participants) RR 0.52, 95% CI 0.38 to 0.70; low certainty). Antiplatelet agents may reduce doubling of serum creatinine in CKD (3 studies, 217 participants: RR 0.39, 95% CI 0.17 to 0.86, I² = 8%; low certainty). The treatment effects of antiplatelet agents on stroke, cardiovascular death, kidney failure, kidney transplant graft loss, transplant rejection, creatinine clearance, proteinuria, dialysis access failure, loss of primary unassisted patency, failure to attain suitability for dialysis, need of intervention and cardiovascular hospitalisation were uncertain. Limited data were available for direct head-to-head comparisons of antiplatelet drugs, including prasugrel, ticagrelor, different doses of clopidogrel, abciximab, defibrotide, sarpogrelate and beraprost.

AUTHORS' CONCLUSIONS

Antiplatelet agents probably reduced myocardial infarction and increased major bleeding, but do not appear to reduce all-cause and cardiovascular death among people with CKD and those treated with dialysis. The treatment effects of antiplatelet agents compared with each other are uncertain.

Incidence of neutropenia in patients with ticlopidine/Ginkgo biloba extract combination drug for vascular events: A post-marketing cohort study

BACKGROUND AND PURPOSE

The ticlopidine/Ginkgo biloba ext. combination drug (Yuclid) is used as an antiplatelet agent for prevention of vascular events since its approval in 2008. The purpose of this study is to explore the safety of ticlopidine/Ginkgo biloba combination, mainly regarding the incidence of neutropenia, through a post-marketing surveillance study.

METHODS

From March 2009 to October 2015, a total of 4839 subjects had been enrolled in this study. The enrollments were conducted by 152 doctors of 89 hospitals according to the regulations for post-marketing surveillance programs in Korea. If a subject was administered the drug once, he/she was included in the safety analysis set for any adverse events and bleedings, and the primary safety evaluation regarding neutropenia was conducted in subjects who completed 3-month blood test follow-up. We predefined that 1% reduction in neutropenia incidence by ticlopidine/Ginkgo biloba ext. combination from the previously reported incidence of ticlopidine of 2.3% was clinically meaningful.

RESULTS

Among the safety analysis set of 4831 patients (99.8% of the enrolled subjects), 3150 (65.1%) completed evaluation for neutropenia at 3 months which is the primary safety endpoint. The major causes of dropout were no follow-up visit at 3 months (n = 1016) and violation of the follow-up period (n = 503). Nine patients experienced neutropenia (Absolute neutrophil count [ANC] ≤ 1200mm3) and the estimated cumulative incidence at 3 months is 0.29% (95% confidence interval, 0.13%- 0.54%). Severe neutropenia (ANC ≤ 450mm3) did not occur in any patients.

CONCLUSIONS

The incidence of neutropenia with addition of Ginkgo biloba ext. to ticlopidine may be lower than the previously reported incidence of neutropenia with ticlopidine, which needs to be confirmed in randomized controlled trials.

Oral antiplatelet agents in cardiovascular disease

Antiplatelet agents significantly reduce mortality and morbidity in ischemic heart disease, cerebrovascular disease and peripheral artery disease (PAD), and are therefore part of guideline-driven daily medical treatment in these patients. Due to its beneficial effects in the secondary prevention of atherothrombotic events, aspirin remains the most frequently prescribed antiplatelet agent in cardiovascular disease. In patients with acute coronary syndromes (ACS) and in those undergoing angioplasty with stent implantation dual antiplatelet therapy with aspirin and an adenosine diphosphate (ADP) receptor antagonist is indicated. The development of the newer ADP P2Y₁₂ inhibitors prasugrel and ticagrelor has further improved prognosis in ACS patients compared to clopidogrel. Moreover, vorapaxar allows the inhibition of platelet activation by thrombin via protease-activated receptor-1 and has been approved for the use in patients with PAD and in those with a history of myocardial infarction. This review article summarizes the current evidence on oral antiplatelet agents in cardiovascular disease. Keywords: Aspirin, clopidogrel, prasugrel, ticagrelor, vorapaxar, cardiovascular disease.

Prasugrel hydrochloride for the treatment of acute coronary syndrome patients

INTRODUCTION

Dual antiplatelet therapy (DAPT) with aspirin combined with either a thienopyridine (clopidogrel or prasugrel) or acyclopentyl-triazolo-pyrimidine (ticagrelor) plays a vital role in the management of acute coronary syndrome (ACS) especially in those undergoing percutaneous coronary intervention (PCI) but even those being managed medically. Observational studies and some formal studies have shown patients on the standard dual antiplatelet regimen (clopidogrel and aspirin) continue to have further ischemic events and can suffer stent thrombosis. It has been demonstrated that clopidogrel is associated with a delayed onset of action with a considerable inter-individual variation to treatment thus making it difficult to achieve an optimal level of platelet inhibition. Areas covered: This article will review the current evidence that is available regarding the effectiveness and safety of prasugrel in ACS patients undergoing percutaneous coronary intervention (PCI). Expert commentary: Prasugrel is an oral third-generation inhibitor of platelet activation and aggregation. Laboratory studies and early phase clinical trials show prasugrel has a faster onset of action, is more potent and has reduced inter-patient response variability compared to clopidogrel. The published studies so far demonstrated that prasugrel when compared to clopidogrel also shows a higher degree of effectiveness in the prevention of platelet-initiated thrombotic events in patients with ACS undergoing PCI, however these benefits are offset somewhat by an increased bleeding risk.

Coexisting Cardiac and Hematologic Disorders

Patients with concomitant cardiac and hematologic disorders presenting for noncardiac surgery are challenging. Anemic patients with cardiac disease should be approached in a methodical fashion. Transfusion triggers and target should be based on underlying symptomatology. The approach to anticoagulation management in patients with artificial heart valves, cardiac devices, or severe heart failure in the operative setting must encompass a complete understanding of the rationale of a patient's therapy as well as calculate the risk of changing this regimen. This article focuses common disorders and discusses strategies to optimize care in patients with coexisting cardiac and hematologic disease.

Acute pancreatitis-induced thrombotic thrombocytopenic purpura with recurrent acute pancreatitis

Recent successive reports on acute pancreatitis-induced thrombotic thrombocytopenic purpura (TTP) have revealed that TTP-related microvascular damage is an aggravating factor of acute pancreatitis. Here, we report the case of a 26-year-old man diagnosed with acute pancreatitis due to high alcohol consumption. The patient was unconscious as he had taken an overdose of medication, and presented with fever and renal failure due to acute pancreatitis on admission. Although the pancreatitis subsequently improved, the symptoms were still observed; on the next day, he exhibited hemoglobinuria, anemia, and thrombocytopenia. Moreover, general blood examinations indicated the presence of schistocytes and reduced activity of ADAMTS13 (a disintegrin-like metalloproteinase with thrombospondin type 1 motif 13) to 47 %. Thus, the patient was diagnosed with TTP, and plasma exchange was performed. After the development of TTP, the acute pancreatitis recurred, but a severe pathogenesis was prevented by plasma exchange. Thus, ADAMTS13 activity may be useful for predicting a severe pathogenesis of acute pancreatitis. In ADAMTS13-deficient cases, plasma exchange may be an effective technique for preventing aggravation of acute pancreatitis.

Clopidogrel-induced Thrombotic Microangiopathy in a Patient with Hypocomplementemia

Clopidogrel was administered to a 67-year-old Japanese man to prevent the recurrence of cerebral infarction. Twelve weeks later, he was admitted to our hospital with acute renal failure, hemolytic anemia and thrombocytopenia, and was diagnosed with clopidogrel-induced thrombotic microangiopathy. Clopidogrel was immediately discontinued and corticosteroid and plasma exchange therapy were administered simultaneously. Thereafter, the patient's condition gradually improved. The patient had a decreased serum complement C3 level. This suggests that the activated alternative pathway is related to thrombotic microangiopathy (TMA). TMA is a critical drug-associated adverse reaction that clinicians should always be vigilant about, because clopidogrel is widely prescribed.

Progress in interventional cardiology: challenges for the future

Cardiovascular disease is the leading cause of death in the western and developing countries. Percutaneous transluminal coronary interventions have become the most prevalent treatment option for coronary artery disease; however, due to serious complications, such as stent thrombosis and in-stent restenosis (ISR), the efficacy and safety of the procedure remain important issues to address. Strategies to overcome these aspects are under extensive investigation. In this review, we summarise relevant milestones during the time to overcome these limitations of coronary stents, such as the development of polymer-free drug-eluting stents (DES) to avoid pro-inflammatory response due to the polymer coating or the developement of stents with cell-directing drugs to, simultaneously, improve re-endothelialisation and inhibit ISR amongst other techniques most recently developed, which have not fully entered the clinical stage. Also the novel concept of fully biodegradable DES featured by the lack of a permanent foreign body promises to be a beneficial and applicable tool to restore a natural vessel with maintained vasomotion and to enable optional subsequent surgical revascularisation.

Comparative effects of the anti-platelet drugs, clopidogrel, ticlopidine, and cilostazol on aspirin-induced gastric bleeding and damage in rats

AIMS

The present study compared the effects of frequently used anti-platelet drugs, such as clopidogrel, ticlopidine, and cilostazol, on the gastric bleeding and ulcerogenic responses induced by intraluminal perfusion with 25 mM aspirin acidified with 25 mM HCl (acidified ASA) in rats.

MAIN METHODS

The stomach was perfused with acidified ASA at a rate of 0.4 ml/min for 60 min under urethane anesthesia, and gastric bleeding was measured as the concentration of hemoglobin in the luminal perfusate, which was collected every 15 min. Clopidogrel (10-100mg/kg), ticlopidine (10-300 mg/kg), or cilostazol (3-30 mg/kg) was given p.o. 24h or 90 min before the perfusion of acidified ASA, respectively.

KEY FINDINGS

Perfusion of the stomach with acidified ASA alone led to slight bleeding and lesions in the stomach. The pretreatment with clopidogrel, even though it did not cause bleeding or damage by itself, dose-dependently increased the gastric bleeding and ulcerogenic responses induced by acidified ASA. Ticlopidine also aggravated the severity of damage by increasing gastric bleeding, and the effects of ticlopidine at 300 mg/kg were equivalent to those of clopidogrel at 100mg/kg. In contrast, cilostazol dose-dependently decreased gastric bleeding and damage in response to acidified ASA.

SIGNIFICANCE

These results demonstrated that clopidogrel and ticlopidine, P2Y12 receptor inhibitors, increased gastric bleeding and ulcerogenic responses to acidified ASA, to the same extent, while cilostazol, a phosphodiesterase III inhibitor, suppressed these responses. Therefore, cilostazol may be safely used in dual anti-platelet therapy combined with ASA, without increasing the risk of gastric bleeding.

Prognostic significance of post percutaneous coronary intervention thrombocytopenia

Several definitions of post percutaneous coronary intervention (PCI) thrombocytopenia (TC) were formulated. Recent studies demonstrated that a relative drop in platelet count ≥ 25% is the most appropriate criterion. By this definition a population is detected that is exposed not only to increased risk of hemorrhagic complications but also to increased risk of ischemic events, which may appear a paradox. In patients with acute coronary syndromes undergoing PCI, several conditions might be associated with TC: cardiopulmonary by-pass and the presence of extra corporeal membrane oxygenators, intra aortic balloon pump (IABP), cardiogenic shock, thrombolytic drugs and anticoagulant or antiplatelet drugs. Several studies demonstrated that TC and ischemic outcomes are related although it is unclear whether this is a direct relationship or TC is just a secondary effect of another cryptic protagonist. It is suggested that further investigations determine whether there is a real link between TC, a probably well defined covariate, and ischemic outcomes or whether IABP is the joining link between these two variables and whose presence needs in any case be considered in multivariable statistics. Post-PCI TC could be only a secondary effect of IABP use. On turn, the prolonged use of heparin necessarily accompanying the use of IABP, and producing a paradoxical pro-thrombotic TC, might also be implicated.

[Thrombotic microangiopathy]

Thrombotic microangiopathy should be suspected every time the combination of microangiopathic hemolytic anemia without a coexisting cause, thrombocytopenia as well as renal and/or neurologic abnormalities occurs. The general term thrombotic microangiopathy includes different subtypes of the disease leading to abnormalities in multiple organ systems by endothelial injury and formation of platelet-rich thrombi in small vessels. The main types include thrombotic thrombocytopenic purpura in case of dominant neurologic abnormalities and the hemolytic uremic syndrome in case of acute kidney injury, respectively. Although these syndromes differ in their etiologies, clinical features, response to treatment, and prognosis, an early initiation of a direct therapeutic intervention frequently determines the clinical course of the patient. Irrespectively of the underlying etiology, plasma exchange is an essential component of acute therapeutic intervention while ongoing diagnostics are used to identify the definite treatment.

Multiple cytochrome P450 isoforms are involved in the generation of a pharmacologically active thiol metabolite, whereas paraoxonase 1 and carboxylesterase 1 catalyze the formation of a thiol metabolite isomer from ticlopidine

Ticlopidine is a first-generation thienopyridine antiplatelet drug that prevents adenosine 5'-diphosphate (ADP)-induced platelet aggregation. We identified the enzymes responsible for the two-step metabolic bioactivation of ticlopidine in human liver microsomes and plasma. Formation of 2-oxo-ticlopidine, an intermediate metabolite, was NADPH dependent and cytochrome P450 (CYP) 1A2, 2B6, 2C19, and 2D6 were involved in this reaction. Conversion of 2-oxo-ticlopidine to thiol metabolites was observed in both microsomes (M1 and M2) and plasma (M1). These two metabolites were considered as isomers, and mass spectral analysis suggested that M2 was a thiol metabolite bearing an exocyclic double bond, whereas M1 was an isomer in which the double bond was migrated to an endocyclic position in the piperidine ring. The conversion of 2-oxo-ticlopidine to M1 in plasma was significantly increased by the addition of 1 mM CaCl2. In contrast, the activity in microsomes was not changed in the presence of CaCl2. M1 formation in plasma was inhibited by EDTA but not by other esterase inhibitors, whereas this activity in microsomes was substantially inhibited by carboxylesterase (CES) inhibitors such as bis-(p-nitrophenyl)phosphate (BNPP), diisopropylphosphorofluoride (DFP), and clopidogrel. The conversion of 2-oxo-ticlopidine to M1 was further confirmed with recombinant paraoxonase 1 (PON1) and CES1. However, M2 was detected only in NADPH-dependent microsomal incubation, and multiple CYP isoforms were involved in M2 formation with highest contribution of CYP2B6. In vitro platelet aggregation assay demonstrated that M2 was pharmacologically active. These results collectively indicated that the formation of M2 was mediated by CYP isoforms whereas M1, an isomer of M2, was generated either by human PON1 in plasma or by CES1 in the human liver.

Pharmacotherapy for the reduction of stent thrombosis

The benefits of percutaneous coronary intervention (PCI) can be offset by periprocedural complications such as acute vessel closure and stent thrombosis in the absence of adequate antiplatelet and antithrombotic therapy. Additionally, conditions occurring after 30 days post-PCI, such as in-stent restenosis or late stent thrombosis can occur. Excess antithrombotic therapy, on the other hand, carries a risk of major gastrointestinal or intracranial bleeding as well as vascular access site bleeding complications. In this review, evidence related to the various pharmacological agents for reduction of stent thrombosis available to clinicians during and after PCI will be explored.

Low ADAMTS-13 in plavix induced thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenia purpura (TTP) was first described in 1924 as a “pathologic alteration of the microvasculature, with detachment or swelling of the endothelium, amorphous material in the sub-endothelial space, and luminal platelet aggregation leading to compromise of the microcirculation”. Ticlopidine induced TTP has been highly associated with autoimmune induced reduction in ADAMTS-13 activity. These findings, to a lesser extent, have also been found in clopidogrel induced TTP. We report a case of clopidogrel associated TTP in a patient that presented with acute stroke, renal failure, and non-ST elevation myocardial infarction.

Ticlopidine-, clopidogrel-, and prasugrel-associated thrombotic thrombocytopenic purpura: a 20-year review from the Southern Network on Adverse Reactions (SONAR)

Thienopyridine-derivatives (ticlopidine, clopidogrel, and prasugrel) are the primary antiplatelet agents. Thrombotic thrombocytopenic purpura (TTP) is a rare drug-associated syndrome, with the thienopyridines being the most common drugs implicated in this syndrome. We reviewed 20 years of information on clinical, epidemiologic, and laboratory findings for thienopyridine-associated TTP. Four, 11, and 11 cases of thienopyridine-associated TTP were reported in the first year of marketing of ticlopidine (1989), clopidogrel (1998), and prasugrel (2010), respectively. As of 2011, the FDA received reports of 97 ticlopidine-, 197 clopidogrel-, and 14 prasugrel-associated TTP cases. Severe deficiency of ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) was present in 80% and antibodies to 100% of these TTP patients on ticlopidine, 0% of the patients with clopidogrel-associated TTP (p < 0.05), and an unknown percentage of patients with prasugrel-associated TTP. TTP is associated with use of each of the three thienopyridines, although the mechanistic pathways may differ.

Aspirin and platelet adenosine diphosphate receptor antagonists in acute coronary syndromes and percutaneous coronary intervention: role in therapy and strategies to overcome resistance

Platelet activation and aggregation are key components in the cascade of events causing thrombosis following plaque rupture. Antiplatelet therapy is essential in the treatment of patients with acute coronary syndromes (ACS) and for those requiring percutaneous coronary intervention (PCI). Aspirin (acetylsalicylic acid) is a well established antiplatelet therapy and is mandated for secondary prevention of cardiovascular events following ACS. In patients with ACS, the addition of clopidogrel to aspirin is more effective than aspirin alone. For patients undergoing PCI, dual antiplatelet therapy with aspirin and clopidogrel is warranted. Aspirin should be continued indefinitely after PCI. Pretreatment of patients with clopidogrel prior to PCI lowers the incidence of cardiovascular events, yet the optimum timing of drug administration and dose are still being investigated, as is the duration of therapy following PCI. Late-stent thrombosis with drug-eluting stents has pushed the recommendation for duration of clopidogrel therapy up to 1 year and perhaps beyond, in patients without risks for bleeding. The concepts of aspirin and clopidogrel resistance are important clinical questions. No uniform definition exists for aspirin or clopidogrel resistance. Measurements of resistance are often highly variable and do not necessarily correlate with clinical resistance. Noncompliance remains the most prominent mode of resistance. Screening of selected patient populations for resistance or pharmacologic intervention of those patients termed 'resistant' warrants further study.

Prasugrel versus clopidogrel antiplatelet therapy after acute coronary syndrome: matching treatments with patients

Antithrombotic therapy is imperative in the management of patients presenting with an acute coronary syndrome (ACS). The combination of antiplatelet therapy in conjunction with antithrombotic therapy has become the standard of care in improving the morbidity and mortality of patients with an ACS and in reducing ischemic complications of percutaneous coronary intervention. Patients with an ACS are at increased risk for a recurrent event, both in-hospital and for several months afterward. Secondary prevention to reduce these events is accomplished through the establishment of appropriate medical therapy. Dual antiplatelet therapy with aspirin and adenosine 5'-diphosphate P2Y(12) receptor blockers such as ticlopidine or clopidogrel are integral components of this regimen; however, both of these thienopyridines have a relatively slow onset of action and variable bioavailability. Prasugrel, a third-generation thienopyridine approved by the US FDA in 2009, has a more rapid onset of platelet inhibition than clopidogrel and ticlopidine because of increased efficiency of prodrug-to-active metabolite conversion. The result is higher and less variable concentration of the active metabolite within 60 minutes following oral dosing. Phase II and III trials assessing the safety and efficacy of prasugrel have been completed, including JUMBO-TIMI 26, PRINCIPLE-TIMI 44, and TRITON-TIMI 38. These trials demonstrated greater inhibition of platelet aggregation and lower rates of the composite endpoint of death, non-fatal myocardial infarction, and stroke compared with clopidogrel. However, major bleeding occurred more frequently with prasugrel treatment than with clopidogrel. This review highlights the current state of evidence-based antiplatelet therapy and provides guidance on appropriate use of prasugrel in cardiovascular medicine.

Novel antiplatelet therapies

Advances in antiplatelet therapy have significantly improved outcomes in patients with ischemic heart disease. Thienopyridines remain a cornerstone of therapy along with aspirin. Recently, concerns have been raised about the use of clopidogrel due to its pharmacokinetic and pharmacogenetic interpatient variability. A third-generation thienopyridine, prasugrel, overcomes some of these problems by improving inhibition of platelet aggregation, but increasing the risk of peri-procedural bleeding. Other novel antiplatelet agents, such as ticagrelor, have shown improved efficacy in recent trials and require further investigations. The field of pharmacotherapy continues to rapidly evolve as newer agents, such as thrombin receptor antagonists, along with older agents, such as cilostazol and glycoprotein IIb/IIIa inhibitors, are being explored.

Antiplatelet drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

The article describes the mechanisms of action, pharmacokinetics, and pharmacodynamics of aspirin, dipyridamole, cilostazol, the thienopyridines, and the glycoprotein IIb/IIIa antagonists. The relationships among dose, efficacy, and safety are discussed along with a mechanistic overview of results of randomized clinical trials. The article does not provide specific management recommendations but highlights important practical aspects of antiplatelet therapy, including optimal dosing, the variable balance between benefits and risks when antiplatelet therapies are used alone or in combination with other antiplatelet drugs in different clinical settings, and the implications of persistently high platelet reactivity despite such treatment.

Managing adverse effects and drug-drug interactions of antiplatelet agents

Antiplatelet therapies have reduced the frequency of adverse events associated with plaque rupture in several clinical situations. These therapies include established antiplatelet agents (such as aspirin, clopidogrel, or glycoprotein IIb/IIIa inhibitors) as well as new agents (such as prasugrel and ticagrelor). In this Review, we address the most important adverse events of antiplatelet therapy, including hemorrhage, hematologic reactions, and dyspnea. We discuss strategies to reduce the incidence of complications and outline potential methods to manage adverse reactions. Interactions between antiplatelet agents and other drugs--such as proton-pump inhibitors, calcium-channel blockers, statins, warfarin, or NSAIDs--are also addressed, as well as specific issues relating to the use of antiplatelet therapies in elderly patients.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

Antiplatelet therapy in secondary stroke prevention--state of the art

Our objective is to provide the reader with an overview as well as an update on current antiplatelet therapy for secondary stroke prevention. Relevant journals were hand-searched by the authors to compile a broad but by far not comprehensive summary of innovative and clinically relevant studies. Aspirin, clopidogrel and the combination of dipyridamole plus aspirin are the cornerstone therapy in secondary prevention after non-cardio-embolic stroke or transient ischaemic attack. A head-to-head comparison showed no difference in the prevention of recurrent stroke between dipyridamole plus aspirin and clopidogrel. More potent antiplatelet drugs or the combination of aspirin and clopidogrel prevent more ischaemic events, but also lead to more bleeding complications. For secondary stroke prevention in patients with atrial fibrillation, oral anticoagulation is more effective than aspirin or the combination of aspirin and clopidogrel.

Thrombocytopenia following percutaneous coronary intervention

BACKGROUND

Thrombocytopenia following percutaneous coronary intervention (PCI) is an underappreciated condition that is often clinically challenging. There are no guidelines on the management of patients with this condition.

OBJECTIVE

To review recent data in etiologies, risk factors, prevention, management, and prognostic implications of thrombocytopenia following PCI.

EVIDENCE ACQUISITION

Search of MEDLINE, EMBASE, the Cochrane Database, and Google Scholar using the term thrombocytopenia + PCI and other relevant keywords to identify systematic reviews, clinical trials, cohort studies, case series, and case reports. The review was limited to English-language articles published between January 1980 and June 2009. Articles on patients with baseline thrombocytopenia prior to PCI were excluded.

EVIDENCE SYNTHESIS

Thrombocytopenia is not infrequent following PCI. The typical patient with post-PCI thrombocytopenia is on multiple therapies that can potentially cause a decrease in the platelet count. Identification of the cause is critical because management of the condition varies significantly based on the etiology. The severity of the thrombocytopenia also determines the clinical management of the patient. Several observational studies have demonstrated the adverse prognostic impact of the complication on clinical outcomes and have identified risk factors.

CONCLUSIONS

Judicious use of therapies that can cause thrombocytopenia, efficient detection of the cause of the decrease in platelet count, and appropriate management of the condition can potentially improve the quality of care and outcomes following PCI. Further research into risk factors that predispose post-PCI patients to developing thrombocytopenia is warranted.

Pharmacokinetics, drug metabolism, and safety of prasugrel and clopidogrel

Thienopyridines are platelet adenosine diphosphate receptor antagonists used in the treatment and prevention of thrombotic events in patients with acute coronary syndrome. The pharmacokinetic profile of the thienopyridine clopidogrel has resulted in highly variable pharmacokinetics and efficacy responses. The purpose of this review is to provide a brief overview of the pharmacokinetics of prasugrel and clopidogrel and discuss factors that would influence the metabolism of those drugs. Clinical studies have shown that the coadministration of prasugrel with other drugs is less likely to result in clinically relevant pharmacokinetic drug interactions compared with clopidogrel. The lack of effect of variant genotypes on the efficacy of prasugrel suggests that more patients will receive adequate platelet inhibition after administration of prasugrel. The efficient generation of the active metabolite of prasugrel results in greater and more rapid inhibition of P2Y(12) receptor-mediated platelet aggregation.

Comparison of in vitro metabolism of ticlopidine by human cytochrome P450 2B6 and rabbit cytochrome P450 2B4

A recent X-ray crystal structure of a rabbit cytochrome P450 2B4 (CYP2B4)-ticlopidine complex indicated that the compound could be modeled with either the thiophene or chlorophenyl group oriented toward the heme prosthetic group. Subsequent NMR relaxation and molecular docking studies suggested that orientation with the chlorophenyl ring closer to the heme was the preferred one. To evaluate the predictive value of these findings, the oxidation of ticlopidine by reconstituted CYP2B4 was studied and compared with CYP2B6, in which the thiophene portion of the molecule likely orients toward the heme. In vitro incubation of ticlopidine with both enzymes yielded the same set of metabolites: 7-hydroxyticlopidine (M1), 2-oxoticlopidine (M2), 5-(2-chlorobenzyl)thieno[3,2-c]pyridin-5-ium metabolite (M3), 5-(2-chlorobenzyl)thieno[3,2-c]pyridin-5-ium metabolite (M4), ticlopidine N-oxide (M5), and ticlopidine S-oxide dimer, a dimerization product of ticlopidine S-oxide (M6). The rates of metabolite formation deviated markedly from linearity with time, consistent with the known inactivation of CYP2B6 by ticlopidine. Fitting to a first-order equation yielded similar rate constants (k(obs)) for both enzymes. However, the amplitude (R(max)) of M1 and M6 formation was 4 to 5 times higher for CYP2B6 than CYP2B4, indicating a greater residence time of ticlopidine with its thiophene ring closer to heme in CYP2B6. In contrast, CYP2B4 formed M4 and M5 in more abundance than CYP2B6, indicating an alternate orientation. Overall, the results suggest that the preferential orientation of ticlopidine in the active site of CYP2B4 predicted by X-ray crystallography and NMR studies is unproductive and that ticlopidine likely reorients within CYP2B4 to a more productive mode.

Antiplatelet therapy in acute coronary syndromes

Antiplatelet therapy is integral to the acute and long-term management of acute coronary syndromes (ACSs) and for minimizing the thrombotic complications of percutaneous coronary intervention (PCI). This article reviews the most commonly used antiplatelet agents in ACS therapy--aspirin, adenosine diphosphate (ADP)-receptor blockers, and glycoprotein IIb/IIIa inhibitors. More recent data are also reviewed on novel ADP-receptor blockers and thrombin inhibitors before addressing issues of adherence to antiplatelet regimens.

A novel, accelerated method of desensitization in a patient with a documented hypersensitivity reaction to clopidogrel

Current standard of care following a percutaneous coronary intervention with stent placement necessitates the use of dual anti-platelet therapy with aspirin and commonly clopidogrel. There is a subset of patients who have a significant clopidogrel allergy and life-threatening hypersensitivity reactions. Desensitization is the process of inducing tolerance to a sensitizing agent via repeated exposure to the agent. There have been previously reported protocols for clopidogrel desensitization. These protocols differ in length and dose escalation and a universally accepted clopidogrel desensitization protocol has yet to be established. We discuss here a novel accelerated approach to clopidogrel desensitization in a patient with a documented hypersensitivity reaction.

Metabolism and disposition of the thienopyridine antiplatelet drugs ticlopidine, clopidogrel, and prasugrel in humans

Ticlopidine, clopidogrel, and prasugrel are thienopyridine prodrugs that inhibit adenosine-5'-diphosphate (ADP)-mediated platelet aggregation in vivo. These compounds are converted to thiol-containing active metabolites through a corresponding thiolactone. The 3 compounds differ in their metabolic pathways to their active metabolites in humans. Whereas ticlopidine and clopidogrel are metabolized to their thiolactones in the liver by cytochromes P450, prasugrel proceeds to its thiolactone following hydrolysis by carboxylesterase 2 during absorption, and a portion of prasugrel's active metabolite is also formed by intestinal CYP3A. Both ticlopidine and clopidogrel are subject to major competing metabolic pathways to inactive metabolites. Thus, varying efficiencies in the formation of active metabolites affect observed effects on the onset of action and extent of inhibition of platelet aggregation (IPA). Knowledge of the CYP-dependent formation of ticlopidine and clopidogrel thiolactones helps explain some of the observed drug-drug interactions with these molecules and, more important, the role of CYP2C19 genetic polymorphism on the pharmacokinetics of and pharmacodynamic response to clopidogrel. The lack of drug interaction potential and the absence of CYP2C19 genetic effect result in a predictable response to thienopyridine antiplatelet therapy with prasugrel. Current literature shows that greater ADP-mediated IPA is associated with significantly better clinical outcomes for patients with acute coronary syndrome.

Thienopyridine derivatives versus aspirin for preventing stroke and other serious vascular events in high vascular risk patients

BACKGROUND

Aspirin is the most widely studied and prescribed antiplatelet agent for preventing serious vascular events, reducing the odds of such events among high vascular risk patients by about a quarter. Thienopyridine derivatives inhibit platelet activation by a different mechanism and so may be more effective.

OBJECTIVES

To determine the effectiveness and safety of thienopyridine derivatives (ticlopidine and clopidogrel) versus aspirin for preventing serious vascular events (stroke, myocardial infarction (MI) or vascular death) in patients at high risk, and specifically in patients with a previous TIA or ischaemic stroke.

SEARCH STRATEGY

We searched the trials registers of the Stroke, Heart and Peripheral Vascular Diseases Cochrane Review Groups (last searched July 2008), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 3, 2008), MEDLINE (1966 to August 2008) and EMBASE (1980 to August 2008). We also searched reference lists of relevant papers, and contacted other researchers and the pharmaceutical company Sanofi-BMS (December 2008).

SELECTION CRITERIA

All unconfounded, double blind, randomised trials directly comparing a thienopyridine derivative with aspirin in high vascular risk patients.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality. We sought additional data from the principal investigators of the largest trials.

MAIN RESULTS

We included 10 trials involving 26,865 high vascular risk patients. The trials were generally of high quality. Aspirin was compared with ticlopidine in nine trials (7633 patients) and with clopidogrel in one trial (19,185 patients). Compared with aspirin, allocation to a thienopyridine produced a modest, just statistically significant, reduction in the odds of a serious vascular event (11.6% versus 12.5%; odds ratio (OR) 0.92, 95% confidence interval (CI) 0.85 to 0.99), corresponding to the avoidance of 10 (95% CI 0 to 20) serious vascular events per 1000 patients treated for about two years. However, the wide confidence interval includes the possibility of negligible additional benefit. Compared with aspirin, thienopyridines significantly reduced gastrointestinal adverse effects. However, thienopyridines increased the odds of skin rash and diarrhoea, ticlopidine more than clopidogrel. Allocation to ticlopidine, but not clopidogrel, significantly increased the odds of neutropenia. In patients with TIA/ischaemic stroke, the results were similar to those for all patients combined.

AUTHORS' CONCLUSIONS

The thienopyridine derivatives are at least as effective as aspirin in preventing serious vascular events in patients at high risk, and possibly somewhat more so. However, the size of any additional benefit is uncertain and could be negligible. Clopidogrel has a more favourable adverse effects profile than ticlopidine and so is the thienopyridine of choice. It should be used as an alternative to aspirin in patients genuinely intolerant of or allergic to aspirin.

Metabolism of ticlopidine in rats: identification of the main biliary metabolite as a glutathione conjugate of ticlopidine S-oxide

We have identified several novel metabolites of ticlopidine, a well known antiplatelet agent and have revealed its metabolic route in rats. The main biliary metabolite of ticlopidine was characterized as a glutathione (GSH) conjugate of ticlopidine S-oxide, in which conjugation had occurred at carbon 7a in the thienopyridine moiety. Quantitative analysis revealed that 29% of the dose was subjected to the formation of reactive intermediates followed by conjugation with GSH after oral administration of ticlopidine (22 mg/kg) to rats. In vitro incubation of ticlopidine with rat liver 9000 g supernatant fraction (S9) fractions led to the formation of multiple metabolites, including 2-oxo-ticlopidine, the precursor for the pharmacologically active ticlopidine metabolite, [1-(2-chlorobenzyl)-4-mercaptopiperidin-(3Z)-ylidene] acetic acid. A novel thiophene ring-opened metabolite with a thioketone group and a carboxylic acid moiety has also been detected after incubation of 2-oxo-ticlopidine with rat liver microsomes or upon incubation of ticlopidine with rat liver S9 fractions.