Thrombotic thrombocytopenic purpura associated with clopidogrel

Thrombotic microangiopathies: an update

Thrombotic microangiopathies (TMA) are microvascular occlusive disorders characterized by hemolytic anemia caused by fragmentation of erythrocytes and thrombocytopenia due to increased platelet aggregation and thrombus formation, eventually leading to disturbed microcirculation with reduced organ perfusion. Although several disease states may manifest as TMA, the two most relevant conditions associated with TMA are thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), characterized by prominent brain or renal lesions, respectively. However, occasionally the clinical distinction between these two conditions can be difficult. In this review, we focus on the epidemiologic and diagnostic criteria as well as on the most recent insights into the pathophysiology and treatment of these two conditions.

Chemical toxicology: reactive intermediates and their role in pharmacology and toxicology

Reactive intermediates formed during the metabolism of drugs have been investigated extensively over the past decades. Today, interest in reactive intermediates in drug discovery is focused on minimising bioactivation in hopes of reducing the risk of causing so-called idiosyncratic toxicity. These efforts are justified based on the 'hapten hypothesis', namely, that on binding to protein, reactive intermediates may elicit an immune response to the modified protein, leading to a cascade of events that ultimately manifests as a toxic outcome. However, the pharmacological action of certain drugs depends on reactive intermediates that modify critical amino acid residues of proteins, typically enzymes, thereby altering their activity. Thus, the notion that reactive intermediates are inherently dangerous is unjustified. When a reactive intermediate is necessary for the desired pharmacological effect of a drug, the selectivity it displays towards the target protein is crucial, as off-target binding may produce unwanted toxicities. On the other hand, reactive intermediates may play no role in toxicity. This review provides a balanced perspective, primarily focusing on the proposed role of reactive intermediates in drug toxicity, while also highlighting examples in which they are involved in causing the desired pharmacology. It is hoped that this knowledge can help scientists involved in drug discovery and development in their challenging task of producing safe and effective drugs.

Therapeutic plasma exchange for the treatment of thrombotic thrombocytopenic purpura: a retrospective multicenter study

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a rare disease that is fatal if it is not treated. Therapeutic plasma exchange (TPE) has resulted in excellent remission and survival rates in TTP patients.

MATERIAL AND METHODS

We describe our experience with 52 TTP patients treated with TPE during the past eight years (65% of the patients were females; patient median age=34 years, range: 17-73). TPE was carried out 1-1.5 times plasma volume. Fresh frozen plasma (FFP) or cryosupernatant plasma (CSP) was used as the replacement fluid. TPE was performed daily until normalization of serum LDH and recovery of the platelet count to >150 x 10(9)/dL; TPE was then slowly tapered. Clinical, laboratory data, the number of TPE, other given therapy modalities, treatment outcomes and survival rate were evaluated retrospectively.

RESULTS

Overall response (OR) and complete response (CR) rates were 77% and 60%, respectively. Response was excellent in 82.8% of the patients with primary TTP among whom 74.2% were CR. Additionally, there were statistical differences in terms of CR rate between patients with primary TTP and secondary TTP (74.2% vs. 29.4%; p=0.005). OR and CR rates were 79% and 57.9% in patients on TPE alone and 75.8% and 60.6% in patients on TPE+prednisolone, respectively (p=1 and p=0.8). Additionally, there were no statistical differences in terms of OR and CR rates between patients on TPE with FFP and CSP (p=0.25 and p=0.16, respectively). The presence of fever and the number of TPE were statistically important factors influencing the probability of response in multivariate logistic regression analysis (p<0.01 and p<0.01, respectively). Additionally, in multivariate Cox's regression analysis, the probability of survival was higher in patients who were responsive to treatment compared to patients who were unresponsive (p<0.001).

CONCLUSION

TPE is an effective treatment for primary TTP; however, it may be used as adjunctive therapy for secondary TTP until it is under control. The addition of steroids to TPE had no advantage compared to TPE alone. CSP as replacement fluid is not superior compared to FFP. Fever appears to be a bad prognostic indicator. Therefore, prolonged treatment with TPE may be needed in patients with fever.

High-Capacity Hydrogen and Nitric Oxide Adsorption and Storage in a Metal−Organic Framework

Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H2 per g of HKUST-1 (22.7 mg g(-)1, 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-)1, 3.6 wt %) at 10 bar. Adsorption of D2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at <100 mbar) times the H2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of approximately 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.

Journey in reverse: TTP from bedside to blood bank to bench

Thrombotic thrombocytopenic purpura (TTP) is the most extensive and dangerous intravascular platelet clumping disorder. For more than a half-century after its initial recognition, mortality was near 100% and the etiology totally obscure. Then, in the late 1970s to early 1980s, empiric, but successful, therapy by a few clinician/blood bank partnerships was followed by sudden laboratory insight into pathophysiology. The discussion that follows was prepared in conjunction with the 2006 Francis Morrison, M.D., Memorial Lecture at the 27th Annual Meeting of the American Society for Apheresis.

Antiplatelet drug induced isolated profound thrombocytopenia in interventional cardiology: a review based on individual case reports

A combination antithrombotic and antiplatelet therapy with clopidogrel, aspirin, glycoprotein IIb/IIIa receptor inhibitors and heparins is routinely used as adjunct therapy in patients undergoing percutaneous coronary intervention (PCI). As all substances inhibit platelet function, bleeding and thrombocytopenia may occur. We report on three patients who developed isolated profound thrombocytopenia (platelet count of < 20,000/mm(3)) within 24 h after initiation of combination antiplatelet and antithrombotic therapy during a 1 year observation period in 443 consecutive patients undergoing PCI and stent implantation. The data from our cardiology unit revealed an incidence of an isolated profound thrombocytopenia in 0.7% of all patients on combination antithrombotic therapy and in 1.5% of patients with GPIIb/IIIa-blockers. In all three cases with isolated profound thrombocytopenia GPIIb/IIIa-blockers were found to be the causative agents. Negative results of HIT-assays excluded heparin induced thrombocytopenia type II. Despite the extremely low platelet count no severe bleeding was observed and in all cases platelet counts normalized within 3-4 days without specific interventions except discontinuation of the responsible agent. These findings are discussed in conjunct with an overview of the recent literature.

[Acquired idiopathic thrombotic thrombocytopenic purpura: arguments for an autoimmune disease]

Thrombotic thrombocytopenic purpura (TTP) is a severe form of thrombotic microangiopathy (TMA) characterized by systemic platelet clumping, hemolytic anemia, and multiorgan failure. TTP results from a defect in ADAMTS13, a plasma enzyme specifically involved in the cleavage of highly hemostatic unusually large (UL) von Willebrand factor (vWF) multimers into smaller and less adhesive vWF forms. Failure to degrade these UL-vWF multimers leads to excessive platelet aggregation and capillary occlusion. ADAMTS13 deficiency is related to mutations of the encoding gene in hereditary TTP, whereas in acquired forms it results from autoantibodies that may alter the protein function. This latter finding strongly suggests that acquired idiopathic TTP corresponds to an autoimmune disease. Acquired idiopathic TTP appears to be associated with clinical features suggestive of autoimmunity in one third of cases. In two thirds, autoantibodies such as antinuclear antibodies may be observed. This review, based on an analysis of the literature and on French experience with TMA, focuses on the different autoimmune manifestations that may be observed in TTP, as well as the putative pathophysiological link between autoimmune manifestations and TTP.

Clopidogrel

Clopidogrel (Plavix), Iscover) selectively and irreversibly inhibits adenosine diphosphate (ADP)-induced platelet aggregation. Long-term administration of clopidogrel was associated with a modest but statistically significant advantage over aspirin in reducing adverse cardiovascular outcomes in patients with established cardiovascular disease in the CAPRIE trial. In other large well designed multicentre trials, such as CURE, COMMIT and CLARITY-TIMI 28, the addition of clopidogrel to aspirin therapy improved outcomes in patients with acute coronary syndromes. However, some issues regarding the use of clopidogrel remain unresolved, such as the optimal loading dose in patients undergoing percutaneous coronary interventions (PCI) and the optimal treatment duration following drug-eluting intracoronary stent placement. Results of several large randomised trials, therefore, have established clopidogrel as an effective and well tolerated antiplatelet agent for the secondary prevention of ischaemic events in patients with various cardiovascular conditions, including those with ischaemic stroke or acute coronary syndromes. In addition, treatment guidelines from the US and Europe acknowledge the importance of clopidogrel in contemporary cardiovascular medicine.

Autoimmune hemolytic anemia in patients with liver transplants for primary biliary cirrhosis: Three case reports and a review of the literature

BACKGROUND

Hemolytic anemia is rare after liver transplant and is usually associated with ABO mistmatch, post-transplant lymphoproliferative disorders, or medications.

CASE REPORTS

We report three patients who had undergone successful liver transplants for primary biliary cirrhosis (PBC) and developed direct antibody test positive autoimmune hemolytic anemia (AIHA) several years into uncomplicated post-transplant management. For two of the patients, the hemolysis responded to steroids and rituximab. One patient required a surgical splenectomy.

DISCUSSION

AIHA is an immune-mediated hemolysis that has been reported in patients with PBC. There are no reports of AIHA in patients following liver transplantation for this disease. AIHA should be considered in stable PBC patients who develop anemia years after liver transplant.

Infection as a cause of early relapse in patients recovering from thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare but severe disorder characterized by hemolytic anemia, thrombocytopenia, fever, renal failure, and neurologic manifestations. Plasma exchange is the most effective treatment for this condition reducing mortality from 90% in untreated patients to 10%. However, infections acquired during the course of therapy could lead to early relapse of TTP. In this case report, we report three patients with TTP who initially responded well to plasma exchange treatments but suffered early relapses following bacterial infections. All these patients achieved remission once appropriate antibiotic therapy was instituted although one patient eventually received four courses of rituximab. This report emphasizes the need to be vigilant for new infections especially urinary tract infections in TTP patients undergoing plasma exchange. Instituting appropriate antibiotic therapy once an infection is suspected may reduce the need for prolonged plasma exchange procedures and extended hospital stay.

Anti-platelet and anti-thrombotic approaches in patients undergoing percutaneous coronary intervention

Over the past three decades, there has been a tremendous increase in the use of percutaneous coronary interventions (PCI) for the treatment of patients with atherosclerotic coronary artery disease. However, PCI causes disruption of atherosclerotic plaque and denudation of the endothelium, leading to stimulation of platelet aggregation and activation of the coagulation cascade. Therefore, anti-platelet and anti-thrombotic agents have a pivotal role as adjuncts before, during and after PCI, in order to minimize the risk of procedural ischemic complications, such as myocardial infarction, stent thrombosis, and various degrees of myonecrosis. The current article presents a comprehensive review of the evolution of current anti-platelet and anticoagulation regimens used in the setting of PCI. It starts with a summary of the current perspective of the coagulation process along with platelet activation and aggregation. The review then focuses specifically on individual anti-platelet and anti-thrombotic drugs including their mechanism of action and the scientific evidence which led to their use in PCI. Finally, we present summary recommendations from the AHA/ACC guidelines for individual anticoagulant and anti-platelet regimens given peri-PCI.

The significance of lower extremity peripheral arterial disease

The role of the cardiologist is expanding and involves the management of patients with lower extremity atherosclerotic occlusive arterial disease. Peripheral arterial disease (PAD) remains an underdiagnosed and undertreated disease. The purpose of this review is to educate the clinician on the significance of lower extremity atherosclerotic occlusive arterial disease. Pathophysiology and anatomy are briefly reviewed. The definition of PAD is based upon both anatomic and functional considerations. Risk factors for PAD include traditional atherosclerotic risk factors. There is a considerable overlap between coronary and cerebrovascular diseases and PAD. Diagnosis is made mainly by history and physical examination. Noninvasive and invasive tests help diagnosis and localize disease. Expanded therapies to improve outcomes include lifestyle changes, medical treatment, interventional cardiovascular procedures, or surgical intervention.

ADAMTS13 and microvascular thrombosis

Interaction between platelet and von Willebrand factor, a circulating adhesive glycoprotein, is essential for hemostasis under the high shear environments of arterioles and capillaries. If unregulated, this interaction may lead to unwarranted platelet thrombosis. ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, number 13), a plasma zinc metalloprotease synthesized primarily in the stellate cells of the liver, cleaves shear stress-activated von Willebrand factor, thereby preventing the occurrence of von Willebrand factor-platelet interaction in the circulation. A profound deficiency of ADAMTS13, due to genetic mutations or autoimmune inhibition, results in intravascular von Willebrand factor platelet aggregation and widespread microvascular thrombosis characteristic of thrombotic thrombocytopenic purpura. Cloning of ADAMTS13 and structure-function analyses of the enzyme are leading to exciting advances in the diagnosis and therapy of this hitherto mysterious disease.

The safety and efficacy of aspirin and clopidogrel as a combination treatment in patients with coronary heart disease

The use of aspirin and clopidogrel in combination has become part of the standard clinical care of patients with coronary artery disease. The use of this combination provides significant benefits compared with the use of aspirin alone in patients with acute coronary syndromes, and in patients treated with percutaneous coronary intervention with stent placement (both bare metal and drug-eluting stents). Clinical trials have demonstrated significant efficacy of this dual therapy; however, there is the potential for significant bleeding complications from the synergistic antiplatelet effects. In total, it appears that when there is vessel injury (mechanical from perctutaneous coronary intervention or a ruptured plaque), dual antiplatelet therapy with aspirin and clopidogrel results in improved outcomes, albeit with a small but significant inherent risk of increased bleeding.

New-onset and idiopathic thrombotic thrombocytopenic purpura: incidence, diagnostic validity, and potential risk factors

OBJECTIVE

The aim of this study was to determine the incidence rate for new-onset and idiopathic thrombotic thrombocytopenic purpura (TTP) among adults 20-64 years old, the validity of diagnostic criteria, and potential risk factors for TTP.

METHODS

This retrospective observational study analyzed automated administrative data from 11 geographically dispersed U.S. health plans. Cases of TTP were identified based on the presence of an inpatient hospital claim for TTP (ICD-9-CM 446.6) between 1/1/97 and 12/31/01 and confirmed by medical record review. Pharmacy and medical claims were used to evaluate outpatient drug exposure and comorbidities preceding hospitalization for TTP. Cases and the base population were screened so as to result in an incidence rate for idiopathic TTP.

RESULTS

We confirmed new-onset and idiopathic TTP in 9 of 15 presumptive cases for an incidence density of 1.4 per million person-years (95% CI: 0.6-2.6). The rate increased to 1.8 per million person-years after projection and age-standardization. The highest incidence rate of TTP was found in patients 50-64 years old (2.8 per million person-years; 95% CI: 0.8-7.1). These 9 patients had no apparent risk factors for TTP based on claims and medical record data.

CONCLUSIONS

In a general U.S. population, the incidence rate of confirmed new-onset and idiopathic TTP was lower than previously reported, but appears to be on the rise. Our findings suggest that administrative claims data are useful for identifying outpatient drug exposures and comorbidities potentially associated with TTP.

The platelet as a therapeutic target for treating vascular diseases and the role of eicosanoid and synthetic PPARgamma ligands

The platelet was traditionally thought only to serve as the instigator of thrombus formation, but now is emerging as a pivotal player in cardiovascular disease and diabetes by inciting and maintaining inflammation. Upon activation, platelets synthesize eicosanoids such as thromboxane A2 (TXA2) and PGE2 and release pro-inflammatory mediators including CD40 ligand (CD40L). These mediators activate not only platelets, but also stimulate vascular endothelial cells and leukocytes. These autocrine and paracrine activation processes make platelets an important target for attenuating inflammation. The growing interest and recent discoveries in platelet biology has lead to the search for therapeutic platelet targets. Recently, platelets, although anucleate, were discovered to possess the transcription factor PPARgamma. Treatment with eicosanoid and synthetic PPARgamma ligands blunts platelet release of the bioactive mediators, soluble (s) CD40L and TXA2, in thrombin-activated platelets. PPARgamma ligand treatment may prove useful for dampening unwanted platelet activation and chronic inflammatory diseases such as cardiovascular disease.

Drug-associated disease: hematologic dysfunction

Hematologic dysfunction, including thrombocytopenia, anemia, neutropenia, thromboses, and coagulopathy, occur commonly during critical illnesses. A major challenge is to identify drug-induced causes of hematologic dysfunction. Given the wide variety of drug-induced hematologic effects, clinicians always should consider any concomitant drugs in the differential diagnosis of acquired hematologic dysfunction. The most severe effects include drug-induced aplastic anemia, heparin-induced thrombocytopenia, and drug-induced thrombotic microangiopathy. Certain drugs are associated with multiple hematologic effects. For example, cisplatin can cause hemolytic uremia syndrome and erythropoietin deficiency, and quinine can precipitate immune-mediated thrombocytopenia, immune-mediated thrombocytopenia, and thrombotic microangiopathy.

An update on the first decade of the European centralized procedure: how many innovative drugs?

AIMS

In a previous paper, we proposed an algorithm to assess the degree of therapeutic innovation of the agents approved by the European centralized procedure, which must be followed by biotechnological products and is optional for drugs claimed as innovative. A low overall degree of therapeutic innovation (about 30%) was found. This figure may be an underestimate of the actual level of innovation, because common biotechnological products, such as recombinant human insulins, must follow this procedure. To test the hypothesis that therapeutic innovation prevails among nonbiotechnological products, we evaluated separately the degree of therapeutic innovation of biotechnological vs. nonbiotechnological agents in the first decade of European Medicines Agency activity, also studying a possible time trend.

METHODS

We assessed, for each drug: (i) the seriousness of the target disease, (ii) the availability of previous treatments, and (iii) the extent of therapeutic effect according to the previously proposed algorithm.

RESULTS

Our analysis considered 251 medicinal products corresponding to 198 active substances, classified according to four main areas as therapeutic agents (88.9%), diagnostics (5.5%), vaccines (5.1%) and life-style drugs (0.5%). Among all therapeutic agents, 49 out of 176 agents (28%) were classified as having an important degree of therapeutic innovation. Fifteen out of 60 biotechnological therapeutic agents were considered important therapeutic innovations (25%), whereas this figure was 29% for nonbiotechnological agents.

CONCLUSIONS

Among active substances claimed as innovative by the manufacturers, only a minority deserve this definition according to our algorithm.

A classification of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura and related disorders

The diagnostic terms hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are based on historical and overlapping clinical descriptions. Advances in understanding some of the causes of the syndrome now permit many patients to be classified according to etiology. The increased precision of a diagnosis based on causation is important for considering logical approaches to treatment and prognosis. It is also essential for research. We propose a classification that accommodates both a current understanding of causation (level 1) and clinical association in cases for whom cause of disease is unclear (level 2). We tested the classification in a pediatric disease registry of HUS. The revised classification is a stimulus to comprehensive investigation of all cases of HUS and TTP and is expected to increase the proportion of cases in whom a level 1 etiological diagnosis is confirmed.

Sub-Tenon's anesthesia with aspirin, warfarin, and clopidogrel

PURPOSE

To review the frequency of hemorrhagic complications with sub-Tenon's anesthesia in patients on aspirin, warfarin or clopidogrel.

SETTING

St. James's University Hospital, Leeds, United Kingdom.

METHODS

Data were collected prospectively for patients having elective phacoemulsification under sub-Tenon's anesthesia. Seventy-five patients were on aspirin, 65 were on warfarin, and 40 were on clopidogrel. Seventy-five patients on no anticoagulants were used as the control group. No changes in the anticoagulant regimen were made prior to surgery.

RESULTS

No sight-threatening hemorrhagic complications were noted, and no surgery was postponed or cancelled due to an anesthesic complication. Subconjunctival hemorrhage occurred in 19% in the control group, 40% in the clopidogrel group, 35% in the warfarin group, and 21% in the aspirin group. The warfarin and clopidogrel groups had the highest incidence of subconjunctival hemorrhage (P<.05). The incidence of hemorrhages involving more than 1 quadrant was highest in these 3 groups; however, this did not achieve statistical significance (P = .37, Fisher exact test).

CONCLUSION

Data from this study support the continued use of anticoagulant agents among routine users during cataract surgery using a sub-Tenon's block.

Clopidogrel in the treatment of ischaemic heart disease

Clopidogrel is an effective antiplatelet agent that has undergone rigorous assessment in the setting of ischaemic heart disease over the last decade. There is extensive evidence for the use of this drug in patients undergoing percutaneous coronary intervention, in those with stable ischaemic heart disease and also in those with acute coronary syndromes. This article examines the use of clopidogrel in patients with ischaemic heart disease.

Update on Anticoagulant Medications for the Interventional Radiologist

For many years, available anticoagulant medications were limited to vitamin K antagonists, unfractionated heparin, and aspirin. However, in the past 20 years, several new agents have been developed for the treatment of thrombosis, and even more are being developed. This increasing number of medications has led to more specific treatment algorithms for the care of venous and arterial thrombotic events. As more agents become available, treatment guidelines are rapidly changing. With increasing frequency, interventional radiologists encounter patients already taking anticoagulant medications prophylactically or therapeutically, or they need to determine which anticoagulant medications need to be initiated for a particular procedure. Therefore, it has become increasingly important to understand the mechanisms, risks, and benefits of anticoagulant medications. A review of the traditional anticoagulants, their new counterparts, and their places in the medication repertoire of interventional radiology will be discussed herein.

NO-releasing zeolites and their antithrombotic properties

Transition metal-exchanged zeolite-A adsorbs and stores nitric oxide in relatively high capacity (up to 1 mmol of NO/g of zeolite). The stored NO is released on contact with an aqueous environment under biologically relevant conditions of temperature and pH. The release of the NO can be tuned by altering the chemical composition of the zeolite, by controlling the amount of water contacting the zeolite, and by blending the zeolite with different polymers. The high capacity of zeolite for NO makes it extremely attractive for use in biological and medical applications, and our experiments indicate that the NO released from Co-exchanged zeolite-A inhibits platelet aggregation and adhesion of human platelets in vitro.

Clinical trial issues in weight-loss therapy

BACKGROUND

Overweight and obesity rates continue to increase nationally, generating significant interest in weight-loss therapies to address both the burden of obesity-associated chronic disease and individual concerns about appearance. Effective obesity therapies also have the potential for off-label use and unintended consequences.

METHODS

The behavioral, pharmacologic, and surgical therapies for obesity are reviewed. Clinical trial issues common to chronic disease states and issues specific to obesity trials are examined. Finally, study designs for obesity therapy, including populations, control arms, sample size, and duration of therapy, are discussed.

Guidelines for Prevention of Stroke in Patients With Ischemic Stroke or Transient Ischemic Attack

The aim of this new statement is to provide comprehensive and timely evidence-based recommendations on the prevention of ischemic stroke among survivors of ischemic stroke or transient ischemic attack. Evidence-based recommendations are included for the control of risk factors, interventional approaches for atherosclerotic disease, antithrombotic treatments for cardioembolism, and the use of antiplatelet agents for noncardioembolic stroke. Further recommendations are provided for the prevention of recurrent stroke in a variety of other specific circumstances, including arterial dissections; patent foramen ovale; hyperhomocysteinemia; hypercoagulable states; sickle cell disease; cerebral venous sinus thrombosis; stroke among women, particularly with regard to pregnancy and the use of postmenopausal hormones; the use of anticoagulation after cerebral hemorrhage; and special approaches for the implementation of guidelines and their use in high-risk populations.

Antithrombotic and Thrombolytic Therapy for Ischemic Stroke

Thrombolytic and antithrombotic agents form the cornerstone of stroke treatment and prevention. Recombinant tissue plasminogen activator improves outcome in patients treated within 3 hours of stroke onset. Emerging trials are directed to extend the therapeutic window and identify agents that could provide better safety profiles. Large, randomized trials have also highlighted the effectiveness and safety of early and continuous antiplatelet therapy in reducing atherothrombotic stroke recurrence. Aspirin has become the antiplatelet treatment standard against which several other antiplatelet agents have been shown to be more effective. The prevention of cardioembolic stroke is best accomplished with oral anticoagulation, barring any contraindications.

Review of antiplatelet therapy in secondary prevention of cerebrovascular events: a need for direct comparisons between antiplatelet agents

Patients experiencing stroke or transient ischemic attack (TIA) are at high risk for recurrent (secondary) strokes, which comprise 29% of all strokes in the United States. Current recommendations for prevention of secondary stroke from the American College of Chest Physicians (ACCP) call for the broad use of platelet antiaggregation (antiplatelet) agents for patients with a history of noncardioembolic stroke or TIA. Five agents--aspirin, ticlopidine, clopidogrel, extended-release dipyridamole (ER-DP), and triflusal--have demonstrated efficacy in large-scale clinical studies in the prevention of recurrent vascular events and/or stroke in patients with a history of stroke. The results of the following studies are reviewed and compared: the Swedish Aspirin Low-Dose Trial (SALT), the United Kingdom Transient Ischaemic Attack (UK-TIA) Aspirin Trial, Dutch Transient Ischemic Attack (Dutch TIA) study (aspirin), the Canadian American Ticlopidine Study (CATS), the Ticlopidine Aspirin Stroke Study (TASS), the African American Antiplatelet Stroke Prevention Study (AAASPS) (ticlopidine), the Clopidogrel versus Aspirin in Patients at Risk of Recurrent Ischemic Events (CAPRIE) trial, the Management of Atherothrombosis With Clopidogrel in High-Risk Patients study (MATCH) (clopidogrel), the second European Stroke Prevention Study (ESPS2) (aspirin plus ER-DP), and the Triflusal versus Aspirin in Cerebral Infarction Prevention (TACIP) study. In comparative monotherapy studies of patients with previous stroke, ticlopidine demonstrates statistically significant improved efficacy over aspirin, and clopidogrel demonstrates nonsignificant slight improvement over aspirin for the prevention of ischemic cardiac and cerebrovascular events; however, the adverse event profile of ticlopidine (including rash, diarrhea, and neutropenia) will probably limit its long-term use. Among combination approaches, only aspirin plus ER-DP has demonstrated statistically significant, clinically meaningful additive benefit over monotherapy with each agent. Clopidogrel plus aspirin did not significantly improve preventive efficacy and increased the risk of serious side effects, including life-threatening bleeding episodes. The 15,500-patient PRoFESS (the Prevention Regimen for Effectively Avoiding Second Strokes) study, with results expected in 2008, will directly compare aspirin plus ER-DP with clopidogrel monotherapy for the prevention of recurrent stroke and should provide statistically robust estimates of comparative efficacy for the development of improved recommendations.

Thrombotic thrombocytopenic purpura: a moving target

Almost 80 years after Eli Moschcowitz published the first description of the disease, most patients with idiopathic thrombotic thrombocytopenic purpura (TTP) were found to have acquired autoantibody inhibitors of the ADAMTS13 metalloprotease. Plasma ADAMTS13 normally cleaves von Willebrand factor within nascent platelet-rich thrombi, and ADAMTS13 deficiency allows unchecked thrombus growth to cause microangiopathic hemolysis, thrombocytopenia, and tissue infarction. At present, ADAMTS13 deficiency with a high-titer inhibitor level appears to be associated with an increased risk of early death and subsequent relapse. Thus, acquired ADAMTS13 deficiency identifies a specific mechanism of TTP and is a potential biomarker of disease activity or risk. At present, two major clinical questions in the field may be summarized as follows. First, by emphasizing TTP caused by ADAMTS13 deficiency, are we in danger of neglecting other causes that should be treated with plasma exchange? Second, should we treat asymptomatic patients who have severe ADAMTS13 deficiency to prevent future disease, and if so, how?

Thrombotic Microangiopathy Syndrome in the ICU

Major studies designed to improve our understanding of the pathophysiology of TMA have been conducted over recent years. This improved knowledge opens up new perspectives for more targeted treatment. However, until these innovative treatments become available, early diagnosis of these diseases is essential in order to rapidly initiate specific treatment, as the interval between diagnosis and initiation of plasma exchange is a decisive element in the prognosis of TTP. Treatment must not be stopped too early or too rapidly and must take into account the various associated factors, especially the presence of infection.

Antiplatelet agents and arterial thrombosis

There is an increase in arterial thrombotic events in the elderly. Elderly patients are more likely to have associated diseases, such as diabetes, hypertension and hypercholesterolemia, and when age is confounded by these other predisposing factors, the risk of an arterial ischemic event increases disproportionately. Antithrombotic therapy for geriatric patients is underused, even when one adjusts for potential drug contraindications. This article focuses on the action of the currently available antiplatelet agents--aspirin, clopidogrel, and glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists, and assesses their effects in different disease states, with special attention to data that examine the geriatric population.

[Antithrombotic drugs in the prevention of ischemic stroke]

Stroke prevention cannot be dissociated from cardiovascular prevention in general. It is based on the correction of vascular risk factors, particularly hypertension and tobacco smoking, and on antithrombotic drugs which tackle the thrombo-embolic process which is the immediate cause of the ischemic event. Ischemic strokes exhibit considerable etiopathogenic diversity, the underlying cause modifying thrombus composition. In atherothrombotic brain infarction, platelets play a major role and antiplatelet drugs have a benefit/risk ratio better than that of oral anticoagulants, with a 25% reduction in the combined risk of ischemic stroke, myocardial infarction and vascular death. Antiplatelet drugs are also used in small artery diseases of the brain although the role of thrombosis is unknown and no specific trial has been devoted to this variety of cerebrovascular disease. In emboligenic cardiac diseases, atrial fibrillation in particular, stasis of the dilated left atrium favors coagulation phenomena, hence the much better efficacy of oral anticoagulants (presently vitamin K antagonists) both in primary and secondary prevention with a 70% risk reduction in cerebral infarction, compared with only 20% for aspirin. The expected benefit of antithrombotic drugs must be weighed against their inherent hemorrhagic risk, which is greatest for oral anticoagulants, slightly less for association of antiplatelet drugs and even less for each antiplatelet drug given alone. The use of antithrombotic drugs allows a targeted prevention of cerebral infarction. It is based on a triple case by case evaluation: that of the cause and of the risk it carries, that of the benefit expected from antithrombotic drugs, and that of their inherent hemorrhagic risk.

The Management of Postoperative Bleeding

This article addresses the management of postoperative bleeding. The problem is called postoperative bleeding rather than postoperative hemorrhage to emphasize the fact that perfect postoperative hemostasis rather than acceptable postoperative blood loss is the ideal. Postoperative bleeding is a risk of all surgical procedures. The best way to reduce the risk of hemorrhage is to identify and correct potential causes of coagulopathy both pre- and post-operatively.

Pharmacological treatment of ischemic stroke

Current pharmacological strategies for acute ischemic stroke largely mirror those employed in acute coronary syndromes. However, important differences in the effectiveness and versatility of the principal agents have emerged between these 2 clinical settings. In general, the level of success achieved with drugs in acute coronary syndromes has not carried over to the same extent when the same drug types are used in stroke. The principal reason is that reperfusion or anticoagulant therapies in the setting of brain infarction run a significant risk of hemorrhagic transformation that has no direct equivalent in myocardial infarction. Consequently, a significant challenge in acute stroke therapeutics is the ability to select patients for drugs where only a narrow therapeutic margin exists and to identify methods that can minimize hemorrhage risk. Other brain-specific vascular factors also pertain in explaining differences in outcome of drugs generally regarded as having a broad cardiovascular remit. The relatively limited efficacy of antiplatelets in stroke might relate to the composition and heterogeneity of the cerebrovascular lesion, while the poor outcome associated with acute anti-hypertensive use is partly due to loss of cerebrovascular autoregulation. Finally, downstream consequences of arterial occlusion within the brain such as excitotoxicity and plasticity are organ specific and, as such, deserve their own pharmacological approaches. In this review, we describe the general mechanism of each drug class used in ischemic stroke and then report on the clinical experience and application for each.

Thrombocytopenic conditions-autoimmunity and hypercoagulability: commonalities and differences in ITP, TTP, HIT, and APS

Immune thrombocytopenia purpura (ITP), thrombotic thrombocytopenia purpura (TTP), heparin-induced thrombocytopenia (HIT), and antiphospholipid syndrome (APS) are clinical conditions associated with significant morbidity and mortality. These well-defined clinical syndromes have in common several properties: (1) their pathogenesis is immune mediated, specifically by autoantibodies; (2) thrombocytopenia is a hallmark in these four conditions; (3) except for the case of ITP, platelet and endothelial cell activation occurs in TTP, HIT, and APS, resulting in a prothrombotic state and an increased risk of thrombosis. Although these four immune-mediated syndromes are well-defined diseases, several case reports and studies have documented the association of two diseases in the same patient, illustrating the concept of the kaleidoscope of autoimmunity.

Clopidogrel in non-ST segment elevation acute coronary syndromes: an overview of the submission by the British Cardiac Society and the Royal College of Physicians of London to the National Institute for Clinical Excellence, and beyond

A comprehensive appraisal was undertaken on behalf of the British Cardiac Society and the Royal College of Physicians of London to assess the use of clopidogrel in acute coronary syndromes. The appraisal was submitted to the National Institute for Clinical Excellence (NICE) in August 2003 and contributed to the development of the recently published guidelines for the use of clopidogrel in acute coronary syndromes. The submission to NICE and more recent publications evaluating the use of clopidogrel are reviewed.

Clopidogrel: cardiologists' panacea or neurologists' headache?

Clopidogrel (Plavix) is a potent platelet inhibitor that has been demonstrated to be significantly more effective than aspirin for the prevention of atherothrombotic events in patients with established atherosclerotic disease in the Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events (CAPRIE) study. Furthermore, the benefit of clopidogrel compared with placebo in patients with acute coronary syndromes, as well as those undergoing percutaneous coronary intervention receiving a standard therapy including aspirin, has been largely demonstrated by the Clopidogrel in Unstable angina to prevent Recurrent Events (CURE), Clopidogrel for the Reduction of Events During Observation (CREDO), CLopidogrel as Adjunctive ReperfusIon TherapY-Thrombolysis In Myocardial Infarction (CLARITY-TIMI)28, and Clopidogrel and Metoprolol in Myocardial Infarction Trial/Secon Chinese Cardiac Study (COMMIT/CCS-2) trials. However, in the Management of Atherothrombosis with Clopidogrel in High-risk patients with recent transient ischemic attack or ischemic stroke (MATCH) trial, there was no clinical benefit of adding aspirin versus placebo to a standard therapy of clopidogrel in patients with cerebrovascular disease. The implications of these findings, as well as future perspectives from upcoming trials, shall be discussed herein.

Thrombotic thrombocytopenic purpura

This overview summarizes the history of thrombotic thrombocytopenic purpura (TTP) from its initial recognition in 1924 as a most often fatal disease to the discovery in 1997 of ADAMTS-13 deficiency as a major risk factor for acute disease manifestation. The cloning of the metalloprotease, ADAMTS-13, an essential regulator of the extremely adhesive unusually large von Willebrand factor (VWF) multimers secreted by endothelial cells, as well as ADAMTS-13 structure and function are reviewed. The complex, initially devised assays for ADAMTS-13 activity and the possible limitations of static in vitro assays are described. A new, simple assay using a recombinant 73-amino acid VWF peptide as substrate will hopefully be useful. Hereditary TTP caused by homozygous or double heterozygous ADAMTS-13 mutations and the nature of the mutations so far identified are discussed. Recognition of this condition by clinicians is of utmost importance, because it can be easily treated and--if untreated--frequently results in death. Acquired TTP is often but not always associated with severe, autoantibody-mediated ADAMTS-13 deficiency. The pathogenesis of cases without severe deficiency of the VWF-cleaving protease remains unknown, affected patients cannot be distinguished clinically from those with severely decreased ADAMTS-13 activity. Survivors of acute TTP, especially those with autoantibody-induced ADAMTS-13 deficiency, are at a high risk for relapse, as are patients with hereditary TTP. Patients with thrombotic microangiopathies (TMA) associated with hematopoietic stem cell transplantation, neo-plasia and several drugs, usually have normal or only moderately reduced ADAMTS-13 activity, with the exception of ticlopidine-induced TMA. Diarrhea-positive-hemolytic uremic syndrome (D+ HUS), mainly occurring in children is due to enterohemorrhagic Escherichia coli infection, and cases with atypical, D- HUS may be associated with factor H abnormalities. Treatment of acquired idiopathic TTP involves plasma exchange with fresh frozen plasma (FFP), and probably immunosuppression with corticosteroids is indicated. We believe that, at present, patients without severe acquired ADAMTS-13 deficiency should be treated with plasma exchange as well, until better strategies become available. Constitutional TTP can be treated by simple FFP infusion that rapidly reverses acute disease and--given prophylactically every 2-3 weeks--prevents relapses. There remains a large research agenda to improve diagnosis of TMA, gain further insight into the pathophysiology of the various TMA and to improve and possibly tailor the management of affected patients.

[Acute coronary syndrome: unstable angina and myocardial infarction]

The acute coronary syndrome comprises unstable angina, non-ST-segment elevation myocardial infarction, and ST-segment elevation myocardial infarction. A successful and stable revascularisation of the infarct related vessel, and the prevention of the loss of myocardium are the main therapeutic targets, as cardiovascular mortality and long term quality of life are essentially determined by left ventricular function. The clinical diagnosis comprises clinical symptoms, ECG-changes, and cardiac troponins. Early percutaneous coronary intervention (PCI) has become the most common method of coronary revascularisation. If PCI is not available, systemic thrombolysis is an alternative after exclusion of contraindications. Parenteral anticoagulation with intravenous or subcutaneous heparines, antithrombotic therapy and HMG-CoA reductase inhibitors are the common secondary drug therapy. Moreover, to prevent left ventricular remodelling ACE-inhibitors, angiotension 2-receptor antagonists, and beta-blocker are indicated.