Aspirin and other platelet-active drugs. The relationship among dose, effectiveness, and side effects

Panax notoginseng Saponins for Treating Coronary Artery Disease: A Functional and Mechanistic Overview

Coronary artery disease (CAD) is a major public health problem and the chief cause of morbidity and mortality worldwide. Panax notoginseng, a valuable herb in traditional Chinese medicine (TCM) with obvious efficacy and favorable safety, shows a great promise as a novel option for CAD and is increasingly recognized clinically. Firstly, this review introduced recent clinical trials on treatment with PNS either alone or in combination with conventional drugs as novel treatment strategies. Then we discussed the mechanisms of P. notoginseng and Panax notoginseng saponins (PNS), which can regulate signaling pathways associated with inflammation, lipid metabolism, the coagulation system, apoptosis, angiogenesis, atherosclerosis, and myocardial ischaemia.

Diabetic muscle infarction: a systematic review

CONTEXT

Diabetic muscle infarction (DMI) is a rare complication associated with poorly controlled diabetes mellitus. Less than 200 cases have been reported in the literature since it was first described over 45 years ago. There is no clear 'standard of care' for managing these patients.

EVIDENCE ACQUISITION

PubMed searches were conducted for 'diabetic muscle infarction' and 'diabetic myonecrosis' from database inception through July 2014. All articles identified by these searches were reviewed in detail if the article text was available in English.

EVIDENCE SYNTHESIS

The current literature exists as case reports or small case series, with no prospective or higher-order treatment studies available. Thus, an evidence-based approach to data synthesis was difficult. The available literature is presented objectively with an attempt to describe clinically relevant trends and findings in the diagnosis and management of DMI.

CONCLUSIONS

Early recognition of DMI is key, so appropriate treatment can be initiated. MRI is the radiological study of choice. A combination of bed rest, glycemic control, and non-steroidal anti-inflammatory drug therapy appears to yield the shortest time to symptom resolution and the lowest risk of recurrence.

Preventive aspects in peripheral artery disease

The prevalence of peripheral artery disease is steadily increasing and is associated with significant morbidity, including a significant percentage of amputations. Peripheral artery disease often goes undiagnosed, making its prevention increasingly important. Patients with peripheral arterial disease are at increased risk of adverse cardiovascular outcomes which makes prevention even more important. Several risk factors have been identified in the pathophysiology of peripheral artery disease which should be modified to decrease risk. Smoking, hyperlipidemia, hypertension, and diabetes are among proven risk factors for the development of peripheral artery disease, thus smoking cessation, lipid control, blood pressure control, and glucose control have been tried and shown to be effective in preventing the morbidity associated with this disease. Pharmacologic agents such as aspirin and clopidogrel alone or in combination have been shown to be effective, though risk of bleeding might be increased with the combination. Anticoagulation use is recommended only for acute embolic cases. Other treatment modalities that have been tried or are under investigation are estrogen replacement, naftidrofuryl, pentoxifylline, hyperbaric oxygen, therapeutic angiogenesis, and advanced glycation inhibitors. The treatment for concomitant vascular diseases does not change in the presence of peripheral artery disease, but aggressive management of risk factors should be undertaken in such cases.

Pathophysiologic bases for adjunctive therapies in the treatment and secondary prevention of acute myocardial infarction

Postmyocardial infarction (MI) survival has been steadily improving. This improvement has been due, in part, to the actions of the adjunctive medical therapies for the treatment of MI. Aspirin, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and lipid-lowering agents have been shown to improve survival in the treatment and secondary prevention of MI. Nitrates have beneficial effects as well. These medications complement the reperfusion strategies through different mechanisms. Other adjunctive medical therapies, namely magnesium, antiarrhythmic agents, and calcium-channel blockers, have not been shown to improve mortality with routine post-MI use despite their theoretical benefits.

Gastric protection and gastrointestinal bleeding with aspirin thromboprophylaxis in hip and knee joint replacements

INTRODUCTION

Upper gastrointestinal (GI) bleeding in patients who undergo hip and knee arthroplasty tends to be associated with non-steroidal anti-inflammatory drug use, steroid intake, pre-existing peptic ulcers and smoking. The use of aspirin for thromboprophylaxis is an added risk for the occurrence of GI bleed. The aim of this study was to determine the incidence of upper GI bleeding and whether the use of peri-operative oral ranitidine reduces the incidence of upper GI bleeding when aspirin thromboprophylaxis is used for hip and knee arthroplasty.

PATIENTS AND METHODS

Data from 1491 and 886 patients who underwent hip and knee replacements at the James Cook University Hospital (group 1) and at Friarage Hospital, Northallerton (group 2), respectively, were analysed in retrospect. All patients received 150 mg of aspirin per day for a period of 6 weeks from the day of surgery. Additionally, patients operated at the Friarage Hospital received 300 mg of oral ranitidine per day, for three postoperative days.

RESULTS

We observed that patients in group 1 had a higher incidence of overt upper GI haemorrhage, which was statistically significant (P <0.014) compared to patients in group 2.

CONCLUSIONS

Based on this experience, we recommend the use of peri-operative gastric protection with ranitidine when aspirin is used for thromboprophylaxis in hip and knee arthroplasty.

The stroke rehabilitation paradigm

The matrix of stroke rehabilitation is evolving as we look outside the box of traditional therapy type, timing, and intensity of rehabilitation techniques. For inpatient wards, the goal of medical stability and prompt resolution of complications to maximize participation in therapy remains paramount. In the current medical model, we focus on teaching compensatory strategies and rarely on restorative approaches because of time and financial limitations. Researchers aim to identify new technologic and molecular approaches to improve functional outcomes and more accurately predict disability. This article examines different concepts surrounding the comprehensive rehabilitation paradigm of stroke survivors.

Acquired platelet dysfunction

Acquired platelet dysfunction is encountered frequently in clinical practice. The usual clinical presentation is that of mucosal bleeding, epistaxis, or superficial epidermal bleeds. Often, the dysfunctional platelets are related to a medication or a systemic disorder. Normally, when platelets are exposed to damaged endothelium, they adhere to the exposed basement membrane collagen and change their shape from smooth disks to spheres with pseudopodia. Then, they secrete the contents of their granules, a process referred to as the release reaction. Additional platelets form aggregates on those platelets that have adhered to the vessel wall. As a result, the primary hemostatic plug is formed, and bleeding is arrested. This article reviews the various forms of acquired platelet dysfunction that result in decreased platelet aggregation, adhesion, or secretion.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Effects of atorvastatin and aspirin combined therapy on inflammatory responses in patients undergoing coronary artery bypass grafting

This study was conducted to compare the effects of atorvastatin plus aspirin combined therapy on inflammatory responses, endothelial cell function, and blood coagulation system in patients undergoing coronary artery bypass grafting (CABG) to aspirin monotherapy. The patients were randomized into atorvastatin plus aspirin combined therapy group and aspirin monotherapy group. Reduced total cholesterol in the combined therapy group was found in a short term of medication for 14 days. On postoperative day (POD)-14, inhibitory effects of the combined therapy on whole blood aggregation as well as platelet activation assessed by flow cytometry were stronger than those of the monotherapy. Furthermore, cytokine, cytokine receptors, c-reactive protein and alpha1-acid glycoprotein in the combined therapy group were down-regulated on POD-14. At the same time, circulating levels of thromboxane A(2), vascular endothelial growth factor and thrombin-antithrombin III complex as well as P-selectin, L-selectin and intercellular adhesion molecule-1 were down-regulated, while E-selectin and transforming growth factor-beta1 was up-regulated. Atorvastatin plus aspirin combined therapy may improve inflammatory responses, accelerated platelet function, vascular endothelial cell function, blood coagulation system at the early stage such as 14th day after CABG. In conclusion, atorvastatin and aspirin combined therapy may bring beneficial effects to the patient after CABG.

Platelet ADP receptor antagonists: ticlopidine and clopidogrel

The central role of platelets in the pathophysiology of arterial vascular disease has focused attention on the development of effective platelet inhibitor modalities to mitigate the clinical consequences of atherothrombotic disease. Aspirin has been the gold standard of therapy and is effective in cerebral, coronary and peripheral arterial disease with a 25% reduction in myocardial infarction, stroke and vascular death. The platelet ADP receptor antagonists were developed to further improve the clinical results of therapy. Ticlopidine provides an additional 10% relative risk reduction over aspirin alone in stroke prevention and coronary stent placement. However, ticlopidine is accompanied by occasional life-threatening adverse hematological events. The action of clopidogrel is similar to that of ticlopidine, and it is comparably effective. However, the side-effect profile of clopidogrel is much more favorable.

Clinical evidence of dose-dependent interaction between aspirin and angiotensin-converting enzyme inhibitors

Since coronary artery and cerebrovascular diseases are the most common serious complications of long standing hypertension, there is a great potential for combining treatment with aspirin and angiotensin-converting enzyme inhibitors (ACE-I). However, the data regarding interaction of aspirin and ACE-I in relation to blood pressure control and survival benefits are controversial and inconclusive. We presumed that the appearance of dry cough in some of the patients following initiation of ACE-I treatment could be used as a marker for the presence of their influence, whereas ACE-I cough attenuation after addition of aspirin to treatment could be a sign of aspirin and ACE-I interaction on clinical level. The present study was aimed to use ACE-I induced cough as a clinical marker of ACE-I activity to determine whether dose-dependent aspirin and ACE-I interaction does exist. In a cohort of 750 consecutive ACE-I treated hypertensive and postinfarction outpatients we identified 78 (10.4%) non-smoking ACE-I related coughers. Out of them, 31 (21 men, 10 women; mean age 61 +/- 0.9 years) agreed to take part in the study, which was aimed to compare two regimens of combined ACE-I and aspirin treatment (self-matched control data): intermediate (500 mg daily) vs low-dose aspirin (100 mg daily). On each visit the life quality, cough severity (CS, 0-4) and frequency (CF, 0-10) scores were registered. Low doses of aspirin demonstrated an excellent safety profile and did not influence any life quality score and ACE-I induced cough. In contrast, intermediate doses completely abolished cough in 17 patients and reduced coughing in other 11 patients. Cough severity and cough frequency scores decreased, respectively, from 2.7 +/- 1.1 to 0.7 +/- 1.2 (P < 0.001) and from 7.1 +/- 2.3 to 2.0 +/- 2.2 (P < 0.0001). Overall, the cough frequency score method alone could identify a clear modification of cough in 26 (84%) patients, and cough severity score method alone in 24 (77%). Using the combined frequency/severity score method a modification of cough could be identified in 28 (90%) of the patients receiving intermediate dose of aspirin. Aspirin did not influence heart rate and blood pressure control either in hypertensives or in postinfarction patients. We conclude that using ACE-I induced cough as a clinical marker of ACE-I activity demonstrates that an interaction between ACE-I and aspirin at 500 mg/day does exist. We did not find any evidence supporting the presence of a clinically significant interaction between ACE-I and aspirin at 100 mg/day. Thus, combined treatment by low dose aspirin and ACE-I seems to be both safe and useful.

Optimizing drug therapy in patients with cardiovascular disease: the impact of pharmacist-managed pharmacotherapy clinics in a primary care setting

We evaluated the effectiveness of pharmacist-managed pharmacotherapy clinics in implementing and maximizing therapy with agents known to reduce the morbidity and mortality associated with cardiovascular disease. This was a retrospective chart review of 150 patients who were treated for coronary artery disease in primary care clinics. Appropriate treatment of hypercholesterolemia occurred in 96% of patients referred to a clinical pharmacy specialist, compared with 68% of those followed by primary care providers alone (p<0.0001). Eighty-five percent and 50%, respectively, achieved goal low-density lipoprotein (LDL) values below 105 mg/dl (p<0.0001). Appropriate therapy with aspirin or other antiplatelet or anticoagulant drugs was prescribed in 97% and 92%, respectively (p=0.146). As appropriate therapy with these agents was high in both groups, the ability to detect a difference between groups was limited. Among patients with an ejection fraction below 40%, appropriate therapy with an angiotensin-converting enzyme inhibitor or acceptable alternative was 89% and 69%, respectively (p<0.05). Twenty-seven cardiac events were documented in the clinical pharmacy group, versus 22 in the primary care group (p=0.475). Despite the relatively high percentage of patients reaching goal LDL in the primary care group, referral to clinical pharmacy specialists resulted in statistically significant increases in the number of patients appropriately treated for hypercholesterolemia and achieving goal LDL.

The role of platelets in peripheral arterial disease: therapeutic implications

Peripheral arterial disease (PAD) is associated with platelet hyperaggregability as well as an increase in morbidity and mortality from myocardial infarction and stroke. Enhanced platelet activation in PAD may substantially contribute to these adverse outcomes. A relative resistance to aspirin therapy has been reported in patients with PAD. Therefore, clopidogrel may be superior to aspirin in treatment of PAD. Furthermore, the aspirin + clopidogrel combination could be more effective than monotherapy but its risk-benefit ratio has yet to be evaluated. Clopidogrel is preferable to ticlopidine because of its safer profile and the convenience of once-daily administration. The glycoprotein (Gp) IIb/IIIa inhibitors may also find a place as short-term therapy after peripheral angioplasty. There is a need to consider the use of clopidogrel in patients who cannot tolerate aspirin. Patients who have an event while taking aspirin also present a problem. One possibility here is to substitute aspirin with clopidogrel or to add clopidogrel to the aspirin. Although these options are currently not evidence based in patients with PAD, there is emerging evidence showing that they are realistic choices.

Effect of antiplatelet and anticoagulant agents on risk of hospitalization for bleeding among a population of elderly nursing home stroke survivors

BACKGROUND AND PURPOSE

Anticoagulants and antiplatelet agents are underutilized in the nursing home setting, perhaps because trials demonstrating treatment efficacy excluded people resembling those with long-term care needs. We sought to quantify the effect of antiplatelet and anticoagulant agents on risk of hospitalization for bleeding among an elderly nursing home population.

METHODS

We used a case-control design and identified first hospitalizations for bleeds using Medicare claims data from 1992 to 1997 as potential cases. Cases had at least one minimum data set (MDS) assessment within the 6 months before that hospitalization and a diagnosis of stroke. We identified up to 5 controls residing in the same facility during the same year and quarter as the case with a diagnosis of stroke. Our sample consisted of 3433 cases and 13 506 controls. Using the MDS, we identified standing orders for aspirin, dipyridamole, ticlopidine, or warfarin and used conditional logistic regression modeling to estimate the effect of these agents on risk of hospitalization for a bleed.

RESULTS

After adjustment, use of warfarin (odds ratio [OR], 1.26; 95% CI, 1.11 to 1.43) and combination therapy (OR, 1.34; 95% CI, 0.99 to 1.82) were associated with an increased risk of hospitalization for a bleed compared with nonusers. The odds of aspirin use was greater among cases than controls (OR, 1.07; 95% CI, 0.96 to 1.18) after adjustment.

CONCLUSIONS

Although present, the risk associated with use of these agents is small. The numbers needed to treat to harm 1 resident with aspirin and warfarin were 467 and 126, respectively.

Prohemorrhagic potential of dipyrone, ibuprofen, ketorolac, and aspirin: mechanisms associated with blood flow and erythrocyte deformability

Dipyrone, ibuprofen, ketorolac, and aspirin were tested in a well-defined perfusion system (shear rates: 300/s, 800/s, and 1,800/s). Whole blood samples were treated with the drugs at analgesic doses and platelet interaction with damaged subendothelium was measured. All the drugs fully inhibited platelet cyclooxygenase, as assessed by classic aggregometry. Perfusion studies showed that there was a general tendency to reduce the percentage of large aggregates (thrombus; %T), to increase the percentage of adhered platelets (adhesion; %A), and to reduce the height of thrombi with respect to control. Aspirin significantly increased %A and reduced %T at all shear rates tested, whereas dipyrone had the same effect at 800/s, and ketorolac and ibuprofen at 1,800/s. In addition, aspirin significantly reduced erythrocyte deformability with respect to the other drugs. In conclusion, under our experimental conditions, aspirin showed the most remarkable effects on platelet function, closely followed by dipyrone. The effects of ketorolac were moderate, whereas ibuprofen had a minor impact on platelet function.

Regional anesthesia and anticoagulation

The perioperative use of neuraxial techniques in the presence of anticoagulation is a controversial issue. There are significant pharmacokinetic differences between anticoagulants that will affect the timing of neuraxial needle insertion or catheter removal. The pharmacologic profiles of commonly used anticoagulants in the perioperative period are reviewed. Studies examining the use of neuraxial techniques in the presence of various anticoagulants are reviewed and evaluated in the context of the American Society of Regional Anesthesia consensus statements.

Antiplatelet therapy in the elderly. Aspirin, ticlopidine-clopidogrel, and GPIIb/GPIIIa antagonists

Antiplatelet agents including aspirin, dipyridamole, the thienopyridines, and the GPIIb/IIIa antagonists have collectively demonstrated their ability to have a significant impact on the incidence of recurrent MIs, strokes, and other vascular ischemic events in the geriatric population. Low-dose aspirin also seems to be effective and safe for the primary prevention of ischemic heart disease in men considered at high risk. There is no evidence that the recommendations from these studies had increased relevance to younger adults, and the studies considering age as a variable found antiplatelet agents had either similar or increased benefit in older patients. In view of the relatively reduced adverse effects of these agents when compared with their potential therapeutic benefit, it is important that they be considered in all older patients for secondary prevention and in certain high-risk groups for primary prevention of cardiovascular morbidity and mortality.

Intermediate but not low doses of aspirin can suppress angiotensin-converting enzyme inhibitor-induced cough

This self-matched control study aimed to compare the efficiency of two different regimens of active treatment: aspirin in low (100 mg daily) versus intermediate (500 mg daily) doses in abolishing angiotensin-converting enzyme inhibitor (ACEI)-induced cough. A dry bothersome cough is the most common adverse class effect of all angiotensin-converting enzyme inhibitors. Prostaglandins (PG) have been pinpointed as playing a leading role in the genesis of ACEI-associated cough. The role of different doses of the most commonly used PG inhibitor-aspirin-in ACEI cough modification was not yet elucidated. Of 350 consecutive ACEI-treated patients, we identified 34 (9.7%) nonsmoking ACEI-related coughers. Patients with lung disease, nonsteroidal anti-inflammatory drug (NSAID) treatment, and those who did not agree to participate in the study were excluded. In the remaining 14 ACEI coughers (eight men, six women; mean age, 63 +/- 11 years), the treatment was discontinued; the dry cough completely disappeared, but returned in all patients within 1 week after ACEI reintroduction. At the end of the rechallenge period, patients started a low dose of aspirin for 1 week, switching thereafter to the intermediate dose of aspirin for an additional week. On each visit the cough severity (CS, 0-4) and frequency (CF, 0-10) scores were registered. Low doses of aspirin were ineffective in suppressing ACEI-induced cough, whereas intermediate doses completely abolished cough in five patients and reduced coughing in all but one patient; CS and CF decreased, respectively, from 2.5 +/- 1.0 to 0.9 +/- 1.1, P < .002 and from 6.6 +/- 2.4 to 2.4 +/- 1.1, P < .0002. Overall, intermediate doses of aspirin beneficially modified cough scores in 13 (93%) patients, enabling nine (64%) to continue ACEI treatment. Aspirin did not influence blood pressure control either in hypertensives or in postinfarction patients. We conclude that intermediate but not low doses of aspirin probably can suppress ACEI-induced cough. These findings propose a new alternative therapeutic approach for patients with ACEI-related cough, especially those in whom ACEI treatment seems to be essential.

Reduced thrombus formation by hyaluronic acid coating of endovascular devices

Biocompatible stent coatings may alleviate problems of increased (sub)acute thrombosis after stent implantation. Hyaluronic acid (HA), a ubiquitous, nonsulfated glycosaminoglycan, inhibits platelet adhesion and aggregation and prolongs bleeding when administered systemically. However, the effects of immobilized HA for reducing stent platelet deposition in vivo are unknown. We therefore quantified the antithrombotic effects of coating stainless steel stents and tubes with HA using an established baboon thrombosis model under physiologically relevant blood flow conditions. HA-coated and uncoated (control) stents (3.5 mm in diameter, n=32) and stainless steel tubes (4.0 mm in diameter, n=18) were deployed into exteriorized arteriovenous shunts of conscious, nonanticoagulated baboons. Accumulation of (111)In-radiolabeled platelets was quantified by continuous gamma-camera imaging during a 2-hour blood exposure period. HA coating resulted in a significant reduction in platelet deposition in long (4 cm) tubes (0.24+/-0.15 x 10(9) versus 6.12+/-0.49 x 10(9) platelets; P<0.03), short (2 cm) stainless steel tubes (0.18+/-0.06 x 10(9) versus 3.03+/-0.56 x 10(9) platelets; P<0.008), and stents (0.82+/-0.20 x 10(9) versus 1.83+/-0. 23 x 10(9) platelets; P<0.02) compared with uncoated control devices. Thus, HA coating reduces platelet thrombus formation on stainless steel stents and tubes in primate thrombosis models. These results indicate that immobilized HA may represent an attractive strategy for improving the thromboresistance of endovascular devices.

Antiplatelet therapy in the prevention of ischemic vascular events: literature review and evidence-based guidelines for drug selection

BACKGROUND

New antiplatelet drugs are being developed and many clinical trials evaluating the benefits of antiplatelet drugs for the secondary prevention of ischemic events in patients with atherosclerotic vascular disease have been performed.

HYPOTHESIS

An updated systematic review and evidence-based guidelines for the appropriate selection of antiplatelet drugs may be beneficial to physicians and healthcare organizations attempting to create or update current clinical practice guidelines or clinical pathways aimed at caring for these patients.

METHODS

(1) A systematic review of the recent literature on the relative efficacy and safety of aspirin, ticlopidine, and clopidogrel was undertaken; (2) an evidence-based, expert panel approach using a modified Delphi technique to create explicit guidelines for prescribing antiplatelet therapy was instituted; and (3) the recommendations of an expert panel were summarized.

RESULTS

Consensus guidelines were developed for the utilization of aspirin, ticlopidine, or clopidogrel for the prevention of ischemic events in patients with manifestations of atherosclerotic vascular disease (prior myocardial infarction, prior ischemic stroke, or established peripheral arterial disease) who are at increased risk for recurrent ischemic events. Based on efficacy and safety, clopidogrel was recommended as the drug of choice for patients with established peripheral arterial disease; aspirin or clopidogrel should be considered in patients with prior myocardial infarction (with clopidogrel favored for patients who have had a recurrent event while on aspirin or in whom aspirin is contraindicated); aspirin or clopidogrel should be considered as first-line treatment in patients with prior ischemic (nonhemorrhagic) stroke--however, clopidogrel is the favored drug in patients in whom other antiplatelet drugs are either contraindicated or who have had recurrent events while on therapy.

CONCLUSIONS

Myocardial infarction, ischemic stroke, and peripheral arterial disease are all clinical manifestations of the same underlying disease process (atherosclerosis), with thrombus formation on the disrupted atherosclerotic plaque (atherothrombosis) being a common precipitating factor of ischemic events in patients suffering from these disorders. An evidence-based approach was used to develop a practice guideline, based on available published evidence, for the appropriate utilization of antiplatelet agents (aspirin, ticlopidine, or clopidogrel). These guidelines may be of use to multidisciplinary teams wishing to create or update clinical guidelines or clinical pathways which address the care of patients with atherosclerotic vascular disease. New antiplatelet agents such as clopidogrel may be more effective and associated with lower risk of selected adverse effects (such as gastrointestinal distress, gastrointestinal hemorrhage, and neutropenia) than those previously used to prevent thrombus formation in the setting of atherosclerotic arterial disease. Combination antiplatelet therapy is being evaluated as an option for those patients who experience recurrent events on a single antiplatelet agent.

[Therapy of acute coronary syndrome. Aspirin, heparin, low-molecular-weight heparin, hirudin and GP-IIb/IIIa blockers]

Plaque rupture with consecutive formation of an intraluminal, platelet-rich thrombus is the central mechanism leading to critical reduction of coronary perfusion in the acute coronary syndrome. Current therapeutic strategies aim at the inhibition of activation of platelets and the coagulation cascade and the suppression of platelet aggregation and fibrin formation. The use of acetylsalicylic acid (ASA) is well established in the therapy of the acute coronary syndrome and its efficacy is documented in several large clinical studies. The results of a respective metaanalysis by the Antiplatelet Trialists' Collaboration are shown in Table 1. Further risk reduction has been achieved with the additional application of heparin during the early phase of treatment. Table 2 shows the results of the Montreal Heart Study of combined vs single drug treatment, and Figure 1 a metaanalysis by Oler et al. of combination therapy with heparin plus ASA compared to monotherapy with ASA. In the past, hirudin and analogues were not superior to heparin as adjunctive treatments to lysis in acute myocardial infarction, but bleeding complications were more frequent. In contrast, in the recently published OASIS-2 study, outcome in patients with unstable angina pectoris was significantly better with hirudin than with heparin. Several large studies have demonstrated at least equivalent efficacy of LMWHs compared to standard heparin. For the early phase of the acute coronary syndrome, the FRIC and ESSENCE studies have even demonstrated improved clinical outcome without increase in bleeding complications. However, in TIMI 11 and FRAXIS, long-term application of LMWH resulted in more bleeding complications and, in FRAXIS, in a trend to a worse clinical outcome. The use of GP-IIb/IIIa blockers, especially the chimeric antibody fragment abciximab, is well established in interventional cardiology. Figure 2 shows the mechanism of action of the GP-IIb/IIIa blockers on platelet aggregation. In addition, their use in conjunction with ASA and heparin in the acute coronary syndrome led to further significant reduction of cardiovascular events in several studies. For example, the reduction of events by abciximab in the CAPTURE-study is delineated in Table 3. The results obtained with several of the new competitive GP-IIb/IIIa receptor antagonists are shown in Table 4.

Impaired antiplatelet effects of aspirin associated with hypoxia and ATP release from erythrocytes. Studies in a system with flowing human blood

BACKGROUND

We have explored how hypoxic conditions may affect the antiplatelet effects of aspirin.

MATERIALS AND METHODS

For this purpose, a perfusion system containing a damaged vessel segment was modified in order to induce hypoxia (low Po2) in flowing blood. Blood samples were incubated with 50 mumol L-1 aspirin and divided into two aliquots, one being perfused under standard conditions (normoxic) and the other under hypoxic conditions. The interaction of platelets with the subendothelium was morphometrically evaluated.

RESULTS

In studies with untreated blood under normoxic conditions, platelet interaction with the subendothelium was 0.3 +/- 0.1% of contact, 5.3 +/- 1.6% of adhesion, 24.3 +/- 3.3% of thrombus and 29.9 +/- 2.7% of total covered surface. Aspirin-treated blood perfused under normoxic conditions showed a marked decrease in thrombus with a concomitant increase in both platelet adhesion and covered surface percentages. However, when aspirin-treated blood was perfused under hypoxic conditions, platelet interaction was not significantly different from that observed in untreated blood. Hypoxia induced a 10-fold increase in ATP release from erythrocytes in the perfusates. If apyrase was added to the perfusates, ATP release was prevented and aspirin effects were evident again.

CONCLUSION

Our results suggest that, under hypoxic conditions, the presence of aspirin would not help to inhibit further platelet activation.

Antiplatelet therapy. Aspirin, ticlopidine/clopidogrel, and anti-integrin agents

Aspirin is the most widely employed antithrombotic agent in use today and has a proven role in the prevention and acute management of atherosclerosis-associated arterial thrombotic events. More recently developed antiplatelet agents have been found to have specific prophylactic roles associated with percutaneous coronary intervention and other clinical settings. This article outlines pharmacologic considerations and current clinical knowledge relevant to the use of aspirin, ticlopidine, clopidogrel, and the GPIIbIIIa antagonists in the management of thrombotic disorders.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

A Double-Blind Randomized Comparison of Combined Aspirin and Ticlopidine Therapy Versus Aspirin or Ticlopidine Alone on Experimental Arterial Thrombogenesis in Humans

No randomized study comparing the effect of combined ticlopidine and aspirin therapy versus each drug alone in reducing poststenting thrombotic complications has been performed. To compare these three antiplatelet regimens versus placebo, we conducted a double-blind randomized study using an ex vivo model of thrombosis. Sixteen healthy male volunteers were assigned to receive for 8 days the following four regimens separated by a 1-month period: aspirin 325 mg/d, ticlopidine 500 mg/d, aspirin 325 mg/d + ticlopidine 500 mg/d, and placebo. At the end of each treatment period, native nonanticoagulated blood was drawn directly from an antecubital vein over collagen- or tissue factor (TF)-coated coverslips positioned in a parallel-plate perfusion chamber at an arterial wall shear rate (2,600 s−1 ) for 3 minutes. Thrombus, which formed on collagen in volunteers treated by placebo, were rich in platelets and poor in fibrin. As compared with placebo, aspirin and ticlopidine alone reduced platelet thrombus formation by only 29% and 15%, respectively (P > .2). In contrast, platelet thrombus formation was blocked by more than 90% in volunteers treated by aspirin + ticlopidine (P < .01v placebo or each treatment alone). Furthermore, the effect of the drug combination therapy was significantly larger than the sum of the two active treatments (P < .05). Thrombus, which formed on TF-coated coverslips in volunteers treated by placebo, were rich in fibrin and platelets. Neither of the three antiplatelet treatments significantly inhibited fibrin deposition and platelet thrombus formation on this surface (P > .2). Thus, the present study shows that combined aspirin and ticlopidine therapy dramatically potentiates the antithrombotic effect of each drug alone, but that the antithrombotic effect of the combined treatment depends on the nature of the thrombogenic surface.

© 1998 by The American Society of Hematology.

A Double-Blind Randomized Comparison of Combined Aspirin and Ticlopidine Therapy Versus Aspirin or Ticlopidine Alone on Experimental Arterial Thrombogenesis in Humans

No randomized study comparing the effect of combined ticlopidine and aspirin therapy versus each drug alone in reducing poststenting thrombotic complications has been performed. To compare these three antiplatelet regimens versus placebo, we conducted a double-blind randomized study using an ex vivo model of thrombosis. Sixteen healthy male volunteers were assigned to receive for 8 days the following four regimens separated by a 1-month period: aspirin 325 mg/d, ticlopidine 500 mg/d, aspirin 325 mg/d + ticlopidine 500 mg/d, and placebo. At the end of each treatment period, native nonanticoagulated blood was drawn directly from an antecubital vein over collagen- or tissue factor (TF)-coated coverslips positioned in a parallel-plate perfusion chamber at an arterial wall shear rate (2,600 s−1 ) for 3 minutes. Thrombus, which formed on collagen in volunteers treated by placebo, were rich in platelets and poor in fibrin. As compared with placebo, aspirin and ticlopidine alone reduced platelet thrombus formation by only 29% and 15%, respectively (P &gt; .2). In contrast, platelet thrombus formation was blocked by more than 90% in volunteers treated by aspirin + ticlopidine (P &lt; .01v placebo or each treatment alone). Furthermore, the effect of the drug combination therapy was significantly larger than the sum of the two active treatments (P &lt; .05). Thrombus, which formed on TF-coated coverslips in volunteers treated by placebo, were rich in fibrin and platelets. Neither of the three antiplatelet treatments significantly inhibited fibrin deposition and platelet thrombus formation on this surface (P &gt; .2). Thus, the present study shows that combined aspirin and ticlopidine therapy dramatically potentiates the antithrombotic effect of each drug alone, but that the antithrombotic effect of the combined treatment depends on the nature of the thrombogenic surface.

© 1998 by The American Society of Hematology.