Thienopyridines or aspirin to prevent stroke and other serious vascular events in patients at high risk of vascular disease? A systematic review of the evidence from randomized trials

BACKGROUND AND PURPOSE: Aspirin is the most widely studied and prescribed antiplatelet drug for patients at high risk of vascular disease. We aimed to establish how the thienopyridines (ticlopidine and clopidogrel) compare with aspirin in terms of effectiveness and safety. METHODS: We did a systematic review of all unconfounded randomized trials comparing either ticlopidine or clopidogrel with aspirin for patients at high risk of vascular disease. The primary outcome was vascular events (stroke, myocardial infarction, or vascular death). Adverse outcomes were intracranial and extracranial hemorrhage, upper and lower gastrointestinal disturbances, neutropenia, thrombocytopenia, and skin rash. RESULTS: In 4 trials among 22 656 patients (including 9840 presenting with a transient ischemic attack/ischemic stroke), the thienopyridines reduced the odds of a vascular event by 9% (odds ratio 0.91, 95% CI 0.84 to 0. 98; 2P=0.01), preventing 11 (95% CI 2 to 19) events per 1000 patients treated for approximately 2 years. The thienopyridines produced significantly less gastrointestinal hemorrhage and upper gastrointestinal upset (indigestion/nausea/vomiting) than did aspirin. Both thienopyridines increased the odds of skin rash and of diarrhea (ticlopidine by approximately 2-fold and clopidogrel by approximately one third). Only ticlopidine increased the odds of neutropenia. CONCLUSIONS: The thienopyridines appear modestly more effective than aspirin in preventing serious vascular events in high-risk patients. Clopidogrel appears to be safer than ticlopidine and as safe as aspirin, making it an appropriate, but more expensive, alternative antiplatelet drug for patients unable to tolerate aspirin. However, there is insufficient information to determine which particular types of patients would benefit most, and which least, from clopidogrel instead of aspirin.     

Adding aspirin to clopidogrel after TIA and ischemic stroke: benefits do not match risks

Antiplatelet therapy is effective for reducing the risk of recurrent stroke and other serious vascular events in patients with recent TIA and ischemic stroke. Effective antiplatelet agents include aspirin, ticlopidine, clopidogrel, dipyridamole, and the combination of aspirin and dipyridamole. The combination of aspirin and clopidogrel is more effective than aspirin in patients with acute coronary syndrome but is more hazardous than clopidogrel alone in patients with recent TIA and ischemic stroke. Further trials are needed to determine whether the combination of aspirin and clopidogrel may have a role immediately after TIA and ischemic stroke in patients with symptomatic large artery atherothromboembolism and continued for approximately 3 months before switching to less hazardous antiplatelet regimens.     

Antiplatelet therapy for secondary prevention of noncardioembolic ischemic stroke: a critical review

For patients with ischemic stroke or transient ischemic attack caused by atherothromboembolism, immediate and long-term aspirin reduces the relative risk of recurrent stroke, MI, and death attributable to vascular causes. Oral anticoagulation is not more effective than aspirin. Long-term clopidogrel reduces the relative risk of stroke, MI, or vascular death by about 9% (0.3% to 16.5%) compared with aspirin. Any long-term benefits of clopidogrel combined with aspirin, compared with aspirin or clopidogrel alone, appear to be offset by increased major bleeding. The combination of aspirin and extended-release dipyridamole reduces the relative odds of stroke, MI, or vascular death by about 18% (odds ratio 0.82, 0.74 to 0.91) compared with aspirin alone without causing more bleeding. Cilostazole reduces the risk of stroke, MI, or vascular death by 39% compared to placebo. A large clinical trial comparing clopidogrel with the combination of aspirin and dipyridamole, in >20 000 patients with recent (<120 days) atherothrombotic ischemic stroke, is expected to report in 2008. Emerging antiplatelet therapies presently being evaluated for secondary prevention of atherothromboembolism include other P(2)Y(12) ADP receptor antagonists (prasugrel, cangrelor, AZD 6140), thromboxane receptor antagonists (eg, S18886 - terutroban), and thrombin receptor (PAR-1) antagonists (eg, SCH530348).     

Evidence with antiplatelet therapy and ADP-receptor antagonists

Antiplatelet drugs have been shown to prevent a range of atherothrombotic events, including transient ischaemic attack (TIA) and ischaemic stroke. Clopidogrel and ticlopidine are adenosine diphosphate (ADP)-receptor antagonists that inhibit ADP-induced fibrinogen binding to platelets, a necessary step in the platelet aggregation process. The Antithrombotic Trialists' Collaboration recently published a major meta-analysis that assessed the effect of antiplatelet therapy in patients with various manifestations of atherosclerosis. In total, this analysis included 135,000 patients in comparisons of antiplatelet agents versus control and 77,000 patients in comparisons of different antiplatelet regimens. This meta-analysis found that overall, antiplatelet therapy reduces the combined odds of stroke, myocardial infarction (MI) or vascular death by 22%, and that antiplatelet agents reduce the odds of a non-fatal stroke by 25% over a wide range of patients with or without a history of cerebrovascular disease. In the CAPRIE trial of clopidogrel versus acetylsalicylic acid (ASA), there was a 10% odds reduction for stroke, MI or vascular death in favour of clopidogrel (p = 0.03). In a meta-analysis performed by the Cochrane Stroke Group, ADP-receptor antagonist therapy significantly reduced the odds of a serious vascular event (stroke, MI or vascular death) by 9% (2p = 0.01) and of any stroke by 12%. The safety/tolerability profile of clopidogrel was superior to that of ticlopidine, and at least as good as that of ASA. In CURE, a long-term benefit was observed with the use of clopidogrel on top of standard therapy (including ASA in all patients), with a 20% relative risk reduction for the primary endpoint of cardiovascular death, MI or stroke (p < 0.001) in patients with unstable angina and non-Q-wave MI. A consistent benefit was seen across all patient subgroups, including patients with a previous history of stroke. More recently, CREDO has demonstrated the incremental benefit of prolonged use of clopidogrel on top of ASA in patients undergoing elective PCI, with a 27% reduction in the combined risk of death, MI or stroke after 12 months of therapy (p = 0.02) and a 25% reduction in stroke over the same time period. The MATCH trial is currently being conducted to test the hypothesis that long-term administration of clopidogrel on top of ASA is superior to clopidogrel alone for the reduction of major ischaemic events in patients with recent TIA or ischaemic stroke who are at high risk of atherothrombotic recurrence. Further trials of clopidogrel on top of standard therapy (including ASA) are planned in neurology; these include SPS3, in patients with small subcortical strokes, and ATARI, in patients who have recently recovered from a TIA.     

Results of the management of atherothrombosis with clopidogrel in high-risk patients trial: implications for the neurologist

The secondary prevention of ischemic stroke is aided by the use of antiplatelet therapy, and the predominant current choices are aspirin, aspirin plus extended-release dipyridamole, and clopidogrel. The potential utility of combining platelet antiaggregants with different mechanisms of action proved successful with aspirin plus extended-release dipyridamole, and this approach has been explored with the combination of clopidogrel and aspirin. In the Management of Atherothrombosis With Clopidogrel in High-Risk Patients trial, this combination was compared with clopidogrel alone for secondary prevention in patients with transient ischemic attack and stroke in a high-risk population with a high prevalence of other vascular risk factors. A nonsignificant trend for a reduction of the combined endpoint of ischemic stroke, myocardial infarction, vascular death, and rehospitalization was observed in the combination therapy group (P = .24). The frequency of serious, life-threatening bleeding adverse effects was almost doubled in the combination arm. Neurologists need to be aware of these results and avoid the use of clopidogrel plus aspirin in patients with stroke or transient ischemic attack until evidence that the combination is safe in this population is provided. Neurologists faced with patients who have had a stroke or transient ischemic attack and are receiving this combination of antiplatelet agents after coronary stenting should inform their cardiology colleagues of the reported bleeding risk, and they should encourage the use of the combination for as short a time period as possible after such coronary intervention.     

Current Status of Antiplatelet Agents to Prevent Stroke

Stroke is one of the leading causes of disability; most are due to atherothrombotic mechanisms. About one third of ischemic strokes are preceded by other stroke or transient ischemic attacks. Stroke survivors are at high risk for vascular events (i.e., cerebrovascular and cardiovascular). Prevention of recurrent stroke and other major vascular events can be accomplished by control of risk factors. Nonetheless, the use of antiplatelet agents remains the fundamental component of secondary stroke prevention strategy in patients with noncardioembolic disease. Currently, the uses of aspirin, clopidogrel, or aspirin plus extended-release dipyridamole are valid alternatives for stroke or transient ischemic attack patients. To maximize the beneficial effects of these agents, the treatment should be initiated as early as possible and continue on a lifelong basis.     

Ischemic stroke prevention: an update on antiplatelet therapy

Stroke is the third leading cause of mortality in the United States. As the leading cause of neurological deficits worldwide, stroke is associated with tremendous costs both to society and to the individuals and families stroke impacts. Antiplatelet agents have demonstrated efficacy in preventing recurrent atherothrombotic strokes and are the principal pharmacologic modality employed. With the recent development of the thienopyridines and the resurgence of dipyridamole, recommendations for antiplatelet therapy have undergone several iterations over the past decade. The focus of this review is to provide an update on the individual antiplatelet agents and recapitulate the current guidelines for antiplatelet selection and use in either transient ischemic attack or noncardiogenic ischemic stroke patients. Mechanisms of action, demonstrated efficacy, adverse effect profiles, and current consensus recommendations are reviewed for four conventional antiplatelet strategies, aspirin, ticlopidine, clopidogrel, and the combination of aspirin and extended-release dipyridamole.     

Clopidogrel in addition to aspirin reduces in-hospital major cardiac and cerebrovascular events in unselected patients with acute ST segment elevation myocardial

We sought to assess the effect of clopidogrel on in-hospital events in unselected patients with acute ST elevation myocardial infarction (STEMI). In a retrospective analysis of consecutive patients enrolled in the Acute Coronary Syndromes (ACOS) registry with acute STEMI we compared outcomes of either adjunctive therapy with aspirin alone or aspirin plus clopidogrel within 24 hours after admission.A total of 7,559 patients were included in this analysis, of whom 3,541 were treated with aspirin alone, and 4,018 with dual antiplatelet therapy.The multivariable analysis with adjustment for baseline characteristics and treatments showed that the rate of in-hospital MACCE (death, non-fatal reinfarction, non-fatal stroke) was significantly lower in the aspirin plus clopidogrel group,compared to the aspirin alone group in the entire cohort and all three reperfusion strategy groups (entire group odds ratio 0.60, 95% CI 0.49-0.72 , no reperfusion OR 0.69,95% CI 0.51-0.94,fibrinolysis OR 0.62,95% CI 0.44-0.88, primary PCI OR 0.54, 95% CI 0.39-0.74).There was a significant increase in major bleeding complications with clopidogrel (7.1% vs. 3.4%, p<0.001). In clinical practice early adjunctive therapy with clopidogrel in addition to aspirin in patients with STEMI is associated with a significant reduction of in-hospital MACCE regardless of the initial reperfusion strategy.This advantage was associated with an increase in major bleeding complications.     

Role of antiplatelet drugs in the prevention of cardiovascular events

Antiplatelet drugs have an established place in the prevention of vascular events in a variety of clinical conditions, such as myocardial infarction, stroke and cardiovascular death. Both European and American guidelines recommend the use of antiplatelet drugs in patients with established coronary heart disease and other atherosclerotic disease. In high-risk patients, such as those with post-acute myocardial infarction (AMI), ischaemic stroke or transient ischaemic attack, and in patients with stable or unstable angina, peripheral arterial occlusive disease or atrial fibrillation, antiplatelet treatment may reduce the risk of a serious cardiovascular event by approximately 25%, including reduction of non-fatal myocardial infarction by 1/6, non-fatal stroke by 1/4 and cardiovascular death by 1/6. Some data indicate that antiplatelet drugs may also have a role in primary prevention. In people who are aged over 65 years, or have hypertension, hypercholesterolaemia, diabetes, obesity or familial history of myocardial infarction at young age, aspirin may reduce both cardiovascular deaths and total cardiovascular events. Aspirin has been studied and used most extensively. It may exert its beneficial effect not only by acting on platelets, but also by other mechanisms, such as preventing thromboxane A₂ (TXA₂)-induced vasoconstriction or reducing inflammation. Indeed, experimental data show that low-dose aspirin may suppress vascular inflammation and thereby increase the stability of atherosclerotic plaque. Moreover, in human studies, aspirin seems to be most effective in those with elevated C-reactive protein levels. Vascular events, however, do occur despite aspirin administration. This may be due to platelet activation by pathways not blocked by aspirin, intake of drugs that interfere with aspirin effect or aspirin resistance. In the CAPRIE (Clopidogrel vs. Aspirin in Patients at Risk of Ischaemic Events) study, long-term clopidogrel administered to patients with atherosclerotic vascular disease was more effective than aspirin in reducing the combined risk of ischaemic stroke, myocardial infarction or vascular death. In the setting of coronary stenting, a double regimen including aspirin and ticlopidine or clopidogrel has proved more effective in the prevention of in-stent thrombosis than aspirin alone. Chronic oral administration of the inhibitors of platelet membrane receptor GP IIb/IIIa has been largely disappointing.     

Ischemic stroke prevention: An update on antiplatelet therapy

Abstract

Stroke is the third leading cause of mortality in the United States. As the leading cause of neurological deficits worldwide, stroke is associated with tremendous costs both to society and to the individuals and families stroke impacts. Antiplatelet agents have demonstrated efficacy in preventing recurrent atherothrombotic strokes and are the principal pharmacologic modality employed. With the recent development of the thienopyridines and the resurgence of dipyridamole, recommendations for antiplatelet therapy have undergone several iterations over the past decade. The focus of this review is to provide an update on the individual antiplatelet agents and recapitulate the current guidelines for antiplatelet selection and use in either transient ischemic attack or noncardiogenic ischemic stroke patients. Mechanisms of action, demonstrated efficacy, adverse effect profiles, and current consensus recommendations are reviewed for four conventional antiplatelet strategies, aspirin, ticlopidine, clopidogrel, and the combination of aspirin and extended-release dipyridamole. [Neurol Res 2002; 24: 381-388]     

The safety and efficacy of clopidogrel versus ticlopidine in Japanese stroke patients: combined results of two Phase III,multicenter, randomized clinical trials

Two Phase III studies comparing the safety and efficacy of clopidogrel with ticlopidine as antiplatelet agents for the secondary prevention of vascular events in patients with prior stroke were performed in Japan. Both studies were randomized, double-blind, double-dummy comparative trials with the primary objective of comparing the clinical safety of treatment with either clopidogrel or ticlopidine for up to 12 months. The secondary objective was to assess the incidence of a combined efficacy endpoint of cerebral infarction, myocardial infarction, and vascular death. Patients with prior stroke were recruited during July 1996–February 1998 and September 2001–November 2003 at centers across Japan. The results of the two studies were combined in this analysis. There were 1,869 patients in the safety population (clopidogrel, 941; ticlopidine, 928). Significantly, fewer patients experienced a safety event in the clopidogrel group than in the ticlopidine group (p < 0.001; hazard ratio, 0.610; 95% confidence interval 0.529, 0.703). Almost twice as many patients in the ticlopidine group (25.6%) experienced hepatic dysfunction than in the clopidogrel group (13.4%). There were 1,862 patients evaluable for efficacy (clopidogrel, 939; ticlopidine, 923). There was no significant difference in the incidence of the combined efficacy endpoint between clopidogrel (2.6% of patients) and ticlopidine (2.5%). Clopidogrel was better tolerated than ticlopidine. There was no difference in the efficacy of the two agents with regard to the secondary prevention of vascular events in patients with prior stroke. This was the first combined analysis of direct comparison of clopidogrel with ticlopidine in the clinical setting.     

Recent clinical trial results with antiplatelet therapy: implications in stroke prevention

Dual antiplatelet therapy that inhibits more than one pathway of platelet activation is appealing and biologically rational. The CURE study evaluated the efficacy and safety of clopidogrel on top of acetylsalicylic acid (ASA) versus standard therapy (including ASA) in over 12,000 patients with unstable angina or non-ST-segment elevation myocardial infarction (MI). Clopidogrel in combination with ASA reduced the relative risk of the combined atherothrombotic endpoint of cardiovascular death, MI or stroke by 20% (95% CI 0.72-0.90; p < 0.001) and the absolute risk of this composite endpoint by 2.1%. While the study was not powered or designed to demonstrate a reduction in stroke, there was a 14% reduction in stroke risk (p > 0.05). Dual antiplatelet therapy was associated with an acceptable 1% increase in the incidence of major bleeding events (p = 0.001). PCI-CURE, a prespecified substudy of patients who underwent percutaneous coronary intervention (PCI) during CURE, confirmed the early and sustained benefits of clopidogrel therapy seen in the overall CURE study. CREDO was a randomized, double-blind, placebo-controlled trial in more than 2,100 patients that evaluated the continuation of clopidogrel on top of standard therapy including ASA for 12 months after PCI, and the benefit of a preprocedural clopidogrel loading dose. The long-term results at 1 year showed that there was a 27% reduction in the risk of stroke, MI or death with long-term clopidogrel therapy (p = 0.02). There was a consistent benefit of extended clopidogrel therapy for each component of the composite endpoint, with a 25.1% relative risk reduction for all-cause stroke. In patients who received clopidogrel > or =6 h before PCI, there was a 39% reduction in the risk of death, MI or urgent target-vessel revascularization at 28 days (p = 0.051). These data suggest important implications in the future for the use of an early loading dose of clopidogrel in patients undergoing carotid stenting and, if proven in current or future trials, the use of a loading dose followed by long-term continuation of clopidogrel in other high-risk atherothrombotic patients such as those with transient ischaemic attack or ischaemic stroke.     

Antiplatelet drugs: how to select them and possibilities of combined treatment

Antiplatelets are the pivotal drugs in preventing recurrent stroke or other major vascular events in patients who have undergone TIA or stroke. Aspirin is the most widely used, although its effect is very modest (relative risk reduction 20%), and most physicians use between 100 and 325 mg daily as a maintenance dose. For patients who develop stroke on aspirin treatment, the options are either to increase the dose of aspirin or to administer another anti-aggregate. No study has yet been performed to support these approaches. In patients who cannot tolerate aspirin, the options are clopidogrel 75 mg once daily or dipyridamole 400 mg combined with 50 mg aspirin. An approach which is very appealing, but not yet proven is to combine different antiplatelet drugs with different modes of action, such as aspirin and clopidogrel, in order to achieve a better and more effective antithrombotic effect. Further controlled trials are needed to justify this approach.     

Ongoing and planned trials of antiplatelet therapy in the acute and long-term management of patients with ischaemic brain syndromes: setting a new standard of care

Among high vascular risk patients, acetylsalicylic acid (ASA) reduces the relative risk of serious vascular events by about one fifth. However, because ASA fails to prevent four fifths of serious vascular events, more effective, yet equally safe and affordable, antiplatelet regimens are desired. Compared with ASA, clopidogrel alone reduces the odds of serious vascular events by about 10%, and the combination of dipyridamole and ASA reduces the odds of serious vascular events by about 6%. Combining ASA with an orally administered platelet glycoprotein (GP) IIb/IIIa blocker is not effective, and indeed more hazardous than ASA alone. Among patients with non-ST-segment acute coronary syndromes (ACS), the addition of an intravenously administered GP IIb/IIIa receptor antagonist to ASA reduces the risk of vascular events by about 10% compared with ASA, and the addition of clopidogrel to ASA reduces the risk of vascular events by 20% compared with ASA alone. Among patients undergoing percutaneous coronary intervention (PCI), both the addition of an intravenously administered GP IIb/IIIa receptor antagonist to ASA, and the addition of clopidogrel to ASA reduce the risk of vascular events by 30% compared with ASA alone. The greater efficacy of the combinations of ASA with clopidogrel, and ASA with an intravenously administered GP IIb/IIIa receptor antagonist, in patients with ACS and those undergoing PCI has fostered several ongoing and planned trials of these regimens in the acute and long-term management of patients with ischaemic brain syndromes. The combination of ASA and clopidogrel is being compared with ASA alone within 12 h of onset of symptoms of TIA in two trials (FASTER, ATARI), and the use of an intravenously administered GP IIb/IIIa receptor antagonist is being compared with placebo within 6 h of onset of acute ischaemic stroke in two trials (AbESST, AbESST-2). Six trials are assessing the combination of clopidogrel and ASA in the long-term management of patients with ischaemic brain syndromes due to atherothrombosis (MATCH, CHARISMA, ARCH, CARESS, SPS3) or atrial fibrillation (ACTIVE). The MATCH trial of clopidogrel and ASA versus clopidogrel alone in patients with recent TIA or ischaemic stroke is the first which is likely to report its results - in mid 2004. The combination of dipyridamole and ASA is being compared with ASA in the ESPRIT trial and with the combination of clopidogrel and ASA in the planned PRoFESS trial. These ongoing and planned clinical trials of antiplatelet therapy promise to further define the role of combination antiplatelet therapy in the acute and long-term management of patients with ischaemic brain syndromes.     

Collagen-Induced Platelet Aggregates,Diabetes, and Aspirin Therapy Predict Clinical Outcomes in Acute Ischemic Stroke

Background: Aggregation of platelets is a trigger for additional development of larger thrombi. This study aimed to identify factors that may affect platelet aggregability and their role in clinical outcomes in acute ischemic stroke. Methods: Consecutive acute ischemic stroke patients (n = 352) who were transferred within 24 hours after its onset were enrolled. Peripheral venous blood was sampled to measure platelet aggregability and other parameters. Results: Mean values of spontaneous small-sized platelet aggregates and collagen- or adenosine diphosphate (ADP)-induced large-sized aggregates were elevated in acute ischemic stroke. In atherothrombotic stroke (n = 178), collagen and ADP-induced large-sized aggregates were positively correlated with HbA1c, respectively. High incidence of the modified Rankin Scales (mRS) 5-6 at discharge was associated with diabetes complication (odds ratio [OR] 8.77, 95% confidence interval [CI] 1.32-57.56). The proportion of patients who were functionally independent (the mRS 0-2) at discharge was lower in the middle tertile of collagen and ADP-induced large-sized aggregates than their low tertile (OR 2.46, 95% CI 1.09-5.58; OR 2.43, 95% CI 1.05-5.59, respectively). Prestroke administration of aspirin recovered the proportion of independence at discharge (OR 0.25, 95% CI 0.06-0.99), and ameliorated incidence of the mRS 5-6. On logistic regression analysis, diabetes, HbA1c, collagen-induced large-sized aggregates, and prestroke administration of aspirin remained independent predictors of clinical outcomes in atherothrombotic stroke. In cardioembolic and lacunar stroke, no relations with clinical outcomes were found. Conclusions: High plasma level of HbA1c is involved in enhanced platelet aggregability in acute atherothrombotic stroke patients, and prestroke administration of aspirin may be beneficial to clinical outcomes.     

Therapeutic benefit. Aspirin revisited in light of the introduction of clopidogrel.

BACKGROUND: Antiplatelet agents are widely recognized for their efficacy in reducing the occurrence of vascular events in patients with atherothrombotic disease. Aspirin is currently considered to be the "reference standard" antiplatelet agent and is recommended by the American Heart Association for use in patients with a wide range of manifestations of cardiovascular disease on the basis of its high benefit-to-risk and benefit-to-cost ratios. Recently, clopidogrel (Plavix, Bristol-Myers Squibb Co), another antiplatelet agent, was approved by the Food and Drug Administration for many of the same indications as aspirin. SUMMARY OF REVIEW: Because physicians will be faced with deciding whether to switch from the well-established practice of recommending aspirin for use in patients with atherothrombotic disease, both aspirin and clopidogrel are compared with respect to the primary factors that influence such decisions (ie, their relative efficacy, safety, cost, and convenience of use). CONCLUSIONS: Based on the available evidence, aspirin is preferred for the majority of stroke or myocardial infarction patients at risk of recurrent atherothrombotic events. Clopidogrel may, however, provide valuable therapeutic benefit over aspirin in patients with peripheral arterial disease and in stroke or myocardial infarction patients for whom aspirin treatment is contraindicated or for whom aspirin fails to achieve the desired therapeutic effect.     

Antiplatelet drugs for prevention of cerebral ischemic accidents]

Antiplatelet (AP) drugs play a major role in stroke prevention. Aspirin (50-1300 mg), ticlopidine (500 mg), clopidogrel (75 mg) and dipyridamole (400 mg) are effective in secondary prevention of atherothrombotic brain infarcts. Aspirin has been the most extensively studied drug and remains the most cost-effective one. The optimal dose is still debated; doses between 100 and 300 mg are the most widely used. The preventive efficacy of aspirin is already present at the acute phase of cerebral infarct. In primary prevention, aspirin nearly halves the risk of myocardial infarction but does not reduce that of stroke. Cardiac diseases with a high embolic risk require the use of oral anticoagulation. In non valvular atrial fibrillation, the choice of antithrombotic drugs depends on risk stratification: oral anticoagulants are indicated in high risk subjects whereas aspirin is recommended in low risk subjects and when oral anticoagulants are contraindicated. Studies with new associations of AP and with new drugs are required to increase the yield of the antiplatelet approach in high risk subjects; this should be done in parallel with efforts to detect and to treat the vascular risk factors associated with the development of a mass approach for stroke primary prevention.     

Aspirin and stroke prevention

According to meta-analyses aspirin provides a relative reduction in the rate of major vascular events of 19% in patients with arterial disease in general, whereas for patients with ischaemic cerebrovascular disease this reduction is only 13%. The discrepancy may well result from pathophysiological differences and not from a play of chance. There is no proven difference in efficacy according to dose. The evidence for this equivalence is most compelling in the range between 75 and 1300 mg daily, but still fairly convincing for doses between 30 and 50 mg. In contrast, side effects are clearly more frequent as the dose is higher. Other antiplatelet agents (sulfinpyrazone, ticlopidine, clopidogrel, dipyridamole, orally administered IIb/IIIa inhibitors) have no clear advantages over aspirin and in some cases definite disadvantages; the combination of aspirin and dipyridamole may be more efficacious than aspirin alone, but the evidence hinges on a single trial. If recurrent TIAs occur under treatment with aspirin, the rational response is not to change to a different antiplatelet agent, but to review the diagnosis and consider causes other than artery-to-artery embolism. Platelet aggregation can probably still occur despite complete acetylation of platelets, via pathways other than COX-1 inhibition, but in vitro aggregation tests are an unreliable measure.     

The United Kingdom transient ischaemic attack (UK-TIA) aspirin trial: final results.

From 1979-85, 2435 patients with a transient ischaemic attack or minor ischaemic stroke were randomly allocated to receive long term "blind" treatment with aspirin 600 mg twice daily (n = 815), aspirin 300 mg once daily (n = 806) or placebo (n = 814). No patient was lost to follow up. The "intention to treat" comparison included all the serious vascular events and deaths which occurred before the end of the follow up period on 30 September 1986. There was no difference in efficacy between the 300 mg and 1200 mg daily doses of aspirin, but the lower dose was undoubtedly less gastrotoxic. Also, there was no definite difference in the response of males and females to aspirin. The odds of suffering a major stroke, myocardial infarction or vascular death were 15% less in the combined aspirin groups compared with the placebo group (95% confidence interval 29% reduction to 3% increase in odds) which is compatible with the continuing overview of all the similar trials of antiplatelet drugs where the relative reduction in odds was 25%. There was no statistically significant reduction in the likelihood of either disabling major stroke and vascular death or vascular death occurring.     

Antiplatelet agents and randomized trials

Patients who have transient ischemic attack (TIA) or ischemic stroke are at a high risk of having a first or recurrent stroke. The annual risk is between 5% and 15%; the risk is highest in the first 48 hours following a TIA and highest in the first 7 days following an ischemic stroke. Secondary prevention includes antithrombotic therapy, treatment of risk factors, and interventional treatment of carotid stenosis. Antithrombotic options can include antiplatelet drugs such as aspirin, aspirin plus extended-release dipyridamole (ER-DP), clopidogrel, or clopidogrel plus aspirin. Oral anticoagulation is used in patients with a cardiac source of embolism such as atrial fibrillation. Aspirin monotherapy offers a modest risk reduction for recurrent stroke and for the combined endpoint of nonfatal stroke, myocardial infarction (MI), and vascular death. The combination of ER-DP and aspirin was shown to be superior to aspirin monotherapy in several trials. Clopidogrel is superior to aspirin in high-risk patients suffering from stroke, MI, or peripheral arterial disease. The combination of clopidogrel plus aspirin is not superior to aspirin or clopidogrel monotherapy and carries a significantly higher bleeding risk. The combination might offer benefit in short-term secondary prevention after TIA or stroke. Another ongoing trial is currently investigating the possible benefit and side effects of aspirin plus ER-DP versus clopidogrel in secondary stroke prevention.