阿司匹林联合双嘧达莫用于缺血性脑卒中二级预防的Meta分析

目的以阿司匹林为对照组,系统评价阿司匹林双嘧达莫联合用药,对缺血性脑卒中二级预防的有效性和安全性。方法通过卒中、非致死性卒中、各种原因引起的死亡及非致死性卒中与各种原因引起的死亡联合事件发生的相对危险度,分析联合用药的有效性,通过出血性并发症及脑出血发生的相对危险度,分析联合用药的安全性。结果 a.与阿司匹林相比较,联合用药能更有效的预防卒中的发生(RR=0.86 95%CI[0.74,1.00]),使非致死性卒中的发生率降低22%(RR=0.78 95%CI[0.67,0.90]),也能明显降低非致死性卒中与各种原因引起的死亡联合事件的发生率(RR=0.87 95%CI[0.79,0.96])。但是,联合用药对各种原因引起的死亡无效(RR=0.98,95%CI[0.85,1.13])。b.与阿司匹林相比较,联合用药不会增加出血性并发症的发生率(RR=0.95,95%CI[0.80,1.12]),但可以使脑出血的发生率增加14%(RR=1.14,95%CI[0.54,2.42]),尽管这一结果无明显统计学意义。结论与阿司匹林相比较,联合用药对卒中、非致死性卒中及非致死性卒中与各种原因引起的死亡联合事件的预防更有效,联合用药不会增加出血性并发症的发生率,但能轻微增加脑出血的发生率。     

Primary and secondary stroke prevention with antiplatelet drugs

Aspirin is not effective in the primary prevention of stroke. Patients with TIA or ischemic stroke carry a risk of recurrent stroke between 5 and 20% per year. In patients with TIA or ischemic stroke of noncardiac origin antiplatelet drugs are able to decrease the risk of stroke by 11-15% and the risk of stroke, MI and vascular death by 15-22%. Aspirin is the most widely used drug. It is affordable and effective. Low doses of 50-325 mg aspirin are as effective as high doses and cause less gastrointestinal side effects. Severe bleeding complications are dose-dependent. The combination of aspirin with slow release dipyridamole is superior to aspirin alone for stroke prevention. Clopidgrel is superior to aspirin in patients at high risk of recurrence. The combination of aspirin plus clopidogrel is not more effective than clopidogrel alone but carries a higher bleeding risk. None of the antiplatelet agents is able to reduce mortality.     

Adverse effects and drug interactions of antithrombotic agents used in prevention of ischaemic stroke

Stroke is the third most common cause of death in the US. Primary prevention of stroke can be achieved by control of risk factors including hypertension, diabetes mellitus, elevated cholesterol levels and smoking. Approximately one-third of all ischaemic strokes occur in patients with a history of stroke or transient ischaemic attack (TIA). The mainstay of secondary prevention of ischaemic stroke is the addition of medical therapy with antithrombotic agents to control the risk factors for stroke. Antithrombotic therapy is associated with significant medical complications, particularly bleeding.Low-dose aspirin (acetylsalicylic acid) has been shown to be as effective as high-dose aspirin in the prevention of stroke, with fewer adverse bleeding events. Aspirin has been shown to be as effective as warfarin in the prevention of noncardioembolic ischaemic stroke, with significantly fewer bleeding complications. Ticlopidine may be more effective in preventing stroke than aspirin, but is associated with unacceptable haematological complications. Clopidogrel may have some benefit over aspirin in preventing myocardial infarction, but has not been shown to be superior to aspirin in the prevention of stroke. The combination of clopidogrel and aspirin may be more effective than aspirin alone in acute coronary syndromes, but the incidence of adverse bleeding is significantly higher. Furthermore, the combination of aspirin with clopidogrel has not been shown to be more effective for prevention of recurrent stroke than clopidogrel alone, while the rate of bleeding complications was significantly higher with combination therapy. The combination of aspirin and extended-release dipyridamole has been demonstrated to be more effective than aspirin alone, with the same rate of adverse bleeding complications as low-dose aspirin. When selecting the appropriate antithrombotic agent for secondary prevention of stroke, the adverse event profile of the drug must be taken into account when assessing the overall efficacy of the treatment plan.     

Clopidogrel hydrogen sulphate for atrial fibrillation

INTRODUCTION: Atrial fibrillation is a common cardiac rhythm abnormality with a considerable cardiovascular disease burden worldwide. It is an independent major risk factor for stroke. Stroke prevention with anticoagulation or antiplatelet agents has been an important area of clinical research. Warfarin is the most widely used antithrombotic therapy for stroke prophylaxis for last several years, and now dabigatran (150 mg b.i.d.) is more effective than warfarin in stroke prevention in individuals at increased of stroke. In addition, several studies have evaluated the efficacy of clopidogrel for stroke prophylaxis either alone or in combination with aspirin. AREAS COVERED: This review summarizes the key findings of the trials looking at the efficacy of clopidogrel in stroke prevention. A literature search was performed using PubMed and Google Scholar. The trials that evaluated the efficacy of clopidogrel in preventing atherothrombotic events or stroke were also included. EXPERT OPINION: Clopidogrel prevents more vascular events, including stroke, in patients with a recent myocardial infarction, stroke or peripheral vascular disease than aspirin. Combination of clopidogrel and aspirin provides a greater reduction of stroke than aspirin or clopidogrel monotherapy, but at an increased risk of bleeding. Dual antiplatelet therapy (clopidogrel and aspirin) is inferior to warfarin in primary stroke prevention for patient with atrial fibrillation and thus should be considered for stroke prophylaxis only in patients ineligible for warfarin. However, with the advent of newer agents, like direct thrombin inhibitors and Factor Xa inhibitors, the role of antiplatelet therapy for stroke prevention in atrial fibrillation remains unclear.     

Clopidogrel hydrogen sulphate for atrial fibrillation

Introduction: Atrial fibrillation is a common cardiac rhythm abnormality with a considerable cardiovascular disease burden worldwide. It is an independent major risk factor for stroke. Stroke prevention with anticoagulation or antiplatelet agents has been an important area of clinical research. Warfarin is the most widely used antithrombotic therapy for stroke prophylaxis for last several years, and now dabigatran (150 mg b.i.d.) is more effective than warfarin in stroke prevention in individuals at increased of stroke. In addition, several studies have evaluated the efficacy of clopidogrel for stroke prophylaxis either alone or in combination with aspirin.

Areas covered: This review summarizes the key findings of the trials looking at the efficacy of clopidogrel in stroke prevention. A literature search was performed using PubMed and Google Scholar. The trials that evaluated the efficacy of clopidogrel in preventing atherothrombotic events or stroke were also included.

Expert opinion: Clopidogrel prevents more vascular events, including stroke, in patients with a recent myocardial infarction, stroke or peripheral vascular disease than aspirin. Combination of clopidogrel and aspirin provides a greater reduction of stroke than aspirin or clopidogrel monotherapy, but at an increased risk of bleeding. Dual antiplatelet therapy (clopidogrel and aspirin) is inferior to warfarin in primary stroke prevention for patient with atrial fibrillation and thus should be considered for stroke prophylaxis only in patients ineligible for warfarin. However, with the advent of newer agents, like direct thrombin inhibitors and Factor Xa inhibitors, the role of antiplatelet therapy for stroke prevention in atrial fibrillation remains unclear.     

Antiplatelet therapy for the prevention of recurrent stroke and other serious vascular events: a review of the clinical trial data and guidelines

ABSTRACT

Background: One strategy of reducing the burden of stroke is the prevention of recurrent stroke, following an initial ischaemic stroke or transient ischaemic attack (TIA) of arterial origin, by means of antiplatelet therapy.

Scope: This review article surveys and discusses the current clinical trial data and guidelines for the use of antiplatelet therapy in the prevention of recurrent stroke/TIA of arterial origin (not stroke due to atrial fibrillation). Based on the latest available evidence, a new antiplatelet treatment algorithm for the long-term treatment of patients following atherothromboembolic ischaemic stroke or TIA is proposed.

Findings: Meta-analyses of randomised clinical trials in patients with TIA and ischaemic stroke of arterial origin indicate that, compared with control, the relative risk reduction (RRR) for recurrent stroke and other serious vascular events is 13% (95% confidence interval [CI] 6% to 19%) with aspirin, 13% (4% to 21%; p = 0.046) with dipyridamole and 34% (24% to 43%) with the combination of aspirin and dipyridamole. Compared with aspirin, the relative risk of recurrent stroke and other serious vascular events is reduced by 7.3% (95% CI –5.7% to 18.7%) with clopidogrel and 18% (9% to 26%; p = 0.0003) with the combination of aspirin and dipyridamole. The combination of aspirin and clopidogrel is not significantly more effective in preventing serious vascular events than clopidogrel alone (RRR 6.4%; –4.6% to 16.3%) in the long-term treatment of patients with previous ischaemic stroke and TIA, mainly because of a cumulative excess of bleeding complications. The relative risks and benefits of long-term treatment with clopidogrel and the combination of aspirin and dipyridamole are being compared in an ongoing large clinical trial (PRoFESS). Current Australian therapeutic guidelines for antiplatelet therapy among patients with TIA and ischaemic stroke of arterial origin have incorporated important new findings from recently published clinical trials and recommend aspirin or the combination of dipyridamole plus aspirin as the preferred long-term antiplatelet therapy.

Conclusion: Whilst awaiting the results of the PRoFESS trial, the combination of dipyridamole plus aspirin is the preferred antiplatelet regimen to reduce the risk of recurrent vascular events among patients with TIA and ischaemic stroke of arterial origin.     

Aspirin for primary prevention of cardiovascular events in the elderly: current status and future directions

The role of aspirin in the secondary prevention of occlusive cardiovascular events has now been well established. Given this, aspirin in primary prevention has been the focus of several large trials and subsequent meta-analyses over the past 3 decades, and yet the issue remains controversial. Recent studies in populations with high baseline risk - such as diabetics and those with asymptomatic peripheral arterial disease - have not found the expected benefits of aspirin on cardiovascular endpoints, which contrasts with earlier studies that reported a reduced relative risk for outcomes such as myocardial infarction and ischaemic stroke, but not for mortality. Furthermore, in healthy populations, the absolute risk reduction conferred by aspirin is small and needs to be balanced against the risk of a major haemorrhage. Older adults have a higher risk for cardiovascular events and therefore might represent the group in which aspirin for primary prevention could deliver the greatest absolute benefit, yet at the same time, the elderly bear an increased vulnerability to major haemorrhage, including haemorrhagic stroke. It is also not known whether older adults experience the same risk reduction from aspirin as middle-aged individuals. The current evidence base does not sufficiently clarify whether aspirin for primary prevention confers a meaningful net benefit in the elderly.     

Clopidogrel: a review of its use in the prevention of atherothrombosis

Clopidogrel is an ADP receptor antagonist that is indicated for the reduction of atherosclerotic events including myocardial infarction, ischaemic stroke and vascular death in patients with atherosclerosis manifested by recent stroke, myocardial infarction or established peripheral vascular disease. In the 19 185 patients enrolled in the multicentre, randomised double-blind CAPRIE study, the annual risk of the combined end-point of ischaemic stroke, myocardial infarction and death from vascular disease (vascular death) was significantly lower during treatment with clopidogrel 75 mg/day than aspirin 325 mg/day [5.3 vs 5.8%/year, respectively; relative risk reduction (RRR) 8.7%, p = 0.043] after a mean follow-up of 1.9 years. Clopidogrel provided even greater reductions in the risk of recurrent ischaemic events than aspirin in patients with a history of coronary artery bypass surgery, diabetes mellitus and in those receiving concomitant lipid-lowering therapy. Moreover there was a significant reduction in the incidence of hospitalisation in patients treated with clopidogrel. In a patient population (Saskatchewan, Canada) with a greater risk of ischaemic events than the CAPRIE study population, the number of patients needed to be treated with clopidogrel to prevent 1 ischaemic event was estimated to be 70 (vs 200 in the CAPRIE study). In randomised trials and registry surveys, clopidogrel 75 mg/day plus aspirin had similar efficacy (as measured by adverse cardiac outcomes) to ticlopidine 250mg twice daily plus aspirin during the 30 days after placement of intracoronary stents. Tolerability of clopidogrel was significantly better than ticlopidine in the randomised, double-blind CLASSICS study. Among patients treated with clopidogrel or aspirin in the CAPRIE study, the overall gastrointestinal tolerability of clopidogrel was generally better than that of aspirin; the frequency of gastrointestinal haemorrhage was significantly lower among patients treated with clopidogrel than aspirin. Diarrhoea, rash and pruritis were significantly more common with clopidogrel than aspirin. CONCLUSION: Clopidogrel was significantly more effective than aspirin in the prevention of vascular events (ischaemic stroke, myocardial infarction or vascular death) [corrected] in patients with atherothrombotic disease manifested by recent myocardial infarction, recent ischaemic stroke or symptomatic peripheral arterial occlusive disease [corrected] in the CAPRIE study. The overall tolerability profile of the drug was similar to that of aspirin, although gastrointestinal haemorrhage occurred significantly less often in clopidogrel recipients. The drug is widely used in combination with aspirin for the prevention of atherothrombosis after placement of intravascular stents, and available data suggest that this combination is as effective as ticlopidine plus aspirin for this indication.     

Safety of clopidogrel and aspirin for stroke prevention: implications of the CHARISMA trial.

Antiplatelet therapy is universally recommended for the prevention of recurrent events in patients with noncardioembolic ischaemic stroke or transient ischaemic attack (TIA), acute and chronic coronary artery disease, or peripheral arterial disease. However, choosing which antiplatelet agents to use in these situations remains controversial. The use of aspirin, aspirin plus extended-release dipyridamole, or clopidogrel is recommended as initial therapy in patients with noncardioembolic ischaemic stroke or TIA to reduce the risk of recurrent stroke and other cardiovascular events. Based on the results of the MATCH trial, combination therapy with aspirin plus clopidogrel is not recommended for patients with ischaemic stroke or TIA due to the increased risk of haemorrhage.The results of the CHARISMA trial support this recommendation; despite previous data demonstrating a favourable benefit-risk profile of aspirin plus clopidogrel in patients with acute coronary syndrome, this combination should not be used in patients at high risk for atherothrombosis and those with previous stroke or TIA. In these patients, the CHARISMA trial demonstrated a lack of significant clinical efficacy and an increased risk of bleeding with clopidogrel plus aspirin compared with aspirin alone.Further research is needed to assess the benefit-risk ratio of clopidogrel plus aspirin in specific subpopulations of patients at high risk for atherothrombotic events, and to determine the role of clopidogrel plus aspirin in preventing cardioembolic stroke or early recurrent stroke after symptomatic large-vessel atherostenosis. Recent and ongoing studies are seeking to better define the roles of different antiplatelet regimens in preventing recurrent stroke.     

Dual antiplatelet therapy for prevention of recurrent ischemic events.

The advantages of dual antiplatelet therapy over monotherapy in preventing recurrent ischemic events are examined. Atherosclerosis is an insidious systemic process involving multiple vascular beds, including the cerebral, coronary, and peripheral arteries. Atherosclerotic plaque rupture is one of the inciting events in the progression of platelet activation, aggregation, and thrombus formation. Patients with any clinical manifestation of atherosclerosis are vulnerable to others in different vascular beds since the disease develops throughout the vasculature, and different vascular events have common predisposing risk factors. Ischemic coronary heart disease and cerebrovascular disease are two of the three most frequent causes of death in the United States. The efficacy of aspirin in the secondary prevention of myocardial infarction (MI) and stroke has been demonstrated in numerous trials. While dipyridamole has not been linked with a greater odds reduction than aspirin in the development of MI, stroke, and vascular death, ticlopidine and clopidogrel have been associated with a greater reduction in the development of acute MI, stroke, and vascular death than aspirin. Clinical trials evaluating the efficacy and safety of combination antiplatelet therapy in the prevention of recurrent ischemic events are ongoing. The rationale for using a combination of two mechanistically different antiplatelet agents is supported by ex vivo and clinical studies. Inhibition of platelet aggregation and thrombus formation is enhanced with dual antiplatelet therapy. Combination antiplatelet regimens with different mechanisms of action to inhibit multiple sites in the thrombotic pathway may further improve long-term clinical outcomes. Dual antiplatelet therapy may have advantages over monotherapy in the prevention of recurrent ischemic events.     

Clinical pharmacokinetics of antiplatelet agents used in the secondary prevention of stroke

Stroke is one of the leading causes of death and debilitation. Several million stroke survivors are alive throughout the world today. Prevention of recurrent stroke is of major importance to stroke survivors. Several pharmacological agents are currently available for use in secondary stroke prevention.Clopidogrel, the combination of immediate-release aspirin and extended-release dipyridamole and aspirin alone are the most widely recommended agents for use in the secondary prevention of strokes. Clopidogrel has shown superiority over aspirin in the combined endpoints of stroke, death and myocardial infarction. The immediate-release aspirin/extended-release dipyridamole combination has shown superiority to aspirin alone in the secondary prevention of stroke.Dipyridamole has been studied as an antiplatelet agent for several decades. Early trials to prove its efficacy compared with aspirin were not favourable, and patients often experienced many adverse effects. Researchers began developing an extended-release formulation in an effort to maintain therapeutic blood concentrations with less frequent daily administration and better adverse effect profile. Pharmacokinetic analysis of this new product showed it to have a more consistent and reproducible absorption compared with immediate-release dipyridamole. The rate of absorption of extended-release dipyridamole is considerably slower than that of immediate-release dipyridamole, while similar plasma concentrations are maintained to optimise antiplatelet efficacy. This allows extended-release dipyridamole to be administered twice daily rather than four times daily.A large-scale randomised trial was conducted with extended-release dipyridamole 200mg in combination with immediate-release aspirin 25mg given twice daily. The combination product showed a greater efficacy at preventing a recurring stroke then either agent administered alone. Indirect comparisons with clopidogrel show that the combination of immediate-release aspirin/extended-release dipyridamole may be more effective than clopidogrel at preventing a recurring stroke.     

Warfarin and aspirin give more benefit than aspirin alone but also more bleeding after myocardial infarction

The anticoagulant, warfarin, and the antiplatelet agent, aspirin, have been shown to have similar benefits after myocardial infarction. As these agents have different mechanisms of action, the beneficial effects of warfarin and aspirin may be additive after myocardial infarction. In the Warfarin, Aspirin, Reinfarction Study (WARIS II), the main outcome was a composite of death, non-fatal reinfarction or thromboembolic stroke, whichever came first over 4 years. Compared to aspirin alone (160 mg/day), the risk reduction was 19% (p = 0.03) with warfarin alone (INR of 2.8 IU) and 29% (p = 0.001) with the combination of aspirin and warfarin (aspirin, 75 mg/day; warfarin, INR of 2.2 IU). This difference in the first event with warfarin alone or the combination, represented a reduction in reinfarction and thromboembolic stroke rather than death. For reinfarction, compared to aspirin alone (117 of 1206), there was a reduction with warfarin alone (90 of 1216) and a further reduction with the combination (69 of 1208). For thromboembolic stroke, compared to aspirin (32 of 1206), there were similar reductions with warfarin and the combination. There were more major and minor bleeding in the warfarin groups than the aspirin group, with major bleeding occurring in 8, 33 and 28 patients taking aspirin, warfarin and aspirin and warfarin, respectively. In conclusion, as compared with aspirin alone, therapy with moderate-intensity warfarin combined with aspirin and high-intensity warfarin alone, resulted in a reduced risk of reinfarction and ischemic stroke but a higher risk of bleeding.     

Antiplatelet therapy in cerebrovascular disorders

Antiplatelet treatment is a mainstay in acute and long-term secondary stroke prevention. Aspirin is still most widely used worldwide, however, there is increasing evidence from small randomised trials that dual antiplatelet therapy combining aspirin with dipyridamole or clopidogrel might be more effective in the acute and early chronic post-ischemic phase (i.e. first 90 days). Both clopidogrel and the combination of aspirin and extended-release dipyridamole are recommended by current guidelines in long-term secondary stroke prevention in patients who are at high risk for a recurrent ischemic stroke, since they are more effective compared with aspirin monotherapy.Antiplatelet agents are the therapy of choice in patients with ischemic stroke due to intracranial stenosis and patent foramen ovale. In contrast, oral anticoagulation is clearly superior to single or double antiplatelet therapy in patients with cardioembolic stroke, mainly caused by atrial fibrillation.Concerning newer antiplatelet agents, only cilostazol appears to be a promising therapeutic option in patients with ischemic stroke in the near future, but so far, only studies in Asian stroke patients have been performed.     

Combination antiplatelet agents for secondary prevention of ischemic stroke

Stroke is a leading cause of death and the primary cause of serious, long-term disability in the United States. Joint guidelines from the American Heart Association (AHA) and American Stroke Association (ASA), as well as recent guidelines from the Eighth American College of Chest Physicians (ACCP) Conference on Antithrombotic and Antiplatelet Therapy, recommend aspirin, clopidogrel, or extended-release dipyridamole plus aspirin as acceptable first-line options for secondary prevention of ischemic events in patients with a history of ischemic stroke or transient ischemic attack (TIA). The ACCP strongly recommends the combination of extended-release dipyridamole plus aspirin over aspirin monotherapy (highest level of evidence) and suggests clopidogrel monotherapy over aspirin monotherapy (lower level of evidence). The AHA-ASA guidelines suggest that either extended-release dipyridamole plus aspirin or clopidogrel monotherapy should be used over aspirin monotherapy. Both guidelines recommend avoiding the combination of clopidogrel and aspirin for most patients with previous stroke or TIA. Results from recent trials evaluating combination antiplatelet therapy have been published that enhance the AHA-ASA recommendations and provide the foundation for the updated ACCP guideline. To identify pertinent combination antiplatelet trials, a MEDLINE search of the literature from 1967-2007 was performed. Two trials were identified--the European-Australasian Stroke Prevention in Reversible Ischemia Trial (ESPRIT) and Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance (CHARISMA). The ESPRIT compared aspirin monotherapy with the combination of aspirin plus extended-release dipyridamole for prevention of secondary ischemic events in patients with a history of TIA or minor stroke. The CHARISMA trial compared aspirin plus clopidogrel with aspirin alone in a population at high risk for atherothrombotic events using the composite outcome of myocardial infarction, stroke, and death from cardiovascular causes. Data from ESPRIT add to evidence that the combination of aspirin plus extended-release dipyridamole is superior to aspirin alone. The findings of the CHARISMA trial reinforce recommendations from both AHA-ASA and ACCP that the combination of aspirin and clopidogrel be reserved for special populations requiring this antiplatelet combination (e.g., those who have had coronary artery stenting).     

Oral antiplatelet therapy in secondary prevention of cardiovascular events: an assessment from the payer's perspective

BACKGROUND: A wide variety of oral antiplatelet trials have been carried out, and a large number of cost-effectiveness estimates based on them have been published. OBJECTIVE: To assess the cost effectiveness of oral antiplatelet treatments in the prevention of cardiovascular events. METHODS: A comprehensive literature search was carried out in PubMed and the Cochrane Library and the data reviewed. Cost-effectiveness or cost-utility studies of oral antiplatelets published since 2000 were selected. Cost-effectiveness analyses from the perspective of the UK NHS were then carried out using a Markov model with a 6-month cycle length and a lifetime horizon. Inputs from the CAPRIE, CHARISMA, (PCI)-CURE, CREDO, COMMIT, CLARITY, ESPS 2 and ESPRIT trials were included. All estimates of cost found (per event avoided, per QALY gained or per life-year gained) were included. Results were analysed in light of the National Institute for Health and Clinical Excellence (NICE) guidelines for the use of antiplatelets for the prevention of cardiovascular events and all estimates were updated to pound (year 2006 values) for easy comparison. RESULTS: Of the initial 141 studies found, 21 were included in the initial review. The literature and the Markov model subsequently used suggest that aspirin (acetylsalicylic acid) dominates placebo for the secondary prevention of cardiovascular events, as it is effective, is also less costly and is as well tolerated as placebo. Additionally, in periods or patients with elevated risk, more intensive treatment with clopidogrel (alone or together with aspirin) is cost effective compared with aspirin alone for the secondary prevention of ischaemic events. For secondary stroke prevention, combination therapy with aspirin and dipyridamole has a favourable incremental cost-effectiveness ratio (ICER) when compared with aspirin alone and, based on an indirect comparison, also when compared with clopidogrel. CONCLUSIONS: The cost-effectiveness estimates presented in this article support the NICE guidelines for the use of antiplatelets for the prevention of cardiovascular events. Based on these pharmacoeconomic data alone, aspirin should be prescribed for primary or secondary prevention among patients at high risk of cardiovascular events, dipyridamole for the secondary prevention of stroke (for a maximum of 5 years), and clopidogrel for the treatment of symptomatic cardiovascular disease or acute coronary syndrome (for a maximum of 2 years). The cost effectiveness of antiplatelets hinges on the patient's initial risk, the risk reduction associated with treatment, and the price of the treatment. Evidence suggests that the cost effectiveness of antiplatelets can be optimized by individualising the treatment decision based on patient risk and expected risk reduction.     

Guidelines for stroke prevention in patients with atrial fibrillation

Atrial fibrillation (AF) is a major independent risk factor for stroke. AF is most commonly associated with nonvalvular cardiovascular disease and is especially frequent among the elderly. The annual risk for stroke in patients with AF is approximately 5% with a wide range depending on the presence of additional risk factors. For patients who cannot successfully be converted and maintained in normal sinus rhythm (NSR), antithrombotic therapy is an effective method for preventing stroke. The 2 drugs which are indicated for stroke prophylaxis in patients with AF are warfarin and aspirin. For primary prevention, warfarin reduces the risk of stroke approximately 68%. Aspirin therapy is less effective, resulting in a 20 to 30% risk reduction. Combination therapy with aspirin and low intensity warfarin adjusted to an International Normalised Ratio (INR) of 1.2 to 1.5 has not been shown to be superior to standard intensity warfarin with a target INR of 2.0 to 3.0. In patients with AF and a prior history of stroke or transient ischaemic attack (TIA), the absolute risk reduction with warfarin is even greater because of the high risk of stroke in this population. In contrast, aspirin has not been shown to significantly reduce the risk of stroke in patients with AF when used for secondary prevention. When appropriately managed, warfarin is associated with a low risk of major bleeding. In controlled trials of highly selected patients, the annual rate of intracranial haemorrhage (ICH) with warfarin was approximately 0.3%. Studies have shown that specialty anticoagulation clinics can achieve similar low rates of major bleeding. However, these results cannot be extrapolated to the general population. Factors which have been identified as predictors of bleeding include advanced age, number of medications and most importantly, the intensity of anticoagulation. INR values above 4.0 have been associated with an increased risk of major bleeding while values below 2.0 have been associated with thrombosis. Slow careful dosage titration, regular laboratory monitoring and patient education can substantially reduce the risk of complications. In patients with AF, antithrombotic therapy has been shown to be cost effective. For high risk patients, warfarin is the most cost-effective therapy, provided the risks for bleeding are minimised. In contrast, aspirin is the most cost-effective agent for low risk patients. Current practice guidelines for stroke prophylaxis recommend warfarin (target INR 2.5: range 2.0 to 3.0) for AF patients at high risk for stroke including those over 75 years of age or younger patients with additional risk factors. Aspirin should be reserved for low risk patients or those unable to take warfarin. Although these recommendations are strongly supported by the clinical trial evidence, studies show that many patients are not receiving appropriate antithrombotic therapy. In particular, warfarin is underutilised in high risk elderly patients. Additional studies are needed to identify barriers that prevent implementation of the clinical trial findings into clinical practice.     

Prevention of ischaemic stroke--antiplatelets

Aspirin is the treatment of first choice for long-term secondary prevention of vascular events in patients with confirmed non-cardioembolic ischaemic stroke or TIA. However, there is no good evidence that it is of benefit in primary stroke prevention. If aspirin is contra-indicated, dipyridamole monotherapy is a relatively cheap, but slightly less effective, alternative. Aspirin and dipyridamole have an additive effect in secondary stroke prevention, but there is a high incidence of side effects and subsequent discontinuation of treatment with combination therapy. It is reasonable to consider clopidogrel for secondary prevention of vascular events in patients with ischaemic stroke who are intolerant of aspirin or dipyridamole, or who have a history of ischaemic heart disease. However, its cost is considerable. Over the next decade, oral antiplatelet agents directed against specific platelet receptors, or a combination of antiplatelet drugs inhibiting different aspects of platelet function, may improve secondary prevention of stroke.     

Antiplatelet therapy in secondary stroke prevention

Stroke is the third leading cause of death in the United States. Antiplatelet agents are the mainstays of ischaemic stroke prevention. The therapies recommended for initial therapy include aspirin (50 - 325 mg) daily, the combination of aspirin (25 mg) and extended-release dipyridamole (200 mg) b.i.d., or clopidogrel (75 mg) daily. Ticlopidine 250 mg b.i.d. is approved for stroke prevention but is no longer a first-line therapy. This article reviews the literature on antiplatelet agents for secondary stroke prevention.     

Antiplatelet therapy in secondary stroke prevention

Stroke is the third leading cause of death in the United States. Antiplatelet agents are the mainstays of ischaemic stroke prevention. The therapies recommended for initial therapy include aspirin (50 - 325 mg) daily, the combination of aspirin (25 mg) and extended-release dipyridamole (200 mg) b.i.d., or clopidogrel (75 mg) daily. Ticlopidine 250 mg b.i.d. is approved for stroke prevention but is no longer a first-line therapy. This article reviews the literature on antiplatelet agents for secondary stroke prevention.     

Secondary stroke prevention: inside the vessels and beyond

Cerebral ischaemic stroke is frequently a relapsing, if not chronic, disease. Its incidence is age-dependent, and with the ageing of society the need for effective therapies increases.This review considers current and alternative hypotheses underlying secondary prevention of stroke. Currently, secondary stroke prevention is widely practiced with aspirin (acetylsalicylic acid), a drug that has been in use for more than 100 years. Newer drugs such as ticlopidine and clopidogrel have subsequently been developed, but their efficacy barely surpasses that of aspirin. Other drugs used in secondary stroke prevention include HMG-CoA reductase inhibitors and antihypertensive agents.The endovascular paradigm has shaped the thinking of secondary stroke prevention, and aspirin, ticlopidine and clopidogrel are known as 'platelet inhibitors'; however, their pharmacological and clinical effects are not fully explained within the platelet paradigm. Moreover, in recent years, reduction of stroke incidence has also been observed with HMG-CoA reductase inhibitors, regardless of their lipid-lowering effects. Hence, current understanding needs to be supplemented by considering mechanisms beyond platelet inhibition. Evidence has shown that aspirin, ticlopidine and clopidogrel share neuroprotective properties not explained by the platelet paradigm and that are reminiscent of a preconditioning effect. This neuroprotective mechanism is also shared with HMG-CoA reductase inhibitors.