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).     

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.     

Antiplatelet Agents for Stroke Prevention

Stroke is one of the leading causes of disability and death. Ischemic stroke is a syndrome with heterogeneous mechanisms and multiple etiologies, rather than a singularly defined disease. Approximately one third of ischemic strokes are preceded by another cerebrovascular ischemic event. Stroke survivors are at high risk of vascular events (i.e., cerebrovascular and cardiovascular events), particularly during the first several months after the ischemic event. The use of antiplatelet agents remains the fundamental component of secondary stroke prevention. Based on the available data, antiplatelet agents should be used for patients with noncardioembolic stroke. The use of combination therapy (aspirin plus clopidogrel) has not been proven to be effective or safe to use for prevention of early stroke recurrence or in long-term treatment. There is no convincing evidence that any of the available antiplatelet agents are superior for a given stroke subtype. Currently, the uses of aspirin, clopidogrel, or aspirin combined with extended release dipyridamole are all valid alternatives after an ischemic stroke or transient ischemic attack. However, to maximize the effects of these agents, the treatment should be initiated as early as possible and be continued on a lifelong basis.     

Prior therapy with antiplatelet agents is not associated with outcome in patients with acute ischemic stroke/TIA

BACKGROUND AND PURPOSE: It is unclear whether prior therapy with antiplatelet agents (APA) is associated with a better outcome in patients with acute ischemic cerebrovascular events. METHODS: Within a multi-center cross-sectional study, nested in a cohort we analyzed the relation between prior therapy with APA and stroke severity in 1643 patients with acute ischemic stroke or TIA. Clinical severity of the vascular event was evaluated by the National Institutes of Health Stroke Scale on admission (NIHSS1) and after 1 week (NIHSS2). By means of analysis of variance we analyzed a possible association of APA with stroke severity and interactions regarding stroke severity between APA and other clinical measures. RESULTS: 475 patients (29 %) received aspirin prior to the cerebrovascular event, 51 patients (3 %) ticlopidine or clopidogrel and 26 patients (1.6%) aspirin combined with extended release dipyridamole. 66% (1091) of patients did not take any antiplatelet medication. Neither the NIHSS1 nor the NIHSS2 nor the change of stroke severity between these time points (NIHSS1- NIHSS2) was associated with prior APA medication. We did not find significant interactions between APA use and clinical measures regarding stroke severity. CONCLUSIONS: Our results do not indicate that prior therapy with APA is associated with a better outcome in acute ischemic cerebrovascular events. There were no interactions found with other features that were associated with stroke severity.     

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.     

Antiplatelet therapy in ischemic stroke

Stroke is the third leading cause of death and the leading cause of disability in the developed world. Atherothrombosis is the underlying condition that results in events leading to ischemic stroke and vascular death. Antiplatelet therapy is commonly used for both acute stroke and in secondary prevention. Numerous trials and meta-analyses have left little doubt that antiplatelet therapy effectively reduces stroke risk in patients with prior stroke or transient ischemic attack. Current antiplatelet agents include acetylsalicylic acid, clopidogrel, ticlopidine and extended release dipyridamole with low doses of acetylsalicyclic acid (aspirin). The optimum doses of antiplatelet drugs depend upon several variables, such as genetic and environmental factors, so that clinical and laboratory response for dosage varies for each patient. Recently, the correlation between the laboratory-measurable effect of antiplatelet agents and the clinical effectiveness on the mortality of ischemic stroke and cardiovascular patients has been documented. Due to the side effect of bleeding with different antithrombotic drugs, their future employment will be determined in combination with low dosages of each component. Laboratory-controlled, tailored drug therapy will be needed for long-lasting secondary prevention of ischemic stroke.     

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.     

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.     

Clinical implications of aspirin resistance

Aspirin reduces major atherothrombotic events across a wide spectrum of patients with atherosclerotic disease. The occurrence of ischemic events despite of aspirin treatment is a failure of therapy, often denoted 'clinical aspirin resistance'. This is distinguished from laboratory assays showing an insufficient inhibition of platelet function, which indicate 'laboratory aspirin resistance'. Laboratory aspirin resistance has been reported in up to 60% of patients after stroke or peripheral arterial disease, up to 70% in stable coronary heart disease and even up to 80% in acute myocardial infarction. However, this data must be interpreted carefully because of small sample sizes and potential confounding factors such as compliance, co-morbidities and large differences between the laboratory methods used for detection. During the past years, evidence has accumulated that laboratory aspirin resistance is associated with an increased incidence of major atherothrombotic events, with an up to 13-fold increased risk of events in patients with cardiovascular disease. Thus, an individualized antiplatelet therapy will have to consider the possibility of aspirin resistance, and the identification of aspirin non-responders may improve antiplatelet therapy in future. Whether an increased dose of aspirin or another antiplatelet drug (e.g. clopidogrel) instead or in addition to aspirin should be given is unclear. Prospective trials are underway which address this issue. This review gives an overview on the various clinical studies that have investigated the prevalence and clinical importance of laboratory aspirin resistance. Moreover, therapeutic options, as well as future perspectives are discussed.     

强化抗血小板治疗在缺血性脑卒中复发高危患者二级预防中的临床研究

目的观察强化抗血小板药物氯吡格雷在缺血性脑卒中复发高危患者二级预防中的长期疗效及安全性。方法采用艾森卒中风险评分（ESRS）量表筛选住院的急性非心源性缺血性脑卒中复发高危患者100例,随机分为氯吡格雷组和阿司匹林组,每组50例。两组均给予脑卒中常规治疗,氯吡格雷组予氯吡格雷75mg及阿司匹林100mg口服,1周后仅予氯吡格雷75mg,口服。阿司匹林组予阿司匹林200mg,口服,1周后改为100mg,口服。随访3个月和1年,观察两组缺血性脑卒中复发率及药物不良反应发生率。结果随访3个月时,脑卒中复发率：阿司匹林组为6．3％,氯吡格雷组为2．0％,差异无统计学意义（P〉0．05）;药物不良反应发生率：阿司匹林组为14％,氯吡格雷组为2％,差异有统计学意义（P〈0．05）。随访1年时,脑卒中复发率：阿司匹林组为13％,氯吡格雷组为2％,差异有统计学意义（P〈0．05）;药物不良反应发生率：阿司匹林组为38％,氯吡格雷组为6％,差异有统计学意义（P〈0．01）。结论缺血性脑卒中复发高危患者二级预防中强化抗血小板治疗可降低脑卒中复发风险,长期应用获益较高,安全性好。     

Aspirin nonresponse in patients with arterial causes of ischemic stroke: considerations in detection and management

Patients with a history of ischemic stroke or transient ischemic attack (TIA) are at risk for recurrent ischemic events in the same or different vascular bed. Due to the central role of platelets in the spectrum of ischemic events in all vascular beds, antiplatelet therapy is a critical component of treatment. Of all antiplatelet therapies approved for the secondary prevention of stroke, aspirin is the most well-established and is recommended for all patients with a history of cerebrovascular disease. However, some patients do not respond to aspirin therapy and are termed "aspirin-resistant." This review discusses issues of, and possible solutions to, decreased platelet response to aspirin in patients with arterial causes of ischemic stroke.     

个体化抗血小板治疗对缺血性卒中二级预防的效果研究

目的 研究个体化抗血小板治疗在缺血性卒中二级预防的效果。 方法 选择2013年3月-2014年5月于陕西省人民医院就诊的急性缺血性卒中患者207例,随机分为 常规治疗组与个体化治疗组。常规治疗组应用阿司匹林100 mg/d抗血小板治疗。个体化治疗组应用 Essen卒中风险评分量表（Essen Stroke Risk Score,ESRS）将高危组给予氯吡格雷75 mg/d,低危组给 予阿司匹林100 mg/d抗血小板治疗。7 d后进行血栓弹力图（thromboela stogram,TEG）及CYP2C19基因型 检测,结合TEG及CYP2C19基因型结果,决定抗血小板治疗方案。随访1年,比较个体化治疗组和常规 治疗组患者终点事件发生率。 结果 CYP2C19快代谢基因型、中间代谢基因型患者应用氯吡格雷的血小板抑制率明显高于慢代谢 型,结果差异有显著性（P =0.018,P =0.015）。个体化治疗组（112例）和常规治疗组组（95例）终点事 件发生率差异无显著性（P＞0.01）。 结论 CYP2C19快代谢基因型、中间代谢基因型患者应用氯吡格雷的血小板抑制率明显高于慢代谢 型。与阿司匹林常规治疗方案相比,利用CYP2C19基因多态性与TEG检测指导下的个体化抗血小板方 案未显示降低缺血性卒中后终点事件发生率,可能需要更大规模、随访时间更长的研究。     

Antiplatelet strategy for acute ischemic stroke: A mini review

Transient ischemic attacks and minor ischemic strokes have a high risk of an unstable clinical course in the initial 48-72 h after symptom onset. Early antiplatelet treatment is recommended to treat most patients with acute ischemic stroke because few patients can be treated with thrombolysis due to the limit of strict indications, such as a time window. Antiplatelets aim to prevent recurrence or deterioration of stroke. The guidelines recommend the use of aspirin in the acute stage based on two clinical trials. However, some patients still developed recurrence or deterioration of stroke despite timely aspirin administration. Thus, the question remains unclear whether another effective and safe antiplatelet strategy for the treatment of acute ischemic stroke exists. Growing evidence shows that combination antiplatelets may be superior to mono antiplatelets in the treatment of acute ischemic stroke.     

Current oral antiplatelet agents to prevent atherothrombosis

Aspirin inhibits platelet activation by irreversibly inhibiting platelet cyclooxygenase and thromboxane production, and reduces the odds of serious vascular events (stroke, myocardial infarction or vascular death) by about one quarter in a range of patients with symptomatic atherosclerosis at high risk of a subsequent event. The adenosine diphosphate (ADP) receptor antagonists clopidogrel and ticlopidine are significantly more effective than aspirin in high-risk vascular patients, further reducing the odds of serious vascular events by about 10% (95% CI 2-19%) over the benefit provided by aspirin. The ADP receptor antagonists are also associated with a significant 30% reduction in the odds of gastrointestinal haemorrhage (odds ratio 0.71, 95% CI 0.59-0.86). Ticlopidine increases the odds of skin rash and of diarrhoea by more than twofold compared with aspirin, whereas clopidogrel is associated with a one-third increase in the odds of rash and of diarrhoea. Only ticlopidine increases the odds of neutropenia compared with aspirin. There is no clear evidence as yet for the benefit of dipyridamole or an oral GP IIb/IIIa receptor antagonist as single antiplatelet agents in atherothrombotic patients. Amongst high vascular risk patients, the combination of low-dose aspirin and high-dose dipyridamole is associated with about a 10% (95% CI 0-20%) reduction in the odds of a serious vascular event. Most of this reduction is due to a 23% reduction in non-fatal stroke. The size of this estimate continues to be investigated in an ongoing study of patients with transient ischaemic attack and stroke. The combined use of aspirin and ticlopidine is markedly superior to heparin, warfarin and aspirin for reducing thrombotic complications after coronary artery stenting. Clopidogrel plus aspirin has been shown to be safer than aspirin and ticlopidine in coronary stenting, and is now under long-term evaluation in unstable angina, and other conditions in which patients are at high risk of atherothrombotic events.     

Efficacy of dual antiplatelet therapy in cerebrovascular disease as demonstrated by a decline in microembolic signals. A report of eight cases

BACKGROUND: The presence of microembolic signals (MES) may indicate an increased risk of recurrent ischemic events in patients with stroke. The optimal management of such patients is uncertain. We report the effect of clopidogrel in addition to aspirin on the number of MES in a series of patients with ischemic stroke and transient ischemic attack (TIA) due to large-vessel disease. METHODS: 8 patients with either extracranial or intracranial artery stenosis were identified in 30-min MES studies by transcranial Doppler sonography as having MES. All patients were on antiplatelet therapy prior to baseline transcranial Doppler monitoring. The patients were subsequently treated with clopidogrel in addition to aspirin. Repeat MES studies were performed between day 3 and 7 with aspirin and clopidogrel. RESULTS: All patients were Chinese. The median interval time from symptom onset to initial MES study was 7 days (range of 2-30). MES donor sites included 4 severely stenosed or occluded internal carotid arteries and 4 stenosed middle cerebral arteries. The median MES number at baseline was 8 (range 3-51). Repeat MES studies showed a significant decrease in MES (p = 0.012, Wilcoxon signed ranks test). 4 patients had complete cessation of MES and all patients showed a decline in MES. No patient had recurrent strokes or bleeding complications. CONCLUSION: The rapid and significant decline of MES in our stroke and TIA patients suggests the possible efficacy of dual antiplatelet therapy with aspirin and clopidogrel in patients with MES and symptomatic large-artery occlusive disease. Randomized controlled trials should be conducted to confirm this preliminary observation.     

Medical Treatment of Patients with Intracranial Atherosclerotic Disease

The medical treatment of patients with symptomatic intracranial atherosclerotic disease (ICAD) is directed toward reducing the risk of new ischemic events. The overall strategy is divided into: (1) prevention of occurrence of intraluminal thrombus, with or without embolism; (2) plaque stabilization and regression; and (3) management of atherogenic risk factors. In patients with ICAD, short-term and long-term anticoagulation (compared with aspirin) has not shown to be beneficial. The current guidelines recommend that aspirin monotherapy, the combination of aspirin and extended release dipyridamole, and clopidogrel monotherapy (rather than oral anticoagulants) are all acceptable options in patients with noncardioembolic ischemic stroke and transient ischemic attack. The findings of another pilot trial suggest that symptomatic ICAD is a dynamic lesion and cilostazol may prevent its progression. Overall, the subgroup analysis from randomized trials, provide evidence about benefit of aggressive atherogenic risk factor management among patients with ICAD. Current guidelines recommend statin therapy with intensive lipid-lowering effects for patients with atherosclerotic ischemic stroke or transient ischemic attack with or without known coronary artery disease to reduce the risk of stroke and cardiovascular events.     

Clopidogrel resistance?

Clopidogrel is an effective inhibitor of platelet activation and aggregation due to its selective and irreversible blockade of the P2Y(12) receptor. Combination antiplatelet therapy with clopidogrel and aspirin is an important strategy for patients with acute coronary syndromes and those undergoing percutaneous interventions. Despite significant benefits demonstrated with combination antiplatelet treatment in large clinical trials, the occurrence of adverse ischemic events, including stent thrombosis, remains a serious clinical problem. Recent studies have demonstrated distinct response variability and nonresponsiveness to clopidogrel therapy based on ex vivo platelet function measurements. Small scale investigations have suggested that nonresponsiveness may be associated with a heightened risk for adverse clinical events. The above findings have stimulated a close examination of clopidogrel metabolism.     

Dual Antiplatelet Therapy after Noncardioembolic Ischemic Stroke or Transient Ischemic Attack: Pros and Cons

Dual antiplatelet therapy simultaneously blocks different platelet activation pathways and might thus be more potent at inhibiting platelet activation and more effective at reducing major ischemic vascular events compared to antiplatelet monotherapy. Aspirin plus clopidogrel dual therapy is now the standard therapy for patients with acute coronary syndrome and for those undergoing percutaneous coronary intervention. However, dual antiplatelet therapy carries an increased risk of bleeding. Patients with ischemic stroke or transient ischemic attack (TIA) are generally older and likely to have a fragile cerebrovascular bed, which further increases the risk of systemic major bleeding events and intracranial hemorrhage. Clinical trials and meta-analyses suggest that in comparison to antiplatelet monotherapy, dual antiplatelet therapy initiated early after noncardioembolic ischemic stroke or TIA further reduces the rate of recurrent stroke and major vascular events without significantly increasing the rate of major bleeding events. In contrast, studies of long-term therapy in patients with noncardioembolic ischemic stroke or TIA have yielded inconsistent data regarding the benefit of dual antiplatelet therapy over monotherapy. However, the harm associated with major bleeding events, including intracranial hemorrhage, which is generally more disabling and more fatal than ischemic stroke, is likely to increase with dual antiplatelet therapy. Physicians should carefully assess the benefits and risks of dual antiplatelet therapy versus antiplatelet monotherapy when managing patients with ischemic stroke or TIA.     

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.