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.     

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 role of antiplatelet therapy in the management of ischemic stroke: implementation of guidelines in current practice

Abstract

Objective: To review and discuss evidence-based guideline recommendations for the use of antiplatelet agents for secondary prevention in patients with ischemic stroke or TIA.

Methods: A literature search was conducted on PubMed through August 2007 using combinations of the following search terms: aspirin, clopidogrel, dipyridamole plus aspirin, transient ischemic attack, secondary prevention, stroke and guidelines.

Results: Modification of risk factors such as hypertension, diabetes, hypercholesterolemia, cigarette smoking and obesity are fundamental to stroke management. Antiplatelet therapy is highly effective in reducing the risk of recurrent vascular events and is recommended over oral anticoagulants for non-cardioembolic stroke. Evidence from head-to-head comparative clinical trials versus aspirin monotherapy has shown that clopidogrel and the combination of aspirin plus dipyridamole are safe and effective therapeutic options.

Discussion: Despite the availability of evidence-based guidelines, recommended interventions are largely underutilized. Quality improvement initiatives such as the ASA's Get with the Guidelines – Stroke and the UCLA stroke PROTECT Program have demonstrated effectiveness in increasing adherence to recommended therapies and thereby improving patient outcomes.     

氯吡格雷联合阿司匹林治疗对轻型卒中与短暂性脑缺血发作患者功能预后的影响：CHANCE与POINT试验联合分析

目的 评价氯吡格雷联合阿司匹林双抗治疗对轻型缺血性卒中与TIA患者功能预后的影响。 方法 提取CHANCE和POINT试验所有的个体数据。这两项试验中,所有纳入患者在症状发作12 h （POINT）或24 h（CHANCE）以内随机接受氯吡格雷联用阿司匹林或单用阿司匹林治疗。结局指标为3个 月时功能预后不良（mRS≥2）,三等级定义卒中复发[致残性或致死性卒中复发（mRS≥2）、非致残性 卒中复发（mRS 0或1）、无卒中复发]。 结果 共10 013例患者纳入分析,其中来自CHANCE试验5132例（51.3%）,来自POINT试验4881例 （48.7%）;氯吡格雷联用阿司匹林组4995例（49.9%）,单用阿司匹林组5018例（50.1%）。氯吡格雷联 用阿司匹林组3个月时功能预后不良的患者比例低于单用阿司匹林组（11.6% vs 12.6%,校正OR 0.82, 95%CI 0.72～0.94,P =0.005）。氯吡格雷联用阿司匹林组致残性或致死性卒中复发（4.6% vs 6.1%, 校正OR 0.73,95%CI 0.61～0.87,P <0.001）、非致残性卒中复发（1.9% vs 3.0%,校正OR 0.62,95%CI 0.47～0.80,P <0.001）和卒中复发的整体致残性（校正cOR 0.70,95%CI 0.60～0.81,P <0.001）低于单 用阿司匹林组。 结论 与单用阿司匹林治疗相比,氯吡格雷联用阿司匹林治疗可进一步改善轻型缺血性卒中和TIA 患者3个月时功能预后,减少致残性卒中复发。     

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 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).     

Dual Antiplatelet Therapy Beyond 90 days in Symptomatic Intracranial Stenosis in the SAMMPRIS Trial

BackgroundThe safety and efficacy of dual antiplatelet use for symptomatic intracranial atherosclerosis beyond 90 days is unknown. Data from SAMMPRIS was used to determine if dual antiplatelet therapy (DAPT) beyond 90 days impacted the risk of ischemic stroke and hemorrhage.MethodsThis post hoc exploratory analysis from SAMMPRIS included patients who did not have a primary endpoint within 90 days after enrollment (n = 397). Patients in both the aggressive medical management (AMM) and percutaneous transluminal angioplasty and stenting (PTAS) arms were included. Baseline features and outcomes during follow-up were compared between patients who remained on DAPT beyond 90 days (on clopidogrel) and patients who discontinued clopidogrel and remained on aspirin alone at 90 days (off clopidogrel) using Fisher's exact tests.ResultsThe stroke rate was numerically lower in the group on clopidogrel vs off clopidogrel among both the AMM alone arm (6.0% versus 10.8%, p = 0.31) and the PTAS arm (8.7% versus 9.8%; p = 0.82), but the difference was not significant. The major hemorrhage rates were numerically higher in the group on clopidogrel vs. off clopidogrel group among both the AMM alone arm (4.0% versus 2.5%; p = 0.67) and the PTAS arm (10.9% versus 3.5%; p = 0.08), but were not significant.ConclusionThis exploratory analysis suggests that prolonged DAPT use may lower the risk of stroke in medically treated patients with intracranial stenosis but may increase the risk of major hemorrhage.     

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.     

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.     

Future perspectives for optimizing oral antiplatelet therapy

Secondary prevention of stroke and other manifestations of atherothrombosis is essential if the burden of disease associated with these events is to be reduced. Therefore, it is important to identify patients most likely to benefit from antiplatelet therapy. There is a good rationale for combining antiplatelet agents with different modes of action, since different signalling pathways contribute to platelet activation. Based on the promising results obtained with an adenosine diphosphate receptor antagonist-aspirin combination in coronary stenting, several additional trials with clopidogrel plus aspirin are ongoing. They include CURE (Clopidogrel in Unstable angina to prevent Recurrent Events, in unstable angina and non-Q-wave myocardial infarction) and COMMIT (in acute myocardial infarction), which compare clopidogrel with placebo in patients receiving aspirin, and CREDO (Clopidogrel for Reduction of Events During extended Observation), a 1-year treatment follow-up to the clopidogrel arms of the CLASSICS trial (Clopidogrel Aspirin Stent International Cooperative Study). Planned trials with clopidogrel in neurology include SPS3 (Secondary Prevention of Small Subcortical Strokes, in patients with symptomatic lacunar stroke), and MATCH (Management of Atherothrombosis with Clopidogrel in High-risk patients, in patients with stroke or transient ischaemic attack plus one additional risk factor), which will compare the efficacy of clopidogrel plus aspirin versus clopidogrel in reducing important ischaemic events. Combination therapy with an oral glycoprotein (GP) IIb/IIIa receptor antagonist plus aspirin has so far been less promising. Trials of three compounds--orbofiban, xemilofiban and sibrafiban--in combination with aspirin for secondary prevention in cardiac patients have reported increased mortality compared with aspirin alone. A similar effect was seen when sibrafiban monotherapy was compared directly with aspirin alone. Trials of newer oral GP IIb/IIIa inhibitors are under way or are planned. The combination of dipyridamole plus aspirin appears to be superior to aspirin alone for the prevention of stroke in patients with stroke or transient ischaemic attack; the effectiveness of this combination is being further investigated in ESPRIT (European/Australian Stroke Prevention in Reversible Ischaemia Trial).     

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.     

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.     

Prevention of stroke recurrence

Stroke recurrence can be reduced substantially by intervention with the appropriate stroke preventive(s). Control of blood pressure, use of one of the antiplatelet agents aspirin, aspirin plus extended (modified)-release dipyridamole, or clopidogrel, administration of warfarin for patients with atrial fibrillation and high-risk profiles for stroke, and use of carotid endarterectomy in patients with high grades of symptomatic carotid artery stenosis are all proven therapies for prevention of stroke recurrence. Newer therapies to reduce the risk of infection and inflammation promise to further reduce the risk of first and recurrent stroke and are undergoing testing. In this article we review standard and more novel means to prevent stroke recurrence.     

Use of antiplatelet agents to prevent stroke: What is the role for combinations of medications?

Antiplatelet agents are the medications of choice for preventing non-cardioembolic strokes. The diverse pathways involved in platelet function suggest the possibility of synergistic effects by combining various agents. In heart disease and in the setting of coronary artery stents, antiplatelet therapy with clopidogrel and aspirin has established benefits. Although it is tempting to extrapolate the benefits of this combination for stroke prevention, recent clinical trials have not borne this out. Unacceptable bleeding risks without additional efficacy weigh against the routine use of clopidogrel with aspirin for stroke prophylaxis. The combination of aspirin and extended-release dipyridamole has demonstrated superiority over aspirin in two large secondary stroke prevention trials.     

Antiplatelet therapy in acute cerebral ischemia

BACKGROUND: Improved recognition of stroke signs and symptoms has paralleled the development of pharmacological strategies that may be examined to reduce stroke mortality and morbidity. Presently, tissue plasminogen activator is the only therapy that significantly improves outcome in acute stroke, with no agent demonstrating a significant reduction in mortality. SUMMARY OF REVIEW: Antiplatelet agents are a heterogenous class of drugs that have been successfully used for more than 2 decades in secondary stroke prevention. These agents include aspirin, with or without dipyridamole, and more recently, the adenosine antagonists ticlopidine and clopidogrel. However, studies of the use of antiplatelet agents within 48 hours of the ictus have examined only aspirin. Only 1 study, the Multicentre Acute Stroke Trial-Italy (MAST-I), entered patients within 6 hours of the ictus. These data suggest that an improvement in mortality may be related to the speed of administration. No significant adverse events were noted with early antiplatelet monotherapy. However, MAST-I did note a significant increase in early mortality in patients receiving aspirin plus streptokinase, a finding not adequately explained by an increase in the intracranial hemorrhage rate. CONCLUSIONS: The use of antiplatelet therapy in acute stroke, clinical or experimental, has only recently received attention. It is likely that the use of antiplatelet agents for acute stroke therapy will be less restrictive than that currently seen for thrombolytics. Future studies should include an examination of those agents that have previously demonstrated efficacy in secondary stroke prevention, most notably, aspirin. The recognition that all platelet stimuli share a final common pathway that is dependent on the surface glycoprotein IIb/IIIa (fibrinogen) receptor has resulted in the development of various agents which block this receptor and are currently the focus for clinical trials. The role of nitric oxide in stroke therapy will depend on minimizing the hypotensive side effects of this agent. Stroke models are needed to provide preliminary data on the efficacy of antiplatelet therapy, especially as relates to the interaction of antiplatelet agents with thrombolytics.     

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.     

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 platelet reactivity on platelet function and clinical outcome in minor stroke or transient ischemic attack

ObjectiveWhether aspirin platelet reactivity affects platelet function and clinical outcomes with different antiplatelet therapies in patients with mild stroke or transient ischemic attack (TIA) remains unclear. We conducted a subgroup analysis of the PRINCE trial.Materials and methodsPatients with mild stroke or TIA were randomized into aspirin+ticagrelor, or aspirin+clopidogrel groups; aspirin reaction units (ARU) were measured at the baseline and after 7 ± 2 days to assess response to treatment. High on-treatment platelet reactivity (HPR) was defined as ≥550 ARU (poor response to aspirin). The platelet functions of ticagrelor and clopidogrel were measured using the VerifyNow P2Y₁₂ assay for P2Y₁₂ reaction units (PRU); HPR to P2Y₁₂ was defined as >208 PRU (poor response to P2Y₁₂). Clinical outcomes included stroke and clinical vascular and bleeding events after 90 days.ResultsAmong 628 enrolled patients, 69 (11%) were poor aspirin responders. After 7 ± 2 days, the proportion of poor P2Y₁₂ responders for ticagrelor versus clopidogrel significantly reduced in poor (2.6% versus 27.4%) and good (14.3% versus 29.4%) aspirin responders. There were significant interactions between treatment groups, and between treatment groups and aspirin platelet reactivity for poor P2Y₁₂ responders (P = 0.01). After 90 ± 7 days, there were no significant interactions between treatment groups and aspirin platelet reactivity for new stroke risk (good aspirin responders: 5.5% versus 8.8%, hazard ratio [HR]: 0.61; 95% confidence interval [CI], 0.32 to 1.16; P = 0.13; poor aspirin responders: 8.6% versus 8.8%, HR: 0.97, 95% CI: 0.20–4.81; P = 0.97; P for interaction = 0.60). Major bleeding was less frequent in poor than good aspirin responders (ticagrelor/aspirin: 0.4%/0%; clopidogrel/aspirin: 1.4%/0%).ConclusionsIn patients with minor stroke or TIA, clopidogrel, and particularly ticagrelor, decreased platelet function in poor versus good aspirin responders. The poor platelet reactivity of aspirin could not sufficiently reduce the risk of recurrent stroke with ticagrelor or clopidogrel; however, HPR (poor aspirin response) may have a protective effect on clinically relevant major bleeding.     

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.