Novel oral anticoagulants in secondary prevention of stroke.

In patients with atrial fibrillation (AF) oral anticoagulation with vitamin-K antagonists (warfarin, phenprocoumon) is effective both for primary and secondary stroke prevention yielding a 60-70% relative reduction in stroke risk compared with placebo, as well as a mortality reduction of 26 percent. Vitamin-K antagonists have a number of well documented shortcomings. Recently the results of randomised trials for three new oral anticoagulants that do not exhibit the limitations of vitamin-K antagonists have been published. These include direct factor Xa inhibitors (rivaroxaban and apixaban) and a direct thrombin inhibitor (dabigatran). The studies (RE-LY, ROCKET-AF, ARISTOTLE, AVERROES) provide promising results for the new agents, including higher efficacy and a significantly lower incidence of intracranial bleeds compared with warfarin or aspirin. The new drugs show similar results in secondary as well as in primary stroke prevention in patients with AF. Apixaban was demonstrated to be clearly superior to aspirin and had the same rate of major bleeding complications. Meta-analyses show that the novel anticoagulants are superior to warfarin for the reduction of stroke, major bleeding and intracranial bleeds. New anticoagulants add to the therapeutic options for patients with AF, and offer a number of advantages over warfarin, for both the clinician and patient, including a favorable bleeding profile and convenience of use. Aspirin is no longer an option in secondary stroke prevention in patients with atrial fibrillation. Consideration of these new anticoagulants will improve clinical decision making.

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).

Design of the blockade of the glycoprotein IIb/IIIa receptor to avoid vascular occlusion (BRAVO) trial.

BACKGROUND: Platelets play a key role in the pathogenesis of atherosclerosis, thrombosis, and acute coronary and cerebrovascular syndromes. Inhibition of platelet function by acetylsalicylic acid (aspirin) has been shown to reduce the incidence atherothrombotic events in patients with coronary, cerebrovascular, or peripheral vascular disease. Thienopyridine agents, however, including ticlopidine and clopidogrel, inhibit the adenosine diphosphate receptor and have modestly superior effects compared with aspirin on reduction of death, myocardial infarction, and stroke among a broad group of patients with vascular disease. More effective antithrombotic agents are still required to treat patients at high risk for recurrent vascular events. METHODS: Lotrafiban, a selective, nonpeptide antagonist of the human platelet fibrinogen receptor (glycoprotein [GP] IIb/IIIa [alphaIIb/beta3 integrin]), blocks the binding of fibrinogen to the GP IIb/IIIa receptor, which is the final common pathway of platelet aggregation. Lotrafiban at doses of up to 50 mg twice daily was well-tolerated in a 12-week, double-blind, placebo-controlled, dose-ranging study in patients with recent myocardial infarction, unstable angina, transient ischemic attack, or stroke when added to aspirin therapy. On the basis of these results, a dosing regimen was selected for the phase III Blockage of the Glycoprotein IIb/IIIa Receptor to Avoid Vascular Occlusion (BRAVO) trial based on pharmacodynamics and drug tolerability. In the pivotal BRAVO study, lotrafiban therapy is being evaluated in patients who have had a recent myocardial infarction, unstable angina, transient ischemic attack, or ischemic stroke, or who present at any time after a diagnosis of peripheral vascular disease combined with either cardiovascular or cerebrovascular disease. RESULTS: The efficacy evaluation will be based on a composite end point of clinical events (death by any cause, myocardial infarction, stroke, recurrent ischemia requiring hospitalization, or urgent ischemia-driven revascularization). The target enrollment is 9200 patients worldwide. Approximately 700 centers will participate and will be distributed within 30 countries across North America, Europe, Australia, and Asia.

Antiplatelet therapy: views from the experts.

Antiplatelet therapy is recommended for stroke prevention in persons with a history of thromboembolic stroke or transient ischemic attack (TIA) that is not of cardiac origin. Aspirin was the first antiplatelet agent to be used in this context and is still the most frequently prescribed preventive treatment for ischemic stroke. However, because the results of clinical studies with aspirin have been inconsistent, the dose of aspirin required for stroke prevention in persons with cerebrovascular disease has been a subject of debate among stroke neurologists. In the present discussion, low-dose aspirin is generally regarded by the experts as equivalent in effectiveness to high-dose aspirin, and its higher tolerability has the potential to significantly increase compliance with long-term therapy. Higher aspirin doses may have clinical utility in particular settings, but this requires further study. Despite the controversy, aspirin is now recognized as the treatment standard against which other antiplatelet agents are compared. Antiplatelet agents that may be more effective than aspirin have now been developed. Although each of these agents has been directly compared with aspirin in a large, randomized clinical trial, the lack of direct comparisons among these alternative antiplatelet therapies complicates decisions regarding long-term care of patients with cerebrovascular disease. An international panel of stroke neurologists reports that their selection of antiplatelet therapies for patients with prior history of TIA or stroke depends most heavily on drug efficacy and safety issues and is limited by availability (approval status of alternatives).

Dipyridamole plus aspirin in cerebrovascular disease.

BACKGROUND: The second European Stroke Prevention Study (ESPS-2) recently reported a substantial benefit of dipyridamole combined with aspirin over aspirin alone in the prevention of stroke. This appears to be at odds with previous studies suggesting that dipyridamole adds nothing to aspirin alone. OBJECTIVES: To review and compare the results of ESPS-2 and previous studies of dipyridamole plus aspirin and aggregate them in a meta-analysis. METHODS: We combined the detailed data provided by the Antiplatelet Trialists' Collaboration on the previous studies of dipyridamole plus aspirin with the results from ESPS-2. The data on the previous trials were listed in the appendix of the 1994 publication of the Antiplatelet Trialists' Collaboration. RESULTS: The results of our meta-analysis demonstrate that for the outcome of nonfatal stroke, ESPS-2 overwhelms previous data, which, even in the aggregate, did not include enough patients or outcome events to exclude efficacy for the combination of dipyridamole and aspirin. Differences between ESPS-2 and previous studies, which may have contributed to different results, include the doses and preparations of aspirin and dipyridamole. CONCLUSIONS: The ESPS-2 showed that dipyridamole alone prevents stroke. More importantly, it showed a substantial benefit for dipyridamole combined with aspirin over aspirin alone. When the ESPS-2 data are aggregated with the 14 previous trials of dipyridamole combined with aspirin over aspirin alone, the combination reduces the risk of stroke by 23% over aspirin alone. Nevertheless, important questions remain unanswered. We conclude that another randomized clinical trial showing a significant benefit of the combination of dipyridamole plus aspirin over aspirin alone may be needed before the addition of dipyridamole to aspirin is widely accepted for prevention of stroke.

Clinical aspects of the use of clopidogrel, a new antiplatelet agent.

Clopidogrel, a new platelet ADP receptor antagonist, is more effective than aspirin in reducing the risk of subsequent vascular ischemic events in patients with a broad spectrum of symptomatic atherosclerosis (recent ischemic stroke, recent myocardial infarction, or symptomatic peripheral arterial disease). In CAPRIE (clopidogrel versus aspirin in patients at risk of ischemic events), a randomized, blinded, active control trial in 19,185 high-risk patients, clopidogrel reduced the combined risk of ischemic stroke, myocardial infarction or vascular death by 8.7% compared with aspirin (p = 0.043). The CAPRIE cohort had a mean age of 62.5 years, which was reflected in the high proportion of patients who had medical conditions other than symptomatic atherosclerosis, and in the extensive use of concurrent therapies, including commonly used cardiovascular drugs. For all concomitant medications analysed, there was no evidence of statistically or clinically significant interactions with clopidogrel. The CAPRIE data confirm the findings of earlier clinical studies, which suggested that clinically significant drug interactions with clopidogrel are rare, that it can safely be prescribed with a range of other drugs (including phenobarbital, cimetidine, estrogen, digoxin, theophylline, atenolol, nifedipine, or nifedipine-atenolol in combination), and that the clinically proven dose of 75 mg once daily is suitable for all age groups studied. Moreover, CAPRIE demonstrated that there is no need for an adjustment of clopidogrel dose on the basis of gender, weight or race, and that there is no need for routine hematological monitoring. Additional clinical pharmacology studies have shown that the absorption of clopidogrel is unaffected by food or antacids, and that no dose adjustment is necessary in patients with renal impairment or with mild-to-moderate hepatic impairment. Due to pharmacologic considerations and limited clinical data, clopidogrel should be used cautiously with heparin, warfarin or non-steroidal anti-inflammatory drugs. With a simple regimen of 75 mg once daily indicated for all patients, clopidogrel combines a favorable risk/benefit ratio with ease of use in clinical practice.

Cardiac evaluation of stroke patients.

There are two potential purposes for cardiac evaluation in patients with cerebrovascular disease: to identify possible cardioembolic pathophysiology for ischemic symptoms and to identify concomitant coronary artery disease. Both have important implications for patient prognosis and treatment, and testing therefore appears to be warranted. On the other hand, the cost conservation movement in medicine dictates that physicians limit unnecessary, costly, possibly risky testing when the diagnostic yield is low. For example, the overall yield of cardiac testing in "usual stroke patients" who have no suggestive history or findings on examination, chest X-ray, or electrocardiogram is less than 10% and may not be indicated routinely. Conversely, young patients with stroke of unknown cause are likely to benefit from aggressive cardiac testing. Many reported series and clinical trials have demonstrated that patients with cerebrovascular disease are more likely to die in follow-up from cardiovascular than from cerebrovascular causes. This risk is best defined and may be highest in patients with carotid disease, in whom the 5-year cardiac mortality rate may be as high as 40 to 50%. Studies have shown that such patients are also likely to have abnormal tests for cardiac ischemia, even when a history of cardiovascular events or symptoms or electrocardiographic abnormalities are lacking. These results, combined with further investigations into which cerebrovascular patients are at highest risk for cardiovascular disease and what testing best identifies underlying, treatable cardiovascular disease, are needed to direct the care and improve the cardiovascular prognosis of patients with cerebrovascular disease.

What have we learned from recent antiplatelet trials?

Aspirin's benefit in preventing vascular outcomes is well established. It reduces the relative risk for stroke, myocardial infarction, and vascular death by about 25% compared with placebo. Almost 10 years ago we learned that ticlopidine is more effective than aspirin (about 12% relative risk reduction for stroke or death). However, ticlopidine has important adverse effects. In 1996, the Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events (CAPRIE) trial showed that clopidogrel, a new thienopyridine similar to ticlopidine, is also more effective than aspirin (by a similar amount) and is as safe as aspirin. Also in 1996, the European Stroke Prevention Study 2 (ESPS-2) showed that dipyridamole alone prevents stroke and that when combined with aspirin it is more effective, probably comparable to ticlopidine and clopidogrel. Dipyridamole combined with aspirin reduced the relative risk for stroke or death by about 13% compared with aspirin alone. Both clopidogrel and dipyridamole are safe but will cost more than aspirin. Aspirin also appears beneficial for acute stroke treatment. The Chinese Acute Stroke Trial (CAST) and the International Stroke Trial (IST) demonstrated that aspirin given at the time of an acute ischemic stroke reduces the risk for early death (about 5 less/1,000 treated), recurrence or death (about 10 less/1,000 treated), and dependence (about 5 less/1,000 treated). Overall, the benefits of aspirin in acute stroke treatment and stroke prevention are definite but modest. Combination therapy with antiplatelet agents that act through different mechanisms is a promising way to maximize the benefits of antiplatelet treatment.

Prevention of stroke in patients with nonvalvular atrial fibrillation.

OBJECTIVE: To review the risk and pathogenesis of stroke associated with nonvalvular atrial fibrillation (AF) and the efficacies and risks of stroke prevention strategies. BACKGROUND: About 16% of ischemic strokes are associated with AF; AF is an independent risk factor for stroke. METHODS: Review of the literature, focusing on 13 randomized trials of antithrombotic therapy. RESULTS: The overall risk of stroke in AF patients averages about 5%/y, but with wide variation depending on the presence of coexistent thromboembolic risk factors. AF patients with low (about 1% per year), moderate (about 3% per year), and high (about 6% per year) stroke risks have been identified, but the generalizability of risk stratification schemes to clinical practice has not been fully assessed. AF patients with prior stroke or transient ischemic attack, even if remote, are at highest risk (about 12% per year). Adjusted-dose warfarin (target International Normalized Ratio [INR] 2-3) is highly efficacious for preventing stroke in AF patients (about 70% risk reduction) and is safe for selected patients, if carefully monitored. Aspirin has a modest effect on reducing stroke (about 20% risk reduction). The numbers of AF patients that would need to be treated with warfarin instead of aspirin for 1 year to prevent one ischemic stroke are about 200, 70, and 20 for those with low, moderate and high risk, respectively. CONCLUSIONS: Many patients with nonvalvular AF have substantial rates of ischemic stroke. Stratification of stroke risk identifies AF patients who benefit most and least from lifelong anticoagulation. Warfarin is recommended for high-risk AF patients who can safely receive it. Aspirin may be indicated for those with a low stroke risk and for those who cannot receive warfarin. For AF patients considered to have a moderate risk of stroke, individual bleeding risk during anticoagulation and patient preference should particularly influence the choice of antithrombotic prophylaxis.