Aspirin and Antiplatelet Medications (cont.)
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It is important to recognize that aspirin is not the preferred treatment for ischemic strokes. Thrombolytic medications (medications that dissolve clots) are used early (as soon as an ischemic stroke is recognized) to open blocked cerebral arteries.
The major limitation for using these medications is time. For example, for an ischemic stroke, thrombolytics must be given within the first three hours after the first symptoms of a stroke. Many people with strokes may not recognize the symptoms and may delay medical attention for several hours if not days after the onset of stroke symptoms.
Another limitation in their use is that only certain patients qualify to receive these medications. As a result, for patients in whom thrombolytic medications cannot be used (most often because of underlying conditions that can cause excessive bleeding), doctors may consider using aspirin. Thus, aspirin is often the drug that patients with stroke will receive when they are seen in the emergency room.
Prevention of strokes
Patients with prior strokes and TIAs (mini-strokes) usually have significant atherosclerosis of the carotid and /or the smaller arteries within the brain and are at risk of further strokes. (These patients often have coronary atherosclerosis as well and are at risk for heart attacks.) Long-term low-to-moderate doses of aspirin (50-325 mg/d) have been found to reduce the risk of strokes as well as heart attacks in these patients.
Aspirin is not the only medication to prevent strokes among patients with atherosclerosis. Another anti-platelet agent, clopidogrel (Plavix), also has been used, especially in patients who are intolerant or allergic to aspirin. Aspirin is sometimes combined with a second anti-platelet agent, dipyridamole (Persantine, Aggrenox), to prevent strokes.
Antiplatelet agents are not the only measures that prevent strokes. For example, aspirin alone may not be sufficient to prevent embolic strokes in patients at risk for these strokes, such as in patients with atrial fibrillation. In these patients, warfarin (Coumadin), an oral anti-coagulant that is a stronger anti-clotting medication than aspirin, may be necessary.
In patients with ischemic strokes or TIAs who have advanced atherosclerosis and narrowing of the carotid arteries, carotid endarterectomy (a surgical procedure to widen the narrowed carotid artery, the main blood vessel feeding the brain) or the introduction of stents within the carotid artery may be necessary to prevent strokes.
How effective is aspirin for preventing heart attacks among healthy subjects?
Long-term, low dose aspirin (75-160 mg/d) infrequently causes serious side effects. Therefore, among patients with advanced atherosclerosis (patients who already have heart attacks and strokes, patients with angina or TIAs, patients who need PTCA and coronary artery bypass surgery, and patients with symptoms of peripheral vascular disease) the benefits of low dose aspirin usually outweigh the risks of long-term aspirin (discussed below).
Unlike the treatment of patients with advanced atherosclerosis, aspirin use among healthy subjects (for example, individuals with no prior heart attacks or strokes) is more controversial. In the U.S. Physicians' Health Study (a study comparing 325 mg of aspirin every other day to placebo among more than 20,000 healthy male doctors), there were fewer heart attacks among aspirin users as compared to placebo users. However, the overall rate of death from heart disease was no different between aspirin users and men on placebo. Furthermore, there is insufficient data to evaluate the benefit of aspirin among healthy women.
Therefore, the potential benefits of long-term aspirin in healthy subjects may not justify the small risks of serious side effects of aspirin, including bleeding from ulcers and blood vessels in the brain. Healthy individuals should discuss long-term therapy with aspirin with their doctors before they start taking aspirin. Most doctors recommend aspirin in healthy subjects who have one or more risk factors for developing atherosclerosis.
What are the latest recommendations on the use of aspirin in the primary prevention of cardiovascular disease?
As described below, the recommendations for the secondary prevention (in people who already have had a heart attack or stroke) of future attacks are more compelling.
In 2009, the U.S. Preventive Services Task Force (USPSTF) has come up with slightly modified recommendations for the primary prevention of cardiovascular disease using aspirin. Based on their review of the published data:
What is the optimal dose of aspirin for treating and preventing heart attacks and strokes?
An ideal dose of aspirin is one that maximizes its benefits but minimizes side effects. However, the ideal dose of aspirin for primary or secondary prevention of ischemic strokes and heart attacks has not been established firmly.
In situations where an immediate antiplatelet effect is needed (for example, in the treatment of acute heart attacks, ischemic strokes, and unstable angina) aspirin at moderate doses (160–325 mg/day) will produce rapid and immediate antiplatelet effects. In the ISIS-2 trial, a dose of 160 mg/day given within 24 hours of the onset of symptoms of heart attack was shown to decrease deaths due to heart attacks by 23%. Therefore, this is the dose recommended for acute heart attacks and unstable angina.
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