Aspirin for treatment of ischemic strokes
Ischemic stroke is a process similar to a heart attack. In general, ischemia means injury to a tissue in the body due to lack of blood flow. Accordingly, an ischemic stroke is injury to the brain tissue due to lack of blood perfusion. This usually happens because of atherosclerosis (narrowing and hardening of the blood vessels) of the arteries in the brain. Heart attack is the ischemia of the heart caused by similar process. Another major process for ischemic stroke may be due to an embolism (a blood clot that dislodges and travels from some other location in the body) to the blood vessels in the brain stopping blood from passing through the blood vessel.
When aspirin at moderate doses (160-350 mg/d) is given to patients as soon as an ischemic stroke is recognized (usually within the first 48 hours of the onset of symptoms), survival is improved, and the risk of additional strokes is reduced. Aspirin is believed to benefit patients having acute ischemic strokes by preventing the propagation (extension or growth) of the blood clots and preventing the complete obstruction of the arteries. However, aspirin is not effective in treating or preventing hemorrhagic strokes. In fact, some studies suggest that long-term aspirin use may increase slightly the risk of developing hemorrhagic strokes.
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 this type of stroke, such as in patients with atrial fibrillation. In these patients, warfarin (Coumadin, Jantoven), 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.
What is aspirin allergy?
Allergy to aspirin is a rare condition in which a patient can develop swelling of tissues, spasm of the airways (bronchospasm) that causes difficulty breathing, and even anaphylaxis, a life-threatening condition. Clearly, patients with a history of allergy to aspirin should not take aspirin. Since aspirin is related chemically to the other NSAIDs, patients who are allergic to the other NSAIDs, such as ibuprofen (Motrin) and naproxen (Aleve), also should not take aspirin.
What drugs might interact with aspirin?
Aspirin may interact with other medications and cause undesirable side effects. For example:
- Aspirin, when taken together with an anti-coagulant such as warfarin (Coumadin) or enoxaparin (Lovenox), can greatly impair the body's ability to form blood clots, resulting in excessive bleeding spontaneously, from ulcers, or related to a procedure. Therefore, patients on such combinations must be closely monitored by a doctor.
- Aspirin can raise levels of uric acid in the blood and may need to be avoided in patients with increased uric acid levels or gout.
- Aspirin can increase the effect of medications used for lowering blood sugar levels in patients with diabetes, resulting in abnormally low blood sugar levels (hypoglycemia). Blood sugar levels may need to be more closely monitored.
- Certain NSAIDs, particularly ibuprofen (Motrin, Advil), if taken just before aspirin or in multiples doses each day, can reduce the anti-platelet effects of aspirin and theoretically render aspirin less effective in preventing heart attacks and ischemic strokes. The ibuprofen molecule is believed to adhere to the COX-1 enzyme, thus keeping aspirin from reaching the enzyme.
What can be done to reduce the risk of ulcers from long-term aspirin use?
Long-term low dose aspirin use is generally safe. An estimated 10% of the patients taking long-term aspirin (75-325 mg/day) can develop ulcers. Most of these ulcers were asymptomatic (no abdominal pain or bleeding). Patients at a higher risk of developing ulcers with low dose aspirin included elderly patients age 70 years and older, and patients with H. pylori stomach infection (see below). The risk of significant ulcer bleeding from aspirin is low (approximately 1%). One can reduce the risk of bleeding by adding a daily dose of a proton pump inhibitor (PPI) that reduces stomach acid, for example, pantoprazole (Protonix), esomeprazole (Nexium), rabeprazole (Aciphex), or lansoprazole (Prevacid, Prevacid SoluTab), and omeprazole (Prilosec, Zegerid).
Misoprostil (Cytotec) is another type of drug that prevents ulcer formation by NSAIDs. It is a prostaglandin and probably prevents the detrimental effects of NSAIDs by replacing the prostaglandins that are not produced because of the inhibition of their formation by NSAIDs.
Chronic H. pylori infection of the stomach is found in up to 30% of adults in the U.S. Patients with gastritis due to H. pylori will have a higher risk of bleeding when given aspirin or NSAIDs long-term. Eradication of H. pylori from the stomach with antibiotics can reduce the risk of bleeding from chronic aspirin use.
Buffered and coated aspirin do not seem to prevent ulcers and ulcer bleeding.
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