75-160mg/day 160-325 mg/day
Therefore, survivors of heart attacks usually take daily low dose (75 mg-160 mg/d) aspirin indefinitely to prevent further heart attacks as well as strokes. Aspirin taken long-term is an important part but NOT the only measure for preventing heart attacks. The improved survival is believed to be due to aspirin's ability to quickly prevent further blood clots and the expansion of existing clots and thus limit the amount of damage to the heart's muscle. Aspirin is easy to use, safe at the low doses used for its antiplatelet action, and fast acting. Aspirin at moderate doses (160-325 mg/day) produces an antiplatelet effect rapidly (within 30 minutes). The current recommendation is to give aspirin immediately to almost all patients as soon as a heart attack is recognized at a dose of 160-325 mg/d and to continue it for one month Aspirin alone after stroke/TIA reduces the odds of a serious vascular event by 17%. 3 Antiplatelet drugs reduce the risk of not only the composite outcome of stroke, MI, and vascular death but also of each of the 3 components separately, more so for nonfatal than fatal events.  despite the fact that a high dose of aspirin (325 mg per day)but not a low dose (75 mg per day) has been shown to beeffective for prevention of stroke, 7,8 the majority of Japanesepatients with NVAF are administered a low dose of aspirin(81 mg per day). Sato et al Aspirin for Stroke Prevention in NVAF 449. bleeding was observed in 4 patients from the aspirin group(0.94%) and 2 patients from the control group (0.45%). Discussion The present study indicated that treatment with aspirin at 150to 200 mg per day did not improve the prognosis of Japanesepatients with NVAF. Among 11 000 patients with a prior stroke or TIA, aspirin therapy was associated with an event rate of 18.4% compared with a rate of 22.2% in control subjects (3-year decrease in absolute event rate of 38 events per 1000 patients).  Human trials demonstrate that low-dose aspirin is at least as effective as high-dose, but significantly less gastrotoxic. In the above-mentioned feline study, the incidence of GI side-effects with high-dose vs low-dose aspirin was 22% and 4%, respectively. Treatment failures occur with aspirin therapy; approx. 40% of human patients on aspirin therapy develop an ischemic event. There are many possible causes for this. Onset of action of these drugs is not immediate; platelet inhibition occurs by 2 days, and reaches a steady state after 5-7 days. As with aspirin, half-life is short, but the defect in platelet function persists for the life of the platelet. 1 Aspirin often is prescribed in moderate doses (160-325 mg/day) for patients who are having heart attacks to limit the extent of damage to the heart's muscle (by preventing blood clot formation in the blood vessels of the heart), prevent additional heart attacks, and improve survival. 1 Aspirin often is prescribed in low doses (75-160 mg/day) on a long-term basis to patients with prior heart attacks or strokes and to patients with TIAs (transient ischemic attacks or mini-strokes) and exertional angina to prevent heart attacks and ischemic strokes. AHA Recommendation. People at high risk of heart attack should take a daily low-dose of aspirin (if told to by their healthcare provider) and that heart attack survivors regularly take low-dose aspirin. You should not start aspirin therapy without first consulting your physician.  In this medium-risk population, the treatment of 1000 patients with aspirin for four years may prevent 51 important cardiovascular events, an absolute benefit at least 10 times greater than that obtained in the American and British doctors' trials. Indirect comparisons of the effects of starting antiplatelet treatment either preoperatively or within 24 hours after the operation indicated that the two approaches yielded similar benefits 70. The effects of doses of aspirin in the range of 100 to 160 mg daily have been studied in three trials 71-73. 1 Aspirin may be used in low dose (75-160mg/day) for prevention of heart attack or stroke in patients with risk factors of these conditions including longstanding diabetes, vascular disease (previous heart attack or stroke, or poor circulation to the legs), or angina. 1 Aspirin often is prescribed in low doses (75-160 mg/day) on a long-term basis to patients with prior heart attacks or strokes and to patients with TIAs (transient ischemic attacks or mini-strokes) and exertional angina to prevent heart attacks and ischemic strokes.
http://www.medicinenet.com/aspirin_and_antiplatelet_medications/page4.htm http://stroke.ahajournals.org/content/33/8/2137.full http://stroke.ahajournals.org/content/37/2/447.full.pdf http://circ.ahajournals.org/content/101/10/1206.full http://www.cuvs.org/pdf/article-antiplatelet-drugs.pdf http://www.medicinenet.com/aspirin_and_antiplatelet_medications/page3.htm http://www.heart.org/HEARTORG/Conditions/HeartAttack/PreventionTreatmentofHeartAttack/Aspirin-and-Heart-Disease_UCM_321714_Article.jsp http://www.nejm.org/doi/full/10.1056/NEJM199405053301808 http://www.medicinenet.com/aspirin_and_antiplatelet_medications/page3.htm
limit of aspirin dose for antiplatelet therapy