TARGET AUDIENCE: All Canadian health care professionals.
To provide information on the use of acetyl salicylic acid in the treatment and prevention of
vascular events.
abdominal aortic aneurysm
acute coronary syndrome
ankle-brachial index
acetyl salicylic acid
coronary artery bypass graft
coronary artery disease
chronic kidney disease
end stage renal disease
heart failure
non-steroidal anti-inflammatory drug
peripheral arterial disease
percutaneous coronary intervention
proton pump inhibitor
transient ischemic attack
thromboxane A2
Acetyl salicylic acid (ASA) is well-established in the treatment of acute myocardial infarction and in
the secondary prevention of cardiovascular disease among both men and women, based on large
randomized trials. The net benefit of ASA use depends on weighing the anticipated reduction in
cardiovascular events against the increased risk of gastrointestinal bleeding.
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ASA irreversibly inhibits platelet aggregation by inhibiting thromboxane A2 (TxA2) synthesis.
1. Antiplatelet therapy is strongly recommended for all patients with the following, unless
a. Cardiac:
For all patients with symptomatic coronary artery disease (CAD), including:
i. Acute coronary syndrome (ACS) patients with and without ST segment
elevation (see STEMI or NSTEMI guides)
ii. Chronic stable angina
iii. Following percutaneous coronary intervention (PCI) or saphenous vein
coronary artery bypass graft (CABG)
b. Cerebrovascular:
i. For patients with non-cardioembolic ischemic stroke or transient ischemic
attack (TIA)
ii. Following carotid endarterectomy
c. Peripheral arterial disease (PAD):
For symptomatic PAD
d. Diabetes:
For secondary prevention in patients with symptomatic cardiovascular disease
2. ASA should be considered in the following, unless contraindicated:
a. PAD patients:
i. Asymptomatic with an ankle brachial index (ABI)<0.9 at high risk because of
associated atherosclerotic risk factors in the absence of risk factors for
ii. Symptomatic without overt CAD or cerebrovascular disease, provided the
risk of bleeding is low
iii. Patients who undergo lower-extremity balloon angioplasty with or without
stenting for chronic symptomatic PAD
iv. For all infrainguinal reconstructions
v. For all patients with abdominal aortic aneurysm (AAA)
b. Primary prevention of cardiovascular morbidity and mortality:
i. In special circumstances in patients without manifest vascular disease in
whom vascular risk is considered high and bleeding risk is considered low
ii. Patients with diabetes and aged >40 years with other cardiovascular risk
factors for which ASA benefits are established and at low risk for major
c. Heart Failure:
i. In patients with heart failure (HF) of ischemic etiology, ASA should be
dictated by underlying CAD
d. Chronic Kidney Disease:
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i. Primary prevention of ischemic vascular events in patients with end stage
renal disease (ESRD) and a low risk of bleeding
ii. Secondary prevention in patients with chronic kidney disease (CKD) and
manifest vascular disease for which ASA benefits are established.
a) The usual antiplatelet dose of ASA is 81 mg daily.
b) A single initial dose of 325 mg is recommended in patients suffering an ACS event, and
then indefinite therapy with 81 mg daily.
c) An initial dose of 81 mg once daily should be utilized in patients suffering a TIA or ischemic
stroke of noncardiac indication.
d) For patients with a history of, or at risk of, gastrointestinal bleeding, co-administration of a
gastroprotective agent should be considered (i.e. proton pump inhibitor (PPI), H2
Routine laboratory monitoring is not necessary.
The most common adverse effects of ASA are bleeding into the gastrointestinal tract (which is
dose-related) as well as dyspepsia.
Patients receiving ASA and:
a) undergoing a diagnostic test,
i. associated with a low risk of bleeding, may continue ASA without interruption.
ii. associated with a high risk of bleeding, should discontinue ASA 7-10 days prior to the
iii. Patients with coronary stents deserve special consideration, and consultation with a
specialist is advised.
b) undergoing arthrocentesis, may continue ASA through the time of the procedure.
c) undergoing a minor dental, eye or skin procedure or surgery, may continue ASA around the
time of the procedure.
d) undergoing elective non-cardiac surgery should discontinue ASA 7-10 days prior to surgery if
the risk for cardiovascular events is low, but continue if cardiovascular risk is high.
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a) In patients at low risk of vascular occlusion (e.g. < 1%/yr), the small reduction of vascular
events is likely offset by bleeding complications. In those at high risk of vascular events (e.g.
> 3%/yr), the absolute benefit of ASA outweighs the harm.
b) Patients taking ASA for vascular protection should avoid the concomitant use of NSAIDs.
c) If a patient taking low-dose ASA for vascular protection requires an anti-inflammatory
agent, specific cyclooxygenase-2 inhibitors should be chosen over traditional NSAIDs.
d) ASA should be used with caution in patients with asthma or nasal polyps; in those at high
risk of bleeding or with recent major bleeding; or in patients with thrombocytopenia or
with familial or acquired bleeding disorders.
ASA may be used in infants and children with congenital or acquired heart disease or with arterial
ischemic stroke. When ASA is used for antiplatelet therapy in children, it is used in doses of 1-5
mg/kg per day. ASA should be held 1 week pre- and 6 weeks post-varicella immunization. ASA is
contraindicated with FluMist; therefore, Agriflu should be used instead. In general, depending on
the underlying etiology of the illness, a subspecialist should be consulted prior to the use of ASA in
Antithrombotic Trialists’ Collaboration. Collaborative meta-analysis of randomised trials of
antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients.
BMJ 2002;324:71-86.
Antithrombotic Trialists' (ATT) Collaboration; Baigent C, Blackwell L, Collins R, et al. Aspirin in the
primary and secondary prevention of vascular disease: collaborative meta-analysis of individual
participant data from randomised trials. Lancet 2009;373:1849-1860.
Bell AD, Roussin A, Cartier R, et al. The use of antiplatelet therapy in the outpatient setting:
Canadian Cardiovascular Society Guidelines. Can J Cardiol 2011;27(Suppl A):S1-S59.
Eikelboom JW, Hirsh J, Spencer FA, et al. Antiplatelet Drugs: Antithrombotic Therapy and
Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical
Practice Guidelines. Chest 2012;141(2 Suppl):e89S-119S.
Monagle P, Chan AK, Goldenberg NA, et al. Antithrombotic therapy in neonates and children:
Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest
Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012;141(2 Suppl):e737S-801S.
© 2013 Thrombosis Canada.
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Please note that the information contained herein is not to be interpreted as an alternative to medical
advice from your doctor or other professional healthcare provider. If you have any specific questions about
any medical matter, you should consult your doctor or other professional healthcare providers, and as such
you should never delay seeking medical advice, disregard medical advice or discontinue medical treatment
because of the information contained herein.
© 2013 Thrombosis Canada.
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