Unstable angina non ST elevation myocardial infarction aspirin therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-in-Chief: Varun Kumar, M.B.B.S.; Lakshmi Gopalakrishnan, M.B.B.S.; Smita Kohli, M.D.

Overview

Antiplatelet therapy plays a major role in the management of unstable angina/NSTEMI. This class of medication is directed towards one of the following three pathways: decreasing thromboxane A2 formation (aspirin), inhibiting the P2Y12 component of the adenosine diphosphate (ADP) receptor pathway (thienopyridines) and direct inhibition of platelet aggregation (GP IIb/IIIa inhibitors).

Aspirin

Mechanism of Benefit

• One of the medications which has consistently been shown to reduce mortality in ACS or CAD patients is aspirin.

Clinical Trial Data

Until recently, no trial had directly compared the efficacy of different doses of ASA in patients who present with unstable angina/NSTEMI.

• CURRENT OASIS 7 trial, which was a randomized, multicenter, multinational trial enrolling 25,087 patients with ACS showed no difference in cardiovascular outcomes of death from MI or stroke between low dose aspirin (75-100mg) compared to high dose aspirin (300-325mg) at the end of 30 days.
• The Second International Study of Infarct Survival (ISIS-2) trial led to the recommendation that ASA be initiated immediately in the emergency room once the diagnosis of ACS is made or suspected. Aspirin therapy can also be initiated in the prehospital setting when ACS is suspected.
• In regards to safety (e.g., gastrointestinal bleeding), a few large observational studies have found that the rate of bleeding appears to be lower with low-dose aspirin (75-100mg daily) when compared with high dose aspirin (325 mg daily) in patients receiving medical therapy, percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG).

Dosing

• Non enteric coated formulations are preferred due to rapid buccal absorption.
• On the basis of previous randomized trials, the current recommendation for initial dose of aspirin is 162-325mg.
• After an initial loading dose of 162 to 325 mg, a dose of 75 to 100mg daily appears sufficient.
• On the basis of current available data, lifelong continuation of aspirin should be encouraged unless contraindicated.
• In patients who have an allergy or who cannot tolerate aspirin, use of clopidogrel is recommended.