Unstable angina / non ST elevation myocardial infarction aspirin therapy


 * Associate Editors-in-Chief: Varun Kumar, M.B.B.S.; Lakshmi Gopalakrishnan, M.B.B.S.; Smita Kohli, M.D.

Overview of Antiplatelet Therapy in Unstable angina / NSTEMI
Antiplatelet therapy plays a major role in the management of Unstable angina/NSTEMI. This class of medication is directed towards one of the three pathways listed below:
 * Decreasing Thromboxane A2 formation(Aspirin)
 * Inhibiting the P2Y12 component of the adenosine diphosphate (ADP) receptor pathway(thienopyridines)
 * Direct inhibitors 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 ASA.

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 ED once the diagnosis of ACS is made or suspected. Aspirin therapy can also be initiated in prehospital setting when ACS is suspected.
 * For safety (e.g., gastrointestinal bleeding), a couple of large observational studies have found that the rate of bleeding appears to be lower with low-dose aspirin (75-100mg daily) as compared with high dose aspirin (325 mg daily) in patients receiving medical therapy, percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG).

Aspirin 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 a contraindication develops.
 * In patients who have an allergy or who cannot tolerate aspirin, use of clopidogrel is recommended.

==ACC / AHA Guidelines for Antiplatelet therapy in Unstable Angina/NSTEMI (DO NOT EDIT) ==

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Class I
1. Aspirin should be administered to Unstable angina/NSTEMI patients as soon as possible after hospital presentation and continued indefinitely in patients who tolerate it. (Level of Evidence: A)

2. Patients with definite Unstable angina / NSTEMI at medium or high risk and in whom an initial invasive strategy is selected should receive dual-antiplatelet therapy on presentation. (Level of Evidence: A) ASA should be initiated on presentation. (Level of Evidence: A) The choice of a second antiplatelet therapy to be added to ASA on presentation includes 1 of the following:

Before PCI:
 * Clopidogrel (Level of Evidence: B); or
 * An IV GP IIb/IIIa inhibitor. (Level of Evidence: A) IV eptifibatide or tirofiban are the preferred GP IIb/IIIa inhibitors.

At the time of PCI:
 * Clopidogrel if not started before PCI (Level of Evidence: A); or
 * Prasugrel (Level of Evidence: B); or
 * An IV GP IIb/IIIa inhibitor. (Level of Evidence: A)

3. For Unstable angina / NSTEMI patients in whom an initial invasive strategy is selected, antiplatelet therapy in addition to aspirin should be initiated before diagnostic angiography (upstream) with either clopidogrel (loading dose followed by daily maintenance dose) or an intravenous GP IIb/IIIa inhibitor. (Level of Evidence: A) Abciximab as the choice for upstream GP IIb/IIIa therapy is indicated only if there is no appreciable delay to angiography and PCI is likely to be performed; otherwise, IV eptifibatide or tirofiban is the preferred choice of GP IIb/IIIa inhibitor. (Level of Evidence: B)}}