What is the initial dose of aspirin (acetylsalicylic acid) for acute myocardial infarction (AMI)?

From the Guidelines

The initial dose of aspirin for acute myocardial infarction (AMI) should be 162-325 mg, administered as soon as possible after symptom onset. Specifically:

• Chew and swallow 162-325 mg of non–enteric-coated aspirin formulation immediately to achieve rapid absorption, as recommended by the American College of Cardiology/American Heart Association task force on performance measures 1.
• If available, use chewable aspirin for faster absorption.
• Continue with a daily maintenance dose of 81-mg thereafter to minimize bleeding risk, as suggested by the 2017 AHA/ACC clinical performance and quality measures for adults with ST-elevation and non-ST-elevation myocardial infarction 1. This high initial dose rapidly inhibits platelet aggregation by inhibiting the formation of thromboxane A2, a potent stimulator of platelet aggregation, helping to prevent further clot formation in the coronary arteries. Aspirin therapy administered within the first 24 h after acute STEMI resulted in a 23% relative risk reduction in 5-week vascular mortality, as well as significant reductions in the incidence of non-fatal reinfarction and stroke, as reported in the 2017 AHA/ACC clinical performance and quality measures for adults with ST-elevation and non-ST-elevation myocardial infarction 1. Aspirin should be given regardless of whether the patient will undergo primary percutaneous coronary intervention (PCI) or receive fibrinolytic therapy, unless there is a clear contraindication such as active bleeding or known aspirin allergy.

From the Research

Initial Dose of Aspirin for Acute Myocardial Infarction (AMI)

The initial dose of aspirin for acute myocardial infarction (AMI) is a crucial aspect of treatment. According to the available evidence:

• A study published in 1995 2 suggests that a high initial dose of aspirin, such as 500 mg to 1 g, may be beneficial in the acute phase of myocardial infarction.
• Another study from 2002 3 recommends a loading dose of 160 mg to 325 mg aspirin during an acute MI.
• A study published in 2008 4 compared the outcomes of ST-elevation myocardial infarction patients treated with fibrinolytic therapy who received an initial aspirin dose of 162 mg versus 325 mg, and found that the lower dose may be as effective and safer.
• A study from 1995 5 recommends a loading dose of 160-325 mg aspirin, followed by 80 mg/day.

Key Findings

• The optimal initial dose of aspirin for AMI is not clearly established, but doses ranging from 160 mg to 325 mg are commonly recommended.
• Higher doses, such as 500 mg to 1 g, may be beneficial in the acute phase, but may also increase the risk of bleeding.
• Lower doses, such as 75 mg to 150 mg, may be as effective as higher doses for long-term treatment, but the effects of doses < 75 mg daily are less certain.

Aspirin Dosing Considerations

• The choice of initial aspirin dose should be individualized based on the patient's specific clinical situation and risk factors.
• The dose of aspirin should be adjusted based on the patient's response to treatment and the presence of any adverse effects.
• Aspirin should be used in conjunction with other evidence-based treatments for AMI, such as fibrinolytic therapy and antiplatelet agents.