From the Guidelines
The loading dose of aspirin (acetylsalicylic acid) should be 162-325 mg, administered as soon as possible, in patients with acute coronary syndromes (ACS) without an absolute contraindication. This recommendation is based on the most recent and highest quality study, the 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline for the management of patients with acute coronary syndromes 1. The guideline suggests that an initial oral loading dose of aspirin, followed by daily low-dose aspirin, is recommended to reduce death and major adverse cardiac events (MACE) in patients with ACS.
The loading dose of 162-325 mg is recommended to achieve rapid platelet inhibition in emergency situations, and patients should chew the tablet rather than swallow it whole to speed absorption, as stated in the 2025 guideline 1. After the loading dose, patients are usually maintained on a lower daily dose of 75-100 mg for long-term therapy.
It is essential to note that the loading dose works by quickly inhibiting cyclooxygenase-1 (COX-1) enzymes in platelets, preventing thromboxane A2 production and reducing platelet aggregation. This rapid antiplatelet effect is crucial in the first hours of treatment for conditions like heart attack or stroke where preventing further clot formation is essential. Patients with known aspirin allergy, active bleeding, or severe liver disease should not receive aspirin loading doses without specialist consultation.
Key points to consider when administering the loading dose of aspirin include:
- The dose should be 162-325 mg, as recommended by the 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline 1
- The tablet should be chewed rather than swallowed whole to speed absorption, as stated in the 2025 guideline 1
- The loading dose should be administered as soon as possible in patients with ACS without an absolute contraindication
- Patients should be maintained on a lower daily dose of 75-100 mg for long-term therapy after the loading dose.
From the Research
Aspirin Loading Dose
The loading dose of aspirin, also known as acetylsalicylic acid, is a topic of interest in the context of treating acute myocardial infarction and other cardiovascular diseases.
- The optimal dose of aspirin for patients presenting with acute myocardial infarction while receiving chronic aspirin therapy has not been clearly established 2.
- A study published in the Journal Platelets in 2014 found that a loading dose of 200-500 mg of aspirin reduced thromboxane A2-dependent platelet reactivity in patients with acute myocardial infarction 2.
- Another study published in Annales de cardiologie et d'angeiologie in 1995 suggested that a higher dose of 500 mg to 1 g of aspirin would have the advantage of more rapidly and more completely blocking platelets during an acute thrombotic phase 3.
- The American journal of cardiovascular drugs published a study in 2004 which stated that for patients with ischemic heart disease, the overall consensus defines a range between 75 and 160 mg/day for the secondary prevention of myocardial infarction, stroke, and vascular death 4.
- A study published in the Journal of cardiovascular pharmacology and therapeutics in 2006 found that in acute myocardial infarction and during acute occlusive stroke, a loading dose of 162.5 to 325 mg is necessary to achieve a rapid clinical antithrombotic effect 5.
Key Findings
- The loading dose of aspirin can range from 162.5 mg to 500 mg, depending on the specific clinical context and patient population 2, 3, 5.
- Higher doses of aspirin may be required in some patients to achieve desired antithrombotic effects, particularly in those with aspirin-resistant populations 4.
- The optimal aspirin dose remains uncertain, and further research is needed to determine the most effective dose for different patient populations and clinical scenarios 2, 4.