What are the indications for aspirin (acetylsalicylic acid) therapy?

Indications for Aspirin Therapy

Aspirin is primarily indicated for secondary prevention of cardiovascular events in patients with established cardiovascular disease, while its role in primary prevention should be limited to select high-risk individuals with favorable risk-benefit profiles. 1

Secondary Prevention Indications

Aspirin therapy at 75-100 mg daily is strongly recommended for:

• Patients with previous myocardial infarction (MI) or coronary revascularization 1
• Patients with documented coronary artery disease (CAD) on imaging 1
• Patients with history of ischemic stroke or transient ischemic attack 1
• Patients with polycythemia vera 1
• Patients with diabetes who have established atherosclerotic cardiovascular disease (ASCVD) 1

Primary Prevention Indications

For primary prevention, aspirin should be considered more selectively:

• Adults at high cardiovascular risk (5-year risk ≥3% or 10-year risk ≥10%) without increased bleeding risk 1
• Adults with diabetes aged ≥50 years with at least one additional major cardiovascular risk factor (family history of premature ASCVD, hypertension, dyslipidemia, smoking, or chronic kidney disease/albuminuria) 1
• Men over age 40, postmenopausal women, and younger persons with risk factors for coronary heart disease 1

Contraindications and Special Considerations

• Not recommended for primary prevention in adults over 70 years due to increased bleeding risk 1
• Not recommended for low-risk individuals (such as those under 50 years with no major risk factors) 1
• Contraindicated in patients under 21 years due to risk of Reye syndrome 1
• Contraindicated in patients with history of aspirin allergy (clopidogrel 75 mg daily is recommended as an alternative) 1
• Use caution in patients with uncontrolled hypertension or concomitant use of other NSAIDs or anticoagulants due to increased bleeding risk 1

Dosing Recommendations

• Secondary prevention: 75-100 mg daily 1
• Primary prevention: 75-100 mg daily 1
• Acute coronary syndrome: Initial loading dose of 162-325 mg, followed by 75-100 mg daily maintenance 1
• Acute ischemic stroke: Initial dose of 160-325 mg 1

Risk-Benefit Assessment Algorithm

1. Assess cardiovascular risk:

   • Calculate 5-year or 10-year cardiovascular risk using validated tools
   • Identify risk factors: age, sex, diabetes, elevated cholesterol, low HDL, hypertension, family history, smoking

2. Assess bleeding risk:

   • Age >70 years
   • History of GI bleeding or peptic ulcer disease
   • Concurrent use of anticoagulants or NSAIDs
   • Uncontrolled hypertension
   • Renal disease or anemia

3. Decision making:

   • High CV risk (≥3% 5-year risk) + Low bleeding risk → Aspirin recommended
   • Moderate CV risk + Low bleeding risk → Consider aspirin based on individual factors
   • Low CV risk OR High bleeding risk → Aspirin not recommended
   • Established ASCVD → Aspirin strongly recommended regardless of bleeding risk (unless absolute contraindication)

Common Pitfalls and Caveats

• Overuse in low-risk patients: The modest benefit of aspirin in primary prevention may not outweigh bleeding risks in low-risk individuals 1
• Enteric-coated formulations: Do not clearly reduce adverse gastrointestinal effects and may have lower bioavailability 1
• Dose confusion: Higher doses (>100 mg daily) do not provide additional cardiovascular protection but increase bleeding risk 1
• Discontinuation risk: Abrupt discontinuation of aspirin in patients with established cardiovascular disease can trigger rebound thrombotic events
• Underuse in secondary prevention: Despite strong evidence, aspirin remains underutilized in patients with established cardiovascular disease who would benefit most

The evidence clearly demonstrates that aspirin's benefit-to-risk ratio is most favorable in secondary prevention settings, where the reduction in cardiovascular events significantly outweighs the increased risk of bleeding 1. For primary prevention, a more selective approach is warranted, targeting those at higher cardiovascular risk without significant bleeding risk factors 1.