When is 100mg of aspirin (acetylsalicylic acid) used for cardiovascular event prevention?

When to Use 100mg Aspirin for Cardiovascular Prevention

Aspirin 100mg daily is primarily indicated for secondary prevention in patients with established atherosclerotic cardiovascular disease, and may be considered for primary prevention in select high-risk patients aged 40-70 years with ≥10% 10-year cardiovascular risk and low bleeding risk. 1, 2, 3

Secondary Prevention (Strong Indication)

For patients with established cardiovascular disease, aspirin 75-100mg daily is recommended as lifelong therapy and the benefits far outweigh bleeding risks. 2, 3

Specific indications include:

• Previous myocardial infarction - aspirin should be continued indefinitely after completion of dual antiplatelet therapy 2, 3
• History of coronary revascularization (PCI or CABG) 2, 3
• Significant obstructive coronary artery disease on imaging 2
• Symptomatic peripheral arterial disease - aspirin 75-160mg daily reduces major adverse cardiovascular events 1
• History of ischemic stroke or TIA 4
• Diabetes with established atherosclerotic cardiovascular disease - aspirin 75-162mg daily is recommended 1, 2

Primary Prevention (Selective Use)

High-Risk Candidates Who May Benefit

Consider aspirin 100mg daily for primary prevention only in patients aged 40-70 years with ≥10% 10-year ASCVD risk who have low bleeding risk. 2, 3 This is a Class IIb recommendation (may be considered), meaning the benefit is small. 3

Specific high-risk scenarios where aspirin may be considered:

• Diabetic patients ≥50 years with at least one additional major risk factor (family history of premature ASCVD, hypertension, dyslipidemia, smoking, or chronic kidney disease/albuminuria) who are not at increased bleeding risk 1, 2

• Hypertensive patients ≥50 years with controlled blood pressure (<150/90 mmHg) and presence of target organ damage, diabetes, or 10-year cardiovascular risk >15% 2, 3

• Women at high stroke risk - aspirin 81-100mg daily or every other day can be useful for first stroke prevention when benefits outweigh risks 1, 2

• Asymptomatic PAD with diabetes - aspirin 75-100mg may be considered in patients with ankle-brachial index abnormalities and diabetes 1

Patients Who Should NOT Receive Aspirin for Primary Prevention

Do not prescribe aspirin for primary prevention in the following situations: 1, 2, 3

• Age >70 years - bleeding risk exceeds benefit 1, 3
• Age <40 years or <50 years with diabetes and no other risk factors - low benefit outweighed by bleeding risk 1, 2, 3
• Low cardiovascular risk (<10% 10-year ASCVD risk) 1, 2, 3
• Diabetes alone without other established cardiovascular disease or additional risk factors 1
• Asymptomatic peripheral artery disease without diabetes or other high-risk features 1
• Age <21 years - contraindicated due to Reye syndrome risk 1, 2

Absolute Contraindications to Aspirin (Any Indication)

Never prescribe aspirin in patients with: 2, 3

• History of gastrointestinal bleeding or active peptic ulcer disease 2, 3
• Uncontrolled hypertension - increases bleeding risk and may attenuate cardiovascular benefits 1, 2, 3
• Concurrent anticoagulation (warfarin, DOACs) unless specific indication exists 1, 2, 3
• Thrombocytopenia or coagulopathy 3
• Concurrent chronic NSAID use - significantly increases bleeding risk 1, 2, 3
• Severe chronic kidney disease 2, 3
• Known aspirin allergy 2

Dosing Considerations

The optimal dose for both primary and secondary prevention is 75-100mg daily, with 81mg being the most common formulation in the United States. 1, 2, 3

• Doses ranging from 75-162mg daily are acceptable, but using the lowest effective dose (75-100mg) reduces bleeding risk while maintaining efficacy 1, 2, 3
• Doses above 100mg provide no additional cardiovascular benefit and may increase bleeding risk, particularly in patients on dual antiplatelet therapy 5
• The ADAPTABLE trial confirmed no difference in outcomes between 81mg and 325mg daily 2

Bleeding Risk Assessment

Before prescribing aspirin, quantify bleeding risk: 1, 2, 3

• Major gastrointestinal bleeding occurs in 2-4 per 1,000 middle-aged adults over 5 years (4-12 per 1,000 in older adults) 1, 2, 3
• Hemorrhagic stroke increases by 0-2 per 1,000 persons over 5 years 1, 2, 3
• Relative risk of major GI bleeding is 1.6 even with low doses 2
• In primary prevention, the number of cardiovascular events prevented may be similar to bleeding events induced in patients with ASCVD risk >1% per year 1

Special Populations

Peripheral Arterial Disease

For symptomatic PAD, aspirin 75-160mg daily or clopidogrel 75mg daily is recommended to reduce major adverse cardiovascular events. 1 For high ischemic risk PAD with non-high bleeding risk, combination therapy with rivaroxaban 2.5mg twice daily plus aspirin 100mg daily should be considered. 1

Post-Revascularization

Following coronary stenting, aspirin 75-100mg daily combined with clopidogrel for up to 6-12 months is the default strategy, then transition to aspirin monotherapy. 2, 3 For lower-limb revascularization in PAD, dual antiplatelet therapy for at least 1 month may be considered. 1

Aspirin Intolerance

For patients with documented aspirin allergy, clopidogrel 75mg daily is the recommended alternative. 2, 3

Common Clinical Pitfalls to Avoid

• Do not prescribe aspirin for low-risk individuals - those with <10% 10-year ASCVD risk derive minimal benefit outweighed by bleeding risk 2, 3
• Do not ignore age cutoffs - patients >70 years have greater bleeding risk than cardiovascular benefit in primary prevention 1, 3
• Do not use aspirin as monotherapy for acute coronary syndrome - dual antiplatelet therapy is required 2, 3
• Do not continue dual antiplatelet therapy indefinitely post-PCI - transition to aspirin monotherapy after 12 months unless specific indications exist 3
• Do not prescribe without assessing bleeding risk factors - always evaluate for GI bleeding history, concurrent anticoagulation, and blood pressure control 2, 3

Risk-Benefit Decision Framework

For secondary prevention: Always prescribe aspirin unless absolute contraindications exist - benefits clearly outweigh risks. 2, 3

For primary prevention: Use this algorithm: 2, 3

1. Calculate 10-year ASCVD risk
2. If risk <10% → Do not prescribe aspirin 2, 3
3. If risk ≥10% and age 40-70 years → Assess bleeding risk factors 2, 3
4. If no high bleeding risk → Consider aspirin 75-100mg daily with shared decision-making 2, 3
5. If age >70 years → Do not prescribe for primary prevention 1, 3

The European Society of Cardiology suggests a more stringent threshold: ≥2 major cardiovascular events per 100 person-years (equivalent to ≥2% annual risk) for primary prevention consideration. 6