What is the recommended daily dose of aspirin (acetylsalicylic acid) for stroke prevention?

Aspirin Dosage for Stroke Prevention

For primary stroke prevention, use aspirin 81 mg daily in women over 65 years with controlled blood pressure and cardiovascular risk factors; for secondary prevention after ischemic stroke or TIA, administer a loading dose of 160-325 mg followed by 81 mg daily maintenance therapy. 1, 2

Primary Prevention Dosing

Women at High Risk

• Aspirin 81 mg daily or 100 mg every other day is recommended for women over 65 years of age when blood pressure is controlled and the 10-year cardiovascular risk exceeds 6-10%, as the benefit for ischemic stroke prevention outweighs bleeding risks 3, 2
• Women with hypertension, hyperlipidemia, diabetes, or 10-year cardiovascular risk ≥10% derive the most consistent benefit from aspirin therapy 3

Men and General Population

• Aspirin 75-81 mg daily is reasonable for cardiovascular prophylaxis (including stroke prevention) in persons with 10-year cardiovascular risk >10%, though the primary benefit in men is reduction of myocardial infarction rather than stroke 3
• The US Preventive Services Task Force supports doses as low as 75 mg daily for cardiovascular prophylaxis 3

When NOT to Use Aspirin for Primary Prevention

• Do not use aspirin in low-risk individuals (10-year cardiovascular risk <6%) as risks outweigh benefits 3, 2
• Aspirin is not useful for primary stroke prevention in patients with diabetes alone or diabetes plus asymptomatic peripheral artery disease (ankle-brachial index ≤0.99) without other established cardiovascular disease 3, 2

Secondary Prevention Dosing (After Stroke or TIA)

Acute Phase Loading Dose

• Administer aspirin 160-325 mg as a single loading dose immediately after intracranial hemorrhage is ruled out on neuroimaging 1
• This loading dose ensures rapid and complete inhibition of thromboxane A2-dependent platelet aggregation 1
• For patients unable to swallow, use rectal aspirin 325 mg daily or aspirin 81 mg daily via enteral tube 1
• Avoid enteric-coated aspirin for loading doses due to slower onset of action 1

Maintenance Therapy

• Continue with aspirin 81 mg daily for long-term secondary prevention after the acute phase 1
• For patients with minor ischemic stroke or high-risk TIA, consider dual antiplatelet therapy (DAPT) with aspirin 81 mg daily plus clopidogrel 75 mg daily for 21 days, then transition to single antiplatelet therapy 1, 4

Dual Antiplatelet Therapy (DAPT) Protocol

• Loading: aspirin 160-325 mg PLUS clopidogrel 300-600 mg within 12-24 hours of symptom onset after excluding hemorrhage 1, 4
• Maintenance: aspirin 81 mg daily PLUS clopidogrel 75 mg daily for 21 days, then single antiplatelet therapy 1, 4
• The clopidogrel loading dose is critical because standard 75 mg daily dosing takes approximately 5 days to achieve maximal platelet inhibition 1, 4

Dose-Response Considerations

Lower doses (75-100 mg daily) are as effective as higher doses (975-1000 mg daily) for stroke prevention while causing significantly less gastrointestinal bleeding 5, 6. However, context matters:

• For acute ischemic stroke treatment: 160-325 mg required 7
• For atrial fibrillation stroke prevention: 325 mg daily required 7
• For carotid arterial disease: 81-325 mg daily 7
• For stable coronary artery disease: 75 mg daily minimum 8
• For history of stroke/TIA: 50 mg daily proven effective 8

Critical Safety Considerations

• Always rule out intracranial hemorrhage on neuroimaging before administering aspirin 1, 4
• Gastrointestinal bleeding risk increases with dose: 0.06% per year with aspirin versus 0.05% per year with placebo (number needed to harm = 10,000) 3
• The risk of major bleeding with 160 mg daily equals that of 80 mg daily (1-2 cases per 1000 patient-years), and fatal bleeding risk is identical 8
• In patients receiving dual antiplatelet therapy with clopidogrel, aspirin doses >100 mg may reduce efficacy and increase bleeding risk 9

Common Pitfalls to Avoid

• Do not combine aspirin with clopidogrel for primary stroke prevention unless specific indications exist, as this increases bleeding without additional benefit 2
• Do not increase aspirin dose in patients who experience ischemic events while on aspirin, as higher doses have not shown additional benefit 2
• Do not use low doses (<100 mg daily) for primary prevention in women, as these have been ineffective; the appropriate dose must exceed 100 mg daily 8
• Do not prescribe aspirin for primary stroke prevention in men based on current evidence, as it has not been proven effective for this specific indication 7