What is the recommended dosage for aspirin (acetylsalicylic acid) therapy?

Aspirin Dosage Recommendations

For cardiovascular disease prevention and treatment, aspirin should be dosed at 75-162 mg daily for long-term therapy, with a loading dose of 162-325 mg in acute settings requiring immediate antiplatelet effect.

Acute Settings (Loading Dose)

When immediate antiplatelet action is required, a higher loading dose is essential:

• Acute coronary syndromes: Administer 162-325 mg orally as a loading dose 1, 2, 3
• Acute ischemic stroke/TIA: Give 160-325 mg as a single loading dose after excluding intracranial hemorrhage 3
• Non-enteric coated aspirin should be chewed when possible to achieve rapid onset of antiplatelet effect 2, 3
• This loading dose applies even if the patient is already taking daily aspirin 2

Long-Term Maintenance Therapy

For chronic cardiovascular protection, lower doses are equally effective and safer:

• Optimal maintenance dose: 75-162 mg daily 1
• The most common low-dose tablet in the U.S. is 81 mg 1
• Lower doses (75-100 mg) are preferred as they minimize gastrointestinal bleeding risk while maintaining full antiplatelet efficacy 1, 2

Evidence Supporting Low-Dose Efficacy

The dose-response relationship demonstrates that lower doses are not inferior:

• Meta-analysis data show 75 mg daily produced 29.7% risk reduction in cardiovascular events, compared to 28.3% with 160-325 mg daily and only 21.4% with 500-1,500 mg daily 1
• No additional cardiovascular benefit occurs with doses above 162 mg daily 1
• The ADAPTABLE trial found no difference in cardiovascular events or major bleeding between 81 mg and 325 mg daily in patients with established cardiovascular disease 1

Clinical Context-Specific Dosing

Secondary Prevention

For patients with established cardiovascular disease (prior MI, stroke, peripheral artery disease, revascularization):

• 75-162 mg daily is recommended 1
• This applies to all forms of atherosclerotic cardiovascular disease 1

Primary Prevention

For patients without prior cardiovascular events but at increased risk:

• 75-162 mg daily for those with diabetes and additional risk factors (age >40, hypertension, smoking, dyslipidemia, family history) 1
• Not recommended for low-risk individuals aged <50 years without other major risk factors 1
• Generally not recommended for adults >70 years in primary prevention due to bleeding risk outweighing benefit 1

Peripheral Artery Disease

• 75-325 mg daily for symptomatic patients with intermittent claudication, critical limb ischemia, or prior lower extremity revascularization 1

Important Contraindications and Precautions

Absolute contraindications include:

• Aspirin allergy 1
• Active bleeding tendency or anticoagulant therapy 1
• Recent gastrointestinal bleeding 1
• Clinically active hepatic disease 1
• Age <21 years due to Reye's syndrome risk 1

Bleeding risk considerations:

• Major gastrointestinal bleeding occurs at approximately 5 per 1,000 patient-years 2
• Risk increases with dose, particularly above 325 mg daily 1, 3
• Patients with uncontrolled hypertension or concurrent NSAID/anticoagulant use have higher bleeding risk 2

Special Considerations

Combination with Other Antiplatelet Agents

• When used with ticagrelor, limit aspirin to ≤100 mg daily 3
• Dual antiplatelet therapy (aspirin plus P2Y12 inhibitor) is indicated for at least one year following acute coronary syndromes 1

Aspirin "Resistance" Concerns

• While platelet function variability exists in diabetes, no evidence supports using higher doses to overcome this 1
• The hypothesis that efficacy decreases in patients >70 kg was not validated by the ASCEND trial 1

Formulation Preferences

• Non-enteric coated formulations are preferred for acute settings 2, 3
• Enteric-coated aspirin (75 mg) is as effective as higher doses for chronic therapy and may theoretically provide more consistent thromboxane suppression when platelet turnover is rapid 1