Timing of Full-Strength Aspirin After Ischemic Stroke
Aspirin 160-325 mg should be initiated within 24-48 hours after ischemic stroke onset, immediately after brain imaging excludes intracranial hemorrhage. 1, 2
Critical Timing Algorithm
Immediate Administration (Within 24-48 Hours)
- Start aspirin 160-325 mg as soon as brain imaging (CT or MRI) excludes hemorrhagic stroke 1, 2
- Perform dysphagia screening before oral administration 2
- This early initiation prevents approximately 10 deaths and early recurrent strokes per 1,000 patients treated 3
- The number needed to treat is 79 to prevent one death or dependency 2
If Thrombolysis Was Given
- Delay aspirin for at least 24 hours after IV thrombolytic therapy 1, 4, 5
- Starting aspirin within 24 hours of thrombolysis significantly increases intracranial hemorrhage risk (Class III recommendation - harm) 1, 4
- After the 24-hour delay, initiate aspirin 160-325 mg 4, 5
Dosing Specifications
- Loading dose: 160-325 mg 2, 5, 6
- Use non-enteric coated formulation for faster buccal absorption 2
- If patient cannot swallow: use enteral tube (80-81 mg daily) or rectal suppository (325 mg daily) 2, 3
- Maintenance dose: 81-325 mg daily for long-term secondary prevention 2
Special Clinical Scenarios
Minor Stroke or High-Risk TIA
- Use dual antiplatelet therapy with higher loading doses 2
- Aspirin 160-325 mg plus clopidogrel 300-600 mg 2
- Continue dual therapy (aspirin 75-100 mg + clopidogrel 75 mg daily) for only 21-30 days 2
- Recent evidence supports dual antiplatelet initiation up to 72 hours after symptom onset with consistent benefit 7
Hemorrhagic Transformation
- For non-lobar hemorrhage with strong indications: restart aspirin at 3-7 days if clinically stable 4, 5
- For lobar hemorrhage: delay aspirin for minimum 4-6 weeks 4, 5
- High-risk features include lobar location, older age, multiple microbleeds on MRI, and apolipoprotein E ε2 or ε4 alleles 4, 5
Evidence Strength
The recommendation is based on two large trials (Chinese Acute Stroke Trial and International Stroke Trial) involving over 40,000 patients, which demonstrated that aspirin started within 48 hours reduces death or dependency with an odds ratio of 0.95 (95% CI 0.91-0.99) 6, 8. The American Heart Association/American Stroke Association provides Class I, Level of Evidence A recommendation for this practice 1. The small increase in symptomatic intracranial hemorrhage is more than offset by reductions in recurrent ischemic stroke and pulmonary embolism 6, 8.
Critical Pitfalls to Avoid
- Do not delay aspirin beyond 48 hours - maximum benefit occurs with early administration 2, 3
- Do not use aspirin as substitute for acute interventions like IV thrombolysis or mechanical thrombectomy (Class III recommendation) 1, 5
- Do not use enteric-coated formulations acutely - they delay absorption when rapid platelet inhibition is needed 2
- Do not combine aspirin with clopidogrel for acute treatment unless stroke is minor (NIHSS ≤3) 5