What is the recommended use of aspirin (acetylsalicylic acid) in adult patients with acute ischemic stroke, considering factors such as timing, dosage, and potential contraindications like bleeding or impaired renal function?

How to Use Aspirin in Ischemic Stroke

Immediate Administration Protocol

Administer aspirin 160-325 mg orally within 24-48 hours of stroke onset after brain imaging excludes intracranial hemorrhage. 1, 2, 3

Timing and Dosing Algorithm

• Initial dose: 160-325 mg aspirin should be given as soon as possible after CT or MRI confirms ischemic stroke and rules out hemorrhage 1
• Optimal window: Start within 48 hours of symptom onset for maximum benefit 1, 4
• Route of administration: Chew the tablet when possible for faster buccal absorption; if patient cannot swallow, use rectal suppository or nasogastric tube 3, 5, 6
• Maintenance dose: After the acute phase, transition to 75-100 mg daily for long-term secondary prevention 3

Critical Contraindications and Timing Restrictions

Do NOT give aspirin within 24 hours of IV alteplase (tPA) administration due to significantly increased bleeding risk. 1, 2, 3

• If thrombolytic therapy is administered, delay aspirin for 24 hours unless there are compelling indications 3
• Aspirin is NOT a substitute for IV tPA in eligible patients—thrombolysis takes priority 1, 2
• For patients presenting within 3 hours of symptom onset who are tPA candidates, administer tPA first (0.9 mg/kg, maximum 90 mg), then start aspirin 24 hours later 2

Evidence-Based Benefits

The recommendation is based on two landmark trials (CAST and IST) involving over 40,000 patients, demonstrating: 3, 4

• Absolute risk reduction: 13 fewer deaths or dependent patients per 1000 treated (NNT = 79) 4, 6
• Mechanism: Primary benefit comes from preventing early recurrent ischemic stroke rather than limiting initial stroke damage 1
• Safety profile: Small increase in symptomatic intracranial hemorrhage is more than offset by reduction in recurrent ischemic strokes and pulmonary emboli 4, 6

Special Populations and Considerations

For large MCA strokes: Exercise particular caution with timing due to higher hemorrhagic transformation risk—ensure imaging excludes hemorrhage and consider waiting closer to 48 hours rather than immediate administration 3

High-risk cardiac sources (mechanical heart valves, intracardiac thrombi): While aspirin is still recommended acutely, these patients may require transition to anticoagulation for long-term management, though the acute phase still favors aspirin over immediate anticoagulation 1

What NOT to Do

• Do not use urgent anticoagulation (heparin, LMWH, heparinoids) instead of aspirin—anticoagulation does NOT improve outcomes and increases bleeding risk significantly 1, 2
• Do not use clopidogrel alone or dual antiplatelet therapy (aspirin + clopidogrel) for acute large territorial strokes—this is reserved for minor strokes or high-risk TIA 1, 3
• Do not delay aspirin for patients ineligible for tPA—start immediately after imaging excludes hemorrhage 2

Monitoring Requirements

After aspirin administration: 2

• Monitor for signs of hemorrhagic transformation
• Assess for gastrointestinal bleeding
• Continue neurological assessments per standard stroke protocol

Practical Implementation

1. Confirm ischemic stroke via CT or MRI (excludes hemorrhage)
2. Determine tPA eligibility: If within 3-4.5 hours and eligible → give tPA, delay aspirin 24 hours
3. If NOT tPA candidate: Give aspirin 160-325 mg immediately (chewed if possible)
4. Continue aspirin 160-325 mg daily for first few days, then transition to 75-100 mg daily for secondary prevention 3, 5

This approach provides a small but statistically significant mortality and morbidity benefit, preventing approximately 5-13 deaths per 1000 patients treated, with Grade 1A evidence supporting this recommendation. 1, 7, 4