What is the recommended dosage of aspirin (acetylsalicylic acid) for patients with ischemic stroke?

Aspirin Dosage in Ischemic Stroke

For acute ischemic stroke, administer a loading dose of 160 mg aspirin immediately after brain imaging excludes hemorrhage, followed by 81-325 mg daily for long-term secondary prevention. 1

Acute Phase Dosing (First 48 Hours)

Loading Dose

• Administer at least 160 mg aspirin as a single loading dose immediately after:
  • Brain imaging excludes intracranial hemorrhage 1
  • Dysphagia screening is performed and passed 1
• This loading dose can range from 160-325 mg 1
• Critical timing: Give within 48 hours of symptom onset for maximum benefit 1, 2

Exception for Thrombolysis Patients

• Delay aspirin for 24 hours in patients receiving alteplase (tPA) 1
• Initiate aspirin only after the 24-hour post-thrombolysis scan excludes intracranial hemorrhage 1

Special Populations: Minor Stroke and High-Risk TIA

For minor stroke (NIHSS ≤3-5) or high-risk TIA (ABCD2 ≥4), use dual antiplatelet therapy with higher loading doses:

Loading Doses for Dual Therapy

• Aspirin: 160-325 mg loading dose 1
• Clopidogrel: 300-600 mg loading dose (300 mg per CHANCE trial, 600 mg per POINT trial) 1

Maintenance Dual Therapy

• Aspirin 75-100 mg daily PLUS clopidogrel 75 mg daily 1
• Continue for 21-30 days only (not 90 days due to increased bleeding risk) 1
• Start within 24 hours of symptom onset, ideally within 12 hours 1
• Then switch to monotherapy (aspirin 81 mg daily OR clopidogrel 75 mg daily) 1

Long-Term Maintenance Dosing

Continue aspirin 81-325 mg daily indefinitely for secondary stroke prevention 1

Dosing Options

• The most commonly recommended range is 81-325 mg daily 1
• Lower doses (75-100 mg) are effective for long-term prevention 1
• No clear superiority of higher versus lower doses for long-term prevention, but lower doses have fewer gastrointestinal side effects 3, 4

Alternative Routes for Dysphagia

When oral administration is not possible:

• Enteral tube: 80-81 mg daily 1
• Rectal suppository: 325 mg daily 1

Clinical Reasoning

The 160 mg loading dose recommendation is based on large trials (IST and CAST) showing that early aspirin reduces:

• Early recurrent ischemic stroke by 7 fewer strokes per 1000 patients treated 2
• Death or dependency by 13 fewer patients per 1000 treated 2
• Overall mortality 1, 2

Key pitfall to avoid: Do not use aspirin doses below 160 mg for acute stroke treatment, as lower doses (50-100 mg) have not been proven effective in the acute setting 5, 4. The acute phase requires higher doses than chronic prevention 4.

The shift to dual antiplatelet therapy for minor strokes is based on the CHANCE and POINT trials, which demonstrated that 15 ischemic strokes are prevented per 1000 patients treated, though at the cost of 5 major hemorrhages per 1000 patients when continued for 90 days—hence the recommendation to limit dual therapy to 21-30 days 1.