What is the recommended dose of Aspirin (acetylsalicylic acid) for acute ischemic stroke?

Aspirin Dosing for Acute Ischemic Stroke

Administer aspirin 160-325 mg within 24-48 hours of acute ischemic stroke onset, but never within 24 hours of thrombolytic therapy. 1

Timing and Dosing Algorithm

For patients NOT receiving IV alteplase (tPA):

• Start aspirin 160-325 mg within 24-48 hours of symptom onset 1, 2
• A single loading dose of 160 mg is recommended after intracranial hemorrhage is ruled out on neuroimaging 1
• This dose range is based on two large clinical trials (IST and CAST) that established safety and efficacy using 160-300 mg 1

For patients receiving IV alteplase:

• Delay aspirin for 24 hours after thrombolytic administration due to increased bleeding risk 1, 2, 3
• The only exception: aspirin might be considered earlier if concomitant conditions exist where withholding treatment poses substantial risk 1

Route of Administration

If swallowing is impaired:

• Rectal aspirin 325 mg daily, OR 1
• Aspirin 81 mg daily via enteral tube, OR 1
• Clopidogrel 75 mg daily via enteral tube 1

Critical Contraindications

Aspirin is NOT a substitute for definitive acute stroke treatment:

• Do not use aspirin instead of IV alteplase in eligible patients (Class III: No Benefit) 1, 3
• Do not use aspirin instead of mechanical thrombectomy in eligible patients 1

Avoid aspirin in:

• Known aspirin allergy 3
• Active gastrointestinal bleeding 3

Evidence Quality and Rationale

The 2018 American Heart Association/American Stroke Association guidelines carry Class I, Level of Evidence A for aspirin administration within 24-48 hours 1, 3. The 2012 American College of Chest Physicians guidelines similarly provide Grade 1A recommendation for early aspirin therapy at 160-325 mg 1.

Why this dose range works:

• The primary benefit is reduction of early recurrent stroke, not limitation of initial stroke consequences 3
• Lower doses (75-100 mg) have similar long-term efficacy with fewer gastrointestinal side effects, but the acute phase requires higher loading doses 3
• Doses above 325 mg increase bleeding without improving efficacy 3

Common Pitfalls to Avoid

1. Never administer aspirin within 24 hours of IV alteplase - this significantly increases hemorrhagic transformation risk 1, 2, 3

2. Do not delay thrombolytic therapy to give aspirin - aspirin provides modest benefit (prevents 13 deaths or recurrent strokes per 1000 patients treated), while alteplase provides substantial benefit when given within the therapeutic window 1, 2

3. Do not use anticoagulation instead - urgent anticoagulation with heparin or low-molecular-weight heparin does NOT improve outcomes and increases bleeding risk (Grade 1A evidence against) 1, 2, 4