Section 13 · Monograph
Aspirin
Reviewed Nov 2026FDA label
Bayer / genericAntiplatelet
- Forms
- Tab: 81, 325mg | EC tab: 81, 325mg
- Dose
- Acute stroke: 160-325mg within 24-48h | Secondary prevention: 50-325mg/day
- MOA
- Irreversible COX-1 inhibition (↓thromboxane A2)
Indications
- Acute ischemic stroke and TIA (160-325mg within 24-48 hours)FDA-labeled
- Secondary prevention of stroke and myocardial infarctionFDA-labeled
- Analgesic and antipyreticFDA-labeled
Off-Label Uses
- Primary prevention of cardiovascular events (shared decision-making; not routine in older adults)Off-label
Mechanism of Action
- Irreversibly acetylates COX-1, decreasing thromboxane A2 and platelet aggregation for the platelet lifespan (7-10 days)
Full Dosing
Adult / usual
- Acute stroke: 160-325mg within 24-48 hours of onset; delay 24 hours after IV thrombolysis
- Secondary prevention: 50-325mg daily (81mg most common)
- If dysphagia: rectal 300mg suppository or per-tube administration
Contraindications
- Aspirin/NSAID hypersensitivity (asthma, urticaria)
- Active GI bleeding or peptic ulcer disease
- Children and teens with viral illness (Reye syndrome)
- Bleeding disorders; hemorrhagic stroke
Drug Interactions
- Anticoagulants, NSAIDs, SSRIs/SNRIs increase bleeding risk
- Ibuprofen may blunt aspirin's antiplatelet effect
- Increases methotrexate toxicity
- High-dose aspirin may blunt ACE inhibitor effect
Adverse Effects
- GI upset, ulcer, bleeding
- Intracranial hemorrhage
- Tinnitus (salicylism)
- Bronchospasm in aspirin-exacerbated respiratory disease
- Reye syndrome in children
Monitoring Parameters
- Signs of bleeding
- Periodic CBC
- Consider GI protection in high-risk patients
Pregnancy & Lactation
- Avoid analgesic doses in the third trimester (premature ductus closure, bleeding); low-dose aspirin is used for preeclampsia prevention under obstetric guidance
- Small amounts in milk; occasional low-dose use generally acceptable