aspirin
Brand: Bayer, Ecotrin, Bufferin
Prototype Drug
Drug Class: antiplatelet / NSAID
Drug Family: antiplatelet
Subclass: COX-1 inhibitor (irreversible antiplatelet) / salicylate
Organ Systems: cardiovascularcnsmusculoskeletal
Mechanism of Action
Irreversibly acetylates COX-1 on platelet (lifetime ~10 days); prevents thromboxane A2 formation reducing platelet aggregation; also analgesic/antipyretic/anti-inflammatory via COX inhibition.
cyclooxygenase-1 (COX-1) — irreversible acetylationCOX-2 (reversible at higher doses)
Indications
- antiplatelet (CV secondary prevention, ACS, stroke/TIA)
- pain and fever (higher doses)
- anti-inflammatory (high dose)
- Kawasaki disease
- preeclampsia prevention (low-dose)
Contraindications
- active bleeding peptic ulcer
- hemorrhagic stroke
- aspirin allergy
- children <12 with viral illness (Reye syndrome)
Adverse Effects
Common
- GI upset
- GI bleeding
- tinnitus (high doses)
- bruising
Serious
- GI hemorrhage
- Reye syndrome in children with viral illness
- salicylate toxicity (tinnitus, tachypnea, metabolic acidosis)
Pharmacokinetics (ADME)
| Absorption | 50-75% oral (varies by dose and formulation) |
| Distribution | widely distributed |
| Metabolism | deacetylation to salicylate (liver and plasma); salicylate conjugated and excreted renally |
| Excretion | renal (dose-dependent) |
| Half-life | 15-20 min (aspirin), 2-3h (salicylate) |
| Onset | 25-40 min |
| Peak | 1-2 hours (salicylate) |
| Duration | 4-6 hours |
| Protein Binding | 80-90% |
| Vd | variable |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| warfarin | additive anticoagulation and bleeding risk | major |
| NSAIDs (ibuprofen, naproxen) | ibuprofen blocks aspirin COX-1 acetylation if taken first — administer aspirin 30 min before ibuprofen | major |
| methotrexate | reduces renal clearance of methotrexate | major |
| probenecid | aspirin antagonizes uricosuric effect | moderate |
Nursing Considerations
- Low-dose (81 mg) for CV antiplatelet; high-dose (325-4000 mg) for analgesia/anti-inflammatory
- Take ibuprofen 30+ minutes AFTER aspirin to avoid COX-1 blockade interference
- Never give to children with viral illnesses (flu, varicella) — Reye syndrome risk
- GI protection: take with food; consider PPI if high GI bleeding risk
Clinical Pearls
- Irreversible COX-1 acetylation: platelets cannot synthesize new COX-1 (anucleate) — antiplatelet effect lasts platelet lifespan (7-10 days)
- Salicylate toxicity triad: tinnitus, tachypnea, metabolic acidosis with elevated anion gap and respiratory alkalosis
- Dose-dependent metabolism: low doses — first-order; high doses — zero-order (Michaelis-Menten)
Safety Profile
Pregnancy avoid
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.