Aspirin (Aspocid, Ezacard)

Pharmacology of aspirin
Abdelwahab Ward, BS Pharm, PharmD
Analgesic, NSAID (nonopioid), anti-inflammatory, antiplatelet, antipyretic and antirheumatic. For further information, see topic on Recommendations for safety use of NSAIDs.

  • Anti-inflammatory effect, inhibits prostaglandin biosynthesis.
  • Analgesic effect, relieves pain of mild to moderate intensity.
  • Antipyretic (lowers temperature).
  • Anti-platelet effect, inhibits thromboxane synthesis (inhibits platelet aggregation). Aspirin poisons the platelets for its remaining life (using an example patient with 250,000 platelet count). New platelets are generated at a rate of 10% per day (25,000/day for a patient with a 250,000 platelet count). By 2 days off aspirin, a patient will have 50,000 normal platelets (enough to counter bleeding). By 7 days off aspirin, a patient will have 70% or 175,000 normal platelets (typical level required for elective surgery). By 10 days off aspirin, a patient will have 100% normal platelets (level required by some clinicians for major surgery).
  • Mild to moderate pain.
  • Fever.
  • Inflammatory conditions: Rheumatic fever, rheumatoid arthritis, osteoarthritis, juvenile rheumatoid arthritis, spondyloarthropathies.
  • Reduction of risk of recurrent TIAs or stroke in patients with history of TIA due to fibrin platelet emboli or ischemic stroke.
  • Reduction of risk of death or nonfatal MI in patients with history of infarction or unstable angina pectoris or suspected acute MI.
  • Patients who have undergone revascularization procedures (e.g., coronary artery bypass graft [CABG], percutaneous transluminal coronary angioplasty [PTCA], endarterectomy).
  • Unlabeled uses: Prophylaxis against cataract formation with long-term use; prosthetic valve thromboprophylaxis, Kawasaki disease, antithrombotic therapy in children with Blalock-Taussing shunt and after Fontan procedure.
  • Use lowest appropriate dose (reduces adverse effects).
  • Anti-platelet action: Do not exceed 81 to 160 mg daily if on warfarin (Marevan).
  • Coronary artery disease.
    • Immediate myocardial infarction management: 325 mg.
    • Primary coronary disease prevention: 81 mg orally daily. As of 2018, aspirin is no longer recommended for primary prevention in most patients.
    • Tertiary prevention (post-MI): aspirin 81 mg orally daily. Similar efficacy in coronary disease prevention as the 325 mg dose. Half the risk of gastrointestinal hemorrhage as the 325 mg dose.
  • Cerebrovascular accident: Prevention in known vascular disease: 160-325 mg daily
  • Antipyretic or analgesic dose: (adult) 600 mg PO q4 hours or 650-1000 mg PO q4-6 hours.
  • Anti-inflammatory dose: (adult) 4 grams maximum per day.
  • Route: Oral, Rectal.
  • Peak: 5–120 min for oral and 4–5 hr for rectal.
  • Duration: 6–8 hr.
  • Metabolism: Hepatic (salicylate); T1/2: 15 min–12 hr.
  • Distribution: Crosses placenta; enters breast milk.
  • Excretion: Urine.
  • Gastrointestinal effects include gastrointestinal intolerance, gastrointestinal bleeding and peptic ulcer disease (Erosive Gastritis). Aspirin higher risk for peptic ulcer disease, for further information, see topic on Peptic ulcer, assessment and management.
  • Central nervous system effects (Salicylism): tinnitus, decreased hearing acuity and vertigo.
  • Central respiratory effects: hyperpnea with very high dose and respiratory depression or apnea with lethal doses.
  • Serum uric acid changes
    • Aspirin < 2 g/day: increases serum uric acid
    • Aspirin > 4 g/day: lowers serum uric acid < 2.5 mg/dL. For further information, see topic on Comparison of gout therapies. 
  • Asymptomatic hepatitis.
  • Exacerbation of renal insufficiency.
  • Hypersensitivity reaction (aspirin allergy) associated with nasal polyps and asthma.
Abdelwahab Ward, BS Pharm, PharmD