Aspirin 💊
⚠️ Always seek cardiology input before stopping antiplatelets after coronary stenting.
📖 About
- Aspirin (acetylsalicylic acid) is a cheap, effective antiplatelet, analgesic, antipyretic, and anti-inflammatory drug.
- Main medical use: irreversible inhibition of platelet cyclooxygenase → ↓ thromboxane A₂.
- Also acts as a non-selective COX inhibitor → ↓ prostaglandins.
- Always check the BNF link here for up-to-date guidance.
⚙️ Properties
- pKa 3.5, rapidly absorbed from the stomach and proximal small bowel.
- Metabolised to salicylate. Renal excretion ↑ in alkaline urine.
🔬 Activity
- Antiplatelet: Irreversibly inhibits platelet thromboxane A₂ synthesis (duration: life of platelet ≈ 7–10 days).
- Anti-inflammatory: via inhibition of prostaglandin synthesis.
- Analgesic & antipyretic: mild to moderate pain and fever relief.
🧩 Mode of Action
- Aspirin acetylates and irreversibly inactivates cyclooxygenase (COX-1 and COX-2).
- Endothelial COX activity can regenerate → platelet inhibition is dominant.
- Platelet inhibition lasts until new platelets are produced (≈10 days).
💊 Indications & Dosing – Aspirin (verify with BNF/datasheet)
- 🩸 Vascular antithrombotic therapy: 75–100 mg PO once daily (low-dose antiplatelet).
- 🧠 Ischaemic stroke / TIA:
- Loading: 300 mg OD × 14 days.
- Maintenance: 75 mg OD lifelong.
- ❤️ ACS / PCI:
- Loading: 300 mg (UK) / 325 mg (US).
- Maintenance: 75–100 mg PO OD lifelong (with other antiplatelets e.g. clopidogrel).
- 🤕 Analgesic / Antipyretic:
- 300–600 mg PO every 4–6 h.
- Max: 3–4 g/day.
- 🦠 Rheumatic fever / Inflammatory arthritis (rare use):
- Up to 3–4 g/day in divided doses.
- Rarely used now due to GI toxicity.
🚫 Contraindications
- Active peptic ulcer disease or recent GI bleed.
- Severe renal or hepatic impairment.
- Bleeding disorders (e.g. haemophilia).
- Children <16 years (risk of Reye’s syndrome).
- Known aspirin hypersensitivity, aspirin-exacerbated asthma.
⚠️ Side Effects
- GI: Dyspepsia, erosions, peptic ulcer, GI bleed (reduced with PPI co-prescription).
- Allergy: urticaria, angioedema, bronchospasm.
- Renal toxicity (esp. with chronic use or in CKD).
- Low doses (<2 g/day) ↑ uric acid; high doses (>2 g/day) ↓ uric acid.
- High dose salicylism: tinnitus, vertigo, nausea, vomiting.
- Overdose: respiratory alkalosis → metabolic acidosis, hyperventilation, seizures, coma, cardiovascular collapse.
🔄 Interactions
- ↑ GI bleeding with NSAIDs, corticosteroids, alcohol.
- ↑ Bleeding risk with anticoagulants (warfarin, DOACs, heparin).
- Competes with other highly protein-bound drugs (e.g. valproate, phenytoin).
- May blunt antihypertensive effects of ACE inhibitors/diuretics.
📚 References
