Always check with cardiologists before stopping antiplatelets post stenting
- Also called Acetylsalicylic acid, a cheap and effective antiplatelet agent and antinflammatory
- Potent inhibitor of cyclooxygenase (COX) which produce prostaglandins
- Main medical effect is inhibiting platelet cyclooxygenase
- Has a pKa of 3.5 and is rapidly absorbed from the stomach
- Main metabolite is salicylate. Renal excretion increased in alkaline urine
- Anti inflammatory: effects are based on its inhibition of prostaglandin synthesis
- Anti platelet: Irreversibly inhibits Thromboxane synthesis in platelets
- Analgesic and antipyretic
Mode of action
- Aspirin acetylates and deactivates cyclooxygenase which makes thromboxane A2
- This reaction is irreversible and if no further Aspirin is given platelet function is impaired for 10 days until a new population appears
- Aspirin also blocks endothelial COX activity but this can regenerate and so the predominant effect is on platelets
- Vascular antithrombotic dose : 75 mg OD, 81 mg OD, 300, 325 mg OD are commonly used doses. Aspirin 300 mg loading dose usually given. Higher doses not necessarily more effective.
- Ischaemic stroke: Aspirin 300 mg (US ASA 325 mg) for 14 days then 75 mg.
- ACS/stent/IHD: Aspirin 75-300 mg OD.
- Analgesic: Aspirin 300-600 mg PO every 4 hours up to 3 g per day
- Rheumatic fever: Aspirin 300-600 mg PO every 4 hours up to 3 g per day
- Rheumatic diseases e.g. ankylosing spondylitis, osteoarthritis, rheumatoid arthritis, and SLE-associated arthritis and pleurisy: Aspirin 3 g per day in divided doses
Dose range:You must check with BNF or drug datasheet
| Aspirin ||75/81 mg ||OD||PO|
| Aspirin||300/325 mg ||OD ||PO or PR|
|Aspirin ||300-600 mg ||4-6 hourly||PO|
- Peptic ulcer, GI bleed, Severe renal or hepatic disease, Known allergy
- Bleeding disorders e.g. haemophilia
- Gastric erosions, dyspepsia, peptic ulcer disease and upper GI Haemorrhage. Often treated with PPI or H2 blocker in those at increased risk of gastric side effects.
- Allergic reactions - angioedema, urticaria, Asthma, Renal toxicity
- Low dose (less than 2 g per day) increases serum uric acid
- High dose (more than 2 g per day) reduces serum uric acid
- High doses - tinnitus, vomiting, vertigo "salicylism"
- Toxicity causes hyperventilation and respiratory alkalosis and then metabolic acidosis, respiratory depression and cardiac toxicity