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Antiplatelet / NSAID / Antipyretic / Analgesic

Aspirin

Brand names: Disprin, Nu-Seals, Micropirin

Adult dose

Dose: Antiplatelet (ACS, secondary prevention): 75 mg once daily; loading dose ACS: 300 mg. Acute ischaemic stroke/TIA: 300 mg for 2 weeks then 75 mg. Analgesia/pyrexia: 300–900 mg every 4–6 hours (max 4 g/day)
Route: Oral
Frequency: Antiplatelet: once daily; Analgesia: every 4–6 hours

Clinical pearls

  • Aspirin irreversibly inhibits cyclooxygenase-1 (and -2), preventing thromboxane A2 synthesis and platelet aggregation — effect lasts platelet lifetime (~7–10 days)
  • NICE NG185 (ACS): dual antiplatelet therapy (aspirin + P2Y12 inhibitor) for up to 12 months post-ACS
  • NICE NG128 (Stroke): aspirin 300 mg for 2 weeks following ischaemic stroke, then clopidogrel 75 mg long-term
  • GI protection: PPI co-prescription recommended in high-risk patients (>60 years, history of peptic ulcer, on steroids/anticoagulants)
  • Low-dose aspirin (75 mg) has minimal analgesic effect — not appropriate for pain management at this dose
  • Primary prevention: aspirin no longer generally recommended (ASCEND, ASPREE trials — bleeding outweighs benefit in low-risk individuals)

Contraindications

  • Active peptic ulcer
  • Aspirin hypersensitivity (aspirin-exacerbated respiratory disease — aspirin-induced asthma/urticaria)
  • Haemophilia or other bleeding disorders
  • Children under 16 years (Reye's syndrome risk) — except under specialist supervision (Kawasaki disease)
  • Severe hepatic or renal impairment
  • Pregnancy (third trimester — risk of premature closure of ductus arteriosus)

Side effects

  • GI irritation, peptic ulceration, haemorrhage
  • Prolonged bleeding time
  • Bronchospasm (aspirin-exacerbated respiratory disease)
  • Tinnitus and hearing loss (salicylate toxicity)
  • Renal impairment (prostaglandin-mediated; high doses)
  • Reye's syndrome in children with viral illness

Interactions

  • Anticoagulants (warfarin, NOACs) — increased bleeding risk; combination sometimes intentional (post-ACS) — must use PPI cover
  • Other NSAIDs — additive GI toxicity
  • SSRIs — additive bleeding risk
  • Methotrexate — aspirin reduces renal excretion; toxicity risk (avoid unless monitored)
  • Valproate — aspirin displaces valproate from protein binding

Monitoring

  • FBC and renal function if long-term use
  • GI symptoms (review PPI co-prescription)
  • Salicylate levels in suspected toxicity
  • Bleeding signs

Reference: BNF; NICE NG185 (ACS, 2020); NICE NG128 (Stroke, 2022); NICE NG17 (Headaches); ESC Guidelines on ACS (2023); ASCEND trial (NEJM 2018); https://bnf.nice.org.uk/drugs/aspirin/. Verify against your local formulary and the latest BNF before prescribing.

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