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Antiplatelet / ACS Pregnancy: Low-dose (75-150 mg) safe in 1st/2nd trimester for pre-eclampsia prevention and APS. AVOID in 3rd trimester — premature closure of ductus arteriosus.

Aspirin (Antiplatelet — ACS/PCI)

Brand names: Disprin, Caprin

Adult dose

Dose: ACS loading: 300 mg immediately (chewed for rapid absorption). ACS maintenance: 75 mg once daily indefinitely. Pre-PCI: 300 mg loading if not on aspirin.
Route: Oral (chewed for loading dose to speed absorption)
Frequency: Loading dose once, then 75 mg OD indefinitely
Max: 300 mg loading; 75 mg/day maintenance
Irreversible COX-1 inhibitor — blocks thromboxane A2-mediated platelet aggregation. Antiplatelet effect lasts platelet lifetime (7-10 days). Dual antiplatelet therapy (DAPT) with P2Y12 inhibitor (ticagrelor/clopidogrel) for 12 months post-ACS/PCI.

Paediatric dose

Route: Oral
Avoid in children under 16 years (Reye's syndrome risk). Kawasaki disease: 30-50 mg/kg/day in acute phase — specialist only.

Dose adjustments

Renal

75 mg OD safe in all eGFR ranges. Avoid high doses (>100 mg) in CKD (bleeding risk + fluid retention).

Hepatic

Avoid in severe hepatic impairment (coagulopathy + bleeding risk)

Clinical pearls

  • Chewing the 300 mg loading dose: absorption is significantly faster when chewed vs swallowed whole — buccal absorption bypasses hepatic first-pass. Critical in ACS where time-to-antiplatelet effect matters.
  • Aspirin resistance: up to 25% of patients have submaximal platelet inhibition on aspirin (COX-1 polymorphisms, concurrent NSAID use, poor compliance). Point-of-care platelet function tests (VerifyNow) can identify resistance.
  • Ibuprofen interaction: ibuprofen competes with aspirin for COX-1 binding, blocking aspirin's irreversible acetylation. Patients taking regular ibuprofen should take aspirin at least 30 minutes before or 8 hours after ibuprofen.
  • DAPT duration after PCI: 12 months aspirin + P2Y12 inhibitor post-ACS. Post-elective PCI: 1-6 months depending on stent type and bleeding risk. Extended DAPT (>12 months) may be considered in high-ischaemic/low-bleeding risk patients (PEGASUS-TIMI 54 trial).
  • GI protection: co-prescribe PPI (lansoprazole 15-30 mg OD or omeprazole 20 mg OD) with DAPT — reduces GI bleeding risk by ~80%. Lansoprazole preferred over omeprazole in clopidogrel-treated patients (less CYP2C19 interaction).

Contraindications

  • Active peptic ulcer (use PPI cover)
  • Haemophilia and bleeding disorders
  • Hypersensitivity to aspirin or NSAIDs (aspirin-exacerbated respiratory disease — AERD/Samter's triad)
  • Children under 16 (Reye's syndrome)
  • Third trimester pregnancy (premature closure of ductus arteriosus)

Side effects

  • GI irritation/peptic ulceration (add PPI with DAPT)
  • Bleeding (GI, intracranial)
  • Bronchospasm in aspirin-sensitive asthma (AERD — COX-1 inhibition shifts arachidonic acid to leukotriene pathway)
  • Reye's syndrome in children (<16 years)
  • Tinnitus/hyperventilation (salicylism — overdose)

Interactions

  • Other antiplatelets/anticoagulants — additive bleeding risk; PPI mandatory with DAPT
  • Ibuprofen — blocks aspirin's antiplatelet effect (competitive COX-1 binding); take aspirin 30 min before ibuprofen
  • Methotrexate — aspirin reduces methotrexate clearance; toxicity risk
  • Warfarin — additive bleeding; avoid combination without specialist indication

Monitoring

  • Signs of bleeding (GI, mucocutaneous)
  • FBC (chronic use — anaemia from occult GI blood loss)
  • Renal function (chronic use in CKD)

Reference: BNFc; BNF 90; ESC STEMI Guidelines 2023; ESC NSTE-ACS Guidelines 2020; NICE NG185 (ACS); SPC Aspirin. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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