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Antiplatelet / ACS Pregnancy: Doses up to 100 mg/day for restricted obstetrical use, which require specialised monitoring, appear safe in clinical studies. During the first and second trimester acetylsalicylic acid should not be given unless clearly necessary, and if used the dose should be kept as low and the duration as short as possible. Doses of 100 mg/day and higher are contraindicated during the third trimester. Breastfeeding: low quantities are excreted into breast milk; short-term use of the recommended dose does not require suspending lactation, but breastfeeding should be discontinued with long-term use and/or higher doses.

Aspirin (Antiplatelet — ACS/PCI)

Brand names: Disprin, Caprin

Used in: Acute Coronary Syndrome & Chest Pain Stroke & TIA

Low-dose aspirin is an antiplatelet used in acute coronary syndromes and for long-term secondary prevention of cardiovascular events; it is not used for routine primary prevention because the bleeding risk usually outweighs benefit.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Acute myocardial infarction: loading dose 150-300 mg, followed by a lower dose (75-160 mg) once daily thereafter
Route: Oral - tablets swallowed with sufficient fluid (half a glass of water)
Frequency: Loading dose once, then once daily
Max: The dose should not exceed 300 mg a day; aspirin should not be used at higher doses unless advised by a doctor
Regimens in the same SPC that are relevant to this page: coronary angioplasty, except during the acute phase - 75-160 mg once daily; history of unstable angina pectoris, except during the acute phase - 75-160 mg once daily; prevention of graft occlusion after coronary artery bypass grafting - 75-160 mg once daily; prevention of cardiovascular morbidity in stable angina pectoris - 75-160 mg once daily; secondary prevention of myocardial infarction - 75-160 mg once daily; secondary prevention of transient ischaemic attack and ischaemic cerebrovascular accident, provided intracerebral haemorrhage has been ruled out - 75-300 mg once daily. IMPORTANT SCOPE LIMIT: the SPC gives no separate peri-procedural loading dose for PCI and explicitly excludes the acute phase from the coronary angioplasty and unstable angina regimens above - a peri-procedural/acute-phase antiplatelet loading regimen must be sourced from national or interventional-cardiology guidance, not from this SPC. Duration: long-term treatment with the lowest possible dose. ELDERLY: use with caution as elderly patients are more prone to adverse events; the usual adult dose is recommended in the absence of severe renal or hepatic insufficiency, with treatment reviewed at regular intervals. PAEDIATRIC (not per kg, so not carried in paedDose): acetylsalicylic acid should not be administered to children and adolescents younger than 16 years except on medical advice where the benefit outweighs the risk (Reye's syndrome association). Increased risk of haemorrhage and prolonged bleeding time during or after surgery, even minor procedures - temporary discontinuation may be necessary. SPC section 4.4 states 'Aspirin is not suitable for use as an anti-inflammatory, analgesic or antipyretic.' The US openFDA label captured in the bundle is an over-the-counter analgesic product ('take 4 to 8 tablets every 4 hours, not to exceed 48 tablets in 24 hours') - a different indication and dose range entirely, and not used here.

Dose adjustments

Renal

Severe renal impairment is a contraindication. Use with caution in patients with moderately impaired renal function or in dehydrated patients, since NSAID use may result in deterioration of renal function. No numeric renal dose adjustment is stated in the source.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Previous hypersensitivity reactions (e.g. asthma, rhinitis, angioedema or urticaria) to salicylates/aspirin or other substances with a similar mechanism of action, especially NSAIDs; a history of asthma caused by salicylates or NSAIDs
  • Acute gastrointestinal ulcers; active or a history of recurrent gastric and duodenal ulcer/haemorrhage with proven ulceration or bleeding; a history of gastrointestinal bleeding or perforation caused by previous NSAID therapy; other kinds of bleeding such as cerebrovascular haemorrhage
  • Haemorrhagic diathesis; coagulation disorders such as haemophilia and thrombocytopenia
  • Severe hepatic impairment; severe renal impairment; severe cardiac insufficiency
  • Doses greater than 100 mg/day during the third trimester of pregnancy
  • Methotrexate used at doses greater than 15 mg/week

Side effects

  • Increased bleeding tendencies; bleeding with prolonged bleeding time such as epistaxis and gingival bleeding, which may persist for 4-8 days after discontinuation, with increased bleeding risk during surgical procedures
  • Overt (haematemesis, melaena) or occult gastrointestinal bleeding which may lead to iron deficiency anaemia; severe gastrointestinal haemorrhage; gastric or duodenal ulcers and perforation
  • Dyspepsia, nausea, vomiting and diarrhoea
  • Hypersensitivity reactions, angio-oedema, allergic oedema and anaphylactic reactions including shock; bronchospasm and asthma attacks
  • Intracranial haemorrhage; headache and vertigo; reduced hearing ability and tinnitus

Interactions

  • Methotrexate at doses greater than 15 mg/week - contraindicated (section 4.3)
  • Drugs that alter haemostasis - anticoagulants, thrombolytic agents, antiplatelet agents, anti-inflammatory drugs and selective serotonin reuptake inhibitors: concomitant treatment is not recommended unless strictly indicated because they may enhance the risk of haemorrhage; if the combination cannot be avoided, close observation for signs of bleeding is recommended (section 4.4)
  • Anticoagulant therapy - aspirin is to be used with caution in patients undergoing therapy with anticoagulants (section 4.4)
  • NOTE: SPC section 4.5 was not captured in this bundle; the entries above are those stated within sections 4.3 and 4.4 - the full interaction section must be checked against the SPC

Clinical monograph

How it works

Aspirin irreversibly acetylates cyclo-oxygenase-1 in platelets, blocking thromboxane A2 production and platelet aggregation for the platelet's lifespan.

Prescribing in practice

  • A higher loading dose is given in ACS, followed by a low maintenance dose.
  • Gastrointestinal bleeding risk rises with age and with other antithrombotics, NSAIDs or steroids; consider gastroprotection in higher-risk patients.
  • Avoid in active peptic ulceration and in children (Reye's syndrome risk), and use caution in aspirin-sensitive asthma.

Monitoring

No routine monitoring; review for dyspepsia or bleeding, particularly in older patients and with co-prescribed antithrombotics.

Counselling the patient

  • Take it with or after food.
  • Report black stools, vomiting blood, or persistent indigestion.
  • Do not stop suddenly after a cardiac event without advice.

Evidence & guidelines

Aspirin is standard in ACS and long-term secondary prevention; routine primary-prevention use is no longer recommended for most people.

Reference: ESC STEMI Guidelines 2023; ESC NSTE-ACS Guidelines 2020; NICE NG185 (ACS); SPC Aspirin; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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