Antiplatelet Agent (Irreversible COX-1 Inhibitor) Pregnancy: Doses up to 100 mg/day for restricted obstetrical use (with specialised monitoring) appear safe. Doses of 100 mg/day and higher are contraindicated during the third trimester. During the first and second trimesters, do not give unless clearly necessary and keep the dose as low and duration as short as possible. Breastfeeding: short-term use of the recommended dose does not require suspending lactation; discontinue breastfeeding with long-term use and/or higher doses.

Aspirin (Low-dose Antiplatelet)

Brand names: Aspirin 75mg (various generics), Nu-Seals 75mg (enteric-coated)

Used in: Stroke & TIA

Low-dose aspirin is used as an antiplatelet agent for the secondary prevention of cardiovascular events, including after myocardial infarction, ischaemic stroke or TIA, and in established cardiovascular disease.

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: 75–160 mg

Route: Oral (swallow with sufficient fluid — half a glass of water)

Frequency: 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

Indication-specific regimens from §4.2: secondary prevention of myocardial infarction 75–160 mg once daily; prevention of cardiovascular morbidity in stable angina pectoris 75–160 mg once daily; history of unstable angina (except during the acute phase) 75–160 mg once daily; prevention of graft occlusion after CABG 75–160 mg once daily; coronary angioplasty (except during the acute phase) 75–160 mg once daily; secondary prevention of TIA and ischaemic CVA (once intracerebral haemorrhage has been ruled out) 75–300 mg once daily; acute myocardial infarction loading dose 150–300 mg followed by a lower dose (75–160 mg) daily thereafter. Duration: long-term treatment with the lowest possible dose. Elderly — the usual adult dose is recommended in the absence of severe renal or hepatic insufficiency; use with caution as elderly patients are more prone to adverse events, and review treatment at regular intervals. Paediatric population: acetylsalicylic acid should not be administered to children and adolescents younger than 16 years except on medical advice where the benefit outweighs the risk (possible contributory factor in Reye's syndrome). Increased risk of haemorrhage and prolonged bleeding time during/after surgery — temporary discontinuation may be necessary.

Dose adjustments

Renal

No dose adjustment is specified. Contraindicated in severe renal impairment. Use with caution in moderately impaired renal function and in dehydrated patients, as NSAID use may result in deterioration of renal function.

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 (asthma, rhinitis, angioedema, urticaria) to salicylates/aspirin or NSAIDs; history of asthma caused by salicylates or NSAIDs
Acute gastrointestinal ulcers; active or recurrent gastric/duodenal ulcer or haemorrhage; history of GI bleeding or perforation caused by previous NSAID therapy; other bleeding such as cerebrovascular haemorrhage
Haemorrhagic diathesis; coagulation disorders such as haemophilia and thrombocytopenia
Severe hepatic impairment
Severe renal impairment
Severe cardiac insufficiency
Doses >100 mg/day during the third trimester of pregnancy
Methotrexate at doses >15 mg/week

Side effects

Increased bleeding tendencies — epistaxis, gingival bleeding; may persist 4–8 days after discontinuation
Gastrointestinal: dyspepsia, nausea, vomiting, diarrhoea; overt or occult GI bleeding leading to iron deficiency anaemia; severe GI haemorrhage, gastric/duodenal ulcers and perforation
Hypersensitivity reactions, angio-oedema, allergic oedema, anaphylactic reactions including shock; bronchospasm and asthma attacks
Intracranial haemorrhage; headache, vertigo; reduced hearing ability and tinnitus
Thrombocytopenia, agranulocytosis, aplastic anaemia; impaired renal function and acute renal failure; Stevens-Johnson syndrome and Lyell's syndrome (rare)

Interactions

Methotrexate >15 mg/week — contraindicated
Drugs that alter haemostasis (anticoagulants, thrombolytic agents, other antiplatelet agents, anti-inflammatory drugs and SSRIs) — concomitant treatment not recommended unless strictly indicated, as risk of haemorrhage is enhanced; if unavoidable, observe closely for signs of bleeding
NSAIDs — overlapping hypersensitivity and gastrointestinal risk (see contraindications and §4.4)

Clinical monograph

How it works

At antiplatelet doses it irreversibly inhibits platelet cyclo-oxygenase-1, reducing thromboxane A2 production and thereby platelet aggregation for the lifespan of the platelet.

Prescribing in practice

The principal risk is gastrointestinal and other bleeding, which is increased by concomitant anticoagulants, other antiplatelets or NSAIDs, and by peptic ulcer history.
It is generally avoided in children and young people because of the association with Reye's syndrome.
Use cautiously in uncontrolled hypertension, asthma where aspirin sensitivity is known, and significant renal or hepatic impairment, and consider gastroprotection in those at higher GI risk.

Monitoring

No routine bloods are mandated for low-dose aspirin alone; monitor clinically for bleeding, dyspepsia and anaemia and review the indication periodically.

Counselling the patient

Take it with or after food to reduce stomach upset.
Report black stools, vomiting blood or unusual bruising or bleeding.
Do not stop it without advice, and tell clinicians and dentists you take it.

Evidence & guidelines

Low-dose aspirin has robust trial evidence for secondary cardiovascular prevention; routine use for primary prevention is no longer generally recommended owing to bleeding risk.

Reference: NICE NG185 (CVD Prevention); NICE NG133 (Hypertension in Pregnancy); ESC Antiplatelet Guidelines; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways