Antiplatelet — COX Inhibitor Pregnancy: Low doses (up to 100 mg/day): clinical studies indicate doses up to 100 mg/day for restricted obstetrical use, which require specialised monitoring, appear safe. Doses of 100 mg/day and higher are CONTRAINDICATED during the third trimester of pregnancy (risk of premature closure of the ductus arteriosus, pulmonary hypertension, renal dysfunction with oligohydramnios, prolonged bleeding time and inhibition of uterine contractions). During the first and second trimesters acetylsalicylic acid should not be given unless clearly necessary, at the lowest dose and shortest duration. Breastfeeding: short-term use of the recommended dose does not require suspending lactation; with long-term use and/or higher doses, breastfeeding should be discontinued.

Aspirin (Antiplatelet)

Brand names: Aspirin 75 mg, Anadin

Low-dose aspirin is an oral antiplatelet agent used for the secondary prevention of cardiovascular and cerebrovascular events and in established peripheral arterial 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 - tablets swallowed with sufficient fluid (half a glass of water)

Frequency: Once daily

Max: 300 mg a day (aspirin should not be used at higher doses unless advised by a doctor, and the dose should not exceed 300 mg a day)

Source: UK SPC (eMC) section 4.2 for Aspirin 75 mg tablets (https://www.medicines.org.uk/emc/product/102206/smpc). The recommended dose is 75-160 mg once daily for each of: secondary prevention of myocardial infarction; prevention of cardiovascular morbidity in stable angina pectoris; history of unstable angina pectoris (except during the acute phase); prevention of graft occlusion after coronary artery bypass grafting (CABG); and coronary angioplasty (except during the acute phase). SECONDARY PREVENTION OF TIA AND ISCHAEMIC CVA (provided intracerebral haemorrhage has been ruled out): 75-300 mg once daily. ACUTE MYOCARDIAL INFARCTION: 'The recommended loading dose is 150-300 mg followed by a lower dose (75-160 mg) daily thereafter.' DURATION: long-term treatment with the lowest possible dose. ELDERLY: acetylsalicylic acid should be used with caution as elderly patients are more prone to adverse events (especially gastrointestinal bleeding and perforation, which may be fatal); the usual adult dose is recommended in the absence of severe renal or hepatic insufficiency, and treatment should be reviewed at regular intervals. This product is not suitable for use as an anti-inflammatory, analgesic or antipyretic. SURGERY: increased risk of haemorrhage and prolongation of bleeding time during or after surgery, even minor procedures such as tooth extraction - temporary discontinuation may be necessary. PAEDIATRIC: the SPC states acetylsalicylic acid should not be administered to children and adolescents younger than 16 years except on medical advice where the benefit outweighs the risk (acetylsalicylic acid may be a contributory factor in Reye's syndrome). Note: the openFDA record fetched for this drug is an over-the-counter analgesic low-dose aspirin label with an analgesic regimen (4 to 8 tablets every 4 hours) that is NOT an antiplatelet regimen - it must not be used for this page. The UK section 4.5 was not retrieved in this bundle - the interactions below come from the section 4.3 and 4.4 text.

Dose adjustments

Renal

Contraindicated in severe renal impairment. Use with caution in patients with moderately impaired renal function and in dehydrated patients, since use of NSAIDs may result in deterioration of renal function. In the elderly the usual adult dose is recommended in the absence of severe renal or hepatic insufficiency. No numeric renal dose reduction is stated in the SPC.

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, 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
History of gastrointestinal bleeding or perforation caused by previous NSAID therapy
Active or history of recurrent gastric and duodenal ulcer/haemorrhage, or other kinds of bleeding such as cerebrovascular haemorrhages
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 used at doses > 15 mg/week

Side effects

Dyspepsia, nausea, vomiting and diarrhoea (common)
Increased bleeding tendencies (common) - epistaxis, gingival bleeding; symptoms may persist for 4-8 days after discontinuation, with increased bleeding risk during surgical procedures
Gastrointestinal haemorrhage, overt (haematemesis, melaena) or occult, which may lead to iron deficiency anaemia; severe gastrointestinal haemorrhage and gastric or duodenal ulcers and perforation (rare)
Hypersensitivity reactions, angio-oedema, allergic oedema and anaphylactic reactions including shock (uncommon); bronchospasm and asthma attacks
Intracranial haemorrhage (uncommon); headache, vertigo, tinnitus and reduced hearing ability; impaired renal function and acute renal failure

Interactions

Methotrexate at doses > 15 mg/week - contraindicated
Anticoagulants - concomitant use enhances the risk of haemorrhage; not recommended unless strictly indicated, with close observation for signs of bleeding
Thrombolytic agents - enhanced risk of haemorrhage; concomitant use not recommended unless strictly indicated
Other antiplatelet agents - enhanced risk of haemorrhage; concomitant use not recommended unless strictly indicated
Anti-inflammatory drugs (NSAIDs) - enhanced risk of haemorrhage; also cross-hypersensitivity risk
Selective serotonin reuptake inhibitors (SSRIs) - enhanced risk of haemorrhage; concomitant use not recommended unless strictly indicated

Clinical monograph

How it works

It irreversibly inhibits platelet cyclo-oxygenase-1, blocking thromboxane A2 production and thereby platelet aggregation for the lifespan of the platelet.

Prescribing in practice

It increases the risk of gastrointestinal and other bleeding, so it is avoided in active peptic ulceration and used cautiously with other antithrombotics, considering gastroprotection where appropriate.
Avoid in known aspirin or NSAID hypersensitivity, including aspirin-exacerbated respiratory disease.
It should not be given to children and young people because of the risk of Reye's syndrome.

Monitoring

Review bleeding symptoms, gastrointestinal tolerance and ongoing indication periodically.

Counselling the patient

Take with or after food and report black stools, vomiting blood or unusual bleeding.
Do not stop abruptly without advice if prescribed for heart or vascular protection.

Evidence & guidelines

Antithrombotic trial meta-analyses confirm low-dose aspirin reduces recurrent vascular events in patients with established cardiovascular disease.

Reference: NICE NG185; AHA 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