Antiplatelet Pregnancy: Low doses (up to 100 mg/day) for restricted obstetrical use, which require specialised monitoring, appear safe. There is insufficient clinical experience with doses of 100-500 mg/day, so the recommendations for 500 mg/day and above apply to that range too. 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. Acetylsalicylic acid at doses of 100 mg/day and higher is CONTRAINDICATED during the third trimester (risks include premature closure of the ductus arteriosus, pulmonary hypertension, foetal renal dysfunction with oligohydramnios, prolonged bleeding time in mother and neonate, and delayed or prolonged labour). Breastfeeding: low quantities of salicylates 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

Brand names: Aspirin, Nu-Seals

Aspirin (acetylsalicylic acid) is an antiplatelet agent used in the acute treatment and secondary prevention of ischaemic stroke and transient ischaemic attack.

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: 75-300 mg once daily (secondary prevention of transient ischaemic attacks (TIA) and ischaemic cerebrovascular accidents (CVA), provided intracerebral haemorrhages have been ruled out)

Route: Oral - the tablets should be swallowed with sufficient fluid (half a glass of water)

Frequency: Once daily

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

PRODUCT: Aspirin 75 mg tablets (UK SPC) - a low-dose antiplatelet product. The dose above is the SPC's own cerebrovascular indication. OTHER LICENSED INDICATIONS in the same SPC, all 75-160 mg once daily: 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); coronary angioplasty (except during the acute phase). ACUTE MYOCARDIAL INFARCTION: recommended loading dose 150-300 mg followed by a lower dose (75-160 mg) daily thereafter. NOTE ON ACUTE STROKE: this SPC gives an acute loading dose only for acute myocardial infarction; it states no separate acute-phase / hyperacute loading regimen for ischaemic stroke or TIA, covering secondary prevention only - a clinician must source any hyperacute stroke loading dose separately. DURATION: long-term treatment with the lowest possible dose. ELDERLY: acetylsalicylic acid should be used with caution in elderly patients, who are more prone to adverse events; the usual adult dose is recommended in the absence of severe renal or hepatic insufficiency, and treatment should be reviewed at regular intervals. PAEDIATRIC: 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 the causation of Reye's Syndrome in some children. PERI-OPERATIVE: increased risk of haemorrhage and prolongation of bleeding time during or after surgery, including minor procedures such as tooth extraction; temporary discontinuation may be necessary. This product is not suitable for use as an anti-inflammatory, analgesic or antipyretic. INTERACTIONS CAVEAT: SPC section 4.5 was not included in this source bundle - the interaction entries below are taken from statements made in sections 4.3 and 4.4 only, and section 4.5 should be reviewed in full.

Dose adjustments

Renal

Contraindicated in severe renal impairment. Use with caution in patients with moderately impaired renal function, and in patients who are dehydrated, since use of NSAIDs may result in deterioration of renal function. No dose-reduction schedule is given 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 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 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 haemorrhages
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 (common); bleeding with prolonged bleeding time such as epistaxis and gingival bleeding, which may persist for 4-8 days after discontinuation, with increased risk of bleeding during surgical procedures
Dyspepsia, nausea, vomiting and diarrhoea (common); severe gastrointestinal haemorrhage, gastric or duodenal ulcers and perforation (rare); occult or overt gastrointestinal bleeding which may lead to iron deficiency anaemia (more common at higher doses)
Hypersensitivity reactions, angio-oedema, allergic oedema, anaphylactic reactions including shock (uncommon); bronchospasm and asthma attacks; rhinitis and dyspnoea
Intracranial haemorrhage (rare); headache and vertigo
Thrombocytopenia, agranulocytosis, aplastic anaemia (uncommon); reduced hearing ability and tinnitus
Serious skin reactions including Stevens-Johnson syndrome and Lyell's syndrome (rare); urticaria; impaired renal function and acute renal failure; Reye's syndrome

Interactions

Methotrexate at doses greater than 15 mg/week - contraindicated with acetylsalicylic acid
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
Other NSAIDs and substances with a similar mechanism of action - shared hypersensitivity and gastrointestinal risk; avoid in patients with a history of asthma caused by salicylates or NSAIDs

Clinical monograph

How it works

It irreversibly acetylates platelet cyclo-oxygenase-1, blocking thromboxane A2 production and thereby inhibiting platelet aggregation for the lifetime of the platelet.

Prescribing in practice

Haemorrhagic stroke must be excluded by imaging before starting, as aspirin increases bleeding risk; the main hazards are gastrointestinal and intracranial haemorrhage.
Use with caution in active peptic ulceration, bleeding disorders and uncontrolled hypertension, and consider gastroprotection in those at risk.
It is started promptly after confirmed ischaemic stroke and may be followed by longer-term antiplatelet therapy.

Monitoring

No routine laboratory monitoring is required, but watch for signs of gastrointestinal or other bleeding.

Counselling the patient

Take with or after food to reduce stomach irritation.
Report black stools, vomiting blood or unusual bruising.
Tell clinicians you take aspirin before any surgery or dental work.

Evidence & guidelines

Early aspirin after acute ischaemic stroke is supported by the CAST and IST trials and recommended by NICE.

Reference: NICE NG128; NICE NG185; 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.

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