Antiplatelet — ACS / Ischaemic Stroke Pregnancy: Doses up to 100 mg/day for restricted obstetrical use appear safe under specialised monitoring. Doses of 100 mg/day and above are CONTRAINDICATED during the third trimester (risk of premature closure of the ductus arteriosus, pulmonary hypertension, fetal renal dysfunction/oligohydramnios, prolonged bleeding time and delayed or prolonged labour). In the first and second trimesters, do not give unless clearly necessary, at the lowest dose and shortest duration. Breast-feeding: short-term use of recommended doses does not require suspending lactation; discontinue breast-feeding with long-term use and/or higher doses.

Aspirin (Loading Dose)

Brand names: Aspirin (generic), Disprin

Used in: Stroke & TIA

This page concerns the aspirin loading dose given orally (usually chewed or dispersible) in the emergency treatment of suspected acute coronary syndrome, where a single larger initial dose is used for rapid antiplatelet effect.

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) daily thereafter

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

Frequency: Single loading dose, 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

Other adult indications from 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 (except during the acute phase); prevention of graft occlusion after CABG; coronary angioplasty (except during the acute phase). Secondary prevention of TIA and ischaemic cerebrovascular accident, once intracerebral haemorrhage has been ruled out: 75-300 mg once daily. 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, but the elderly are more prone to adverse events (especially gastrointestinal bleeding and perforation) and treatment should be reviewed at regular intervals. PAEDIATRIC: acetylsalicylic acid should not be given to children and adolescents younger than 16 years except on medical advice where the benefit outweighs the risk — no paediatric dose is stated in this SPC (risk of Reye's syndrome); verify against a children's formulary. SOURCE PRODUCT NOTE: the eMC record fetched was Aspirin 75 mg tablets (oral). The US openFDA record fetched was an OTC 'Low Dose Aspirin' analgesic label (4-8 tablets every 4 hours) with a different indication and was NOT used.

Dose adjustments

Renal

No dose adjustment stated. Contraindicated in severe renal impairment; use with caution in moderately impaired renal function and in dehydrated patients, since NSAID use may cause deterioration in 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 or urticaria) to salicylates/aspirin or to NSAIDs; history of asthma caused by salicylates or NSAIDs
Acute gastrointestinal ulcers; active or recurrent gastric/duodenal ulcer or haemorrhage; history of gastrointestinal 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 and gingival bleeding with prolonged bleeding time, persisting 4-8 days after discontinuation; overt or occult gastrointestinal bleeding leading to iron deficiency anaemia
Dyspepsia, nausea, vomiting, diarrhoea; severe gastrointestinal haemorrhage, gastric or duodenal ulcers and perforation
Hypersensitivity reactions, angio-oedema, allergic oedema, anaphylactic reactions including shock; bronchospasm and asthma attacks; rhinitis, dyspnoea
Intracranial haemorrhage; headache, vertigo; reduced hearing ability and tinnitus
Impaired renal function and acute renal failure; hepatic insufficiency and raised hepatic enzymes; Reye's syndrome; serious skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis (rare)

Interactions

Methotrexate at doses >15 mg/week — contraindicated (section 4.3)
Drugs that alter haemostasis — anticoagulants, thrombolytic agents, antiplatelet agents, anti-inflammatory drugs and SSRIs — concomitant treatment is not recommended unless strictly indicated, as the risk of haemorrhage is enhanced; if unavoidable, observe closely for bleeding (section 4.4)
Note: the full section 4.5 interactions list was not captured in this source bundle — clinician to verify against the SPC

Clinical monograph

How it works

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

Prescribing in practice

Give the loading dose immediately in suspected acute coronary syndrome unless there is true aspirin allergy or active significant bleeding, as early administration improves outcomes.
Chewing or using a dispersible preparation speeds absorption and onset compared with swallowing a whole enteric-coated tablet.
Caution applies in active peptic ulceration, bleeding disorders and severe uncontrolled hypertension, and bleeding risk rises when combined with other antiplatelets and anticoagulants.

Monitoring

Monitor for signs of gastrointestinal or other bleeding and confirm the indication and absence of contraindications before the loading dose.

Counselling the patient

Ask the patient to chew the tablet for faster effect in suspected heart attack.
Check for prior aspirin allergy or recent significant bleeding first.
Continued low-dose therapy will usually follow the loading dose.

Evidence & guidelines

Early aspirin in acute coronary syndrome is supported by the ISIS-2 trial and is standard in NICE acute coronary syndrome guidance (NG185).

Reference: NICE NG185 (ACS); NICE NG128 (Stroke/TIA); 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

📚 MRCEM Revision

Featured in these MRCEM clinical pathways

Aspirin (Loading Dose) is a core drug in the following exam-focused workups on our sister siteReviseMRCEM.

MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.