Acetylsalicylic acid

Antiplatelet agents

ATC code: B01AC06 (Acetylsalicylic acid)

Mechanism of action

Irreversibly acetylates COX-1 in platelets, blocking thromboxane A2 synthesis – a potent inducer of aggregation and vasoconstriction. Platelets lack a nucleus and cannot resynthesize the enzyme, so the antiplatelet effect persists for the platelet's entire lifespan of 7–10 days. Low doses of 75–100 mg daily suffice for antiplatelet action.

Indications

Established ASCVD, secondary prevention

First line

Low-dose aspirin (75–100 mg daily) is the cornerstone of secondary prevention in established ASCVD. It reduces the risk of recurrent MI, stroke, and vascular death by 20–25 %. Prescribed lifelong if no absolute contraindications exist. After ACS or stenting, dual antiplatelet therapy (aspirin plus clopidogrel, ticagrelor, or prasugrel) is given for 6–12 months.

Primary cardiovascular prevention with aspirin

Individual decision

Routine aspirin for primary prevention is not recommended. ASPREE, ARRIVE, and ASCEND trials showed that in moderate-risk patients, the reduction in ischemic events is offset by increased bleeding. USPSTF 2022 recommends against initiating aspirin in adults 60 and older for primary prevention. In adults 40–59 with a 10-year ASCVD risk of 10 % or more, the decision is individualized.

Practical notes

Timing and administration

Take low doses (75–100 mg) once daily. Morning vs evening dosing has no proven clinical difference. Enteric coating does not protect against systemic GI damage (the mechanism is systemic via prostaglandin depletion, not local). Take after food to reduce local irritation.

Special situations

Before elective surgery, discontinue aspirin 7 days in advance (full platelet pool turnover). In emergency surgery, increased bleeding persists. Ibuprofen may attenuate aspirin's antiplatelet effect – separate dosing times. With a history of GI bleeding, add a PPI.

Safety

Contraindications

Active GI bleeding
Severe thrombocytopenia
Hemorrhagic diathesis
Aspirin allergy or aspirin-exacerbated respiratory disease
Severe hepatic failure

Serious adverse effects

GI bleeding (higher risk in elderly, with concurrent anticoagulants or NSAIDs)
Hemorrhagic stroke (very rare at low doses)
Reye syndrome in children under 15 (contraindicated in viral infections)

Common adverse effects

Dyspepsia, heartburn
Increased bleeding tendency (epistaxis, bruising)
Nausea

PregnancyFDA D

FDA category D at full analgesic doses. Low doses (75–150 mg) are prescribed for specific indications such as preeclampsia prevention from week 12 to week 36. Contraindicated after 36 weeks.

Breastfeeding

Excreted in breast milk. Low antiplatelet doses (75–100 mg) are acceptable during breastfeeding. High analgesic doses are not recommended.