Low-dose aspirin

Generic Name

Acetylsalicylic acid (ASA)

Common Strengths Labeled as Low-Dose

75 mg

81 mg (common in North America, known as “baby aspirin”)

100 mg

150 mg

These doses are intended for antiplatelet rather than analgesic or antipyretic effects

Brand Names (Low-Dose Variants)

Aspirin Protect

Cardiprin

Disprin CV

Ecosprin

Cartia

Micropirin

Aspec

ASA EC

Bayer Low Dose

Bufferin Low Dose

Available as enteric-coated tablets, dispersible tablets, or chewable formulations

Drug Class

Nonsteroidal anti-inflammatory drug (NSAID)

Salicylate

Antiplatelet agent at low doses

Cyclooxygenase (COX) inhibitor

Mechanism of Action

Low-dose aspirin irreversibly inhibits the cyclooxygenase-1 (COX-1) enzyme in platelets

This prevents the conversion of arachidonic acid to thromboxane A2 (TXA2), a potent vasoconstrictor and promoter of platelet aggregation

Platelets, lacking a nucleus, cannot synthesize new COX-1 enzyme

As a result, a single dose affects platelet function for the lifespan of the platelet (7–10 days)

At low doses, the inhibition is selective for COX-1, sparing COX-2 and minimizing anti-inflammatory and gastrointestinal effects seen at higher doses

Indications

Primary Prevention (in select populations only)

Patients aged 40–70 years with high cardiovascular risk but low bleeding risk (per US Preventive Services Task Force 2022)

Not routinely recommended for individuals over 70 years or with low cardiovascular risk

Secondary Prevention

Acute coronary syndromes (ACS): unstable angina, NSTEMI, STEMI

Post-myocardial infarction (MI)

After percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG)

Ischemic stroke or transient ischemic attack (TIA)

Established peripheral arterial disease (PAD)

Stable atherosclerotic cardiovascular disease (ASCVD)

Other Indications

Prophylaxis of venous thromboembolism (VTE) in certain orthopedic surgeries (e.g., total hip or knee replacement)

Adjunct to anticoagulation in certain mechanical heart valves

Antithrombotic prophylaxis in patients with atrial fibrillation not eligible for oral anticoagulants

Prevention of preeclampsia in high-risk pregnancies (off-label, supported by guidelines)

Colorectal cancer chemoprevention in select populations (long-term use; under investigation and guideline-specific)

Off-Label Uses

Kawasaki disease (as part of IVIG regimen)

Migraine with aura (in select patients)

Post-liver transplantation vascular prophylaxis

Dosage and Administration

Standard Adult Dose for Antiplatelet Effect

75–100 mg orally once daily

Common regimens include 81 mg or 100 mg once daily

May be initiated at 150 mg in some acute settings, then reduced to maintenance dose

Acute Coronary Syndromes

Initial loading dose: 150–325 mg chewed immediately

Then maintenance: 75–100 mg daily long-term

Stroke or TIA

Initial: 160–300 mg orally as soon as possible

Maintenance: 75–100 mg once daily thereafter

Pregnancy (Preeclampsia Prevention)

75–150 mg daily (initiated at 12–16 weeks and continued until 36–37 weeks gestation)

Used in women with high risk for preeclampsia (e.g., previous history, chronic hypertension, diabetes, renal disease)

Administration Notes

Enteric-coated tablets should not be crushed or chewed

Take with food or after meals to minimize gastric irritation

Dispersible forms may be dissolved in water for faster onset

Pharmacokinetics

Absorption

Rapidly absorbed from the gastrointestinal tract

Peak plasma concentrations in 1–2 hours

Enteric-coated tablets may have delayed absorption (3–4 hours)

Distribution

Protein binding: 80–90%

Crosses placenta and enters breast milk

Metabolism

Hydrolyzed in liver and plasma to active metabolite salicylic acid

Further conjugated in liver

Elimination

Primarily renal excretion

Half-life:

– Aspirin: 15–20 minutes

– Salicylic acid: 2–3 hours (low dose)

Duration of antiplatelet effect: ~7–10 days (irreversible)

Contraindications

Known hypersensitivity to salicylates or NSAIDs

Active gastrointestinal bleeding or peptic ulcer disease

Hemophilia or other bleeding disorders

Severe hepatic or renal impairment

Children under 16 years (risk of Reye’s syndrome)

Pregnant women in the third trimester (due to risk of premature closure of ductus arteriosus)

History of aspirin-induced asthma or nasal polyps

Warnings and Precautions

Gastrointestinal Risk

Risk of gastric mucosal irritation, ulceration, or bleeding increases with age, history of ulcers, alcohol use, corticosteroids, or concurrent NSAIDs

Consider gastroprotection (e.g., PPI) in high-risk individuals

Bleeding Risk

Aspirin prolongs bleeding time

Avoid in patients with bleeding diathesis or concurrent use of anticoagulants unless clearly indicated

Monitor for signs of occult bleeding (e.g., melena, anemia)

Renal Impairment

Use with caution in patients with chronic kidney disease

Avoid long-term use in advanced renal impairment

Asthma

Aspirin-exacerbated respiratory disease (AERD) may present with bronchospasm

Use caution in asthmatic patients with nasal polyps or prior aspirin sensitivity

Surgery and Invasive Procedures

Generally withheld 5–7 days before elective surgery unless continued use is deemed necessary for cardiovascular protection

Pregnancy and Lactation

Pregnancy

Category D (third trimester): avoid due to fetal risks

Low-dose aspirin may be used in 1st and 2nd trimester for preeclampsia prevention under medical supervision

Lactation

Present in breast milk in small amounts

Generally considered safe in low doses but prolonged use not advised

Adverse Effects

Common

Dyspepsia

Heartburn

Nausea

Epigastric discomfort

Bruising

Less Common

Gastric or duodenal ulcers

Bleeding (gastrointestinal, intracranial)

Tinnitus (high doses)

Hypersensitivity reactions (urticaria, angioedema, bronchospasm)

Rare

Hepatic dysfunction

Reye’s syndrome (in children)

Anemia from chronic blood loss

Renal papillary necrosis (with chronic NSAID use)

Overdose

Usually associated with high-dose (not low-dose) formulations

Symptoms: vomiting, tinnitus, hyperventilation, metabolic acidosis, confusion, seizures, coma

Management: activated charcoal, correction of acidosis, forced alkaline diuresis, dialysis in severe cases

Drug Interactions

Anticoagulants (warfarin, DOACs)

Increased risk of bleeding

Monitor INR closely in warfarin users

Use dual therapy only when indicated (e.g., recent MI with atrial fibrillation)

Other NSAIDs (ibuprofen, naproxen)

Compete for COX-1 and may reduce aspirin’s antiplatelet effect

Administer aspirin at least 30 minutes before or 8 hours after NSAIDs

SSRIs/SNRIs

Increased gastrointestinal bleeding risk

Corticosteroids

Additive gastrointestinal toxicity

ACE Inhibitors, ARBs, Diuretics

Reduced renal perfusion; monitor renal function

Methotrexate

Increased risk of methotrexate toxicity

Avoid or monitor levels

Valproic acid

Aspirin can displace valproate from protein-binding sites, increasing free levels

Alcohol

Enhances GI bleeding risk

Monitoring Parameters

Bleeding (bruising, stools, gum bleeding)

Hemoglobin, hematocrit (long-term use)

Renal function (in elderly or those with CKD)

Signs of hypersensitivity (especially in asthma)

Platelet function not routinely monitored

Formulations

Oral

75 mg, 81 mg, 100 mg, 150 mg, 300 mg

Enteric-coated tablets

Chewable tablets

Dispersible tablets

Gastro-resistant formulations

Rectal Suppositories

Available in some regions but not preferred

Comparison with Other Antiplatelet Agents

Aspirin vs Clopidogrel

Clopidogrel more effective in preventing recurrent ischemic events in certain populations (e.g., post-stent)

Dual antiplatelet therapy (DAPT) used after PCI (aspirin + P2Y12 inhibitor)

Aspirin vs Dipyridamole

Aspirin/dipyridamole combination used in stroke prevention (e.g., Aggrenox)

More side effects (e.g., headache) with dipyridamole

Aspirin vs Warfarin/DOACs

Different mechanisms: anticoagulants inhibit clotting factors

Aspirin inhibits platelet aggregation

Combination therapy increases bleeding risk but sometimes warranted

Legal and Regulatory Status

OTC and prescription product depending on dose and country

Included in WHO Model List of Essential Medicines

Long-established global use for CVD prevention