Back to Drug Database

Aspirin

Acetylsalicylic Acid

Bayer Ecotrin Durlaza Aspergum Bufferin

12 views

Updated: October 17, 2025

Overview

Aspirin (acetylsalicylic acid) is one of the most widely used medications globally, first introduced in 1899. It belongs to the salicylate class of drugs and functions as a nonsteroidal anti-inflammatory drug (NSAID). Aspirin exhibits analgesic, antipyretic, and anti-inflammatory properties at higher doses, while low-dose aspirin (81 mg) is primarily used for its antiplatelet effects to prevent cardiovascular events. Its therapeutic benefits stem from irreversible inhibition of cyclooxygenase (COX) enzymes, which reduces prostaglandin synthesis. While generally safe, aspirin carries risks of gastrointestinal irritation and bleeding, particularly with long-term use. It remains a cornerstone in secondary prevention of myocardial infarction and stroke.

Drug Class

Salicylate, Nonsteroidal Anti-Inflammatory Drug (NSAID), Platelet Aggregation Inhibitor

Mechanism of Action

Irreversibly inhibits cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes by acetylating serine residues, reducing prostaglandin and thromboxane synthesis: • COX-1 inhibition in platelets blocks thromboxane A2 production, preventing platelet aggregation • COX-2 inhibition in inflammatory cells decreases prostaglandin-mediated pain and inflammation • Central antipyretic action via hypothalamic prostaglandin inhibition

Pharmacokinetics

Absorption: Rapidly absorbed in stomach and small intestine (pH-dependent) Distribution: Widely distributed (Vd 0.15 L/kg), 50-80% protein-bound Metabolism: Hydrolyzed to salicylic acid in liver (first-pass metabolism) Excretion: Renal elimination (urine pH-dependent) Half-life: 15-20 minutes (aspirin); 2-3 hours (salicylic acid at low doses), up to 30 hours at toxic doses

Pharmacodynamics

• Analgesic: Reduces peripheral pain mediators • Antipyretic: Resets hypothalamic thermostat • Anti-inflammatory: Decreases prostaglandins in inflamed tissues • Antiplatelet: Sustained inhibition of platelet aggregation for 7-10 days • Uricosuric effect at high doses (>3 g/day)

Indications

• Mild to moderate pain (headache, muscle pain): 325-650 mg every 4-6 hours • Fever reduction: 325-650 mg every 4 hours • Anti-inflammatory in rheumatic diseases: 3-6 g/day divided doses • Acute coronary syndrome: 160-325 mg chewed at onset • Secondary prevention of cardiovascular events: 81-325 mg daily • Kawasaki disease: 80-100 mg/kg/day divided doses (pediatrics)

Contraindications

Absolute: • Hypersensitivity to salicylates or NSAIDs • Reye's syndrome (children <16 years with viral illness) • Active gastrointestinal bleeding Relative: • History of peptic ulcer disease • Severe renal/hepatic impairment • Asthma with nasal polyps (ASA triad) • Gout

Dosage & Administration

Pain/Fever (Adults): 325-650 mg orally every 4-6 hours (max 4 g/day) Acute MI: 160-325 mg chewed immediately, then 81-325 mg daily Secondary CVD Prevention: 81-325 mg once daily Rheumatoid Arthritis: 3-6 g/day in divided doses Kawasaki Disease: 80-100 mg/kg/day divided every 6 hours (high-dose phase)

Special Populations

Pediatric: Avoid in viral infections due to Reye's risk; Kawasaki dosing requires strict weight-based calculation Geriatric: Increased bleeding risk; consider lower maintenance doses (81 mg) Renal impairment: Avoid if CrCl <10 mL/min; monitor salicylate levels in chronic kidney disease Hepatic impairment: Use with caution; reduced clearance in severe cirrhosis

Adverse Effects

Common (>10%): • Gastrointestinal irritation (dyspepsia, nausea) • Increased bleeding time • Tinnitus (sign of toxicity) Serious (<1%): • Gastrointestinal hemorrhage • Anaphylaxis • Reye's syndrome • Acute kidney injury • Hemolytic anemia (G6PD deficiency)

Drug Interactions

• Warfarin: Increased bleeding risk (synergistic anticoagulation) • Other NSAIDs: Reduced cardioprotective effects of aspirin • Corticosteroids: Increased ulcer risk • Methotrexate: Reduced renal clearance increases toxicity • ACE Inhibitors: Reduced antihypertensive effect

Warnings & Precautions

• Black Box Warning: Risk of serious gastrointestinal bleeding, especially in elderly • May trigger bronchospasm in aspirin-exacerbated respiratory disease (AERD) • Discontinue 5-7 days before elective surgery • Avoid in third trimester pregnancy (premature closure of ductus arteriosus) • Chronic use associated with iron-deficiency anemia

Pregnancy & Lactation

Pregnancy: Category D in third trimester; avoid after 30 weeks gestation. Low-dose may be used in first/second trimester for CVD prevention Lactation: Small amounts excreted in milk; consider pumping/discarding if high doses used

Monitoring Parameters

• Hemoglobin/hematocrit (chronic use) • Renal function tests • Stool occult blood • Salicylate levels in overdose (>30 mg/dL toxic) • Hearing changes (tinnitus) • Liver function in long-term high-dose use

Patient Counseling

• Take with food or full glass of water to reduce GI upset • Report black stools, abdominal pain, or vomiting blood • Avoid alcohol (increases bleeding risk) • Do not crush enteric-coated tablets • Inform dentists/surgeons about aspirin use • Stop use 1 week before procedures if advised

Storage & Stability

Store at 20-25°C (68-77°F) in tight, light-resistant container. Protect from moisture. Discard if vinegar-like odor develops.

Clinical Pearls

• Enteric coating does NOT reduce gastrointestinal bleeding risk • Dual antiplatelet therapy (DAPT) with clopidogrel requires full 81 mg dose • Consider PPI co-therapy for high GI risk patients • Low-dose aspirin shows chemopreventive effects in colorectal cancer • Avoid alternating with ibuprofen (competes for COX-1 binding)

References

• Goodman & Gilman's: The Pharmacological Basis of Therapeutics, 14th ed • UpToDate: Aspirin in the primary prevention of cardiovascular disease • FDA Prescribing Information: Bayer Aspirin (2023 revision) • AHA/ACC Guideline on Secondary Prevention of Coronary Artery Disease (2023)