Drug reference

Aspirin

NSAID · Analgesic

Also known as Acetylsalicylic acid, ASA

START

75-100 mg PO once daily (antiplatelet)

TYPICAL MAX

300-650 mg q4-6h PRN (analgesic) · max 4 g/day

STOP IF

Active GI bleed · age <16 (Reye's) · severe asthma

WATCH

GI bleed · tinnitus · uric acid · platelet effect 7-10d after dose

CDSCO approvedOTC (for low-dose formulations used for antiplatelet effect, or as analgesic for specific pack sizes and strengths); Schedule H for higher strengths or specific formulations as per state regulations.Jan AushadhiATC B01AC06

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 30min · platelet COX-1 inhibition
PEAK: 1h · Cmax (chewed: faster)
t½: 18min · salicylate t½ (active 2-3h, dose-dependent)
DURATION: 1.4w · platelet effect lifetime (7-10 days)

EXCRETION

Hepatic deacetylation · renal salicylate metabolites

route + CYP

INTERACTIONS

12 major

incl. contraindicated

PREGNANCY

Category C (low-dose) / D (high-dose 3rd trimester)

FDA category + note

Top interactionssee all 12 →

AlcoholContraindicatedTextbook-citedKDT 7e · p950
MethotrexateContraindicatedTextbook-citedKDT 7e · p949
SulfasalazineContraindicatedTextbookG&G 14e · p1112
KetorolacContraindicatedDatabaseKimi deep-research + Cla

Available in India

188 branded formulations and 676 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Jan Aushadhi — generic available at GoI pharmacies

Mechanism

Aspirin irreversibly inhibits cyclooxygenase (COX-1 and COX-2) enzymes by acetylation, thereby blocking the synthesis of prostaglandins and thromboxane A2 (TXA2). This leads to its anti-inflammatory, analgesic, and antipyretic effects. Its antiplatelet action is primarily due to the irreversible inhibition of TXA2 in platelets, which prevents platelet aggregation for their lifespan.

Indications

Mild to moderate pain reliefFever reductionInflammatory conditions (e.g., rheumatoid arthritis, osteoarthritis)Acute myocardial infarction (MI)Prevention of cardiovascular events (secondary prevention of MI, stroke, transient ischemic attack)Kawasaki disease (off-label)Prevention of pre-eclampsia (off-label)Colorectal cancer prevention (off-label)prevention of major adverse cardiac and limb events in patients with coronary or peripheral artery disease (in combination with low-dose rivaroxaban)acute myocardial infarctionacute ischemic strokesecondary prevention in patients with stroke, coronary artery disease, or peripheral artery diseaseCardioprotection (low dose)AnalgesiaAntipyresisAnti-inflammationRheumatic feverKawasaki diseasePreeclampsia (low-dose, 81 or 100 mg, reduces incidence of preterm preeclampsia in women at increased risk)Cancer chemoprevention (colorectal cancer, especially in Lynch syndrome)Systemic mastocytosis (adjunct therapy for PGD2-mediated symptoms)Niacin tolerability (inhibits facial flushing)Closure of inappropriately patent ductus arteriosus in neonates (off-label)PainFeverInflammationVascular indicationsRheumatoid diseaseReduces the risk of recurrent adenomas in persons with a history of colorectal cancer or adenomasheadacheantiplateletrheumatoid arthritisRelief of dysmenorrhoeaAntithrombotic effectAntipyreticReduction of colon cancer incidenceheadache (including mild migraine)backachemyalgiajoint painpulled muscletoothacheneuralgiasdysmenorrhoeaacute rheumatic feverosteoarthritis (symptomatic relief)postmyocardial infarction (lowers incidence of reinfarction)poststroke (lowers incidence of stroke)pregnancy-induced hypertension and pre-eclampsia (low dose)patent ductus arteriosus (closure)familial colonic polyposis (suppress polyp formation)prevention of colon cancerprevention of flushing attending nicotinic acid ingestionProphylaxis of thromboembolic disordersPrevention of MI (primary and secondary)Coronary artery diseaseAcute coronary syndromes (unstable angina, NSTEMI, STEMI)Prevention of reinfarction and reduction of mortality in post-MI patientsCerebrovascular disease (TIAs, stroke prevention)Prosthetic heart valves (reduce microthrombi and embolism)Arteriovenous shunts (reduce microthrombi and embolism)Peripheral vascular disease (intermittent claudication, thromboembolism reduction)Prophylaxis for hospitalized cancer patientsProphylaxis for cancer patients receiving a thalidomide analogueAntiplatelet therapy for NSTE-ACSManagement of patients with suspected ST-segment elevation myocardial infarction (STEMI)Secondary prevention after STEMIprophylaxis for VTE after major orthopedic surgery

Dosing

Adult: Analgesic/Antipyretic: 300-650 mg orally every 4-6 hours as needed; max 4g/day. Anti-inflammatory: 2.4-4 g/day orally in divided doses. Antiplatelet (secondary prevention): 75-150 mg orally once daily. Acute MI: Initial dose 150-300 mg orally, chewed, then 75-150 mg daily.
Pediatric: Not recommended for analgesic/antipyretic in children <16 years due to Reye's syndrome risk. Kawasaki disease (off-label): Initial 80-100 mg/kg/day in 4 divided doses until afebrile for 48-72 hours, then 3-5 mg/kg/day once daily for 6-8 weeks.
Renal adjustment: eGFR 10-50 mL/min: Use with caution, consider dose reduction. eGFR <10 mL/min: Avoid or use with extreme caution.
Hepatic adjustment: Mild-to-moderate impairment: Use with caution, monitor for signs of toxicity. Severe impairment: Contraindicated.
Geriatric: Use lowest effective dose. Increased risk of GI bleeding and renal impairment. Monitor renal function and for signs of bleeding.
Max dose: 4g/day (for analgesic/antipyretic); 150 mg/day (for antiplatelet secondary prevention)

Pharmacokinetics

Onset

Analgesic/Antipyretic: 5-30 minutes. Antiplatelet: Within 1 hour (irreversible effect).

Peak effect

1-2 hours (for parent drug); 2-4 hours (for salicylic acid metabolite).

Duration

Analgesic: 4-6 hours. Antiplatelet: 7-10 days (for the lifespan of platelets).

Half-life

Aspirin: 15-20 minutes. Salicylic acid (active metabolite): Dose-dependent, 2-3 hours at low doses, up to 15-30 hours at anti-inflammatory doses.

Bioavailability

Rapid and complete absorption from GI tract, but undergoes extensive first-pass hydrolysis to salicylic acid.

Protein binding

Salicylic acid: 70-90% (dose-dependent).

Metabolism

Primarily hydrolyzed to salicylic acid in the gastrointestinal mucosa, liver, and blood. Salicylic acid is further conjugated in the liver.

Excretion

Mainly renal, as salicylic acid and its conjugated metabolites.

Contraindications

Hypersensitivity to aspirin, other salicylates, or NSAIDs
Asthma, rhinitis, and nasal polyps (NSAID-exacerbated respiratory disease)
Children or adolescents with viral infections (risk of Reye's syndrome)
Active peptic ulcer disease or gastrointestinal bleeding
Bleeding disorders (e.g., hemophilia)
Severe renal impairment
Severe hepatic impairment
Third trimester of pregnancy
Concomitant use with methotrexate (>15 mg/week)
Children and young adults less than 20 years of age with viral illness–associated fever (risk of Reye syndrome)
Severe hepatic damage
Hypoprothrombinemia
Vitamin K deficiency
Hemophilia
Third trimester of pregnancy (risk of premature closure of ductus arteriosus)
Use in children (limited due to Reye syndrome association)
patients sensitive to it
peptic ulcer
bleeding tendencies
children suffering from chickenpox or influenza (due to risk of Reye's syndrome)
chronic liver disease (cautious use)
diabetics (cautious use)
low cardiac reserve or frank CHF (cautious use)
juvenile rheumatoid arthritis (cautious use)
at or near term pregnancy
G-6PD deficient individuals (high doses)
Severe active bleeding
Aspirin allergy

Side effects

Common

DyspepsiaNauseaHeartburnGI discomfortTinnitus (at higher doses)bleeding (increased with higher doses)Epigastric distressVomitingErosive and reactive gastropathiesGI ulcerationGI hemorrhage (can be painless, leading to iron-deficiency anemia)Increased fecal blood lossHearing impairmentTinnitusChanges in perceived soundsFatigueMuscle weaknessDiarrheaDehydrationHeadacheDizzinessDrowsinessSweatingThirstHyperventilationPrimarily GIPrimarily cardiovascularInduction of asthma (in some individuals)increased occult blood loss in stoolsgastric mucosal damagepeptic ulcerationGastrointestinal (dyspepsia, erosive gastritis, peptic ulcers with bleeding and perforation)

Serious

Gastrointestinal bleeding
Peptic ulceration
Reye's syndrome (in children with viral infections)
Hypersensitivity reactions (bronchospasm, angioedema, anaphylaxis)
Renal dysfunction
Hepatic toxicity
Prolonged bleeding time
Hemorrhagic stroke
Reye syndrome
Liver injury (with high doses, >150 μg/mL plasma salicylate)
Congestive cardiac failure (high doses)
Pulmonary edema (high doses, noncardiogenic)
Bleeding/hemorrhage (especially with severe hepatic damage, hypoprothrombinemia, vitamin K deficiency, or hemophilia)
Hyperkalemia (in combination with ACE inhibitors)
Acute kidney injury
Acute interstitial nephritis
Anemia
Hemolysis (in G6PD deficiency)
Myocardial infarction (in primary prevention, balanced by GI bleeding risk)
Intracranial bleeds (low dose)
Respiratory depression (toxic doses)
Circulatory collapse (toxic doses)
Petechiae (toxic doses)
Hyperglycemia
Glycosuria
Hypoglycemic coma (in children with toxic doses)
Negative nitrogen balance
Convulsions (toxic doses)
Delirium (toxic doses)
Psychosis (toxic doses)
Stupor (toxic doses)
Coma (toxic doses)
Metabolic acidosis (toxic doses)
Salicylate intoxication
haemolysis in G-6PD deficient individuals
premature closure of ductus arteriosus (teratogenic)
peptic ulcer
profuse gastric bleeding
salicylism (dizziness, tinnitus, vertigo, reversible impairment of hearing and vision, excitement and mental confusion, hyperventilation and electrolyte imbalance)
insidious onset hepatic injury (long-term high dose)
acute salicylate poisoning (vomiting, dehydration, electrolyte imbalance, acidotic breathing, hyper/hypoglycaemia, petechial haemorrhages, restlessness, delirium, hallucinations, hyperpyrexia, convulsions, coma, respiratory failure, cardiovascular collapse)
Reye's syndrome (in children with viral infection)
negative N2 balance
haemolysis (in G-6PD deficient individuals)
respiratory depression (at higher doses)
metabolic acidosis (at higher doses)
dehydration
precipitation of CHF (in patients with low cardiac reserve)
angioneurotic swellings
urticaria
rhinitis
asthma
anaphylactoid reactions
G.i. bleeding (especially when combined with anticoagulants)
Cerebral haemorrhage (increased risk in primary prevention)
Major bleeding (1–3% per year)
Intracerebral hemorrhage

Pregnancy & lactation

Pregnancy

Category C (low-dose) / D (high-dose 3rd trimester)

Lactation

Aspirin and its metabolites are excreted into breast milk. High doses or chronic use should be avoided due to potential risk of Reye's syndrome in infants. Low-dose (75-150 mg/day) may be considered with caution under medical supervision, but paracetamol or ibuprofen are generally preferred.