Aspirin (Acetylsalicylic Acid)

Medically Reviewed By

Mr. Jitendra K Das M.Pharma • Pharmacology Jitendra K Das is a qualified pharmacist (M.Pharma-Pharmacology) with 9+ years of experience in hospital pharmacy and occupational healthcare. Currently working as Cluster Head in a leading Healthcare sector, he specializes in medication management, patient safety, and clinical support services.

This article has been medically reviewed for accuracy, clinical relevance, and evidence-based medical information.

Last medically reviewed: September 5, 2026

What Is Aspirin?

What is aspirin?

Aspirin is a medication belonging to the salicylate family used to reduce pain, fever, and inflammation, and to prevent blood clots. Its clinical effects are highly dependent on the dose administered.

Acetylsalicylic acid (ASA) is the active chemical compound in aspirin. While frequently used as a simple household remedy for headaches or muscle aches, it is also a vital, life-saving medication used by paramedics and emergency room physicians during acute heart attacks to prevent clot expansion.

Composition

Active ingredient: Acetylsalicylic acid (Aspirin).

The exact composition, strength, and excipients (inactive ingredients like corn starch, hypromellose, or enteric coatings) depend on the specific product and manufacturer. Many low-dose products are “enteric-coated” (gastro-resistant), designed to pass through the stomach and dissolve in the intestines to minimize stomach irritation.

Dosage Forms and Strengths

Note: Availability varies by country. Standard low-dose aspirin is typically 81 mg in the US and 75 mg or 150 mg in the UK, India, and Europe.

Dosage Form	Example Strengths	Route	Clinical Considerations
Standard Tablets	300 mg, 325 mg, 500 mg	Oral	Rapid absorption; typically used for pain/fever.
Chewable Tablets	75 mg, 81 mg, 300 mg	Oral	Rapid onset; preferred during suspected acute heart attacks.
Enteric-Coated	75 mg, 81 mg, 150 mg, 325 mg	Oral	Delayed absorption; used for chronic daily prevention to reduce stomach lining irritation.
Effervescent	300 mg, 500 mg (often with Vitamin C/Antacids)	Oral (dissolved)	Rapid absorption; high sodium content in some formulations.
Suppositories	150 mg, 300 mg	Rectal	Used when oral administration is impossible (e.g., severe vomiting).

Drug Classification

Aspirin is broadly classified as a:

• Non-Steroidal Anti-Inflammatory Drug (NSAID): It reduces inflammation.
• Salicylate: Derived from salicylic acid.
• Non-opioid Analgesic: Relieves pain without acting on opioid receptors.
• Antipyretic: Reduces fever.
• Antiplatelet Agent: Inhibits platelet aggregation (clotting).

Crucial Distinction: Unlike other NSAIDs (like ibuprofen), aspirin is the only NSAID that causes irreversible inhibition of platelets, making it uniquely effective for cardiovascular protection.

How Aspirin Works

LEVEL 1 — GENERAL READER:

How does aspirin prevent blood clots?

Aspirin works by permanently blocking an enzyme inside blood cells called platelets. Platelets normally stick together to form clots and stop bleeding. By making these platelets less “sticky,” aspirin prevents dangerous clots from forming inside arteries that supply the heart and brain. At higher doses, it blocks the production of chemicals called prostaglandins, which cause pain, fever, and swelling.

LEVEL 2 — PROFESSIONAL:

Aspirin acts through the inhibition of the cyclooxygenase (COX) enzymes, COX-1 and COX-2, preventing the conversion of arachidonic acid to prostaglandins and thromboxane A2 (TXA2).

• Antiplatelet Effect (Low Dose): Aspirin irreversibly acetylates a specific serine residue (Ser-529) on the COX-1 enzyme inside platelets. Because mature platelets lack a nucleus, they cannot synthesize new COX-1. Thus, TXA2 production (a potent vasoconstrictor and platelet aggregator) is inhibited for the entire 7–10 day lifespan of the platelet.
• Analgesic/Anti-inflammatory Effect (High Dose): At higher doses, aspirin inhibits both COX-1 and COX-2 throughout the body, reducing the synthesis of pro-inflammatory prostaglandins (PGE2), lowering the hypothalamic set-point for fever, and reducing peripheral pain receptor sensitization.

Pharmacodynamics

• Irreversible Platelet Inhibition: Once a platelet is exposed to aspirin, it is permanently inhibited. Normal clotting function only returns as the bone marrow produces new platelets (approx. 10% platelet turnover per day).
• Dose-Response Relationship: Complete suppression of TXA2 occurs at very low doses (75–100 mg/day). Higher doses do not increase the antiplatelet efficacy but dramatically increase the risk of gastrointestinal toxicity and bleeding. Anti-inflammatory effects require high, regular dosing (e.g., 3 to 4 grams per day), which is rarely utilized today due to safer alternatives.

Pharmacokinetics

• Absorption: Rapidly absorbed from the stomach and upper small intestine. Enteric-coated formulations delay absorption by up to 3–4 hours.
• Metabolism: Rapidly hydrolyzed in the blood, liver, and intestinal wall to its active metabolite, salicylate.
• Half-Life: Aspirin’s half-life is incredibly short (15–20 minutes), but its platelet effect lasts 7–10 days due to irreversible COX-1 acetylation. Salicylate has a half-life of 2-3 hours at low doses.
• Excretion: Eliminated via the kidneys.
• Toxicity Kinetics: At high therapeutic or toxic doses, hepatic metabolic pathways become saturated. The pharmacokinetics shift from first-order (linear) to zero-order (non-linear). This means a small increase in dose can lead to a massive, disproportionate increase in blood salicylate levels.

Uses and Indications

Aspirin is indicated for specific, distinct conditions depending on the dose.

A. Pain Relief and Fever (Analgesic/Antipyretic)

• Mild-to-moderate pain (headache, toothache, muscular aches).
• Fever reduction in adults.
• Note: Paracetamol or ibuprofen are often preferred first-line for routine pain/fever due to aspirin’s GI side effects.

B. Inflammatory Conditions

• Historically used for rheumatoid arthritis and osteoarthritis, though now largely replaced by other NSAIDs.
• High doses remain part of the guideline-directed treatment for Kawasaki disease and acute rheumatic fever in pediatric populations (specialist-directed use only).

C. Cardiovascular Medicine (Antiplatelet)

• Acute Coronary Syndrome (ACS): Suspected myocardial infarction (heart attack) or unstable angina.
• Secondary Prevention: Long-term prevention of recurrent heart attacks, ischemic strokes, and transient ischemic attacks (TIAs).
• Post-Procedural: Following coronary stent placement (PCI) or coronary artery bypass grafting (CABG).

Aspirin for Heart Attack

Can aspirin help during a heart attack?

Yes. In the event of a suspected heart attack, emergency medical guidelines strongly recommend the immediate administration of aspirin (unless the patient has a severe allergy or active life-threatening bleeding).

• Mechanism: It rapidly inhibits platelets, stopping the blood clot in the coronary artery from growing larger.
• Administration: It must be chewed or crushed (even if it’s not a chewable tablet) rather than swallowed whole. Chewing allows rapid absorption through the lining of the mouth and stomach. Enteric-coated tablets should ideally be avoided in an emergency as they absorb too slowly, but should be chewed if nothing else is available.
• Emergency Warning: Aspirin DOES NOT replace the need for an ambulance. If a heart attack is suspected, immediately call emergency services and follow the dispatcher’s guidance before taking aspirin.

Aspirin for Stroke

The use of aspirin in stroke requires exact diagnosis.

• Ischemic Stroke: (Caused by a clot). Aspirin is highly beneficial and often given within 24-48 hours to prevent early recurrence.
• Hemorrhagic Stroke: (Caused by a bleeding vessel). Aspirin is dangerous and strictly contraindicated. It will worsen bleeding in the brain.
• Warning: Never self-administer aspirin for sudden stroke symptoms (facial drooping, arm weakness, speech difficulty). A CT scan is required at the hospital to rule out brain bleeding before aspirin can be safely given.

Primary vs Secondary Prevention

Should everyone take aspirin to prevent a heart attack?

No. The clinical approach to cardiovascular prevention depends entirely on patient history.

• Secondary Prevention (Established Disease): If you have already had a heart attack, ischemic stroke, TIA, angina, or a stent, daily low-dose aspirin is unequivocally recommended by major cardiological guidelines (e.g., AHA, ACC, ESC) to prevent a second event. The benefit of preventing another clot heavily outweighs the risk of bleeding.
• Primary Prevention (No Established Disease): If you have never had a heart attack or stroke, current guidelines strongly advise against the routine use of daily aspirin for healthy adults. In these patients, the risk of causing severe gastrointestinal or brain bleeding outweighs the small potential benefit of preventing a first heart attack. Primary prevention is now only considered on a highly individualized basis for select high-risk patients by a cardiologist.

Low-Dose Aspirin

What is low-dose aspirin?

Low-dose aspirin refers to doses typically ranging between 75 mg and 150 mg daily (81 mg in the US, known colloquially as “baby aspirin,” though it is absolutely not for babies).

• It is not simply a “weaker painkiller.” At these low doses, aspirin is essentially ineffective for pain relief but highly effective as an antiplatelet agent.
• If prescribed by a doctor for your heart, you should never stop taking it independently. Discontinuing aspirin can cause a “rebound effect,” making platelets hyper-reactive and significantly increasing the risk of a clot or stent thrombosis within days.

Dosage and Administration

Always follow your healthcare provider’s exact instructions. Dosages differ drastically based on the indication.

A. Pain / Fever (Adults)

• Dose: 300 mg to 650 mg orally every 4 to 6 hours as needed.
• Maximum: Do not exceed 4,000 mg (4 grams) in 24 hours. Do not use for more than 10 days for pain, or 3 days for fever, without a doctor’s advice.

B. Suspected Heart Attack (Acute Coronary Syndrome)

• Dose: 160 mg to 325 mg (or 300 mg depending on regional availability).
• Route: Chewed immediately.

C. Secondary Cardiovascular Prevention (Antiplatelet)

• Dose: 75 mg to 100 mg daily (up to 150 mg in some protocols/countries).
• Route: Oral (often enteric-coated), swallowed whole with a glass of water. Do not crush or chew enteric-coated tablets for daily maintenance.

Missed Dose

If you are taking daily low-dose aspirin for your heart and miss a dose, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose. Do not double the dose to make up for a missed one.

Aspirin Overdose / Salicylate Toxicity

What is salicylate toxicity?

Aspirin overdose leads to salicylate toxicity—a complex, life-threatening medical emergency affecting the brain, lungs, and metabolic systems.

Early Symptoms:

• Tinnitus (ringing in the ears) – A classic hallmark of toxicity.
• Nausea, vomiting, and abdominal pain.
• Sweating and flushing.
• Hyperventilation (rapid, deep breathing).

Progression of Toxicity:

Salicylates directly stimulate the brain’s respiratory center, causing the patient to hyperventilate and breathe out too much CO2, leading to respiratory alkalosis. The body later accumulates organic acids and salicylate, uncoupling oxidative phosphorylation and causing severe metabolic acidosis.

Severe Toxicity Signs: Altered mental status, confusion, seizures, hyperthermia (dangerously high fever), pulmonary edema (fluid in lungs), coma, and death.

Management (For Healthcare Professionals):

• This is a critical emergency. Assess ABCs.
• Monitor serum salicylate concentrations, arterial blood gases, and electrolytes (potassium is often depleted).
• Administer activated charcoal if presentation is acute and recent.
• Urinary Alkalinization: IV sodium bicarbonate is used to raise urine pH above 7.5, trapping the salicylate ion in the urine and vastly accelerating its elimination.
• Hemodialysis: Required for severe toxicity, coma, renal failure, or failure of alkalinization.

Do NOT attempt to treat aspirin overdose at home. Seek immediate emergency medical care.

Side Effects

Can aspirin cause stomach bleeding?

Yes. Aspirin is a well-known cause of gastrointestinal irritation, ulceration, and bleeding.

• Common Side Effects: Dyspepsia (indigestion), heartburn, nausea, minor bruising.
• Less Common: Vomiting, gastritis, tinnitus.
• Serious Adverse Effects (Seek immediate help):
  • Gastrointestinal Bleeding: Manifesting as black, tarry stools, or vomiting blood/material that looks like coffee grounds.
  • Intracranial Hemorrhage: Severe sudden headache, confusion, neurological deficits.
  • Allergic Reactions/Anaphylaxis: Hives, swelling of the face/throat.
  • Bronchospasm: Severe shortness of breath/wheezing (especially in asthmatics).

Gastrointestinal Bleeding and Bleeding Risk

Aspirin causes GI damage through two mechanisms: directly irritating the stomach lining (mitigated slightly by enteric coating) and systemically blocking protective stomach prostaglandins (which cannot be prevented by enteric coating).

Risk Factors for Bleeding:

• Advanced age (over 65).
• History of peptic ulcers or previous GI bleed.
• Concurrent use of anticoagulants (blood thinners), other NSAIDs, or systemic corticosteroids.
• Heavy alcohol consumption.
• Note: Doctors often prescribe a Proton Pump Inhibitor (PPI) like pantoprazole or omeprazole alongside aspirin to protect the stomach in high-risk patients.

Contraindications

Aspirin should not be used in patients with:

• Absolute hypersensitivity (allergy) to aspirin or other NSAIDs.
• Active peptic ulcer disease or a history of severe GI bleeding.
• Bleeding disorders like hemophilia or severe thrombocytopenia.
• Severe untreated renal or hepatic failure.
• Children/adolescents with viral infections (due to Reye syndrome).

Precautions and Warnings

Aspirin and Asthma (AERD)

Up to 10-20% of adults with asthma have Aspirin-Exacerbated Respiratory Disease (AERD), formerly known as Samter’s Triad (Asthma, Nasal Polyps, and Aspirin Sensitivity). In these individuals, taking aspirin shifts arachidonic acid metabolism toward the production of leukotrienes, triggering severe, potentially fatal bronchospasms (asthma attacks). Asthmatics should use aspirin with caution.

Aspirin and Children (Reye Syndrome)

Can children take aspirin?

No. Aspirin is strongly contraindicated in children and teenagers (under 16 in the UK, under 19 in the US) recovering from viral illnesses, particularly influenza and varicella (chickenpox).

What is Reye Syndrome?

It is a rare but highly fatal syndrome triggered by aspirin use during a viral illness in children. It causes rapid, massive swelling in the brain (encephalopathy) and severe liver damage. Symptoms include relentless vomiting, lethargy, confusion, seizures, and coma. Due to this risk, paracetamol (acetaminophen) or ibuprofen are strictly preferred for pediatric pain and fever. Aspirin is only given to children by specialists for specific rare conditions like Kawasaki disease.

Pregnancy

Aspirin use in pregnancy is highly dose- and indication-dependent.

• High-Dose / Analgesic Use: Avoided, particularly in the third trimester (after 20 weeks). It can cause premature closure of the fetal ductus arteriosus, fetal renal impairment leading to low amniotic fluid (oligohydramnios), and increased maternal/fetal bleeding during delivery.
• Low-Dose Use: Obstetricians often intentionally prescribe low-dose aspirin (e.g., 81–150 mg) starting between 12–16 weeks of gestation for women at high risk of developing preeclampsia (severe high blood pressure in pregnancy).

Breastfeeding

Salicylates cross into breast milk. While an occasional low dose may be permissible if advised by a physician, high or continuous doses are generally avoided due to the potential risk of adverse effects (including bleeding or Reye-like symptoms) in the nursing infant.

Older Adults, Kidney, and Liver Disease

• Older Adults: High risk for GI bleeding and falls resulting in severe hematomas. Dose adjustments and GI protection are vital.
• Kidney Disease: Aspirin decreases renal blood flow in sensitive individuals. Excretion of salicylate is reduced in renal failure, increasing toxicity risk.
• Liver Disease: Salicylates are metabolized in the liver; severe impairment increases bleeding risk and toxicity.

Drug-Drug Interactions

Medicine / Class	Interaction Mechanism / Consequence	Clinical Advice
Warfarin / DOACs (Apixaban, Rivaroxaban)	Synergistic bleeding risk (antiplatelet + anticoagulant).	Highest risk for severe bleeding. Only combine if explicitly instructed by a cardiologist (e.g., dual/triple therapy).
Ibuprofen (and other NSAIDs)	Ibuprofen competitively blocks aspirin from reaching COX-1, neutralizing its cardiovascular protection; combined use also doubles GI bleeding risk.	If prescribed both, take aspirin at least 2 hours before or 8 hours after ibuprofen. Consult your doctor.
Clopidogrel / Prasugrel / Ticagrelor	Additive antiplatelet effects.	Frequently prescribed together (“Dual Antiplatelet Therapy” or DAPT) after stents/heart attacks, but increases bleeding risk.
Corticosteroids (Prednisone)	Increased risk of gastrointestinal ulceration.	Usually requires a protective stomach medication (PPI).
SSRIs / SNRIs (Antidepressants)	Serotonergic drugs inhibit platelet serotonin uptake, enhancing bleeding risk when combined with aspirin.	Monitor for unusual bruising or bleeding.
Methotrexate	Aspirin decreases renal clearance of methotrexate, potentially causing severe bone marrow and liver toxicity.	Avoid combination unless strictly monitored by a rheumatologist.

Aspirin and Alcohol

Excessive alcohol consumption while taking aspirin severely irritates the stomach lining and prolongs bleeding time. This combination drastically increases the likelihood of a major gastrointestinal bleed.

Surgery and Dental Procedures

Because aspirin stops platelets from clotting for 7–10 days, it increases surgical bleeding risk.

• For minor procedures (e.g., routine dental extraction, cataract surgery): Low-dose aspirin is often continued as the risk of a heart attack off the medicine is higher than the risk of manageable bleeding.
• For major surgeries: Surgeons may request stopping aspirin 5 to 7 days prior.
• Crucial Rule: If you are on prescribed aspirin for a stent or previous heart attack, never stop it for surgery without clearance from your cardiologist.

Onset and Duration

• Onset: Analgesic and antiplatelet effects begin within 15 to 30 minutes for plain uncoated tablets, especially if chewed. Enteric-coated tablets may take 3 to 4 hours.
• Duration: Pain and fever relief lasts 4 to 6 hours. The antiplatelet (blood-thinning) effect lasts for the lifetime of the affected platelet (7 to 10 days).

Medicine Comparisons

Aspirin vs Other NSAIDs (e.g., Ibuprofen, Naproxen)

Feature	Aspirin	Ibuprofen / Naproxen
Platelet Effect	Irreversible (lasts 7-10 days). Used for heart protection.	Reversible (wears off when drug leaves body). Does not protect the heart.
Cardiovascular Risk	Decreases risk of heart attacks.	Long-term use can increase the risk of heart attacks and strokes.
GI Risk	High risk of ulcers and bleeding.	Moderate-to-high risk depending on dose.

Aspirin vs Paracetamol (Acetaminophen)

Feature	Aspirin	Paracetamol
Inflammation	Yes (reduces inflammation).	No anti-inflammatory action.
Bleeding Risk	Yes (thins blood).	No effect on platelets or bleeding.
Stomach Risk	Can cause ulcers/GI bleeding.	Extremely safe for the stomach.
Pediatric Use	Strictly avoided (Reye syndrome).	Safe and widely used for kids.

Storage

Store at room temperature (below 25°C/77°F). Protect from moisture and direct sunlight. Keep out of reach of children. Note: If your aspirin has a strong smell resembling vinegar (acetic acid), it has degraded due to moisture and should be discarded.

How to Take Aspirin Safely (Patient Checklist)

• Know why you are taking it: Are you taking it for a headache or for your heart? The doses and rules differ.
• Verify the strength: Always check the milligram (mg) dose on the packet.
• Do not stop abruptly: Never independently stop prescribed daily low-dose aspirin without consulting your doctor.
• Take with food: Taking it with or after a meal can help reduce mild stomach upset (though it does not prevent ulcers).
• Disclose use: Tell all doctors, dentists, and pharmacists that you take aspirin.
• Check combination products: Many over-the-counter cold, flu, and pain remedies contain aspirin. Check labels to avoid accidental overdoses.

When to Seek Urgent Medical Help

Go to the nearest emergency department if you experience:

• Vomiting blood or material resembling coffee grounds.
• Stools that are black, tarry, or bloody.
• Unexplained, severe dizziness, weakness, or fainting.
• Severe allergic reaction (facial swelling, throat closing, severe wheezing).
• Ringing in the ears accompanied by rapid breathing and confusion (signs of toxicity).
• Any signs of a stroke (sudden numbness, weakness, loss of speech).

Pharmacy Counselling Points

• Verify Indication: Confirm if the patient is buying it for acute pain or for cardiovascular prevention.
• Check Age: Explicitly ask if the medication is for anyone under 16-19 years old. If yes, counsel aggressively on Reye syndrome and recommend paracetamol.
• Check GI History: Inquire about previous ulcers, severe indigestion, or black stools.
• Medication Reconciliation: Check for Warfarin, DOACs, Methotrexate, and SSRIs.
• The Ibuprofen Interaction: Advise patients taking low-dose aspirin for heart protection to avoid routine ibuprofen, as it nullifies the heart protection.
• Administration: Instruct to chew uncoated aspirin during a suspected heart attack; swallow enteric-coated whole for daily maintenance.

Clinical Pearls (For Healthcare Professionals)

1. Aspirin irreversibly acetylates Ser-529 on platelet COX-1; therefore, the antiplatelet effect lasts the lifetime of the platelet (7-10 days), long after the drug has cleared the plasma.
2. Ibuprofen exerts reversible, competitive binding at the same COX-1 site, preventing aspirin from accessing it.
3. Enteric-coated aspirin offers no reduction in the risk of lower GI bleeding; it only mildly reduces upper GI dyspepsia.
4. Zero-order kinetics apply in overdose: a small increase in ingestion can lead to a massive spike in serum salicylate.
5. Aspirin-Exacerbated Respiratory Disease (AERD) is not a true IgE-mediated allergy, but rather a shift in arachidonic acid metabolism to leukotrienes.
6. Routine use of aspirin for primary cardiovascular prevention in healthy adults over 60 is now widely depreciated due to net harm (bleeding).
7. Urine alkalinization (pH > 7.5) is the cornerstone of treating salicylate toxicity to ion-trap the drug in the renal tubules.
8. In suspected ACS, 162-325 mg must be chewed to facilitate rapid buccal and gastric absorption, bypassing some first-pass metabolism.
9. Aspirin can trigger gout attacks at low doses by decreasing renal uric acid excretion, whereas high doses are uricosuric.
10. Low-dose aspirin is a standard recommendation for women at high risk of preeclampsia, safely starting at 12–16 weeks gestation.

Common Mistakes

• Assuming it’s just a painkiller: Ignoring the profound blood-thinning effects.
• Stopping before dental cleaning: Unnecessarily stopping cardiac aspirin for minor dental work, risking a heart attack.
• Taking for primary prevention without asking a doctor: Healthy 65-year-olds taking daily aspirin because they read it’s “good for the heart,” thereby exposing themselves to dangerous bleeding risks.
• Giving to children: Using aspirin for a child’s fever because paracetamol wasn’t available.
• Ignoring the vinegar smell: Taking degraded aspirin that has broken down into salicylic and acetic acid.

Myths vs Facts

• MYTH: “Low-dose aspirin is completely safe for everyone.”
• FACT: Even at low doses, aspirin increases the risk of serious gastrointestinal bleeding. It should only be taken if prescribed.
• MYTH: “You should stop aspirin before any medical or dental procedure.”
• FACT: For many minor procedures (and even some major ones), the risk of stopping aspirin is far more dangerous than the surgical bleeding risk. Always follow specialist advice.
• MYTH: “Aspirin is safe for children as long as it’s a small dose.”
• FACT: Aspirin of any dose is contraindicated in children with viral illnesses due to the risk of life-threatening Reye syndrome.
• MYTH: “Taking an aspirin every day will prevent a first heart attack in healthy people.”
• FACT: Current guidelines advise against routine daily aspirin for primary prevention in healthy older adults due to the lack of net benefit over bleeding risks.

Patient FAQs

Pharmacy Student Section

Key Exam Points:

• Class: Salicylate NSAID.
• Mechanism: Irreversible non-selective COX-1 and COX-2 inhibitor (acetylates serine residues).
• Platelet Kinetic: Lifespan of platelet is 7-10 days; lack of nucleus prevents re-synthesis of COX-1.
• Metabolism: Hepatic. Switches to zero-order kinetics at high/toxic doses.
• Adverse Effects: GI bleeds, nephrotoxicity, bronchospasm, tinnitus (toxicity hallmark).
• Drug Interactions: Highly protein-bound; interacts with warfarin, methotrexate. Ibuprofen pharmacodynamic antagonism at COX-1.
• Contraindications: Hemophilia, active GI ulcers, children with viral infections.

Medical Student Quick Review

Topic	Key Point
MOA	Irreversible inhibition of COX-1 and COX-2 via acetylation.
Antiplatelet Effect	Blocks TXA2 synthesis in platelets for their 7-10 day lifespan.
Uses	ACS (chewed 162-325mg), Secondary CV prevention (75-100mg), Kawasaki disease (high dose).
Toxicity Progression	Direct respiratory center stimulation (Resp Alkalosis) → Uncoupled oxidative phosphorylation (High Anion Gap Metabolic Acidosis).
Reye Syndrome	Hepatoencephalopathy in children given ASA during viral illnesses (VZV, Influenza).
Pregnancy	Low-dose used for preeclampsia prophylaxis. Standard dose contraindicated >20wks (premature PDA closure, oligohydramnios).

Salicylate Toxicity for Students (Pathophysiology)

Acute salicylate toxicity presents a classic mixed acid-base disturbance.

1. Phase 1: Salicylates directly stimulate the medullary respiratory center, causing hyperventilation and a primary respiratory alkalosis. The kidneys compensate by excreting bicarbonate.
2. Phase 2: Salicylates accumulate and uncouple oxidative phosphorylation in the mitochondria. Cells switch to anaerobic metabolism, producing massive amounts of lactic acid and ketoacids. This causes a high anion gap metabolic acidosis.
3. Presentation: Tinnitus, hyperthermia, tachypnea, altered mental status.
4. Management Principles: ABCs, activated charcoal, fluid resuscitation, and IV Sodium Bicarbonate to alkalinize the urine (pH 7.5 – 8.0) to ion-trap salicylates. Hemodialysis for severe cases.

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