What is Aspirin?
Aspirin (acetylsalicylic acid) reduces pain, fever, and inflammation. It is a nonsteroidal anti-inflammatory drug (NSAID) that works by blocking production of the chemicals that drive inflammation. It comes as tablets, chewable tablets, and suppositories. Taken as directed it is generally safe, but it can cause upset stomach, heartburn, and allergic reactions, and it must be used cautiously in patients with ulcers or bleeding disorders. It should not be given to children or teenagers with a fever or chickenpox because of the rare but serious risk of Reye's syndrome.
Generic Name
- acetylsalicylic acid, ASA
Brand Names
Alka-Seltzer, Anacin, Asaphen, Aspergum, Aspir-Low, Aspirtab, Bayer Aspirin, Bayer Timed-Release Arthritic Pain Formula, Bufferin, Easprin, Ecotrin, 8-Hour Bayer Timed-Release, Ecotrin, Empirin, Entrophen, Excedrin, Goody's Headache Powder, Halfprin, Healthprin, Lowprin, Norwich Aspirin, Novasen, Rivasa, Sloprin, St. Joseph Adult Chewable Aspirin, Therapy Bayer, ZORprin
Drug Classification
Therapeutic class: antipyretics, nonopioid analgesics. Pharmacologic class: salicylates.
Indications and Therapeutic Effects
Aspirin relieves mild to moderate pain (headache, toothache, muscle aches, arthritis), reduces the inflammation of rheumatoid arthritis, osteoarthritis, and other conditions, and lowers fever from infection or other causes. It also prevents blood clots, which is why it is used to lower heart attack and stroke risk in patients with heart disease or other risk factors. Unlabeled use: adjunctive treatment of Kawasaki disease.
The antiplatelet picture has narrowed for primary prevention. In its 2022 statement, the US Preventive Services Task Force recommends against starting low-dose aspirin to prevent a first cardiovascular event in adults 60 and older, and advises an individualized decision for adults 40 to 59 with a 10 percent or greater 10-year cardiovascular risk who are not at increased bleeding risk (USPSTF). Aspirin remains a mainstay of secondary prevention in patients with established cardiovascular disease.
Mechanism of Action
Aspirin inhibits production of prostaglandins, the chemicals involved in inflammation and pain, by blocking the enzyme cyclooxygenase (COX). There are two isoforms. COX-1 produces prostaglandins for normal physiology, such as maintaining the stomach lining and regulating renal blood flow. COX-2 is induced by inflammation and produces the prostaglandins that drive pain and inflammation.
Aspirin is a non-selective COX inhibitor, hitting both COX-1 and COX-2. That is why it relieves pain and inflammation but also irritates the stomach and causes bleeding, because it disrupts the prostaglandins that protect the stomach lining. Newer selective COX-2 inhibitors such as celecoxib (Celebrex) spare COX-1 and may carry a lower risk of stomach irritation and bleeding.
Precautions and Contraindications
Do not use in patients allergic to aspirin or other NSAIDs; signs of an allergic reaction include difficulty breathing, hives, and swelling of the face, lips, tongue, or throat. Aspirin raises the risk of stomach bleeding, especially with a history of ulcers or GI bleeding, so screen for that history first. Use caution in patients with bleeding disorders or on blood thinners. Use caution in pregnancy and breastfeeding; it is not recommended in the third trimester because it may increase bleeding in mother and baby. Do not give to children or teenagers who have or are recovering from chickenpox or flu-like symptoms, because of Reye's syndrome. Aspirin interacts with many drugs, and cross-sensitivity with other NSAIDs may exist (less with nonaspirin salicylates), so review all current medications first.
Use cautiously with a history of GI bleeding or ulcer disease, substance abuse such as chronic alcohol use, severe hepatic or renal disease, and in lactation (safety not established). In obstetrics, salicylates may harm the fetus and mother and should be avoided during pregnancy, especially the 3rd trimester. Geriatric patients face increased risk of adverse reactions, especially GI bleeding, and are more sensitive to toxic levels.
Drug Interactions
Drug-Drug
Aspirin increases bleeding risk with blood thinners such as warfarin, heparin, heparin-like agents, thrombolytic agents, dipyridamole, clopidogrel, tirofiban, or eptifibatide, although these are frequently used safely in combination and in sequence. Combined with other NSAIDs such as ibuprofen or naproxen, it raises the risk of stomach bleeding. It can interfere with the blood-thinning effect of SSRIs such as fluoxetine and sertraline, with gout medications such as probenecid and sulfinpyrazone, and with the blood-sugar-lowering effect of some diabetes medications such as glimepiride and glyburide.
Drug-Natural Products
These products may increase the anticoagulant effect and bleeding risk: arnica, chamomile, clove, feverfew, garlic, ginger, ginkgo, and Panax ginseng.
Drug-Food
Foods that acidify the urine may raise serum salicylate levels. Cranberry juice makes the urine more acidic. Alkaline foods such as bananas and avocados make the urine less acidic.
Adverse Effects
Stomach irritation: epigastric distress, indigestion, heartburn, nausea, or vomiting. Allergic reactions: rash, hives, urticaria, difficulty breathing, and swelling of the face, lips, tongue, or throat, up to anaphylaxis and laryngeal edema. Bleeding, particularly in patients with bleeding disorders or on blood thinners, leading to anemia and hemolysis. Tinnitus, a ringing or buzzing in the ears.
Administration Considerations
Available Forms
- Tablets: 81 mg, 162.5 mg, 325 mg, 500 mg, 650 mg, 975 mg.
- Chewable tablets: 80 mg, 81 mg.
- Chewing gum: 227 mg.
- Dispersible tablets: 325 mg, 500 mg.
- Enteric-coated (delayed-release) tablets: 80 mg, 165 mg, 300 mg, 325 mg, 500 mg, 600 mg, 650 mg, and 975 mg.
- Extended-release tablets: 325 mg, 650 mg, 800 mg.
- Delayed-release capsules: 325 mg, 500 mg.
- Suppositories: 60 mg, 120 mg, 125 mg, 130 mg, 150 mg, 160 mg, 195 mg, 200 mg, 300 mg, 320 mg, 325 mg, 600 mg, 640 mg, 650 mg, 1.2 g.
- In combination with: antihistamines, decongestants, cough suppressants, opioids, and omeprazole (Yosprala).
Dosage for Children
- For pain or fever
- PO, Rect (Children 2 – 11 yr): 10 – 15 mg/kg/dose every 4 – 6 hr; maximum dose: 4 g/day.
- For inflammation
- PO (Children): 60 – 100 mg/kg/day in divided doses (up to 130 mg/kg/day for acute rheumatic fever).
- Prevention of Myocardial Infarction/Antiplatelet Effects
- PO (Children): 3 – 10 mg/kg/day given once daily.
- Kawasaki Disease
- PO (Children): 80 – 100 mg/kg/day in 4 divided doses until fever resolves; may be followed by a maintenance dose of 3 – 5 mg/kg/day as a single dose for up to 8 wk.
Dosage for Adults
- For pain or fever
- PO, Rect (Adults): 325 – 1000 mg every 4 – 6 hr (not to exceed 4 g/day).
- Extended-release tablets, 650 mg every 8 hr or 800 mg every 12 hr.
- For Inflammation
- PO (Adults): 2.4 g/day initially; increase to a maintenance dose of 3.6 – 5.4 g/day in divided doses (up to 7.8 g/day for acute rheumatic fever).
- Prevention of Transient Ischemic Attacks
- PO (Adults): 50 – 325 mg once daily.
- Prevention of Myocardial Infarction/Antiplatelet Effects
- PO (Adults): 80 – 325 mg once daily.
- Suspected acute MI, 160 mg as soon as MI is suspected.
Pharmacokinetics
Aspirin's absorption, distribution, metabolism, and elimination vary with age, body weight, and liver and kidney function, which shape the right dose and frequency.
- Absorption. After oral administration, aspirin is rapidly absorbed from the GI tract and distributed throughout the body.
- Distribution. Rapidly and widely distributed; crosses the placenta and enters breast milk.
- Metabolism and Excretion. Metabolized primarily in the liver to salicylic acid, the active metabolite, which is further metabolized to inactive compounds excreted in the urine. Aspirin is also converted to salicylic acid by esterases in the blood and tissues. The amount excreted unchanged by the kidneys depends on urine pH; as pH increases, the unchanged fraction rises from 2 – 3% up to 80%.
- Half-life. The elimination half-life is approximately 20 to 30 minutes, so the drug clears quickly, but its effects last longer because it inhibits prostaglandin synthesis. Duration of action depends on dose and condition: 2–3 hr for low doses, up to 15–30 hr with larger doses because of saturation of liver metabolism.
Nursing Considerations for Aspirin
Nursing Assessment
Evaluate the patient's lifestyle, including alcohol use, tobacco use, and diet, which affect the safety and effectiveness of aspirin therapy. Review the health history for GI bleeding or ulceration, liver or kidney disease, and bleeding disorders. Ask about aspirin allergies and intolerances; patients with asthma, allergies, nasal polyps, or tartrazine allergy are at higher risk for hypersensitivity reactions. Determine the current aspirin regimen (dose, frequency, route). Assess pain and limitation of movement by type, location, and intensity before and at the peak after administration. Assess fever and note associated signs (diaphoresis, tachycardia, malaise, chills) for baseline data and to gauge effectiveness.
Monitor hepatic function before antirheumatic therapy and if signs of hepatotoxicity appear; risk is higher in patients, especially children, with rheumatic fever, systemic lupus erythematosus, juvenile arthritis, or pre-existing hepatic disease. Aspirin may raise serum AST, ALT, and alkaline phosphatase, especially when plasma concentrations exceed 25 mg/100 mL; values may normalize despite continued use or dose reduction, but if severe abnormalities or active liver disease occur, discontinue and use cautiously in the future. Monitor serum salicylate levels periodically with prolonged high-dose therapy, especially in children with Kawasaki disease. Be aware aspirin can alter serum uric acid, urine vanillylmandelic acid (VMA), protirelin-induced TSH, urine 5-HIAA determinations, and radionuclide thyroid imaging. Monitor hematocrit periodically in prolonged high-dose therapy to catch GI blood loss. Aspirin prolongs bleeding time for 4 – 7 days and, in large doses, may prolong prothrombin time, since it alters platelet function through interference with prostaglandin biosynthesis. Watch for toxicity and overdose: fever, tinnitus, headache, drowsiness, hyperventilation, agitation, mental confusion, lethargy, diarrhea, and sweating; if these appear, withhold the medication and notify the provider immediately.
Nursing Diagnosis
Acute pain, when aspirin is used for postoperative, dental, or injury pain. Risk for bleeding, because aspirin is an antiplatelet agent that interferes with normal clotting. Risk for injury, since dizziness and drowsiness raise fall risk. Deficient knowledge about proper dosing and side effects. If aspirin overdose or poisoning is suspected: risk for fluid volume deficit related to vomiting and diarrhea, risk for altered body temperature related to fever, and risk for altered mental status related to overdose.
Aspirin Nursing Interventions
Use the lowest effective dose for the shortest time; a low dose still exerts maximal inhibition of platelet function while minimizing adverse effects and limiting prostacyclin production in the vessel wall. Give aspirin after meals or with food or an antacid to reduce gastric irritation; food slows but does not change the total amount absorbed. Tell patients not to crush or chew enteric-coated tablets, which are designed to pass through the stomach and dissolve in the small intestine, and not to take antacids within 1 – 2 hr of enteric-coated aspirin, since calcium carbonate can decrease aspirin's effects. Manage side effects such as stomach irritation by taking the dose with food or switching to a different NSAID, and administer all doses exactly as prescribed.
For aspirin overdose, additional interventions may apply. Removing aspirin from the stomach by inducing vomiting is rarely recommended and usually inappropriate, because it can cause aspiration in patients with altered mental status or convulsions. Activated charcoal can prevent further absorption of salicylate; early administration decreases absorption, and bicarbonate enhances elimination. A laxative may be given with activated charcoal to speed GI evacuation. Provide supportive care, including IV fluids to maintain blood pressure and support the organs, and provide patient education on dosing, side effects, and precautions.
Patient Education and Teaching
Give patients written instructions and time to ask questions, and encourage them to voice any doubts before taking the medication. Have patients take salicylates with a full glass of water and stay upright for 15 – 30 min after a dose to prevent irritation that can cause trouble swallowing. Tell patients to report tinnitus; unusual bleeding of the gums; bruising; black, tarry stools; or fever lasting longer than 3 days, as these signal adverse reactions. Caution against concurrent alcohol use to reduce gastric irritation, since 3 or more glasses of alcohol per day raise GI bleeding risk. Warn against taking aspirin concurrently with acetaminophen or NSAIDs for more than a few days unless directed, to prevent analgesic nephropathy (kidney damage from long-term use of analgesics, especially OTC products containing phenacetin or acetaminophen, and NSAIDs such as aspirin or ibuprofen). Explain that aspirin interferes with normal clotting and raises bleeding risk, and to use caution with activities that could cause injury. Teach patients on a sodium-restricted diet to avoid effervescent or buffered-aspirin preparations because of their high sodium content. Tell patients not to take aspirin with a strong vinegar-like odor, which means it is breaking down and should be discarded. Advise patients on long-term therapy to tell providers about the regimen before surgery; aspirin may need to be withheld for one week before surgery because of perioperative bleeding risk. Public health authorities warn against giving aspirin to children or adolescents with varicella (chickenpox) or influenza-like or viral illness because of the association with Reye's syndrome; more than 80 percent of children diagnosed with Reye's had taken aspirin in the preceding weeks, and reported cases fell sharply once the warnings spread, so acetaminophen or ibuprofen is used instead (AAP). Although aspirin is approved for children older than age 3, those recovering from chickenpox or flu-like symptoms should never take it. Patients on prophylactic aspirin should take only the prescribed dose, since higher doses provide no added benefit.
Evaluation and Desired Outcomes
Desired outcomes depend on the indication: relief of mild to moderate pain (headache, toothache, muscle aches), reduction of inflammation and swelling in arthritis and other inflammatory conditions, prevention of blood clots to lower heart attack and stroke risk, reduction of fever, and improved blood flow in conditions such as peripheral artery disease.
Frequently Asked Questions
Why should aspirin never be given to a child with fever or the flu?
Because of Reye's syndrome, a rare but serious illness that damages the liver and brain and is linked to aspirin use during a viral infection such as chickenpox or influenza. Acetaminophen or ibuprofen is used instead for fever or pain in children and teenagers.
Is a daily aspirin still recommended to prevent a first heart attack?
Not for everyone. The 2022 USPSTF guidance recommends against starting low-dose aspirin for primary prevention in adults 60 and older and calls for an individualized decision in adults 40 to 59 at higher cardiovascular risk. Patients who already have heart disease (secondary prevention) generally continue aspirin as directed.
How long before surgery should aspirin be stopped?
Aspirin may need to be withheld for about a week before surgery because it prolongs bleeding time for 4 to 7 days. Patients on long-term therapy should tell their provider about the regimen so the timing can be planned, not stopped on their own.
What is the main adverse effect to watch for?
Bleeding. That includes GI bleeding, prolonged bleeding time, and bruising, with higher risk in patients who have ulcer disease or who take other blood thinners or NSAIDs. Report black tarry stools, unusual bruising, or bleeding gums.
Why does aspirin's antiplatelet effect last longer than its short half-life?
Aspirin blocks the cyclooxygenase enzyme in platelets irreversibly. A platelet cannot make new enzyme, so the effect lasts the platelet's lifespan (about 7 to 10 days) even though the drug itself clears from the blood in roughly 20 to 30 minutes.
What are early signs of aspirin toxicity?
Ringing in the ears (tinnitus), headache, hyperventilation, drowsiness, confusion, nausea, sweating, and agitation. If these appear, withhold the dose and notify the provider, since salicylate toxicity can escalate.