Aspirin is an acetylated salicylate . The analgesic , antipyretic , and anti – inflammatory effects of aspirin are due to actions by both the acetyl and the salicylate portions of the intact molecule as well as by the active salicylate metabolite . Aspirin directly inhibits the activity of the enzyme cyclo – oxygenase to decrease the formation of precursors of prostaglandins and thromboxanes from arachidonic acid . Salicylate may competitively inhibit prostaglandin formation . Aspirin may produce antipyresis by inhibition of prostaglandin synthesis in the hypothalamus to produce peripheral vasodilation resulting in increased cutaneous blood flow , sweating , and heat loss . The platelet aggregation – inhibiting effect of aspirin specifically involves the compound's ability to act as an acetyl donor to the platelet membrane . Aspirin affects platelet function by inhibiting the enzyme prostaglandin cyclooxygenase in platelets , thereby preventing the formation of the aggregating agent thromboxane A₂. This is irreversible ; the effects persist for the life of the platelets exposed . Aspirin may also inhibit formation of the platelet aggregation inhibitor prostacyclin ( prostaglandin I₂ ) in blood vessels ; however ; this action is reversible.

Pain and fever ( treatment ) – Aspirin is indicated to relieve mild to moderate pain such as headache , toothache , and menstrual cramps and to reduce fever . Nonrheumatic inflammation ( treatment ) – Aspirin is indicated to relieve myalgia , musculoskeletal pain , and other symptoms of nonrheumatic inflammatory conditions such as athletic injuries , bursitis , capsulitis , tendinitis , and nonspecific acute tenosynovitis . Rheumatoid arthritis , juvenile arthritis , osteoarthritis and related rheumatic diseases ( treatment ) ; rheumatic fever ( treatment ) . Platelet aggregation ( prophylaxis ) – Aspirin is indicated as a platelet aggregation inhibitor in the following : Transient ischemic attacks in males ; Cerebral thromboembolism ; Myocardial infarction ; Myocardial reinfarction ; thromboembolism following orthopedic ( hip ) surgery ( especially total hip replacement ) and in patients with arteriovenous shunts . Aspirin , alone or in combination with dipyridamole , may provide some protection against the development of thromboembolic complications in patients with mechanical prosthetic heart valves . Aspirin is also indicated , alone or in combination with dipyridamol , to reduce the risk of thrombosis and / or reocclusion of saphenous vein aortocoronary bypass grafts following coronary bypass surgery and of prosthetic or saphenous vein femoral popliteal bypass grafts . Long – term aspirin therapy may also be indicated for maintaining patency following coronary or peripheral vascular angioplasty and for treating patients with peripheral vascular insufficiency caused by arteriosclerosis . Aspirin is indicated for its anti – inflammatory , antipyretic , and antithrombotic effects in the treatment of Kawasaki disease in children .

a – Those indicating need for medical attention: Anaphylactoid reaction ( bluish discoloration or flushing or redness of skin ; coughing ; difficulty in swallowing ; dizziness or feeling faint ; stuffy nose ; swelling of eyelids , face or lips ) ; Anemia ; Hemolytic anemia ; Bronchospastic allergic reaction ( shortness of breath , troubled breathing in chest and / or wheezing ) ; Allergic dermatitis ( skin rash , hives or itching ) ; Gastrointestinal ulceration , possible with bleeding ; Hearing loss ; Tinnitus .
b – Those indicating need for medical attention only if they continue or are bothersome: Gastrointestinal irritation ( mild stomach pain ; heartburn or indigestion ; nausea with or without vomiting ) .

Hypersensitivity to salicylates , other NSAIDs , or any component of the formulation ; Asthma ; Rhinitis ; Nasal polyps ; Inherited or acquired bleeding disorders ( including factor VII and factor IX deficiency ) ; Use in children ( < 16 years of age ) for viral infections ( chickenpox or flu symptoms ) ; Pregnancy ( 3rd trimester especially ).

Risk – benefit should be considered when the following medical problems exist : Anemia ; Conditions predisposing to fluid retention , such as compromised cardiac function or hypertension ; Erosive gastritis or peptic ulcer ; Gout ; Hepatic function impairment ; Hypoprothrombinemia or vitamin K deficiency ; Renal function impairment ; Thyrotoxicosis ; Glucose – 6 – phosphate dehydrogenase ( G6PD ) deficiency .

Prolonged concurrent use of acetaminophen with aspirin is not recommended because chronic , high dose administration of the combined analgesics significantly increases the risk of analgesic nephropathy . Acidification of the urine by urinary acidifiers such as ammonium chloride , vitamin C and potassium or sodium phosphates decreases salicylate excretion , leading to increased salicylate plasma concentrations . Concurrent use of alcohol or other NSAIDs with aspirin may increase the risk of gastrointestinal side effects , including ulceration and GI blood loss . Alkalinization of the urine by urinary alkalizers such as carbonic anhydrase inhibitors , citrates or sodium bicarbonate and chronic high – dose use of antacids , especially calcium and / or magnesium containing , increases salicylate excretion , leading to decreased salicylate plasma concentrations , reduced effectiveness , and shortened duration of action . Aspirin may displace a coumarin – or indandione – derivative anticoagulant from its protein – binding sites , and in high doses , may cause hypoprothrombinemia , leading to increased anticoagulation and risk of bleeding . The potential occurrence of GI ulceration or hemorrhage during aspirin therapy may cause increased risk to patients receiving anticoagulant or thrombolytic therapy . Aspirin may decrease hydantoin metabolism , leading to increases in hydantoin plasma concentrations , efficacy , and / or toxicity . The effects of oral antidiabetic agents or insulin may be increased by large doses of aspirin . Concurrent use of bismuth subsalicylate with large doses of aspirin may increase the risk of salicylate toxicity . Valproic acid may cause hypoprothrombinemia and inhibit platelet aggregation ; concurrent use with aspirin may increase the risk of bleeding because of additive interferences with blood clotting . Corticosteroids or corticotropin may increase salicylate excretion , resulting in lower plasma concentrations and increased salicylate dosage requirement . In addition to increasing the risk of ototoxicity , concurrent use of furosemide with high doses of aspirin may lead to salicylate toxicity because of competition for renal excretory sites . Concurrent use with cellulose – containing laxatives may reduce the salicylate effect because of physical binding or other absorptive hindrance ; medications should be administered 2 hours apart . Aspirin may displace methotrexate from its binding sites and decrease its renal clearance , leading to toxic methotrexate plasma concentrations . Concurrent or sequential administration of vancomycin with aspirin should be avoided because the potential for ototoxicity may be increased . Concurrent use of aspirin is not recommended when probenecid or sulfinpyrazone are used to treat hyperuricemia or gout , because the uricosuric effect of these medications may be decreased . Also , these medications may decrease renal excretion and increase plasma concentrations and toxicity of aspirin . Concurrent use of salicylate acid or other topical salicylates may increase the risk of salicylate toxicity if significant quantities are absorbed .

During prolonged high – dose therapy – Hematocrit determinations ; Hepatic function determinations ; Serum salicylate concentrations .

Take with food or large volume of water or milk to minimize GI upset .

Usual adult and adolescent dose :
Analgesic / antipyretic – Oral , 325 to 500 mg every three hours , 325 to 650 mg every four hours , or 650 mg to 1000 mg every six hours . Antirheumatic ( nonsteroidal anti – inflammatory ) – Oral , 3.6 to 5.4 grams a day in divided doses . In acute rheumatic fever , up to 7.8 grams a day in divided doses may be given . Platelet aggregation inhibitor – Oral , 80 to 325 mg a day with the following exceptions : Transient ischemic attacks in males or cerebral thromboembolism – Oral , 1 gram a day . Dosage may be reduced to 325 mg a day if the patient is unable to tolerate the higher dose . Transient ischemic attacks occurring in association with mitral valve prolapse – Oral , 325 mg to 1 gram a day . Prevention of thrombosis or occlusion of coronary bypass graft – Oral , 325 mg seven hours postoperatively ( via a nasogastric tube ) , then 325 mg three times daily , concurrently with 75 mg of dipyridamole . Dipyrida – mole may be discontinued one week postoperatively , but aspirin should be continued indefinitely .

Usual pediatric dose :
Analgesic / antipyretic – Oral , 1.5 grams per square meter of body surface a day in 4 to 6 divided doses ; or for
Children up to 2 years of age : Dosage must be individualized by physician .
Children 2 to 4 years of age : Oral , 160 mg every 4 hours .
Children 4 to 6 years of age : Oral , 240 mg every 4 hours .
Children 6 to 9 years of age : Oral , 320 to 325 mg every 4 hours .
Children 9 to 11 years of age : Oral 320 to 400 mg every 4 hours .
Children 11 to 12 years of age : Oral , 320 to 480 mg every 4 hours .
Antirheumatic ( nonsteroidal anti – inflammatory ) – Oral , 80 to 100 mg per kg of body weight a day in divided doses .
Kawasaki disease – During the early febrile stage : Oral , 80 to 120 mg ( average 100 mg ) per kg of body weight a day in 4 divided doses for 14 days or until inflammation has subsided .
Kawasaki disease – During the convalescent stage : Oral , 3 to 5 mg per kg of body weight a day as a single dose . If no coronary artery abnormalities occur , treatment is usually continued for a minimum of eight weeks . If coronary artery abnormalities occur , it is recommended that treatment be continued for at least one year , even if the abnormalities regress , and longer if abnormalities persist .

• Tablet , 80 mg .

• USP DI, 2004
• Up To Date, Vol. 13.3 (2005)
• Martindale, The Complete Drug Reference, 34 rd edition 2005