Aspirin (ASA)
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Pharmacology`ASA interferes with the production of prostaglandins in various organs and tissues through acetylation of the enzyme cyclo-oxygenase. Prostaglandins are themselves powerful irritants and produce headaches and pain on injection in man. Prostaglandins also appear to sensitize pain receptors to other noxious substances such as histamine and bradykinin. By preventing the synthesis and release of prostaglandins in inflammation, ASA may avert the sensitization of pain receptors.
The antipyretic activity of ASA is due to its ability to interfere with the production of prostaglandinE 1 in the brain. ProstaglandinE 1 is one of the most powerful pyretic agents known.
The inhibition of platelet aggregation by ASA is due to its ability to interfere with the production of thromboxaneA 2 within the platelet. ThromboxaneA 2 is largely responsible for the aggregating properties of platelets.
When ASA is taken orally, it is rapidly absorbed from the stomach and proximal small intestine. The gastric mucosa is permeable to the nonionized form of ASA, which passes through the stomach wall by a passive diffusion process.
Optimum absorption of salicylate in the human stomach occurs in the pH range of2.15to 4.10. Absorption in the small intestine occurs at a significantly faster rate than in the stomach. After an oral dose of650mg Aspirin, the plasma acetylsalicylate concentration in man usually reaches a level between 0.6and 1.0mg% in 20minutes after ingestion and drops to 0.2mg% within an hour. Within the same period of time, half or more of the ingested dose is hydrolyzed to salicylic acid by esterases in the gastrointestinal mucosa and the liver, the total plasma salicylate concentration reaching a peak between 1or 2hours after ingestion, averaging between 3and 7mg%. Many factors influence the speed of absorption of ASA in a particular individual at a given time; tablet disintegration, solubility, particle size, gastric emptying time, psychological state, physical condition, nature and quantity of gastric contents, etc., all affect absorption.
Distribution of salicylate throughout most body fluids and tissues proceeds at a rapid rate after absorption. Aside from the plasma itself, fluids which have been found to contain substantial amounts of salicylate after oral ingestion include spinal, peritoneal and synovial fluids, saliva and milk. Tissues containing high concentrations of the drug are the kidney, liver, heart and lungs. Concentrations in the brain are usually low, and are minimal in feces, bile and sweat.
The drug readily crosses the placental barrier. At clinical concentrations, from 50%to 90% of the salicylate is bound to plasma proteins especially albumin, while ASA itself is bound to only a very limited extent. However, ASA has the capacity of acetylating various proteins, hormones, DNA, platelets and hemoglobin, which at least partly explains its wide-ranging pharmacological actions.
The liver appears to be the principal site for salicylate metabolism, although other tissues may also be involved. The three chief metabolic products of salicylic acid are salicyluric acid, the ether or phenolic glucuronide and the ester or acyl glucuronide. A small fraction is also converted to gentisic acid and other hydroxybenzoic acids. The half-life of ASA in the circulation is from 13to 19minutes so that the blood level drops quickly after absorption is complete. However, the half-life of the salicylate ranges between 3.5and 4.5hours, which means that 50% of the ingested dose leaves the circulation within that time.
Excretion of salicylates occurs principally via the kidney, through a combination of glomerular filtration and tubular excretion, in the form of free salicylic acid, salicyluric acid, as well as phenolic and acyl glucuronides. Salicylate can be detected in the urine shortly after its ingestion but the full dose requires up to 48hours for complete elimination. The rate of excretion of free salicylate is extremely variable, reported recovery rates in human urine ranging from 10%to 85%, depending largely on urinary pH. In general, it can be stated that acid urine facilitates reabsorption of salicylate by renal tubules, while alkaline urine promotes excretion of the drug.
Indications`ASA Interferes With The Production Of Prostaglandins In Various Organs And Tissues Through Acetylation Of The Enzyme Cyclo-oxygenase. Prostaglandins Are Themselves Powerful Irritants And Produce Headaches And Pain On Injection In Man. Prostaglandins Also Appear To Sensitize Pain Receptors To Other Noxious Substances Such As Histamine And Bradykinin. By Preventing The Synthesis And Release Of Prostaglandins In Inflammation, ASA May Avert The Sensitization Of Pain Receptors.
The Antipyretic Activity Of ASA Is Due To Its Ability To Interfere With The Production Of ProstaglandinE 1 In The Brain. ProstaglandinE 1 Is One Of The Most Powerful Pyretic Agents Known.
The Inhibition Of Platelet Aggregation By ASA Is Due To Its Ability To Interfere With The Production Of ThromboxaneA 2 Within The Platelet. ThromboxaneA 2 Is Largely Responsible For The Aggregating Properties Of Platelets.
When ASA Is Taken Orally, It Is Rapidly Absorbed From The Stomach And Proximal Small Intestine. The Gastric Mucosa Is Permeable To The Nonionized Form Of ASA, Which Passes Through The Stomach Wall By A Passive Diffusion Process.
Optimum Absorption Of Salicylate In The Human Stomach Occurs In The PH Range Of2.15to 4.10. Absorption In The Small Intestine Occurs At A Significantly Faster Rate Than In The Stomach. After An Oral Dose Of650mg Aspirin, The Plasma Acetylsalicylate Concentration In Man Usually Reaches A Level Between 0.6and 1.0mg% In 20minutes After Ingestion And Drops To 0.2mg% Within An Hour. Within The Same Period Of Time, Half Or More Of The Ingested Dose Is Hydrolyzed To Salicylic Acid By Esterases In The Gastrointestinal Mucosa And The Liver, The Total Plasma Salicylate Concentration Reaching A Peak Between 1or 2hours After Ingestion, Averaging Between 3and 7mg%. Many Factors Influence The Speed Of Absorption Of ASA In A Particular Individual At A Given Time; Tablet Disintegration, Solubility, Particle Size, Gastric Emptying Time, Psychological State, Physical Condition, Nature And Quantity Of Gastric Contents, Etc., All Affect Absorption.
Distribution Of Salicylate Throughout Most Body Fluids And Tissues Proceeds At A Rapid Rate After Absorption. Aside From The Plasma Itself, Fluids Which Have Been Found To Contain Substantial Amounts Of Salicylate After Oral Ingestion Include Spinal, Peritoneal And Synovial Fluids, Saliva And Milk. Tissues Containing High Concentrations Of The Drug Are The Kidney, Liver, Heart And Lungs. Concentrations In The Brain Are Usually Low, And Are Minimal In Feces, Bile And Sweat.
The Drug Readily Crosses The Placental Barrier. At Clinical Concentrations, From 50%to 90% Of The Salicylate Is Bound To Plasma Proteins Especially Albumin, While ASA Itself Is Bound To Only A Very Limited Extent. However, ASA Has The Capacity Of Acetylating Various Proteins, Hormones, DNA, Platelets And Hemoglobin, Which At Least Partly Explains Its Wide-ranging Pharmacological Actions.
The Liver Appears To Be The Principal Site For Salicylate Metabolism, Although Other Tissues May Also Be Involved. The Three Chief Metabolic Products Of Salicylic Acid Are Salicyluric Acid, The Ether Or Phenolic Glucuronide And The Ester Or Acyl Glucuronide. A Small Fraction Is Also Converted To Gentisic Acid And Other Hydroxybenzoic Acids. The Half-life Of ASA In The Circulation Is From 13to 19minutes So That The Blood Level Drops Quickly After Absorption Is Complete. However, The Half-life Of The Salicylate Ranges Between 3.5and 4.5hours, Which Means That 50% Of The Ingested Dose Leaves The Circulation Within That Time.
Excretion Of Salicylates Occurs Principally Via The Kidney, Through A Combination Of Glomerular Filtration And Tubular Excretion, In The Form Of Free Salicylic Acid, Salicyluric Acid, As Well As Phenolic And Acyl Glucuronides. Salicylate Can Be Detected In The Urine Shortly After Its Ingestion But The Full Dose Requires Up To 48hours For Complete Elimination. The Rate Of Excretion Of Free Salicylate Is Extremely Variable, Reported Recovery Rates In Human Urine Ranging From 10%to 85%, Depending Largely On Urinary PH. In General, It Can Be Stated That Acid Urine Facilitates Reabsorption Of Salicylate By Renal Tubules, While Alkaline Urine Promotes Excretion Of The Drug.
Safety Information / Warning ASA is one of the most frequent causes of accidental poisonings in toddlers and infants. Tablets should be kept well out of the reach of children.
A possible association between Reye's syndrome and the use of salicylates has been suggested but not established. Reye's syndrome has also occurred in many patients not exposed to salicylates. However, caution is advised when prescribing salicylate-containing medications for children and teenagers with influenza or chickenpox.
Precautions Salicylates should be administered cautiously to patients with asthma and other allergic conditions, a history of gastrointestinal ulcerations, bleeding tendencies, significant anemia or hypoprothrombinemia.
Patients taking ASA daily are at an increased risk of developing gastrointestinal bleeding following the ingestion of alcohol.
Caution is necessary when salicylates and anticoagulants are prescribed concurrently, as salicylates can depress the concentration of prothrombin in the plasma.
Diabetics receiving concurrent salicylate and hypoglycemic therapy should be monitored closely: reduction of the sulfonylurea hypoglycemic drug dosage may be necessary; insulin requirements may change.
Pregnancy: High doses (3g daily) of ASA during pregnancy may lengthen the gestation and parturition time.
Salicylates can produce changes in thyroid function tests.
Sodium excretion produced by spironolactone may be decreased by salicylate administration.
Salicylates in large doses are uricosuric agents, smaller amounts may depress uric acid clearance and thus decrease the uricosuric effects of other drugs.
Salicylates also retard the renal elimination of methotrexate.
Salicylates may alter valproic acid (VPA) metabolism and may displace VPA from protein binding sites, possibly intensifying the effects of VPA. Caution is recommended when VPA is administered concomitantly with salicylates.
Side Effects / Adverse Effects Gastrointestinal: (the frequency and severity of these adverse effects are dose related) nausea, vomiting, diarrhea, gastrointestinal bleeding and/or ulceration, dyspepsia, heartburn.
Ear: tinnitus, vertigo, hearing loss.
Hematologic: leukopenia, thrombocytopenia, purpura, anemia.
Dermatologic and hypersensitivity: urticaria, angioedema, pruritus, skin eruptions, asthma, anaphylaxis.
Miscellaneous: mental confusion, drowsiness, sweating, thirst.
OverdoseSymptoms: In mild overdosage these may include rapid and deep breathing, nausea, vomiting, vertigo, tinnitus, flushing, sweating, thirst and tachycardia. In more severe cases, acid-base disturbances including respiratory alkalosis and metabolic acidosis can occur. Severe cases may show fever, hemorrhage, excitement, confusion, convulsions or coma and respiratory failure.
Treatment: Treatment consists of prevention and management of acid-base and fluid and electrolyte disturbances. Renal clearance is increased by increasing urine flow and by alkaline diuresis but care must be taken in this approach to not further aggravate metabolic acidosis and hypokalemia. Acidemia should be prevented by administration of adequate sodium containing fluids and sodium bicarbonate. Hypoglycemia is an occasional accompaniment of salicylate overdosage and can be managed by glucose solutions. If a hemorrhagic diathesis is evident, give vitaminK. Hemodialysis may be useful in complex acid base disturbances particularly in the presence of abnormal renal function.
Recommended Dosage Analgesic and Antipyretic: Adults: 1 to 2tablets (325to 650mg) orally every 4hours. Children under12: 10to 15mg/kg every 6hours, not to exceed total daily dose of2.4g.
Anti-inflammatory: Adults: 3tablets (975mg) 4to 6times a day, up to 30tablets daily, may be required for optimal anti-inflammatory effect. A blood level between 15and 30mg/100mL is in the desirable therapeutic range.
Children: 60to 125mg/kg daily in 4to 6divided doses.
Platelet Aggregation Inhibitor: For reducing the risk of morbidity and death in patients with unstable angina and in those with previous myocardial infarction: 80to 325mg daily according to the individual needs of the patient, as determined by the physician. Coated Aspirin Daily Low Dose is specifically indicated for these uses.
For reducing the risk of transient ischemic attacks (TIA) and for secondary prevention of atherothrombotic cerebral infarction: 80to 325mg daily according to the individual needs of the patient, as determined by the physician. Coated Aspirin Daily Low Dose is specifically indicated for these uses.
For prophylaxis of venous thromboembolism after total hip replacement: 650mg twice a day (1300mg daily), started 1day before surgery and continued for 14days.
For other platelet aggregation inhibitory uses: 325to 1300mg daily according to individual needs and generally accepted standards of care for each indication.
Supplied / Packaging Aspirin Tablets, 325 mg: Each white tablet, with the Bayer Cross on both sides, contains: ASA 325 mg. Nonmedicinal ingredients: cornstarch, hydroxypropyl methylcellulose and triacetin. Alcohol-, lactose-, paraben-, sodium-, sulfite- and tartrazine-free. Packages of 12, 24, 50, 100 and 200.
Aspirin Caplets, 325 mg: Each white, capsule-shaped tablet (caplet), with BAYER on one side and a score on the other, contains: ASA 325 mg. Nonmedicinal ingredients: cornstarch, hydroxypropyl methylcellulose and triacetin. Alcohol-, lactose-, paraben-, sodium-, sulfite- and tartrazine-free. Packages of 50 and 100.
Aspirin Extra Strength Tablets, 500 mg: Each white tablet, with the Bayer Cross in red ink on one side, contains: ASA 500 mg. Nonmedicinal ingredients: cornstarch, D&C Red #7, FD&C Blue #2, FD&C Red #40, hydroxypropyl methylcellulose, titanium dioxide and triacetin. Alcohol-, lactose-, paraben-, sodium-, sulfite- and tartrazine-free. Packages of 30, 50 and 100.
Aspirin With Stomach Guard 325 mg Tablets: Each round, white, film-coated tablet, with BAYER PLUS in blue ink on one side, contains: ASA 325 mg, calcium carbonate 160 mg, magnesium carbonate 34 mg and magnesium oxide 63 mg. Nonmedicinal ingredients: acacia, carnauba wax, cornstarch, croscarmellose sodium, FD&C Blue #2, hydrogenated vegetable oil, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate 80, polyvinylpyrrolidone, propylene glycol, silicon dioxide, sodium lauryl sulfate, talc, titanium dioxide and triacetin. Lactose-, paraben-, sulfite- and tartrazine-free. Packages of 36.
Aspirin With Stomach Guard Extra Strength 500 mg Caplets: Each white, film-coated caplet, with BAYER PLUS over 500 on one side in blue ink, contains: ASA 500 mg, calcium carbonate 246.2mg, magnesium carbonate 52.3 mg and magnesium oxide 96.9mg. Nonmedicinal ingredients: acacia, carnauba wax, cornstarch, croscarmellose sodium, FD&C Blue #2, hydrogenated vegetable oil, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate 80, polyvinylpyrrolidone, propylene glycol, silicon dioxide, sodium lauryl sulfate, talc, titanium dioxide and triacetin. Lactose-, paraben-, sulfite- and tartrazine-free. Packages of 30 and 60.
Coated Aspirin Caplets, 325 mg: Each pale yellow, enteric coated caplet, with BAYER 325 in brown ink on one side, contains: ASA 325mg. Nonmedicinal ingredients: carnauba wax, cornstarch, D&C Yellow #10, FD&C Yellow #6, hydroxypropyl methylcellulose, methacrylic acid copolymer, polysorbate 80, potassium hydroxide, sodium lauryl sulfate, synthetic black and brown oxides, titanium dioxide and triacetin. Alcohol-, lactose, paraben-, sulfite- and tartrazine-free. Bottles of 50, 100 and 200.
Coated Aspirin Extra Strength Caplets, 500 mg: Each pale yellow, enteric coated caplet, with BAYER 500 in brown ink on one side, contains: ASA 500 mg. Nonmedicinal ingredients: carnauba wax, cornstarch, D&C Yellow #10, FD&C Yellow #6, hydroxypropyl methylcellulose, methacrylic acid copolymer, polysorbate 80, potassium hydroxide, sodium lauryl sulfate, synthetic black and brown oxides, titanium dioxide and triacetin. Alcohol-, lactose-, paraben-, sulfite- and tartrazine-free. Bottles of 50 and 100.
Coated Aspirin Arthritis Pain Relief Caplets, 650 mg: Each orange, enteric coated caplet, with B embossed on one side, contains: ASA 650 mg. Nonmedicinal ingredients: colloidal silicon dioxide, cornstarch, FD&C Yellow #6, gelatin, lactose, maltodextrin, methacrylic acid copolymer, polethylene glycol, sodium hydroxide, sodium lauryl sulfate, talc, titanium dioxide and triethyl citrate. Alcohol-, paraben-, sulfite- and tartrazine-free. Bottles of 100.
Children's Size Aspirin: Each peach-colored tablet, with a pleasant orange taste, with the Bayer Cross on one side and ASPIRIN in a semicircle along the circumference of the other, contains: ASA 80mg USP. Nonmedicinal ingredients: cornstarch, dextrose, FD&C Yellow #6, orange juice flavor and sodium cyclamate. Alcohol-, lactose-, paraben-, sulfite- and tartrazine-free. Bottles of 24 and 90.
Coated Aspirin Daily Low Dose Tablets, 81 mg: Each pale blue colored enteric coated tablet, with 81 in dark blue ink on one side, contains: ASA 81 mg USP. Nonmedicinal ingredients: carnauba wax, cornstarch, croscarmellose sodium, FD&C Blue #1, FD&C Blue #2, hydroxypropyl methylcellulose, lactose, methacrylic acid copolymer, microcrystalline cellulose, polysorbate 80, propylene glycol, sodium lauryl sulfate, titanium dioxide and triacetin. Alcohol-, paraben-, sulfite- and tartrazine-free. Bottles of 24 and 120.