Aspirin

Contents

Indication

Listed in Dosage.

Dosage / Direction For Use

Adult : PO Mild to moderate pain; Fever Initial: 300-900 mg, repeated 4-6 hrly. Max: 4 g daily. Rheumatic disorders 4-8 g daily in divided doses for acute disorders. 5.4 g daily in divided doses for chronic conditions. Angina pectoris; Myocardial Infarction; Acute ischaemic stroke Loading: 150-300 mg. Prophylaxis of cardiovascular events in high-risk patients Long term: 75-150 mg once daily. Short term: 150-300 mg daily. Rectal Mild to moderate pain; Fever As sup: 450-900 mg 4 hrly. Max: 3.6 g daily

Overdosage

Symptoms: Vomiting, dehydration, tinnitus, vertigo, deafness, sweating, warm extremities with bounding pulses, increased respiratory rate, hyperventilation, acid-base disturbance, haematemesis, hyperpyrexia, hypoglycaemia, hypokalaemia, thrombocytopenia, increased INR/PTR, intravascular coagulation, renal failure, pulmonary oedema, CNS effects (e.g. confusion, disorientation, coma, convulsion). Management: Administer activated charcoal if patient presents ingestion of >250 mg/kg within 1 hr. Perform urinary alkalinisation by administration of 1.26% Na bicarbonate then monitor urine pH. Correct metabolic acidosis with 8.4% Na bicarbonate IV. For severe poisoning (plasma conc: >700 mg/L), haemodialysis is the treatment of choice.

Administration

Should be taken with food.

Contraindication

Hypersensitivity to aspirin or other NSAIDs. Peptic ulcer, haemorrhagic disease, coagulation disorder (e.g. haemophilia, thrombocytopenia), gout. Severe hepatic and renal impairment. Children <16 years and recovering from viral infection. Pregnancy (doses >100 mg daily during 3rd trimester) and lactation. Concomitant use with other NSAIDs and methotrexate.

Special Precaution

Patient with dyspepsia or lesion of the GI mucosa, asthma or allergic disorders, anaemia, dehydration, menorrhagia, uncontrolled hypertension, G6PD deficiency, thyrotoxicosis. Patients undergoing surgical procedures. Moderate hepatic and renal impairment. Pregnancy.

Adverse Reactions

Significant: Salicylate sensitivity, tinnitus.Blood and lymphatic system disorders: Anaemia, hypoprothrombinaemia, thrombocytopenia.Gastrointestinal disorders: Dyspepsia, gastric irritation, nausea, vomiting.Nervous system disorders: Dizziness, confusion.Respiratory, thoracic and mediastinal disorders: Asthma, bronchospasm, dyspnea, rhinitis.Skin and subcutaneous tissue disorders: Rash, urticaria.Potentially Fatal: Paroxysmal bronchospasm and dyspnoea. Coma, CV collapse, resp failure, severe hypoglycaemia. Rarely, Reye’s syndrome. Hypersensitivity reactions (e.g. Stevens Johnson syndrome, angioedema), gastrointestinal bleeding and perforation.

Drug Interaction

Increased risk of GI bleeding and ulceration with corticosteroids. Increased risk of bleeding with coumarin anticoagulants (e.g. heparin, warfarin, phenindione) and antiplatelet agents (e.g. clopidogrel, dipyridamole). May result in severe acidosis and increased CNS toxicity with carbonic anhydrase inhibitors (e.g. acetazolamide). Increases the hypoglycaemic effect of sulfonylureas. Reduces binding of phenytoin and valproate to serum albumin leading to increased free concentration of the drugs. Reduces the effect of uricosurics (e.g. probenecid, sulfinpyrazone). Impairs the renal excretion of lithium and digoxin.Potentially Fatal: Increased risk of GI bleeding and ulceration with other NSAIDs. Increased risk of haematological toxicity of methotrexate.

Storage

Store below 25°C

Description

Action

Description: Aspirin is a salicylate that exhibits analgesic, anti-inflammatory, and antipyretic activities. It is a selective and irreversible inhibitor of cyclooxygenase-1 (COX-1) enzyme resulting in direct inhibition of the biosynthesis of prostaglandins and thromboxanes from arachidonic acid. Additionally, it also inhibits platelet aggregation.Synonym: acetylsalicylic acid (ASA).Onset: Platelet inhibition: Within 1 hr (nonenteric-coated); delayed (enteric-coated); 20 minutes (if chewed).Duration: 4-6 hours (immediate-release); Platelet inhibition: Approx 10 days.Pharmacokinetics:Absorption: Rapidly absorbed from the gastrointestinal tract; less reliable (rectal); absorbed through the skin. Partially hydrolysed by esterases to salicylate during absorption in the GI tract. Bioavailability: 50-75% (immediate-release). Time to peak plasma concentration: Approx 1-2 hours (nonenteric-coated); 3-4 hours (enteric-coated); Approx 2 hours (extended-release cap).Distribution: Widely and rapidly distributed into most body tissues and fluids. Crosses the placenta and enters breast milk. Volume of distribution: 170 mL/kg. Plasma protein binding: 80-90%.Metabolism: Metabolised in the liver into salicyluric acid, salicyl phenolic glucuronide, salicylic acyl glucuronide, gentisic acid, and gentisuric acid. Undergoes first-pass metabolism.Excretion: Via urine (75% as salicyluric acid, 10% as salicylic acid). Elimination half-life: 15-20 minutes.