| Aspirin Pharmacology |
| Aspirin |
| About Aspirin |
| Salicylate, Non narcotic analgesic, anti pyretic ,anti inflammatory. |
| Mechanism of Action of Aspirin |
| Aspirin has analgesic, anti-inflammatory and antipyretic action. Analgesic action: Central action: Aspirin acts on the Hypothalamus and inhibits the generation of pain impulses. Peripheral action: It acts by inhibition of Prostaglandin (PGs) synthesis by blocking the activity of the precursor enzyme cyclo-oxygenase. Anti-inflammatory action: It acts by inhibiting Prostaglandin (PGs) synthesis and their release at the site of injury. Prostaglandins cause tenderness and amplify the action of other algesics. Aspirin inhibits cyclo-oxygenase enzyme and antagonizes prostaglandin actions. It also inhibits other inflammatory mediators. Antipyretic action: Aspirin lowers fever by affecting thermoregulation in the CNS and by inhibiting the action of prostaglandins peripherally. Aspirin inhibits the production of prostaglandin E1 which is the powerful pyretic agent. Anticoagulant action: Aspirin inhibits the synthesis of Thromboxane A2 and Prostacyclin (PGI2). This leads to inhibition of platelet aggregation. |
| Pharmacokinets of Aspirin |
| Absorption: Aspirin is rapidly and completely absorbed after oral administration. Distribution: It is widely distributed in the body in protein bound form. Metabolism: It is completely metabolised in the liver. Excretion: Excreted in the urine. |
| Onset of Action for Aspirin |
| 5-30 minutes |
| Duration of Action for Aspirin |
| 1 – 4 hours |
| Half Life of Aspirin |
| 15 – 20 minutes |
| Side Effects of Aspirin |
| 1.Nausea, 2.Vomiting, 3.Diarrhoea, 4.Gastrointestinal bleeding, 5.Abdominal distress, 6.Dyspepsia, 7.Dizziness, 8.Blurred vision, 9.Tinnitus, 10.Rash, 11.Pruritis 12.Ototoxicity |
| Contra-indications of Aspirin |
| 1.Hypersensitivity to Aspirin and other NSAIDs, 2.Peptic ulcer, 3.Bleeding disorders- Haemophilia, von Willebrand`s disease 4.Chicken pox and flu like syndrome in children |
| Special Precautions while taking Aspirin |
| 1.Hepatic impairment 2.Renal impairment 3.Cardiovascular diseases- hypertension 4.Gastrointestinal diseases 5.Hypoprothrombinemia 6.Pre existing asthma 7.Patient on anticoagulant therapy 8.Diabetes |
| Pregnancy Related Information |
| Use with caution 3rd trimester: Contraindicated |
| Old Age Related Information |
| Use with caution |
| Breast Feeding Related Information |
| Use with caution. |
| Children Related Information |
| Use with caution NEONATES: contraindicated |
| Indications for Aspirin |
| 1.Rheumatoid arthritis, 2.Ankylosing spondylitis, 3.Acute gout, 4.Joint disorders e.g. inflammatory disease in joints, crystal deposition in the joints, 5.Osteoarthritis, 6.For the relief of fever, pain and inflammation in dental, minor surgery and orthopedic 7.Dysmenorrhoea, 8.Rheumatic fever 9. Juvenile arthritis 10.Migraine |
| Interactions for Aspirin |
| Drugs Affecting Aspirin: Activated charcoal: Decreases absorption of aspirin. Antacids Urinary alkalizers and Cortiosteroids: Decrease efficacy of aspirin. Drugs affected by aspirin: Alcohol: Risk of G.I. ulceration increases; may also prolong bleeding time. ACE inhibitors: Antihypertensive action decreased. Oral Anticoagulants : May potentiate effect. Methotrexate: Effect potentiated. Tetracycline: Efficacy decreased. Tricyclic Antidepressants – Effect potentiated. Nitroglycerin: May result in unexpected hypotension. Beta-adrenergic Blockers – Antihypertensive effect blunted. NSAIDs: May decrease serum concentration. Sulfonylureas and Exogenous Insulin: In high doses may potentiate these drugs. Valproic Acid: Potentiates effect. Spironolactone: May inhibit diuretic effect. Probenecid & Sulfinpyrazone : Antagonise uricosuric effect (In doses > 3gm/day – uricosuric effect) Lab Tests: Thyroid Function Tests: Increase in PBI Serum Uric Acid Levels: Increased by levels less than 10 mg/dl and decreased by levels> 10 mg/dl. Urine Glucose: False negative by glucose oxidase method. False positive results by reduction method. Urinary Ketones: Produce reddish colour. |
| Typical Dosage for Aspirin |
| Adult: Analgesic, antipyretic: 325 – 650mg 3 -4 times daily. Anti-inflammatory, Arthritis: 3 g / day in divided doses increases the dose if needed. Maintenance: 3.6 – 5.4 g / day in divided doses. Rheumatic fever: 4.9 – 7.8 g / day in 3 – 4 divided doses for 1- 2 weeks For prophylaxis of venous thromboembolism after total hip replacement: 650 mg twice a day started 1 day before surgery and continued for 2 weeks. For other platelet aggregation inhibitory uses: 325 to 1300 mg daily according to individual needs. For migraine: 300 – 600 mg to be taken at the first sign of migraine attack and repeated 4 – 6 hourly until suppress mild attacks. Children: Arthritis: 60 – 130 mg / kg body weight /day in divided doses Anti-inflammatory: 60 – 125 mg / kg daily in 4 – 6 hours Analgesic and Antipyretic: Adults: 1 to 2 tablets (325 to 650 mg) orally every 4 hours. Children under 12: 10 to 15 mg/kg every 6 hours, not to exceed total daily dose of 2.4 g. |
| Schedule of Aspirin |
| N/A |
| Storage Requirements for Aspirin |
| N/A |
| Effects of Missed Dosage of Aspirin |
| N/A |
| Effects of Overdose of Aspirin |
| N/A |