WHO Model Prescribing Information: Drugs Used in Anaesthesia
(1989; 60 pages) [French] View the PDF document
Table of Contents
View the documentPreface
View the documentIntroduction
Open this folder and view contentsPremedication
Open this folder and view contentsGeneral anaesthetics and oxygen
Open this folder and view contentsLocal anaesthetics
Close this folderNon-opioid analgesics
View the documentAcetylsalicylic acid
View the documentParacetamol
Open this folder and view contentsOpioid analgesics and antagonists
Open this folder and view contentsMuscle relaxants and cholinesterase inhibitors
Open this folder and view contentsBlood substitutes
Open this folder and view contentsSolutions for correcting water and electrolyte imbalance
Open this folder and view contentsAntacid for use in obstetric practice
View the documentAnaesthesia at the District Hospital
View the documentSelected WHO publications of related interest
View the documentBack cover
 

Acetylsalicylic acid

Group: non-opioid analgesic
Tablet: 100-500 mg
Suppository: 50-150 mg

General information

Acetylsalicylic add has anti-inflammatory, analgesic, antipyretic, antirheumatic and antithrombotic activity. In part these effects are due to inhibition of the synthesis of endogenous prostaglandins.

It is hydrolysed primarily in the gut and the liver and excreted mainly in the urine, both as free salicylic acid and as inactive metabolites. The plasma half-life of salicylate resulting from doses of 2-3 g of acetylsalicylic acid is approximately 3 hours. With higher doses it is significantly longer.

Clinical information

Uses

Symptomatic relief of mild to moderate pain.

Dosage and administration

Adults: 300-900 mg every 4-6 hours as required (max 4 g/day).

Children:

6-12 years: 300-400 mg every 6 hours.
3-5 years: 200-300 mg every 8 hours.
1-2 years: 50-150 mg every 6 hours.

Treatment should not be continued for more than 5 days except on medical advice.

Administration with food or a full glass of water reduces gastric irritation. Rectal absorption is slow and incomplete, but suppositories are of value in patients unable to take oral dosage forms.

Contraindications

• Hypersensitivity to acetylsalicylic acid.

• Bleeding disorders, anticoagulant therapy, haemorrhagic stroke, active peptic ulcer or gastritis.

• Chronic renal insufficiency.

Reye’s syndrome (a rare but often fatal non-inflammatory encephalopathy and fatty metamorphosis of the liver) has been reported in children and adolescents with influenza or chickenpox who have received acetylsalicylic acid. The risk is remote but it is readily avoided by withholding the drug in these circumstances.

To avoid the risk of haemorrhage acetylsalicylic acid should not be administered within 7 days of an elective surgical operation.

Precautions

Symptoms of hypersensitivity are more likely to occur in:

• patients with asthma, urticaria or chronic rhinitis

• patients who have developed skin rashes or anaphylactic phenomena after exposure to other nonsteroidal anti-inflammatory agents.

A mild haemolytic reaction may occur in patients with glucose-6-phosphate dehydrogenase deficiency.

Young children are particularly susceptible to the dose-related toxic effects of acetylsalicylic acid. They should never receive more than the maximum recommended dose and stocks of tablets should never be left within their reach.

Use in pregnancy

Normal use of acetylsalicylic add carries no apparent risk during early pregnancy. However, it should not be taken in the last 3 months of pregnancy since it has been reported to prolong labour and contribute to maternal and neonatal bleeding.

Adverse effects

Hypersensitivity reactions, which may occasionally be severe, include urticaria, angio-oedema, pruritus and anaphylactic phenomena.

Gastrointestinal effects including dyspepsia, heartburn, epigastric distress and nausea are common and sometimes severe. Gastrointestinal bleeding can result from acute mucosal erosion or reactivation of peptic ulceration. It is commonly occult but occasionally profuse and even fatal.

Inhibition of platelet aggregation may result in prolongation of bleeding time. Leukopenia, thrombocytopenia, purpura and pancytopenia have rarely been reported.

Drug interactions

The therapeutic actions of anticoagulants may be potentiated.

Conversely, the efficacy of uricosuric agents and spironolactone may be reduced.

Co-administration of acetylsalicylic acid and corticosteroids greatly increases the risk of gastrointestinal bleeding.

Overdosage

Acute ingestion of 20-25 g by an adult, or 4 g by a small child, can be lethal and smaller quantities can cause serious toxic effects.

Characteristic early signs of overdosage include nausea and vomiting, abdominal pain and tinnitus that may ultimately progress to deafness. These are followed by flushing, sweating and hyperventilation with respiratory alkalosis. In severe cases metabolic acidosis and coma supervene.

Gastric lavage should be carried out immediately. Failing this, vomiting should be induced. Hyperthermia, dehydration, acidosis and potassium deficiency should be corrected symptomatically.

Whole blood transfusion may be necessary in the event of spontaneous haemorrhage. It is unnecessary additionally to prescribe vitamin K routinely.

Forced alkaline diuresis accelerates excretion of salicylate. However, when the serum salicylate concentration is dangerously high or when grave signs develop, such as unresponsive acidosis, impaired urinary output, pulmonary oedema, persistent seizures or coma, haemodialysis may offer the only hope of survival.

Storage

Acetylsalicylic add tablets should be kept in tightly closed containers. If an odour of acetic acid is perceptible on opening the container, the tablets should be discarded. Suppositories should be stored below 15°C.

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