Aspirin overdose

Question 1

What happens to aspirin in the body?

Answer 1

Aspirin = acetylsalicylic acid

rapidly hydrolysed to salicylate in GI tract and blood

Question 2

What is aspirin overdose also known as?

Answer 2

salicylate poisoning

Question 3

What dosage defines acute and chronic aspirin overdose?

Answer 3

• Acute toxicity = single ingestion >150mg/kg or >6.5g

* Chronic toxicity = repeated exposure of over >100mg/kg/day

Question 4

Aetiology of aspirin overdose?

Answer 4

• Usually due to accidental ingestion, self-harm, attempted suicide, and incorrect dosing
• Many cold and influenza preparations contain salicylates, meaning consumers may expose themselves to cumulative poisoning

Question 5

Risk factors for aspirin overdose?

Answer 5

• History of self-harm or suicide attempt
• Children <3 years
• Adults >70 years

Question 6

Describe the pathophysiology of aspirin overdose

Answer 6

• Initial systemic effect of tachypnoea due to direct stimulation of brainstem respiratory centre, thus leading to respiratory alkalosis
• Uncoupling of oxidative phosphorylation then occurs to cause concomitant metabolic acidosis

Question 7

How does the half-life of aspirin vary depending on dose?

Answer 7

• Serum-half life increases as the total-body burden of salicylate increases
o Low-dose = 2-4 hours
o Anti-inflammatory dose = 12 hours
o Overdose = over 15 hours

Question 8

Epidemiology of aspirin overdose?

Answer 8

• Reduced by 22% in 1998 with legislation limiting the pack size of analgesics
• Degree of toxicity more severe in elderly, infants, and those with coexisting morbidity
• Use of aspirin in children declined since it was associated with Reye syndrome
• Incidence of unintentional toddler overdose declined by limiting dose of aspirin in chewable, flavoured tablets, restricting the number of tablets in a bottle, and using child-resistant packaging

Question 9

Presenting symptoms of aspirin overdose?

Answer 9

•	Nausea and vomiting
•	Haematemesis
•	Epigastric pain
•	SOB
•	Tinnitus/deafness
•	Malaise and dizziness
•	Coma
•	Seizures
- resp alkalosis
- met acidosis

Question 10

Signs of aspirin overdose on examination

Answer 10

• Tinnitis and/or deafness – early stages of ingestion
• Abnormal behaviour
• Fever and diaphoresis (sweating)
• Tachypnoea
• Hyperpnoea
• Kussmaul’s respirations (deep laboured breathing)
o Often associated with severe metabolic acidosis
• Movement disorders
• Asterixis = Flapping tremor
• Stupor
• Confusion and delirium
• Papilloedema (optic disc swelling caused by increased in ICP)
• Rales (discontinuous clicking/rattling/crackling)
• Low O2 saturations
• Volume depletion

Question 11

Investigations for aspirin overdose?

Answer 11

o ABG – initially respiratory alkalosis, later metabolic acidosis (wide anion gap)
o Blood tests especially:
 Electrolytes
 Serum salicylate level
o CXR (pulmonary oedema)
o ECG (Sinus tachycardia, prolonged corrected QT)