Aspirin overdose
D E F I N I T I ON
Excessive ingestion of aspirin causing toxicity.
AET IOLOGY
Overdose can occur as a result of deliberate self-harm, suicidal intent or by
accident (e.g. in children). Ingestion of 10–20 g can cause moderate-to-severe toxicity
in adults.
Aspirin (acetylsalicylate) increases respiratory rate and depth by stimulating the CNS respiratory
centre. This hyperventilation produces respiratory alkalosis in the early phase. The
body then compensates by increasing urinary bicarbonate and K
þ
excretion, causing
dehydration and hypokalaemia. Loss of bicarbonate together with the uncoupling of
mitochondrial oxidative phosphorylation by salicylic acid and build up of lactic acid can
lead to metabolic acidosis.
In severe overdoses, CNS depression and respiratory failure can occur.
E P IDEMI OLOGY
One of the most common drug overdoses.
H ISTORY
Ascertain the key facts:
. How much aspirin?
. When?
. Any other drugs?
. Have you had any alcohol?
The patient may be asymptomatic initially.
Early symptoms: Flushed appearance, fever, sweating, hyperventilation, dizziness, tinnitus,
deafness.
Late symptoms: Lethargy, confusion, convulsions, drowsiness, respiratory depression, coma.
EXAMI N A T ION
Fever, tachycardia, hyperventilation, epigastric tenderness.
I N V E S T IGATIONS
Blood: Salicylate levels (500–750 mg/L is a moderate overdose; >750 mg/L is a severe
overdose), FBC, U&E (particularly # K
þ
if vomiting), LFT (" AST/ALT), clotting screen
(" PT), glucose and other drug levels (e.g. paracetamol). ABG: May show mixed
metabolic acidosis and respiratory alkalosis.
ECG: May show signs of hypokalaemia – small T waves, U waves.
MANAGEMENT
Acute: Resuscitate with attention to respiratory rate and blood gases. Treat hypovolaemia
(rehydrate), hypokalaemia, hypoglycaemia; vitamin K for hypoprothrombinaemia
(occasionally).
If < 12 h after ingestion: Gastric lavage to empty the stomach, and oral activated charcoal
to bind to and # absorption of the drug.
Moderate cases (500–750 mg/L): Urine alkalinization with IV NaHCO3 (with IV potassium
chloride for hypokalaemia) aims to " salicylate excretion (aim for urine pH 7.5–8.5).
Severe cases (> 750 mg/L) or in severe acidosis: Consider haemodialysis.
In all cases, monitor U&E, glucose (may " or #), temperature, pulse, respiratory rate, BP, urine
output.
COMPL I C A T IONS
Cerebral and pulmonary oedema (" capillary permeability).
Metabolic disturbances (# K
þ, # or " Na
þ, # or " glucose).
Acute renal failure.
P ROGNOS I S
If treated early, prognosis is good.
Note: In children < 4 years, even low doses of aspirin are associated with an increased risk of
developing Reye’s syndrome (metabolic acidosis, liver and CNS disturbances). Aspirin can
also trigger an asthma attack in certain individuals.
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