Aspirin Overdose Flashcards
Define aspirin overdose.
Salicylate poisoning is the result of ingestion of chemicals metabolised to salicylate. Acute or chronic salicylate exposure, characterised by acid-base disturbances, electrolyte abnormalities, and CNS effects.
The most common source of salicylate poisoning = aspirin (acetylsalicylic acid), which is rapidly hydrolysed to salicylate in the GI tract, liver, and bloodstream.
What dosages of aspirin are required for acute and chronic poisoning?
Acute toxicity may occur after ingestion of a single dose of aspirin or the equivalent of >150 mg/kg or >6.5 g.
Chronic poisoning tends to occur as a result of repeated exposure to high-dose aspirin or equivalent (150 mg/kg/day), particularly in the setting of renal insufficiency.
What is each tablet of aspirin dose? What is the maximum recommended dosage?
- Aspirin usually comes as 300mg tablets.
- The usual dose is 1 or 2 tablets every 4 to 6 hours.
- You shouldn’t take more than 12 in 24hours
How common is aspirin overdose?
In 2000 about 1 million deaths were due to suicide of which a quarter were attributed to ingestion of chemicals.
In the UK, deaths by suicidal overdose of analgesics, including salicylates, were reduced by 22% in the year immediately after the introduction in 1998 of legislation limiting the pack size of analgesics that could be purchased
What are the dose related toxicities?
- 150mg/kg: mild toxicity.
- 250mg/kg: moderate
- >500mg/kg: severe toxicity. Levels over 700mg/L are potentially fatal.
What are the signs and symptoms of aspirin overdose?
Unlike paracetamol, there are many early features:
- Vomiting, dehydration, hyperventilation, tinnitus, vertigo, sweating.
- Rarely ↓GCS, seizures, ↓BP and heart block, pulmonary oedema, hyperthermia.
Patients present initially with respiratory alkalosis due to a direct stimulation of the central respiratory centres and then develop a metabolic acidosis. Hyper- or hypoglycaemia may occur.
What metabolic abnormalities occur with aspirin overdose and why?
Patients present initially with respiratory alkalosis due to a direct stimulation of the central respiratory centres and then develop a metabolic acidosis
How do you diagnose aspirin overdose?
- Mainly from history but patient may not tell truth about what has been taken
- Use MIMS colour index, EMIMS images, BNF descriptors or computerised system “TICTAC” to identlfy tablets and plan specific treatment
- Use TOXBASE for managing acute poisoning
Bloods:
- Check paracetamol and salicylate levels - always
How do you manage acute posioning?
List some common causes of acute posioning that can cause these presentations:
- Fast/irregular pulse
- Respiratory depression
- Hypothermia
- Hyperthermia
- Coma
- Seizures
- Constricted pupils
- Fast or irregular pulse: Salbutamol, antimuscarinics, tricyclics, quinine, or phenothiazine poisoning.
- Respiratory depression: Opiate or benzodiazepine toxicity.
- Hypothermia: Phenothiazines, barbiturates.
- Hyperthermia: Amphetamines, maois, cocaine, or ecstasy.
- Coma: Benzodiazepines, alcohol, opiates, tricyclics, or barbiturates.
- Seizures: Recreational drugs, hypoglycaemic agents, tricyclics, phenothiazines, or theophyllines.
- Constricted pupils: Opiates or insecticides (organophosphates.
List some common causes of acute poisoning which can present with:
- dilated pupils
- hyperglycaemia
- hypoglycaemia
- renal impairment
- metabolic acidosis
- increased osmolality
- Dilated pupils: Amphetamines, cocaine, quinine, or tricyclics.
- Hyperglycaemia: Organophosphates, theophyllines, or maois.
- Hypoglycaemia: Insulin, oral hypoglycaemics, alcohol, or salicylates.
- Renal impairment: Salicylate, paracetamol, or ethylene glycol.
- Metabolic acidosis: Alcohol, ethylene glycol, methanol, paracetamol, or carbon monoxide poisoning.
- ↑Osmolality: Alcohols (ethyl or methyl); ethylene glycol
What other investigations would you do for aspirin overdose?
- ABG - first respiratory alkalosis then metabolic acidosis; wide anion gap
- U&Es - hypokalaemia, hypocalcaemia, and/or hypomagnesaemia may be present
- Serum salicylate - +ve/-ve; check every 2-4 hours to peak. Repeated after 2h, due to continuing absorption if a potentially toxic dose has been taken
- Urea and creatinine - but renal failure is rare
- Toxicology screen - broad work up
- Urinalysis - pH and monitor output (?catheterisation)
- Other: glucose (beware of hypoglycaemia), ketones, FBC, LFTs (AST/ALT may be elevated with coagulopathy),
Imaging:
- ECG - common sinus tachycardia, prolonged QT or ventricular dysrhythmia; torsades de pointes may be present, monomorphic ventricular tachycardia
- CXR - pulmonary oedema (indication for urgent haemodialysis)
How do you manage aspirin overdose?
ABCDE
Correct dehydration
Keep monitoring
Give activated charcoal - GI tract decontamination
- If presents <1hr
- In delayed presentation too or slow-release formulations or bezoar formation (can delay absorption) -
- At least one dose of 1g/kg (max50g) but consider repeat doses 4hr apart.
Correct acidosis.
- If plasma salicylate level >500mg/L (3.6mmol/L) or severe metabolic acidosis, consider alkalinization of the urine, eg with 1.5L 1.26% sodium bicarbonate iv over 3h.
- Aim for urine pH 7.5–8. nb: monitor serum K+ as hypokalaemia may occur, and should be treated (caution if aki).
Dialysis
- may well be needed if salicylate level >700mg/L, and if aki or heart failure, pulmonary or cerebral oedema, confusion or seizures, severe acidosis despite best medical therapy, or persistently ↑plasma salicylate.
- Contact nephrology early.
Refer to psychiatry
What are the complications of aspirin overdose?
ARDS - probability in patients with salicylate levels of 80 mg/dL or higher, or with lower levels if ingestion is subacute or chronic.
Cardiac arrest - probability in patients with prolonged corrected QT interval, particularly when combined with bradycardia or extremes of pH.
Seizures - with salicylate levels of 80 mg/dL or higher.
Drug-induced hepatitis
What is the prognosis with aspirin overdose?
Salicylate levels are predictors of outcome - >80mg/dL in adults –> increased likelihood of fatal ingestion
Time from ingestion to treatment - substantial mortality if interval between ingestion and treatment exceeds 12 hours
