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Toxicology [advanced]

Include in assessment

  • History – what taken, how much, when, why, co-ingestion (e.g. alcohol)
  • Examination – GCS, pupils, localising signs, track marks, burns/blistering, skin colour/sweating
  • 12 lead ECG
  • Bloods: usual bloods (FBC, U&Es, LFTs, INR, CRP, glucose) plus venous blood gas, urine tox screen if available, paracetamol level, and salicylate level if salicylism/↓GCS/↑anion gap
  • Osmolar gap (true measured serum osmolality – calculated serum osmolality (Na+x2 + urea + glucose)): if >10, something else is in system causing difference e.g. alcohols/glycols
  • Anion gap ((Na+ + K+) – (Cl- + HCO3-)): normal is 3-12, increases when a new acid has been added to body (e.g. a toxin which has been converted to an acid; lactate; ketoacids)

Common toxidromes

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Management

General management

  • Activated charcoal (50g drink)
    • Can be given in overdoses <1 hour of ingestion (<4 hours if tricyclic) to reduce absorption of many orally ingested toxins
    • Only if patient can swallow properly (must have GCS 15)
    • NOT FOR: acids&alkalis, alcohols, metals, organic solvents 
  • Supportive ABCDE-style management is the major part of management for most overdoses is continuous, supportive ABCDE-style management
    • A: recovery position, airway adjuncts
    • B: oxygen, treat hypoventilation
    • C: cardiac monitor, IV fluids to maintain BP, treat brady/tachycardias (bicarbonate for acidosis)
    • D: diazepam for seizures, treat hypo/hyperthermia
  • Control adverse effects e.g. seizures
  • Haemofiltration may be required (lithium, salicylate, ethanol, ethylene glycol, methanol)

Specific antidotes

A database (e.g. Toxbase) should be used to guide specific management (but examples for common overdoses are below)

  • Paracetamol → N-acetylcysteine
  • Morphine → Naloxone
  • Beta-blocker → Atropine, glucagon
  • Benzodiazepam → Flumazenil (NOT given for overdoses – risk of seizures)
  • Digoxin → Digibind
  • Warfarin → Vitamin K, prothrombin complex concentrate
  • Heparin → Protamine sulphate
  • Carbon monoxide → high-flow oxygen
  • Volatile solvents → Methylene blue for slate-grey cyanosis
  • Iron → Deferoxamine
  • Sulfonylurea → Octreotide
  • Lead → Sodium calcium edetate
  • Cyanide → Vitamin B12
  • Copper → Penicillamine
  • Methotrexate → Folinic acid (Leucovorin), glucarpidase
  • Ethylene glycol or methanol (e.g. antifreeze) → Fomepizole (or, if unavailable, ethanol)
  • Organophosphate (e.g. pesticide) → Atropine, pralidoxime

Psychological management (in deliberate overdose)

  • Assess risk to self/others (consider section if tries to leave)
  • Assess capacity if tries to abscond or refuses treatment
  • Psychiatric referral

Common overdoses

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Test your knowledge

What characteristic ECG changes may be seen in digoxin toxicity?

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What is the most important laboratory result to determine liver function after paracetamol overdose?

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List three toxins that cause a raised anion gap metabolic acidosis

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