Toxicology
Core concepts
Master the toxidromes (sympathomimetic, anticholinergic, opioid, cholinergic, sedative-hypnotic) and the antidotes: naloxone, N-acetylcysteine, sodium bicarbonate for tricyclics, glucagon and high-dose insulin for beta-blocker overdose, lipid emulsion for local anaesthetic toxicity, and fomepizole for toxic alcohols. Understand the paracetamol nomogram and the timing of N-acetylcysteine. Know the management of organophosphate poisoning (atropine plus pralidoxime) and carbon monoxide (high-flow oxygen, hyperbaric criteria). Cover decontamination principles and the role of activated charcoal.
Traps
Examiners test the mixed overdose where naloxone precipitates withdrawal. Beware the tricyclic overdose with a widened QRS - the answer is sodium bicarbonate, not a class-specific antiarrhythmic. A normal paracetamol level taken too early is falsely reassuring. In organophosphate poisoning, atropine is titrated to secretions, not pupil size.
Rule of thumb
For any overdose with a widened QRS, think tricyclic and give sodium bicarbonate. For any poisoned patient with altered consciousness and hypoventilation, consider naloxone but protect the airway first.
Worked example
A 30-year-old presents drowsy with a respiratory rate of 6, pinpoint pupils, and needle marks: give naloxone titrated to breathing, support ventilation, and observe for re-sedation as naloxone wears off.