Management and Treatment of Poisoning
This domain tests decisions, not lists. Candidates must sequence resuscitation before decontamination, justify whether charcoal is indicated, match antidotes to mechanisms, and recognise the narrow set of situations where extracorporeal elimination genuinely alters outcome.
Resuscitation and decontamination
Airway, breathing, circulation and glucose come first; most poisoned patients recover with supportive care. Activated charcoal adsorbs drug if given early - ideally within one hour - at about 1 g/kg with a maximum of 50 g, and is contraindicated with unprotected airway, caustic or hydrocarbon ingestion, ileus or obstruction. It binds poorly to alcohols, metals such as iron and lithium, and strong acids or alkalis. Gastric lavage is reserved for very recent, life-threatening ingestions; whole-bowel irrigation is considered for sustained-release products, pharmacobezoars, and iron or body packers.
Antidotes tied to mechanism
N-acetylcysteine for acetaminophen, naloxone for opioids, fomepizole for methanol and ethylene glycol, hydroxocobalamin for cyanide, physostigmine for anticholinergic delirium (with caution in conduction disease), glucagon and high-dose insulin for beta-blocker toxicity, sodium bicarbonate for tricyclic cardiotoxicity and salicylate alkalinisation, and lipid emulsion for local anaesthetic toxicity.
Enhanced elimination
Haemodialysis is favoured by low molecular weight, low Vd, low protein binding, high water solubility, and toxicity that would otherwise be prolonged. Intermittent haemodialysis is standard for severe salicylate, methanol, ethylene glycol, lithium and theophylline poisoning. Multiple-dose charcoal interrupts enterohepatic recirculation for agents such as carbamazepine and theophylline.
Worked example. A 70 kg adult presents six hours after a salicylate overdose with tinnitus, tachypnoea, altered mental status and arterial pH 7.25; the level is 60 mg/dL. Level alone (>60 mg/dL in chronic exposure, >100 mg/dL acute) would raise the question, but here central nervous system depression and refractory acidosis independently justify haemodialysis. Alkalinisation of urine and serum is started immediately while dialysis is arranged, because it reduces tissue penetration even before elimination is enhanced. Note that the mixed respiratory alkalosis and metabolic acidosis of early salicylism can mask severity on a single gas.
Traps that cost marks
- Giving flumazenil in a mixed overdose or in a benzodiazepine-dependent patient (seizure risk).
- Recommending haemodialysis for a drug with a huge Vd or high protein binding.
- Assuming charcoal works hours after ingestion of a rapidly absorbed drug.
- Withholding acetylcysteine because the nomogram window has passed.