Toxicology and Clinical Toxicology
Core concepts
Understand dose–response and the therapeutic index, then the principles of toxico-kinetics: absorption, distribution, metabolism (including bioactivation to reactive metabolites), and elimination. Know toxidromes: opioid (miosis, respiratory depression, CNS depression), anticholinergic (dry skin, flushing, mydriasis, delirium, urinary retention), cholinergic (SLUDGE: salivation, lacrimation, urination, diarrhea, GI cramping, emesis, plus bradycardia and bronchorrhea), sympathomimetic (tachycardia, hypertension, agitation, mydriasis), and serotonin syndrome (clonus, hyperreflexia, hyperthermia).
Management principles
Learn the sequence: stabilize airway/breathing/circulation, decontaminate when appropriate (activated charcoal within about an hour for many ingestions, not for corrosives or hydrocarbons), enhance elimination when indicated (urinary alkalinization for salicylates, hemodialysis for certain toxins), and give specific antidotes. Know key antidotes: naloxone (opioids), N-acetylcysteine (paracetamol), atropine plus pralidoxime (organophosphates), flumazenil (benzodiazepines, cautiously), sodium bicarbonate (tricyclic cardiotoxicity, salicylates), and chelators for heavy metals.
Traps in questions
- Giving activated charcoal for a corrosive or hydrocarbon ingestion (contraindicated).
- Missing that paracetamol toxicity is delayed; early levels may be normal while liver injury evolves.
- Confusing anticholinergic and sympathomimetic toxidromes (both cause tachycardia and mydriasis; anticholinergic adds dry skin and urinary retention).
- Forgetting that flumazenil can precipitate seizures in mixed overdose or chronic benzodiazepine use.
Worked example (rule of thumb)
For a suspected opioid overdose (pinpoint pupils, slow breathing), give naloxone and titrate to adequate respiration, not full arousal. For organophosphate poisoning (cholinergic toxidrome), atropine controls secretions and bradycardia while pralidoxime reactivates the enzyme - give both.