PharmacologyTier 1Medical Sciences concept

Toxidrome recognition (cholinergic, anticholinergic, sympathomimetic, opioid)

Core concept

A toxidrome is the receptor pharmacology read off the bedside: pupils, skin, bowel sounds, temperature, mental state, vitals
Two discriminators do most of the work: the skin (sweaty vs dry) and the bowel sounds

	Pupils	Skin	Bowel sounds	HR/BP	Mental state
Cholinergic	Miosis	Wet - sweaty, salivating	Hyperactive, diarrhoea	Brady, hypotension	Confusion, coma, fasciculations
Anticholinergic	Mydriasis	Dry, hot, flushed	Absent, retention	Tachy, hypertension	Agitated delirium, mumbling
Sympathomimetic	Mydriasis	Wet - diaphoretic	Normal/inc	Tachy, hypertension	Agitation, psychosis
Opioid	Pinpoint miosis	Normal	dec	Brady, hypotension	dec consciousness, dec RR
Sedative-hypnotic	Normal	Normal	Normal/dec	Normal or dec	CNS depression, normal vitals otherwise
Serotonergic	Mydriasis	Wet	inc	Tachy	Clonus, hyperreflexia

Anticholinergic vs sympathomimetic - both dilated and tachycardic; the skin separates them (dry vs sweaty)
Opioid vs sedative-hypnotic - both depressed; the pupils and respiratory rate separate them

Cholinergic - organophosphates, carbamates, nerve agents, physostigmine, nicotine
- Muscarinic: DUMBELS - Diarrhoea, Urination, Miosis, Bronchorrhoea/Bronchospasm, Emesis, Lacrimation, Salivation
- Nicotinic: MTWtHF - Mydriasis, Tachycardia, Weakness, Hypertension, Fasciculations
- Bronchorrhoea and bronchospasm kill, not bradycardia
- Atropine titrated to drying of secretions (large doses, doubling) + pralidoxime (reactivates cholinesterase before "ageing") + benzodiazepines
Anticholinergic - TCAs, antihistamines, antipsychotics, atropine, benztropine, datura
- Blind as a bat, dry as a bone, red as a beet, hot as a hare, mad as a hatter, full as a flask
- Check the ECG for QRS widening - a TCA is the one that kills
Sympathomimetic - amphetamines, cocaine, MDMA, synthetic cathinones, theophylline, salbutamol
- Benzodiazepines are the treatment for agitation, hypertension and tachycardia
- Cocaine chest pain: benzodiazepines, nitrates, aspirin - avoid pure beta-blockade (unopposed alpha)
Opioid - naloxone 100-400 mcg IV titrated to respiratory rate, not consciousness
- Naloxone half-life ~1 h is shorter than most opioids -> infusion or observation
Sedative-hypnotic - benzodiazepines, GHB, zolpidem, barbiturates; supportive care
- Flumazenil is rarely indicated - it precipitates seizures in chronic users and in TCA co-ingestion

Approach: resuscitation -> risk assessment (agent, dose, time) -> supportive care and monitoring -> decontamination -> antidote -> enhanced elimination -> disposition
- Supportive care is what saves lives; antidotes exist for a minority
Always check: BSL, ECG (QRS and QTc), paracetamol level in every deliberate self-poisoning
Mixed ingestions blur toxidromes - identify the most dangerous component and treat that
Anticholinergic delirium: benzodiazepines first; physostigmine only in specialist hands and never with QRS widening
Australian Poisons Information Centre 13 11 26 for every significant ingestion
Toxidrome-agent mismatch is a clue to an unexpected agent - a sympathomimetic picture with dry skin is anticholinergic; miosis with tachycardia suggests a mixed ingestion

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