Toxidromes — Recognising Drug Classes Clinically

A toxidrome is a syndrome (a constellation of signs and symptoms) that is characteristic of poisoning by a particular class of drug. Recognising toxidromes allows you to identify the likely causative agent quickly and direct specific treatment, even when the patient cannot communicate or the history is unknown.

ToxidromeCausative AgentsClinical FeaturesSpecific Treatment
OpioidHeroin, morphine, codeine, methadone, fentanylMiosis (pinpoint pupils), respiratory depression, reduced GCS, cyanosisNaloxone IV/IM — start 0.4 mg, repeat every 2–3 min up to 10 mg; infusion if recurrent
SympathomimeticCocaine, amphetamines, MDMA (ecstasy), methamphetamineTachycardia, hypertension, hyperthermia, agitation, mydriasis, diaphoresis, seizuresBenzodiazepines for agitation/seizures; cooling; avoid beta-blockers (risk of unopposed alpha)
AnticholinergicTricyclic antidepressants, antihistamines, atropine, antipsychotics‘Hot as a hare, dry as a bone, red as a beet, mad as a hatter, blind as a bat’ — hyperthermia, dry skin, flushing, confusion, urinary retention, mydriasis, ileusPhysostigmine (specialist use); benzodiazepines for agitation; cooling
CholinergicOrganophosphates, nerve agents, carbamate insecticidesSLUDGE: Salivation, Lacrimation, Urination, Defaecation, GI upset, Emesis; plus bronchospasm, bradycardia, miosisAtropine (large doses may be needed); pralidoxime (reactivates AChE if given early)
Sedative-hypnoticBenzodiazepines, barbiturates, GHB, alcoholDrowsiness, slurred speech, ataxia, respiratory depression; pupils normal or mildly constrictedSupportive (airway, ventilation); flumazenil for benzodiazepines (caution — may precipitate seizures in mixed overdose)
Serotonin syndromeSSRIs, SNRIs, MAOIs, tramadol, linezolid, triptans (combinations)Agitation, clonus (especially lower limbs), diaphoresis, hyperthermia, tachycardia, hypertensionCyproheptadine (serotonin antagonist); benzodiazepines; cooling; stop causative drugs; ICU if severe