Toxidromes: Recognizing Poisoning Patterns in EMS

By Jointra Editorial Team, Certified EMT

Why Toxidromes Matter

In the pre-hospital setting, identifying the specific agent responsible for a poisoning is rarely possible. Pill bottles may be empty, histories may be unreliable, and patients may be unconscious. Toxidrome recognition — identifying the pattern of signs and symptoms that corresponds to a class of drug — allows targeted treatment before laboratory confirmation.

The Major Toxidromes

Opioid Toxidrome

Mechanism: Mu-opioid receptor agonism causing CNS and respiratory depression

Signs:

• Miosis (pinpoint pupils)
• CNS depression / unconsciousness
• Respiratory depression (the lethal mechanism)
• Bradycardia, hypotension (less pronounced)
• Hypothermia
• Decreased bowel sounds

Treatment: Naloxone (antagonist). Titrate to adequate respirations — not full consciousness (to avoid acute withdrawal in dependent patients).

Sympathomimetic Toxidrome

Agents: Cocaine, methamphetamine, amphetamines, PCP (partial), ephedrine, synthetic cathinones ("bath salts")

Mechanism: Excess catecholamine activity (norepinephrine, dopamine)

Signs:

• Mydriasis (dilated pupils)
• Tachycardia
• Hypertension
• Hyperthermia
• Diaphoresis (sweating)
• Agitation, psychosis
• Seizures (cocaine especially)

Treatment: Benzodiazepines for agitation, seizures, hypertension. Active cooling for hyperthermia. Do not use beta-blockers (unopposed alpha stimulation worsens coronary vasospasm with cocaine).

Anticholinergic Toxidrome

Agents: Diphenhydramine (Benadryl), atropine, tricyclic antidepressants (TCAs), scopolamine, jimsonweed

Mnemonic: "Mad as a hatter, dry as a bone, red as a beet, blind as a bat, hot as Hades"

Signs:

• Mydriasis (dilated pupils)
• Dry skin and mucous membranes
• Flushing
• Urinary retention
• Decreased bowel sounds
• Hyperthermia
• Tachycardia
• AMS, agitation, hallucinations
• QRS prolongation (TCA overdose specifically — risk of ventricular arrhythmia)

Treatment: Benzodiazepines for agitation. TCA overdose: sodium bicarbonate for wide QRS (>120ms) or ventricular arrhythmia. Do NOT give physostigmine pre-hospital.

Cholinergic Toxidrome

Agents: Organophosphate and carbamate pesticides, nerve agents (sarin, VX)

Mechanism: Acetylcholinesterase inhibition → acetylcholine accumulation

Mnemonic: SLUDGE or DUMBELS

• Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis
• Defecation, Urination, Miosis, Bradycardia/Bronchospasm/Bronchorrhea, Emesis, Lacrimation, Salivation

Signs: Miosis, bradycardia, bronchospasm, bronchorrhea (the lethal mechanism — patients drown in secretions), excessive secretions from all orifices, seizures

Treatment: Atropine aggressively (2–4mg IV q5 minutes until secretions dry — much more than diagnostic doses); pralidoxime (2-PAM) within 24 hours of exposure. Personal protection — organophosphates absorb through skin.

Sedative-Hypnotic Toxidrome

Agents: Benzodiazepines, barbiturates, GHB, alcohol (overlap), zolpidem (Ambien)

Signs:

• CNS depression
• Slurred speech
• Ataxia
• Respiratory depression (severe in barbiturates; less so in benzodiazepines alone)
• Nystagmus (barbiturates, alcohol, GHB)
• Normal or small pupils (vs. opioids where pinpoint pupils are more pronounced)

Treatment: Supportive. Flumazenil (benzodiazepine reversal agent) is rarely used pre-hospital — risks precipitating seizures in chronic benzo users.

Mixed Toxidromes

Many overdose patients have ingested multiple agents. The clinical picture may not fit cleanly into one toxidrome. Treat the most dangerous presenting feature and transport.