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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Organophosphate toxidrome = cholinergic excess: salivation, lacrimation, urination, diarrhea, bronchorrhea, bronchospasm, bradycardia, miosis, fasciculations.
- Treat organophosphate poisoning with PPE/decontamination, airway suction/oxygen, atropine until secretions dry, and pralidoxime early.
- Anticholinergic toxidrome = hot, dry, flushed, mydriatic, urinary retention, ileus, tachycardic delirium.
- Treat anticholinergic toxicity with supportive care, benzodiazepines, cooling, and physostigmine only in selected cases after ECG/toxicology review.
- The exam distinction: wet patient with pinpoint pupils = cholinergic; dry delirious patient with big pupils = anticholinergic.
Overview
Contrasting toxidromes: organophosphate poisoning causes cholinergic excess treated with decontamination, atropine, and pralidoxime; anticholinergic poisoning causes dry delirium treated with supportive care and selected physostigmine. Emergency management focuses on early recognition, stabilization, targeted investigation, and prompt definitive therapy while avoiding common pitfalls tested on USMLE Step 2 CK.
Epidemiology
This presentation is encountered in emergency and acute care settings. Risk varies by exposure, comorbidity, age, mechanism, and timeliness of treatment. Morbidity and mortality increase when recognition is delayed or when airway, breathing, circulation, antidotal therapy, or definitive source control is postponed.
Clinical Features
Symptoms
Organophosphate: tearing, salivation, sweating, vomiting, diarrhea, urinary incontinence, dyspnea
Organophosphate: muscle cramps, fasciculations, weakness, seizures, confusion
Anticholinergic: agitation, hallucinations, delirium, blurred vision, dry mouth, urinary retention
Anticholinergic: hyperthermia, decreased sweating, constipation, inability to void
Medication history: antihistamines, TCAs, antipsychotics, antiparkinsonian drugs, pesticides, nerve agents, plants
Signs
Organophosphate: miosis, bronchorrhea, bronchospasm, bradycardia, diaphoresis, fasciculations
Organophosphate severe toxicity: respiratory failure, seizures, paralysis, coma
Anticholinergic: mydriasis, dry flushed skin, tachycardia, hyperthermia, absent bowel sounds, urinary retention
Wide QRS or ventricular dysrhythmia suggests TCA/diphenhydramine sodium-channel blockade
Rhabdomyolysis may occur with prolonged agitation, seizures, or hyperthermia
Investigations
First-line
Clinical toxidrome assessmentDiagnosis is clinical; distinguish wet cholinergic patient from dry anticholinergic patient.
ECGCritical in anticholinergic overdose to identify QRS widening, QT prolongation, or TCA-like sodium-channel blockade.
Glucose, electrolytes, temperature, CK, renal functionEvaluate altered mental status, hyperthermia, rhabdomyolysis, and complications.
Second-line
Cholinesterase activityRBC acetylcholinesterase and plasma pseudocholinesterase can support organophosphate diagnosis but treatment should not wait.
Overdose labsAcetaminophen and salicylate levels, pregnancy test, blood gas/lactate if critically ill, toxicology screen if helpful.
Bladder scanAssess urinary retention in anticholinergic toxicity.
Specialist
Poison center / hazardous materials consultationFor organophosphate exposure, nerve agent concern, physostigmine decision-making, severe hyperthermia, or mixed overdose.
Management
CDC/NIOSH hazardous exposure principles and American College of Medical Toxicology practice1
Organophosphate poisoning
- Protect staff with PPE; remove patient from exposure and decontaminate by removing clothing and washing skin.
- Airway support, high-flow oxygen, aggressive suctioning, and early intubation if respiratory failure.
- Atropine IV repeated rapidly until bronchorrhea and bronchospasm improve; endpoint is drying of secretions.
- Pralidoxime as early as possible to reactivate acetylcholinesterase before aging.
- Benzodiazepines for seizures and severe agitation.
2
Anticholinergic toxicity
- Supportive care in a quiet environment; IV fluids, cooling, and cardiac monitoring.
- Benzodiazepines for agitation, seizures, or severe sympathetic activation.
- Treat hyperthermia with external cooling; antipyretics do not help.
- Urinary catheterization for significant retention.
- Activated charcoal if early and airway protected.
3
Physostigmine decision
- Consider physostigmine for severe pure anticholinergic delirium after toxicology consultation.
- Avoid physostigmine if QRS widening, bradycardia, AV block, seizure, suspected TCA overdose, or mixed overdose.
- If QRS widening from sodium-channel blockade, treat with sodium bicarbonate.
4
Disposition
- ICU for respiratory failure, seizures, severe organophosphate poisoning, hyperthermia, significant dysrhythmia, or need for repeated antidotes.
- Observe anticholinergic toxicity until mental status, temperature, ECG, and urinary retention normalize.
Complications
- Respiratory failure: Organophosphate bronchorrhea, bronchospasm, and neuromuscular weakness can be fatal
- Intermediate syndrome: Delayed weakness after organophosphate exposure
- Seizures: Can occur in both toxidromes
- Hyperthermia/rhabdomyolysis: Particularly with anticholinergic agitation
- Dysrhythmia: Sodium-channel blockade from diphenhydramine or TCA co-ingestion
USMLE Step 2 CK Exam Tips
- 1Organophosphate = wet toxidrome: SLUDGE/DUMBBELS plus bronchorrhea and fasciculations.
- 2Atropine endpoint in organophosphate poisoning is drying secretions, not pupil dilation.
- 3Pralidoxime treats nicotinic effects and should be given early.
- 4Anticholinergic = hot as a hare, dry as a bone, blind as a bat, mad as a hatter, full as a flask.
- 5Physostigmine is not for TCA overdose or wide QRS.
- 6Wide QRS after diphenhydramine/TCA overdose = sodium bicarbonate.
practicetest your knowledge on toxic ingestions — organophosphate & anticholinergicApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — emergency medicine and beyond.
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