Organophosphate (OP) poisoning results from acetylcholinesterase inhibition by compounds found in pesticides, nerve agents, and some medications, producing a characteristic cholinergic toxidrome with muscarinic, nicotinic, and CNS effects. [1-2] Lethality is primarily driven by respiratory failure from bronchorrhea, bronchospasm, central apnea, and respiratory muscle paralysis. [3] The cornerstones of emergency treatment are decontamination, atropine, pralidoxime, and benzodiazepines. [2]
1. History
- Exposure route and timing: Ingestion (30–90 min onset), inhalation (seconds to minutes), dermal (up to 48 hours delayed) [3]
- Agent identification: Specific pesticide name, concentration, amount ingested; nerve agent vs. pesticide
- Intent: Intentional (suicidal) vs. accidental vs. occupational — OP ingestion with suicidal intent is extremely common in developing countries [3]
- Symptom progression: Ask about salivation, lacrimation, urination, defecation, GI cramping, emesis (SLUDGE), blurred vision, muscle twitching, weakness, breathing difficulty [1][4]
- Co-ingestants: Alcohol, other pesticides, hydrocarbon solvents (aspiration risk) [3]
- Time since exposure: Critical for determining oxime utility (aging window) [1]
2. Alarm Features
- Respiratory distress: Bronchorrhea, bronchospasm, central apnea, respiratory muscle paralysis — the primary cause of death [3]
- Altered mental status / loss of consciousness [5]
- Seizures or status epilepticus [2]
- Severe muscular twitching, generalized weakness, or paralysis [5]
- Cardiovascular collapse: Bradycardia, hypotension, cardiac arrest [1-2]
- Involuntary urination/defecation [5]
- Excessive airway secretions [5]
- Fasciculations at presentation — present in 90% of patients who died in one prospective study [6]
3. Medications
Antidotes
- Atropine: Adults 1–2 mg IV initially (3–5 mg if severe/hemodynamically compromised); double every 5 min until atropinized (clear lungs, HR >80, SBP >80); then infusion at 10–20% of total loading dose/hr [2]
- Pralidoxime: 2 g IV over 15–30 min, then 1 g/hr infusion; high-dose regimens favored over low-dose [2][7]
- Benzodiazepines: Diazepam 5–10 mg IV (first-line) or midazolam for seizures/agitation [2]
Contraindicated/Caution
- Succinylcholine: Prolonged paralysis (hours) due to pseudocholinesterase inhibition — use rocuronium or vecuronium instead if NMB needed [1-2]
- Morphine, theophylline, aminophylline, phenothiazines: Avoid in OP poisoning [7]
- Atropine before correcting hypoxia: Risk of atropine-induced ventricular fibrillation [7]
4. Diet
- NPO during acute management
- GI decontamination (activated charcoal) only after full resuscitation and stabilization [4]
- Hydration: IV NS targeting SBP >80 mmHg and urine output >0.5 mL/kg/hr [4]
5. Review of Systems
- Eyes: Blurred vision, miosis, lacrimation, eye pain [5][8]
- Respiratory: Dyspnea, wheezing, cough, copious secretions [5]
- GI: Nausea, vomiting, abdominal cramping, diarrhea, fecal incontinence [4]
- GU: Urinary incontinence [4]
- Neuro: Confusion, agitation, headache, seizures, weakness [4]
- MSK: Fasciculations, muscle twitching, weakness [4]
- Skin: Diaphoresis, localized sweating at exposure site [3]
- Cardiac: Palpitations, chest tightness [5]
6. Collateral History and Family History
- Collateral: Witnesses to exposure, empty containers, suicide note, occupational exposure context
- Psychiatric history: Prior suicide attempts, depression, substance use — mood disorders present in ~39% of OP poisoning cases [9]
- Occupational: Agricultural workers, pesticide applicators at highest risk [3]
- Family history: Not directly relevant, but family may provide exposure details and psychiatric context
- PPE for providers: Healthcare workers have developed symptoms from unprotected contact with contaminated patients [2]
7. Risk Factors
- Occupational exposure: Agricultural workers, pesticide handlers [3]
- Intentional self-harm: Most common context in developing countries [3]
- Geographic: Higher incidence in South/Southeast Asia, sub-Saharan Africa [4]
- Age: Advanced age associated with higher mortality (mean age 47 in non-survivors vs. 29 in survivors) [6]
- Psychiatric comorbidities: Depression, adjustment disorders [9]
- Access to highly toxic OP compounds (e.g., methamidophos, mevinphos, chlorpyrifos) [9]
8. Differential Diagnosis
- Carbamate poisoning: Clinically indistinguishable; carbamates spontaneously dissociate from AChE (shorter duration) [1][4]
- Nerve agent exposure: Sarin, VX, Novichok — more rapid onset, especially via inhalation [3]
- Nicotine poisoning: Cholinergic features but predominantly nicotinic [10]
- Mushroom poisoning (muscarinic type): SLUDGE symptoms without nicotinic features
- Cholinergic medication overdose: Neostigmine, physostigmine, pyridostigmine [3]
- Myasthenia gravis crisis: Weakness/paralysis but without cholinergic excess
- Botulism: Descending paralysis, mydriasis (opposite of OP miosis) [10]
- Acute gastroenteritis: May mimic GI symptoms but lacks full toxidrome
9. Past Medical History
- Prior OP exposure or poisoning episodes
- Baseline pseudocholinesterase deficiency (prolongs succinylcholine effect)
- Asthma/COPD (increased vulnerability to bronchospasm)
- Cardiac disease (arrhythmia risk)
- Hepatic/renal disease (altered metabolism)
- Psychiatric history (intentional ingestion)
10. Physical Exam
Vital Signs
- Bradycardia (muscarinic) or tachycardia (nicotinic/sympathetic) [4]
- Hypotension or hypertension [4]
- Tachypnea, hypoxia
Focused Exam
- Eyes: Miosis (classic), occasionally mydriasis from nicotinic stimulation [1][4]
- Lungs: Wheezing, rhonchi, copious secretions (bronchorrhea) — clearing of the chest is the primary endpoint for atropine titration [2]
- Skin: Profuse diaphoresis, possible chemical odor (garlic/petroleum) [4]
- Neuro: Fasciculations, muscle weakness (proximal > distal), altered mental status, seizures [4]
- GI: Hyperactive bowel sounds, abdominal tenderness
- Secretions: Excessive salivation, lacrimation, rhinorrhea [4]
11. Lab Studies
- Serum/plasma butyrylcholinesterase (pseudocholinesterase): Rapidly depressed; more readily available but less specific [3-4]
- RBC acetylcholinesterase: More specific marker of synaptic AChE inhibition; not widely available emergently [3][8]
- ABG/VBG: Acidosis (pH <7.35) present in 73% of non-survivors [6]
- Serum lactate: >2 mmol/L in 90% of non-survivors [6]
- BMP: Hypokalemia (73% of non-survivors), hyperglycemia [6]
- Troponin I: Elevated in ~34% of severe cases; peaks at ~15 hours [11]
- CBC, CRP, LDH, CPK: May be elevated; useful adjunctive markers [12]
- Amylase/lipase: May be elevated in OP poisoning [12]
⚠️ Do not delay treatment awaiting lab results — diagnosis is clinical [3][8]
12. Imaging
- Chest X-ray: Assess for pulmonary edema (non-cardiogenic, seen in ~43%), aspiration pneumonia (~51% in elderly) [9][13]
- CT head: If altered mental status or seizures with unclear etiology
- Imaging is generally not the priority — clinical toxidrome recognition and antidote administration take precedence
13. Special Tests
- Response to empirical atropine: Diagnostic and therapeutic — failure to develop tachycardia/mydriasis after standard atropine doses supports cholinesterase inhibitor poisoning [3]
- Repetitive nerve stimulation (RNS): Decremental response at 30 Hz may predict intermediate syndrome [14]
- Single-fiber EMG: Prolonged jitter <24 hours post-ingestion strongly predicts intermediate syndrome (OR 8.9) [15]
- Echocardiography: May show reversible LV dysfunction (EF dropping to ~42% acutely, recovering to ~59%) [16]
14. ECG
ECG abnormalities are common and potentially lethal in OP poisoning: [17-18]
- QTc prolongation: Most common abnormality (~56–67% of patients) [13][19]
- Sinus tachycardia (~32–90%) or sinus bradycardia (~28%) [13][19]
- ST-T changes: ST elevation, ST depression, low-amplitude T waves (~18–41%) [13][19]
- AV conduction disturbances [17]
- Torsades de pointes / polymorphic VT: Potentially lethal, may occur late [17-18]
- Ventricular fibrillation: Cause of death in some cases [13]
⚠️ Prolonged cardiac monitoring is essential — arrhythmias may develop hours to days after initial stabilization [18]
15. Assessment
Severity Stratification
- Mild: Blurred vision, miosis, lacrimation, salivation, chest tightness, tremors, nausea [5]
- Severe: AMS/LOC, respiratory distress, excessive airway secretions, paralysis, seizures, cardiovascular collapse [5]
Prognostic Markers of Poor Outcome
Delayed Complications
- Intermediate syndrome: Proximal muscle weakness, neck flexor weakness, cranial nerve palsies, respiratory paralysis occurring 24–96 hours after initial cholinergic crisis; major cause of in-hospital death [4][20]
- OP-induced delayed neuropathy (OPIDN): Peripheral neuropathy 1–3 weeks post-exposure [21-22]
- Chronic OP-induced neuropsychiatric disorder (COPIND): Long-term cognitive/behavioral effects [21]
16. Treatment Plan
Initial Stabilization (ABCs)
- Airway: Suction secretions aggressively; early intubation improves outcomes [2]
- Breathing: High-flow O₂; correct hypoxia BEFORE atropine (risk of V-fib) [7]
- Decontamination: Remove clothing, wash skin with soap and water — providers must wear PPE [2]
Antidote Protocol
Key Pearls
- Atropine endpoint = dry lungs on auscultation, NOT pupil size [2][4]
- Atropine does NOT reverse paralysis — only muscarinic effects [1]
- Maintain atropinization for ≥48 hours; monitor for recurrent cholinergic features [7]
- GI decontamination (activated charcoal) only after full stabilization [4]
- Monitor for intermediate syndrome (days 1–4): worsening proximal weakness, respiratory failure [20]
17. Disposition
- All symptomatic patients require admission, typically to ICU [13]
- ICU admission criteria: Any respiratory distress, need for atropine infusion, hemodynamic instability, seizures, AMS, significant fasciculations/weakness
- Cardiac monitoring: Prolonged monitoring essential due to risk of delayed arrhythmias (QT prolongation, torsades) [18]
- Observation ≥24 hours minimum even for mild cases — dermal exposures may have delayed onset up to 48 hours [3]
- Psychiatry consultation: Mandatory for intentional ingestions before discharge
- Poison Control Center: Contact early for agent-specific guidance
- Toxicology consultation: For severe cases, unclear agents, or refractory symptoms
18. Follow Up / Return Precautions
- Monitor for intermediate syndrome: Days 1–4 post-exposure — sudden respiratory failure despite apparent recovery from cholinergic crisis [4][20]
- Monitor for delayed neuropathy: 1–3 weeks post-exposure — distal sensorimotor neuropathy [21-22]
- Neuropsychiatric follow-up: Cognitive impairment, depression, anxiety may persist chronically [21][23]
- Return precautions: Worsening weakness, difficulty breathing, new muscle twitching, confusion, palpitations
- Occupational: Ensure safe return-to-work protocols; repeat cholinesterase levels before re-exposure
- Psychiatric follow-up: Essential for intentional ingestions — safety planning before discharge
References
1. 2023 American Heart Association Focused Update on the Management of Patients With Cardiac Arrest or Life-Threatening Toxicity Due to Poisoning: An Update to the American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Lavonas EJ, Akpunonu PD, Arens AM, et al. Circulation. 2023.
2. Part 10: Adult and Pediatric Special Circumstances of Resuscitation: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Cao D, Arens AM, Chow SL, et al. Circulation. 2025.
3. Hazardous Chemical Emergencies and Poisonings. — Henretig FM, Kirk MA, McKay CA. The New England Journal of Medicine. 2019.
4. Management of Acute Organophosphorus Pesticide Poisoning. — Eddleston M, Buckley NA, Eyer P, Dawson AH. Lancet. 2008.
5. FDA Drug Label. — Updated date: 2026-02-18. Food and Drug Administration.
6. Early Markers in Severe Organophosphorus Poisoning and Their Association With Mortality. — Parrey AH, Koka M, Ismail M, Ashraf M, Lone H. The Journal of Emergency Medicine. 2025.
7. FDA Drug Label. — Updated date: 2026-04-01. Food and Drug Administration.
8. Acute Chemical Emergencies. — Kales SN, Christiani DC. The New England Journal of Medicine. 2004.
9. Outcomes of Elderly Patients With Organophosphate Intoxication. — Yu JR, Hou YC, Fu JF, et al. Scientific Reports. 2021.
10. Chemical-Biological Terrorism and Its Impact on Children. — Chung S, Baum CR, Nyquist AC. Pediatrics. 2020.
11. Features of Myocardial Injury in Severe Organophosphate Poisoning. — Cha YS, Kim H, Go J, et al. Clinical Toxicology. 2014.
12. Biochemical Responses as Early and Reliable Biomarkers of Organophosphate and Carbamate Pesticides Intoxication: A Systematic Literature Review. — Sepahi S, Gerayli S, Delirrad M, et al. Journal of Biochemical and Molecular Toxicology. 2023.
13. Cardiac Manifestations of Acute Carbamate and Organophosphate Poisoning. — Saadeh AM, Farsakh NA, al-Ali MK. Heart. 1997.
14. A Comprehensive Review on Experimental and Clinical Findings in Intermediate Syndrome Caused by Organophosphate Poisoning. — Abdollahi M, Karami-Mohajeri S. Toxicology and Applied Pharmacology. 2012.
15. Prediction of Organophosphorus Insecticide-Induced Intermediate Syndrome With Stimulated Concentric Needle Single Fibre Electromyography. — Alahakoon C, Dassanayake TL, Gawarammana IB, et al. PloS One. 2018.
16. Cardiac Abnormalities in Severe Acute Dichlorvos Poisoning. — He X, Li C, Wei D, et al. Critical Care Medicine. 2011.
17. Water, Soil, Noise, and Light Pollution: JACC Focus Seminar, Part 2. — Miller MR, Landrigan PJ, Arora M, et al. Journal of the American College of Cardiology. 2024.
18. Guidelines for Treating Cardiac Manifestations of Organophosphates Poisoning With Special Emphasis on Long QT and Torsades De Pointes. — Bar-Meir E, Schein O, Eisenkraft A, et al. Critical Reviews in Toxicology. 2007.
19. Electrocardiographic Findings of Acute Organophosphate Poisoning. — Yurumez Y, Yavuz Y, Saglam H, et al. The Journal of Emergency Medicine. 2009.
20. Neurotoxic Effects of Organophosphorus Insecticides. An Intermediate Syndrome. — Senanayake N, Karalliedde L. The New England Journal of Medicine. 1987.
21. Mechanisms and Treatment Strategies of Organophosphate Pesticide Induced Neurotoxicity in Humans: A Critical Appraisal. — Ganie SY, Javaid D, Hajam YA, Reshi MS. Toxicology. 2022.
22. Neurotoxic Effects of Organophosphorus Pesticides and Possible Association With Neurodegenerative Diseases in Man: A Review. — Jokanović M. Toxicology. 2018.
23. A Review on Oxidative Stress in Organophosphate-Induced Neurotoxicity. — Lorke DE, Oz M. The International Journal of Biochemistry & Cell Biology. 2025.