Treatment of Organophosphate Poisoning
Immediate Life-Saving Interventions
Atropine is the immediate first-line treatment and must be administered without delay at 1-2 mg IV for adults (0.02 mg/kg for children, minimum 0.1 mg, maximum single dose 0.5 mg) for severe manifestations including bronchospasm, bronchorrhea, seizures, or significant bradycardia. 1, 2
Critical First Steps (Within Minutes)
Personal protective equipment must be worn by all healthcare providers to prevent secondary contamination 1, 3
Immediate decontamination through removal of all contaminated clothing and copious irrigation with soap and water (or sodium bicarbonate/alcohol for dermal exposure) 1, 4
Secure airway early - endotracheal intubation is recommended for life-threatening poisoning, particularly when bronchorrhea, bronchospasm, or altered mental status threatens airway protection 1, 2
Atropine Dosing Algorithm
The therapeutic endpoint is control of life-threatening muscarinic symptoms (bronchorrhea, bronchospasm, adequate blood pressure), NOT heart rate normalization. 2
Escalation Protocol
Double the atropine dose every 5 minutes until full atropinization is achieved 1, 2, 3
Signs of adequate atropinization include:
Maintain atropinization with continuous infusion after initial bolus dosing for at least 48 hours 1, 3
Critical Pitfall: Tachycardia During Atropinization
Atropine-induced tachycardia is an expected pharmacologic effect and is NOT a contraindication to continued atropine administration. 1, 2 The tachycardia may actually originate from nicotinic receptor overstimulation by the organophosphate itself, not from atropine 1, 2. The risk of undertreating organophosphate poisoning far exceeds the risk of atropine-induced tachycardia—inadequate atropinization leads to respiratory failure and death. 2
Pralidoxime (2-PAM) Administration
Pralidoxime should be administered early to reactivate acetylcholinesterase and must not be withheld when the class of poison is unknown (Class 2a recommendation, Level A evidence). 1, 4
Dosing Protocol
Initial adult dose: 1-2 g IV administered slowly over 15-30 minutes, preferably as an infusion in 100 mL normal saline 1, 4
Maintenance therapy: 400-600 mg/hour for adults or 10-20 mg/kg/hour for children via continuous infusion 1, 2
Timing is critical: Pralidoxime is most effective when administered early, before "aging" of the phosphorylated enzyme occurs (generally within 36 hours of exposure) 1, 4
Repeat dosing: Additional doses may be given every 10-12 hours if muscle weakness persists 4
Mechanism and Rationale
Pralidoxime reactivates acetylcholinesterase by competing with the bond between organophosphates and the enzyme, and reverses nicotinic effects (muscle weakness, fasciculations, potentially some tachycardia) that atropine cannot address 1, 2. Atropine must always be administered concurrently with pralidoxime, as pralidoxime alone is insufficient to manage respiratory depression. 1
Seizure and Agitation Management
Benzodiazepines (diazepam first-line or midazolam) should be administered to treat seizures and agitation 1, 2, 3
Benzodiazepines also facilitate mechanical ventilation when needed 1
Monitoring Strategy
Immediate Monitoring (Every 5-10 Minutes During Escalation)
Continuous cardiac monitoring to detect dysrhythmias, not to limit atropine dosing 2
Serial respiratory assessments to auscultate for bronchorrhea resolution 1, 2
Extended Monitoring (48-72 Hours Minimum)
All patients must be observed for at least 48-72 hours as delayed complications and fatal relapses can occur, especially with ingested organophosphates due to continued absorption from the GI tract. 1, 2, 4
Watch for intermediate syndrome: Delayed muscle weakness can follow the initial cholinergic crisis as late as 4 days after acute exposure 1, 5, 6
Monitor for complications: Aspiration pneumonia from bronchorrhea, rhabdomyolysis, myonecrosis, and renal damage 1, 3
Assess for atropine CNS effects: High-dose atropine can cause hallucinations and fever 1
Special Considerations
Continuing Absorption and Relapse
When organophosphate has been ingested, additional doses of pralidoxime may be needed every 3-8 hours due to continuing absorption from the lower bowel—fatal relapses have been reported after initial improvement. 4 The patient should be "titrated" with pralidoxime as long as signs of poisoning recur 4.
Carbamate vs. Organophosphate Poisoning
Organophosphates cause permanent inactivation ("aging") of acetylcholinesterase through covalent bonding, while carbamates spontaneously dissociate 1
Pralidoxime should not be withheld when the class of poison is unknown, as organophosphate and carbamate poisoning are clinically indistinguishable and organophosphates require early oxime therapy 1, 3
Pediatric Considerations
Children require relatively higher atropine doses compared to standard pediatric resuscitation doses—the standard doses are insufficient 1, 2
Tachycardia is even less of a concern in children than adults, and atropine should not be stopped in the presence of tachycardia 1
Drugs to Avoid
Succinylcholine and mivacurium (metabolized by cholinesterase) 1, 3, 4
Morphine, theophylline, aminophylline, reserpine, and phenothiazine-type tranquilizers should be avoided 4
Atropine should not be given in the presence of significant hypoxia due to risk of atropine-induced ventricular fibrillation—improve hypoxemia first 4