Treatment of Organophosphorus Poisoning
The treatment of organophosphorus poisoning requires immediate administration of atropine, pralidoxime (2-PAM), benzodiazepines, and supportive care including decontamination, airway management, and close monitoring for at least 48-72 hours. 1
Initial Management
- Ensure proper personal protective equipment (PPE) when caring for patients with organophosphate exposure to prevent contamination of healthcare providers 1
- Immediate dermal decontamination for external exposure by removing contaminated clothing and copious irrigation with soap and water 1, 2
- Secure airway, breathing, and circulation as the first priority in treatment 1
- Early endotracheal intubation is recommended for life-threatening organophosphate poisoning, with observational data suggesting better outcomes 1
Atropine Administration
- Administer atropine immediately at 1-2 mg IV for adults (0.02-0.1 mg/kg for children), doubling the dose every 5 minutes until bronchorrhea, bronchospasm, and bradycardia resolve 1, 2
- Atropine should be given as soon as possible after hypoxemia is improved but should not be given in the presence of significant hypoxia due to risk of atropine-induced ventricular fibrillation 2
- High-dose atropine may be required - studies have reported doses up to 100 mg/hour and total doses of 11.6 g over 12 days in severe cases 3
- Maintain atropinization for at least 48 hours and until any depressed blood cholinesterase activity is reversed 2
Pralidoxime (2-PAM) Therapy
- Administer pralidoxime after the effects of atropine become apparent 2
- Initial adult dose: 1-2 g IV administered slowly, preferably by infusion over 15-30 minutes 1, 2
- If IV administration is not feasible, intramuscular or subcutaneous injection should be used 2
- Maintenance therapy: 400-600 mg/hour for adults or 10-20 mg/kg/hour for children 1
- Additional doses may be needed every 3-8 hours if signs of poisoning recur; patients should be "titrated" with pralidoxime as long as signs of poisoning recur 2
- Treatment is most effective if initiated immediately after poisoning; generally little is accomplished if pralidoxime is given more than 36 hours after exposure 2
Seizure Management
- Administer benzodiazepines (such as diazepam or midazolam) to treat seizures and agitation 1
- Benzodiazepines also help facilitate mechanical ventilation if needed 1
Special Considerations
- Avoid neuromuscular blockers metabolized by cholinesterase (succinylcholine and mivacurium) as they may cause prolonged paralysis 1, 2
- Avoid morphine, theophylline, aminophylline, reserpine, and phenothiazine-type tranquilizers in patients with organophosphate poisoning 2
- Monitor for delayed muscle weakness, which can follow the initial cholinergic crisis even as late as 4 days after acute exposure 1
- Watch for complications such as myonecrosis, rhabdomyolysis, and renal damage 1
- Keep the patient under observation for at least 48 to 72 hours, as fatal relapses have been reported after initial improvement 2
Treatment Algorithm
- Ensure personal protection and patient decontamination
- Secure airway, breathing, and circulation
- Administer atropine immediately and titrate dose until secretions are inhibited
- Administer pralidoxime after atropine effects are apparent
- Give benzodiazepines for seizures or agitation
- Provide supportive care including respiratory and cardiovascular support
- Monitor for at least 48-72 hours
Common Pitfalls and Caveats
- Underdosing of atropine is common - studies show that some textbook recommendations would take hours or even days to stabilize a patient 4
- When the poison has been ingested, consider the likelihood of continuing absorption from the lower bowel, which constitutes new exposure 2
- The effectiveness of pralidoxime has been questioned in some studies, but the American Heart Association still recommends its use (Class 2a recommendation with Level A evidence) 1, 5
- Pralidoxime is most effective when administered early, before "aging" of the phosphorylated enzyme occurs 1