What is the treatment for organophosphorus poisoning?

Treatment of Organophosphorus Poisoning

Immediate Life-Saving Interventions

Administer atropine 1-2 mg IV immediately for adults (0.02 mg/kg for children, minimum 0.1 mg, maximum single dose 0.5 mg) and double the dose every 5 minutes until full atropinization is achieved—this is your first and most critical intervention with Class 1, Level A evidence. 1, 2

Atropine Dosing Algorithm

• Initial dose: 1-2 mg IV for adults; 0.02 mg/kg for children (minimum 0.1 mg, maximum 0.5 mg single dose) 1, 2
• Escalation: Double the dose every 5 minutes until endpoints are reached 1, 2
• Therapeutic endpoints for full atropinization:
  • Clear chest on auscultation (resolution of bronchorrhea) 2
  • Heart rate >80/min 2
  • Systolic blood pressure >80 mm Hg 2
  • Dry skin and mucous membranes 1, 2
  • Mydriasis 2
• Maintenance: Continue atropine infusion to maintain atropinization for at least 48-72 hours 1, 2

Critical pitfall: Children require much higher doses than standard pediatric resuscitation doses—do not underdose based on typical bradycardia treatment protocols 1, 2

Decontamination and Personal Protection

• Healthcare provider safety: Use appropriate personal protective equipment (PPE) to prevent contamination of caregivers 1, 3
• Patient decontamination: Immediately remove all contaminated clothing and perform copious irrigation with soap and water for external exposure 1, 3

Pralidoxime (Oxime) Therapy

Administer pralidoxime early—it has Class 2a recommendation with Level A evidence and should not be delayed or withheld, even when the class of poison is unknown. 1, 4

Pralidoxime Dosing Protocol

• Initial adult dose: 1-2 g IV administered slowly over 15-30 minutes, preferably as an infusion in 100 mL normal saline 2, 4
• Maintenance infusion: 400-600 mg/hour for adults or 10-20 mg/kg/hour for children 1, 2
• Timing is critical: Pralidoxime is most effective when administered early, before "aging" of the phosphorylated enzyme occurs (generally within 36 hours) 1, 4
• Duration: Continue pralidoxime as long as signs of poisoning recur, particularly with ingested organophosphates where continued GI absorption can cause fatal relapses 1, 4

Essential principle: Always administer atropine concurrently with pralidoxime—pralidoxime alone is insufficient to manage respiratory depression 1, 2

Airway Management

• Early intubation: Perform endotracheal intubation for life-threatening organophosphate poisoning, particularly when bronchorrhea, bronchospasm, or altered mental status threatens airway protection 1, 2, 3
• Neuromuscular blocker selection: Avoid succinylcholine and mivacurium as they are metabolized by cholinesterase and are contraindicated 1, 2, 3, 4

Seizure and Agitation Management

• Benzodiazepines: Administer diazepam (first-line) or midazolam to treat seizures and agitation 1, 2, 3

Critical Management Principles for Common Complications

Atropine-Induced Tachycardia

Never withhold or stop atropine due to tachycardia—it is an expected pharmacologic effect and NOT a contraindication to continued administration. 1, 2

• The therapeutic endpoint is control of life-threatening muscarinic symptoms (bronchorrhea, bronchospasm), not heart rate normalization 1, 2
• Tachycardia may 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 1, 2
• Pralidoxime reverses nicotinic effects (including muscle weakness and potentially some tachycardia) that atropine cannot address 1, 2

Atropine-Induced Fever

• Fever is an expected adverse effect with high-dose atropine therapy and does not indicate treatment failure 1
• Never withhold or prematurely discontinue atropine due to fever 1
• Fever may have multiple etiologies: atropine's central effects, nicotinic-induced muscle fasciculations, or aspiration pneumonia 1

Monitoring and Supportive Care

• Duration of observation: Monitor closely for at least 48-72 hours as delayed complications and relapses can occur, especially with ingested organophosphates due to continued GI absorption 1, 2, 4
• Continuous cardiac monitoring: Watch for dysrhythmias, but do not use this to limit atropine dosing 1, 2
• Serial respiratory assessments: Auscultate every 5-10 minutes during escalation phase for bronchorrhea resolution 2
• Delayed complications: Monitor for intermediate syndrome (delayed muscle weakness occurring up to 4 days post-exposure), myonecrosis, rhabdomyolysis, and renal damage 1

Treatment Sequence Based on Severity

• Severe poisoning (bronchospasm, bronchorrhea, seizures, significant bradycardia): Immediate atropine + early intubation + pralidoxime + benzodiazepines 1, 2
• All cases: Decontamination, supportive care, continuous monitoring for 48-72 hours 1, 2, 4

Special Considerations

Organophosphates vs. Carbamates

• Organophosphates cause permanent inactivation ("aging") of acetylcholinesterase through covalent bonding 1
• Carbamates spontaneously dissociate from acetylcholinesterase 1
• Critical principle: Do not withhold pralidoxime when the class of poison is unknown—organophosphate and carbamate poisoning are clinically indistinguishable, and early oxime therapy is essential for organophosphates 1, 3

Drugs to Avoid

• Morphine, theophylline, aminophylline, reserpine, and phenothiazine-type tranquilizers should be avoided 4
• Succinylcholine and mivacurium are contraindicated for intubation 1, 2, 3, 4