What is the treatment for monochrotophos poisoning?

Treatment of Monochrotophos Poisoning

Monochrotophos poisoning should be treated identically to other organophosphate poisonings with immediate atropine administration, pralidoxime, benzodiazepines for seizures, aggressive supportive care including early intubation when indicated, and decontamination—atropine is the immediate life-saving intervention and should never be delayed. 1

Immediate Management and Decontamination

Personal protective equipment is mandatory when caring for patients with monochrotophos exposure to prevent healthcare provider contamination. 1

Decontamination must be performed immediately:

• Remove all contaminated clothing 1
• Perform copious irrigation with soap and water for external exposure 1
• Gastric lavage and activated charcoal administration via nasogastric tube for ingestions 2

Atropine Administration (First-Line, Life-Saving Treatment)

Atropine should be administered immediately for severe manifestations including bronchospasm, bronchorrhea, seizures, or significant bradycardia—this has Class 1, Level A evidence and is the cornerstone of treatment. 1

Dosing algorithm:

• Adults: 1-2 mg IV initially (FDA label recommends 2-4 mg) 1, 3
• Children: 0.02 mg/kg IV (minimum 0.1 mg, maximum single dose 0.5 mg) 1
• Double the dose every 5 minutes until full atropinization is achieved 1, 3
• Continue until bronchorrhea, bronchospasm, and bradycardia resolve 1

Therapeutic endpoints (signs of adequate atropinization):

• Clear chest on auscultation 1
• Heart rate >80/min 4
• Systolic blood pressure >80 mm Hg 4
• Dry skin and mucous membranes 1
• Mydriasis 1

Maintenance: Continue atropinization via continuous infusion for at least 48 hours until depressed cholinesterase activity reverses. 1, 3

Critical pitfall: Atropine-induced tachycardia is an expected pharmacologic effect and is NOT a contraindication to continued administration—never stop atropine due to tachycardia as the risk of undertreating far exceeds the risk of tachycardia. 1

Pralidoxime (Oxime Therapy)

Pralidoxime should be administered early (Class 2a recommendation, Level A evidence) to reactivate acetylcholinesterase before "aging" of the phosphorylated enzyme occurs. 1, 3

Dosing:

• Adults: 1-2 g IV administered slowly over 15-30 minutes, preferably by infusion in 100 mL normal saline 1, 3
• Maintenance: 400-600 mg/hour continuous infusion for adults 1
• Children: 10-20 mg/kg/hour 1
• A second dose of 1-2 g may be given after 1 hour if muscle weakness persists 3
• Additional doses every 10-12 hours if muscle weakness continues 3

Timing is critical: Pralidoxime is most effective when given within 36 hours of exposure, though treatment should not be withheld even if this window has passed. 3

Important consideration: Monochrotophos has a renal elimination half-life of approximately 3.3 hours (range 1.9-5.0 hours), suggesting rapid clearance but with possible redistribution causing secondary plasma level rises around 10 hours post-exposure. 5 This supports the need for prolonged pralidoxime therapy and extended monitoring.

Airway Management

Early endotracheal intubation is recommended for life-threatening poisoning, particularly when bronchorrhea, bronchospasm, or altered mental status threatens airway protection. 1, 4

Critical contraindication: Avoid neuromuscular blockers metabolized by cholinesterase (succinylcholine and mivacurium) as they are contraindicated and can cause prolonged paralysis. 1, 4, 3

Mechanical ventilation considerations:

• Use synchronized intermittent mandatory ventilation + pressure support mode 2
• Titrate PEEP to maintain SaO₂ >94% with FiO₂ ≤40% 2
• Monitor respiratory rate closely—increases from baseline (e.g., 22 to 38 breaths/min) indicate impending respiratory failure requiring immediate intubation 2

Seizure and Agitation Management

Benzodiazepines should be administered to treat seizures and agitation—diazepam is first-line, with midazolam as an alternative. 1, 4

Supportive Care Essentials

• Establish IV access and provide fluid resuscitation 4
• Supplemental oxygen and ventilatory support as needed 4
• Continuous cardiac monitoring for dysrhythmias 1, 4
• Correct metabolic abnormalities 3

Monitoring and Duration

Patients must be observed for at least 48-72 hours as delayed complications can occur, including: 1, 4, 3

• Intermediate syndrome (occurs in ~19% of OP poisoning cases, presenting with delayed muscle weakness 24-96 hours post-exposure) 1, 2
• Aspiration pneumonia (occurs in ~21% of cases) 2
• Respiratory failure (most common complication, occurring in ~74% of severe cases) 2
• Rhabdomyolysis and renal damage 1

Special consideration for ingestions: When monochrotophos has been ingested, continuing absorption from the lower bowel constitutes ongoing exposure—fatal relapses have been reported after initial improvement, requiring additional pralidoxime doses every 3-8 hours based on recurring symptoms. 3

Drugs to Avoid

Contraindicated medications in organophosphate poisoning include: 3

• Morphine
• Theophylline and aminophylline
• Reserpine
• Phenothiazine-type tranquilizers
• Succinylcholine and mivacurium (as noted above)

Expert Consultation

Contact poison control (1-800-222-1222 in the US) for expert guidance on specific case management. 4

Prognosis

Monochrotophos is associated with high mortality (24% in one series) among organophosphate compounds. 5 Early recognition of respiratory failure and prompt intubation are life-saving interventions that significantly impact outcomes. 2 The mortality rate for patients requiring mechanical ventilation is approximately 50%, compared to 21.6% for those not requiring ventilation. 2