What is the treatment for chlorpyrifos poisoning?

Treatment of Chlorpyrifos Poisoning

Immediate treatment of chlorpyrifos poisoning requires supportive care with airway management, decontamination, atropinization (after correcting hypoxemia), and pralidoxime chloride administration, ideally within 36 hours of exposure. 1

Immediate Management Algorithm

1. Decontamination and Supportive Care

• Remove all contaminated clothing immediately and wash hair and skin thoroughly with sodium bicarbonate or alcohol to prevent ongoing dermal absorption 1
• Provide aggressive supportive care including airway management, respiratory support, cardiovascular monitoring, correction of metabolic abnormalities, and seizure control as needed 1
• Maintain observation for at least 48-72 hours due to risk of fatal relapses from continued gastrointestinal absorption 1

2. Atropinization Protocol

• Correct hypoxemia FIRST before giving atropine - atropine administration in the presence of significant hypoxia can trigger ventricular fibrillation 1
• Administer atropine 2-4 mg IV in adults, repeating every 5-10 minutes until full atropinization (secretions inhibited) or toxicity appears (delirium, hyperthermia, muscle twitching) 1
• Maintain some degree of atropinization for at least 48 hours until depressed blood cholinesterase activity reverses 1
• Exercise caution with atropine in patients with chest pain or known coronary disease as it increases heart rate and myocardial oxygen consumption, potentially precipitating myocardial infarction 2

3. Pralidoxime Chloride (PROTOPAM) Administration

• Administer after atropine effects become apparent 1
• Initial dose: 1000-2000 mg IV, preferably as infusion in 100 mL normal saline over 15-30 minutes 1
• Treatment is most effective if initiated immediately and provides little benefit if given more than 36 hours after exposure termination 1
• For ingestion cases with ongoing absorption, additional doses may be needed every 3-8 hours - essentially "titrate" the patient with pralidoxime as long as poisoning signs recur 1
• Therapeutic plasma concentration target is ≥4 µg/mL, achieved approximately 16 minutes after 600 mg injection 1

4. Medications to Avoid

• Do not use morphine, theophylline, aminophylline, reserpine, or phenothiazine-type tranquilizers in organophosphate poisoning 1
• Use succinylcholine with extreme caution as prolonged paralysis can occur when combined with anticholinesterase activity 1

Critical Clinical Pitfalls

Ongoing Absorption Risk

The most dangerous pitfall is underestimating continued absorption from the gastrointestinal tract after ingestion, which constitutes new exposure and has caused fatal relapses after initial improvement 1. This necessitates repeated pralidoxime dosing and extended observation periods.

Delayed Neurological Complications

• Chlorpyrifos can cause delayed myelopathy and pure motor neuropathy appearing 6-8 weeks after initial recovery from cholinergic crisis 3
• Permanent paralysis can occur at sites of dermal exposure, particularly affecting hands and feet with atrophy and loss of function 4
• These delayed complications occur despite adequate initial treatment and represent central-peripheral distal axonopathy 3

Cardiac Complications

Acute myocardial infarction is a rare but serious complication requiring careful balance between atropinization needs and cardiac oxygen demands 2. The conflict between rapid atropinization (which increases heart rate) and AMI management (which requires reduced myocardial oxygen consumption) must be carefully navigated 2.

Pathophysiology Context

Chlorpyrifos causes irreversible acetylcholinesterase inhibition leading to acetylcholine accumulation and cholinergic syndrome 5. However, toxicity extends beyond simple cholinesterase inhibition to include neuroinflammation and disruption of multiple neurotransmitter systems 5. Importantly, acetylcholinesterase inhibition is uninformative regarding neurodevelopmental effects, as toxic effects from chronic low-level exposure occur at concentrations too low to inhibit cholinesterase 6.

Monitoring Parameters

• Maintain continuous observation for recurrence of cholinergic symptoms (muscarinic and nicotinic) 1
• Monitor for severe symptoms including respiratory distress, severe muscular twitching, convulsions, and altered consciousness 1
• Assess for cardiac complications in patients with chest pain 2
• Follow patients long-term for delayed neurological sequelae appearing weeks after initial recovery 3