What is the initial treatment protocol for a 3-year-old child weighing 13 kg with suspected organophosphorus (OP) poisoning, specifically regarding the administration of atropine and pralidoxime?

Organophosphorus Poisoning Management in a 3-Year-Old, 13 kg Child

Immediate Atropine Administration

For this 3-year-old child weighing 13 kg, administer atropine 0.26 mg IV/IO immediately (0.02 mg/kg), then double the dose every 5 minutes until full atropinization is achieved—defined as clear lungs, dry skin, heart rate >80/min, and adequate blood pressure. 1, 2, 3

Critical Dosing Details for Atropine

• Initial dose: 0.26 mg IV/IO (0.02 mg/kg × 13 kg) 1
• Minimum single dose: 0.1 mg (this child exceeds the minimum) 1
• Maximum single dose: 0.5 mg per dose in children 1
• Escalation protocol: Double the dose every 5 minutes until bronchorrhea, bronchospasm, and bradycardia resolve 1, 2, 3
• Expected total requirements: Children with severe organophosphate poisoning require much higher doses than standard pediatric resuscitation doses—cumulative doses may reach 10-20 mg in the first 2-3 hours 1, 2

Therapeutic Endpoints for Atropinization

Monitor for these specific signs of adequate atropinization 3:

• Clear chest on auscultation (resolution of bronchorrhea)
• Heart rate >80/min
• Systolic blood pressure >80 mm Hg
• Dry skin and mucous membranes
• Mydriasis (dilated pupils)

Critical pitfall: Do NOT stop atropine administration if tachycardia develops—tachycardia is an expected pharmacologic effect and NOT a contraindication to continued therapy. 2, 3 The tachycardia may actually originate from nicotinic receptor overstimulation by the organophosphate itself, not from atropine. 3

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Pralidoxime (2-PAM) Administration

Administer pralidoxime 325-650 mg IV (25-50 mg/kg × 13 kg) as a loading dose over 15-30 minutes, followed by continuous infusion at 130-260 mg/hour (10-20 mg/kg/hour). 2, 4, 5

Specific Pralidoxime Dosing for This Child

• Loading dose: 325-650 mg IV (25-50 mg/kg) administered slowly over 15-30 minutes 4, 5
• Maintenance infusion: 130-260 mg/hour (10-20 mg/kg/hour) 2, 5
• Timing: Administer pralidoxime after atropine effects become apparent, but do not delay—early administration is critical before "aging" of the phosphorylated enzyme occurs 1, 2, 4

Rationale for Continuous Infusion

Continuous infusion maintains therapeutic plasma levels (>4 µg/mL) longer than intermittent bolus dosing. 4 In pediatric studies, a loading dose of 25-50 mg/kg followed by 10-20 mg/kg/hour infusion achieved steady-state concentrations of 22.2 mg/L and resulted in complete clinical recovery. 5 More severely poisoned patients may require the higher end of this dosing range (50 mg/kg loading dose). 5

Critical Timing Considerations

• Pralidoxime must be given early—the organophosphate-enzyme bond undergoes "aging" within minutes to hours, after which pralidoxime becomes ineffective 1, 2
• Do not withhold pralidoxime even if the specific poison class (organophosphate vs. carbamate) is unknown 2, 6
• Treatment is most effective if initiated immediately after poisoning 4

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Essential Concurrent Therapies

Benzodiazepines for Seizures and Agitation

Administer diazepam 2.6 mg IV (0.2 mg/kg × 13 kg) or midazolam 0.65-1.3 mg IV (0.05-0.1 mg/kg × 13 kg) in fractionated doses for seizures or agitation. 1, 2

Airway Management

• Early endotracheal intubation is recommended for life-threatening organophosphate poisoning 2, 3
• Avoid succinylcholine and mivacurium—these neuromuscular blockers are metabolized by cholinesterase and are contraindicated in organophosphate poisoning 1, 2, 3

Decontamination

• Remove all contaminated clothing immediately 2
• Wash hair and skin thoroughly with soap and water 2, 4
• Healthcare workers must use personal protective equipment (PPE) to prevent secondary exposure 2

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Monitoring and Duration of Therapy

Observation Period

Keep the patient under close observation for at least 48-72 hours as delayed complications and relapses can occur, especially with ingested organophosphates due to continued absorption from the GI tract. 2, 3, 4

Repeat Dosing Strategy

• Pralidoxime: Repeat doses every 3-8 hours as needed if signs of poisoning recur 4
• Atropine: Maintain some degree of atropinization for at least 48 hours until depressed blood cholinesterase activity is reversed 4
• In effect, "titrate" the patient with both drugs as long as signs of poisoning recur 4

Monitoring Parameters

• Continuous cardiac monitoring for dysrhythmias 3
• Serial respiratory assessments every 5-10 minutes during escalation phase 3
• Monitor for complications: rhabdomyolysis (check creatine kinase), myoglobinuria, renal damage 2

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Common Pitfalls to Avoid

1. Undertreating with atropine: The risk of inadequate atropinization (leading to respiratory failure and death) far exceeds the risk of atropine-induced tachycardia or fever. 2, 3 Standard pediatric resuscitation doses are insufficient—children require relatively higher doses. 2

2. Stopping atropine due to tachycardia: Tachycardia is an expected effect and represents adequate muscarinic receptor blockade. 3 Continue escalating until life-threatening muscarinic symptoms resolve.

3. Delaying or withholding pralidoxime: Pralidoxime must be given early before enzyme "aging" occurs. 1, 2 Do not withhold it even if the specific poison class is unknown. 2, 6

4. Premature discontinuation: Fatal relapses have been reported after initial improvement due to continued absorption from the GI tract. 4 Continue therapy for at least 48-72 hours. 2, 3, 4

5. Using succinylcholine for intubation: This causes prolonged paralysis in organophosphate poisoning and is contraindicated. 1, 2, 3, 4