What is the recommended dose of atropine for treating tachyarrhythmias (abnormally fast heart rate) resulting from organophosphorus poisoning?

Atropine Dosing for Tachyarrhythmias in Organophosphorus Poisoning

For tachyarrhythmias resulting from organophosphorus poisoning, administer atropine at an initial dose of 2-3 mg intravenously, repeated every 20-30 minutes until symptoms resolve. 1

Dosing Protocol for Organophosphorus Poisoning

Initial Management

• Initial IV bolus: 2-3 mg atropine 1
• Repeat every 20-30 minutes until muscarinic symptoms are controlled 1
• For severe poisoning cases, higher doses are often required:
  • Initial bolus of 5 mg may be given 2
  • Follow with 2.5 mg every 5-10 minutes until atropinization is achieved 2

Atropinization Endpoints

Titrate atropine until the following clinical endpoints are reached:

• Clear chest on auscultation (absence of bronchorrhea)
• Heart rate >80/min
• Systolic blood pressure >80 mm Hg 3

Maintenance Dosing

• After initial atropinization, maintain with continuous atropine infusion 3
• Total doses required may be substantial - case reports document requirements ranging from 85-3000 mg in the first 24 hours 2

Important Clinical Considerations

Monitoring During Treatment

• Continuous cardiac monitoring is essential
• Monitor for signs of atropine toxicity: extreme tachycardia, hyperthermia, agitation, delirium
• Assess respiratory status frequently as respiratory failure is a common complication

Adjunctive Treatments

• Early endotracheal intubation is recommended for life-threatening organophosphate poisoning 3
• Benzodiazepines (diazepam preferred) should be administered to treat seizures and agitation 3
• Pralidoxime (2-PAM) is reasonable for organophosphate poisoning 3
  • Recommended as continuous infusion at 7.5 mg/kg/hour after initial bolus 2

Common Pitfalls to Avoid

1. Underdosing atropine: Organophosphate poisoning requires much higher doses than typical bradycardia treatment
2. Failure to recognize tachycardia as part of toxidrome: Nicotinic effects of organophosphates can cause tachycardia even before atropine administration
3. Premature discontinuation: Atropine should be continued until secretions are completely controlled
4. Inadequate respiratory support: Early intubation is critical in severe cases
5. Insufficient monitoring: Continuous cardiac and respiratory monitoring is essential

Special Populations

• Pediatric patients: Atropine dose is 0.02-0.05 mg/kg IV/IO, with minimum dose of 0.1 mg and maximum single dose of 0.5 mg 3
• Patients with coronary artery disease: Limit total atropine dose to 0.03-0.04 mg/kg to minimize risk of myocardial ischemia 1

The aggressive atropinization approach has been shown to improve outcomes in severe organophosphate poisoning cases requiring mechanical ventilation, with one study reporting 87.5% survival rate using this approach 2. Some patients may require extremely high cumulative doses (up to 11.6 g over 12 days) 4.