What is the recommended intramuscular (IM) dose of atropine for adults and children, including repeat dosing intervals and maximum total dose?

Atropine Intramuscular Dosing

For adults, administer atropine 0.4 to 0.6 mg IM every 4 to 6 hours for standard antimuscarinic indications, with context-specific dosing ranging from 1 mg IM for gastrointestinal radiography to 2-5 mg IM for organophosphate poisoning. 1

Adult IM Dosing by Indication

Standard Antimuscarinic Use

• Dose: 400 to 600 mcg (0.4 to 0.6 mg) IM every 4 to 6 hours 1
• This represents the FDA-approved baseline dosing for routine antimuscarinic effects 1

Preanesthesia (Antisialagogue)

• Dose: 200 to 600 mcg (0.2 to 0.6 mg) IM administered 30 to 60 minutes before surgery 1
• Timing is critical—administration 15 minutes before entering the operating room optimizes effect while minimizing excessive sedation when combined with other agents 2

Gastrointestinal Radiography

• Dose: 1 mg IM 1

Organophosphate/Nerve Agent Poisoning

• Initial dose: 2 to 5 mg IM, repeated every 20 to 30 minutes until muscarinic symptoms resolve 3, 4, 1
• Escalation: Double the dose with each administration if inadequate response 3
• No arbitrary maximum: Cumulative doses may reach 10-20 mg in the first 2-3 hours, with total 24-hour doses up to 50 mg or more 3
• Endpoints of adequate atropinization: Clear chest on auscultation, heart rate >80/min, systolic BP >80 mmHg, drying of secretions, and resolution of miosis 3, 4

Critical pitfall: In organophosphate poisoning, underdosing is more dangerous than overdosing—aggressive titration is essential and standard cardiac dose limits do not apply 3

Muscarine Poisoning (Mushrooms)

• Dose: 1 to 2 mg IM every hour until respiratory effects subside 1

Pediatric IM Dosing

Standard Antimuscarinic Use

• Dose: 10 mcg (0.01 mg)/kg IM, not to exceed 400 mcg (0.4 mg), or 300 mcg (0.3 mg)/m² body surface area, every 4 to 6 hours 1

Weight-Based Preanesthesia Dosing (Subcutaneous/IM)

• Up to 3 kg: 100 mcg (0.1 mg) 1
• 7 to 9 kg: 200 mcg (0.2 mg) 1
• 12 to 16 kg: 300 mcg (0.3 mg) 1
• 20 to 27 kg: 400 mcg (0.4 mg) 1
• 32 kg: 500 mcg (0.5 mg) 1
• 41 kg: 600 mcg (0.6 mg) 1

Organophosphate Poisoning (Pediatric)

• Initial dose: 0.02 to 0.05 mg/kg IV (preferred route), but can be given IM if IV access unavailable 4
• Maximum single dose: Typically 2-3 mg 4
• Repeat dosing: 0.5 to 1 mg every 5 to 10 minutes until muscarinic symptoms disappear or signs of atropine toxicity appear 1

Administration Technique & Pharmacokinetics

IM Injection Considerations

• Absorption enhancement: Automatic injector devices substantially enhance drug absorption rate compared to manual IM injection 5
• Site selection matters: Devices that deliver atropine into separate IM sites (away from pralidoxime when co-administered) produce faster absorption in the first 30 minutes 5
• Onset: IM atropine has slower onset than IV (which peaks within 3 minutes), making IV the preferred route for emergencies 3

When IM Is Appropriate

• Moderately ill victims who don't require IV access for other care 6
• Mass casualty scenarios where IM administration is faster and easier than establishing IV access 6
• Preanesthesia antisialagogue use where rapid onset is not critical 1

Critical Dosing Warnings

Paradoxical Bradycardia

• Doses below 0.5 mg can paradoxically worsen bradycardia through central vagal stimulation in adults 3
• This warning applies primarily to IV administration; IM dosing of 0.4-0.6 mg is FDA-approved but should be used cautiously in bradycardic patients 1

Pediatric Minimum Dose Controversy

• Older guidelines recommended a minimum dose of 0.1 mg to avoid paradoxical bradycardia 7
• 2015 American Heart Association guidelines eliminated this minimum dose requirement after evidence showed 0.02 mg/kg without a minimum is effective and safe 7
• For neonates specifically, use 0.01-0.03 mg/kg IV/IO without a minimum dose 7

Contraindications

• Heart transplant recipients: Atropine is contraindicated for treating bradycardia in denervated hearts without autonomic re-innervation 3

Monitoring Parameters

• Continuous ECG monitoring during administration for cardiac indications 3
• Heart rate, blood pressure, pupil size (resolution of miosis indicates adequate dosing in poisoning) 3, 4
• Respiratory status and secretion clearance in organophosphate poisoning 3
• Signs of excessive dosing: tachycardia >120/min, anticholinergic toxicity (fever, delirium, urinary retention, dry flushed skin) 3

Practical Considerations for Mass Casualty Preparedness

• Stock augmentation: Existing 0.4 mg/mL or 1 mg/mL atropine can be fortified with pharmaceutical-grade atropine powder to 2 mg/mL concentration, facilitating IM administration of larger doses 6
• Stability: Compounded high-concentration atropine maintains potency for 8 weeks refrigerated or 4 weeks at room temperature 6
• Compounding time: Approximately 1 hour to prepare fortified stocks once materials are available 6