What is the recommended dose of atropine (antimuscarinic agent) for a 3-month-old infant weighing 5 kg?

Atropine Dosing for a 3-Month-Old Infant (5 kg)

For a 3-month-old infant weighing 5 kg, administer atropine at 0.01-0.03 mg/kg IV/IO (0.05-0.15 mg total dose), with no minimum dose requirement per current guidelines. 1, 2

Dose Calculation by Clinical Indication

For Symptomatic Bradycardia

• Standard dose: 0.02 mg/kg IV/IO = 0.1 mg for this 5 kg infant 1
• The 2015 American Heart Association guidelines eliminated the previous 0.1 mg minimum dose requirement for neonates and young infants, as evidence demonstrated that weight-based dosing (0.02 mg/kg) without a minimum is both effective and safe 1
• Maximum single dose: 0.5 mg for children 1
• May repeat every 5 minutes if needed, up to maximum total dose of 1 mg 1

For Rapid Sequence Intubation (RSI) Premedication

• Dose: 0.01-0.02 mg/kg IV/IO = 0.05-0.1 mg for this infant 1
• However, routine atropine premedication before RSI in young infants is not recommended based on lack of evidence for clinically significant bradycardia with single-dose succinylcholine 3, 4
• The 2015 guidelines state that 0.02 mg/kg with no minimum dose may be considered when used as premedication for emergency intubation, but this is not routine practice 1

For Organophosphate/Anticholinesterase Poisoning

• Initial dose: 0.02-0.05 mg/kg IV = 0.1-0.25 mg for this infant 1, 5
• Repeat as needed for clinical effect (resolution of muscarinic symptoms: excessive secretions, bronchospasm, bradycardia) 5
• Much higher cumulative doses may be required in severe poisoning 5

Route of Administration

Intravenous/Intraosseous (Preferred)

• Administer by slow IV push for cardiac arrest 1
• Titrate based on heart rate, PR interval, blood pressure, and symptoms 2

Endotracheal (If IV/IO Access Unavailable)

• Dose: 0.01-0.03 mg/kg for neonates = 0.05-0.15 mg for this infant 1
• Follow with or dilute in saline flush (1-5 mL) based on patient size 1

Critical Safety Considerations

Debunking the "Paradoxical Bradycardia" Myth

• The historical concern that atropine doses <0.1 mg cause paradoxical bradycardia in infants has been definitively refuted 6
• A prospective study of 60 infants demonstrated zero incidence of bradycardia with mean atropine dose of 40.9 µg (well below 0.1 mg), with upper 95% confidence interval for bradycardia occurrence of only 5% 6
• Heart rate actually increased by 7% at 30 seconds, 14% at 1 minute, and 25% at 5 minutes after low-dose atropine 6

First-Line Treatment Priorities

• For hypoxia-induced bradycardia, oxygenation and ventilation are essential first maneuvers 1
• Epinephrine is the drug of choice if oxygen and adequate ventilation are not effective, not atropine 1
• Atropine is specifically indicated for vagally-mediated bradycardia or AV block 1

Concentration and Preparation Caveats

• Atropine sulfate comes in different concentrations—calculate dosage carefully 1
• Common concentrations: 0.4 mg/mL and 1 mg/mL 2
• For this 5 kg infant receiving 0.1 mg dose: use 0.25 mL of 0.4 mg/mL concentration OR 0.1 mL of 1 mg/mL concentration
• Each vial is intended for single dose only; discard unused portion 2
• Inspect visually for particulate matter and discoloration; do not administer unless solution is clear and seal is intact 2

Potential Adverse Effects

• May cause tachycardia, which could worsen ischemia in patients with underlying cardiac disease 1
• In patients with coronary artery disease (rare in this age group), limit total dose to 0.03-0.04 mg/kg 2
• Tachycardia occurred in 48% of infants in one study, lasting mean 223 seconds 6