Atropine

Introduction to Atropine

Atropine is a crucial anticholinergic medication used in pediatric emergency medicine, primarily for the management of bradyarrhythmias and as an antidote for certain poisonings.

Key Points:

Anticholinergic agent (muscarinic receptor antagonist)
Rapid onset of action
Used in bradycardia, organophosphate poisoning, and as a premedication
Available in various formulations (IV, IM, endotracheal, ophthalmic)
Paradoxical effect at very low doses in infants and young children

Pharmacology of Atropine

Atropine's pharmacological effects are primarily due to its antagonism of muscarinic acetylcholine receptors.

Mechanism of Action:

Competitive antagonist at muscarinic acetylcholine receptors
Blocks the effects of the parasympathetic nervous system
Increases heart rate by blocking vagal tone
Reduces secretions in the respiratory and gastrointestinal tracts
Causes mydriasis and cycloplegia in the eyes

Pharmacokinetics:

Onset of action: IV - immediate; IM - 20-30 minutes
Peak effect: IV - 2-4 minutes; IM - 30 minutes
Duration of action: 4-6 hours
Half-life: Approximately 2-3 hours
Metabolism: Hepatic
Excretion: Primarily renal (30-50% as unchanged drug)

Clinical Applications in Pediatric Emergency Medicine

Atropine has several important applications in pediatric emergency situations.

Primary Indications:

Symptomatic bradycardia: Especially if secondary to increased vagal tone or AV block
Organophosphate poisoning: As an antidote for cholinergic crisis
Premedication for intubation: To reduce secretions and prevent bradycardia

Secondary Indications:

Reversal of muscarinic effects in tricyclic antidepressant overdose
Management of bradycardia associated with beta-blocker or calcium channel blocker toxicity
Prevention of contrast-induced bradycardia during radiological procedures

Contraindications:

Hypersensitivity to atropine
Narrow-angle glaucoma (relative contraindication)
Obstructive gastrointestinal or genitourinary conditions
Myasthenia gravis (relative contraindication)

Dosing and Administration

Atropine dosing in pediatrics varies based on the indication and route of administration.

Pediatric Dosing for Bradycardia:

IV/IO: 0.02 mg/kg (minimum dose 0.1 mg, maximum single dose 0.5 mg for child, 1 mg for adolescent)
May repeat every 3-5 minutes to a maximum total dose of 1 mg in a child, 2 mg in an adolescent
Endotracheal: 0.04-0.06 mg/kg

Pediatric Dosing for Organophosphate Poisoning:

Initial dose: 0.05-0.1 mg/kg IV/IM (minimum 0.1 mg)
Double the dose every 3-5 minutes until muscarinic symptoms resolve
No maximum dose in this scenario; guided by clinical response

Administration Considerations:

For IV administration, may be given undiluted as a rapid push
Minimum dose of 0.1 mg to avoid paradoxical bradycardia
In cardiac arrest, higher initial doses may be considered
For organophosphate poisoning, continuous infusion may be necessary

Adverse Effects and Precautions

While generally safe at recommended doses, atropine can cause significant side effects, especially at higher doses.

Common Adverse Effects:

Tachycardia
Dry mouth
Blurred vision
Urinary retention
Constipation
Flushing and dry skin

Serious Adverse Effects:

Hyperthermia (especially in infants)
Central anticholinergic syndrome (confusion, agitation, hallucinations)
Paradoxical bradycardia (with very low doses)
Acute narrow-angle glaucoma exacerbation

Precautions and Monitoring:

Monitor heart rate and rhythm continuously during administration
Be aware of the potential for paradoxical bradycardia with doses <0.1 mg
Use with caution in patients with Down syndrome (increased sensitivity)
Monitor for signs of anticholinergic toxicity, especially with repeated doses
In organophosphate poisoning, titrate to effect (clear lung secretions, resolve bradycardia)