Bedside Snapshot
  • Core dose: Symptomatic bradycardia: 1 mg IV/IO every 3–5 min (max 3 mg total); organophosphate poisoning: 1–2 mg IV, double every 3–5 min until secretions dry and ventilation improves
  • Onset/duration: IV onset within minutes; duration 30–60 min (cardiac effects), up to 4 h (antisialagogue effects); half-life 2–4 h
  • Key danger: Paradoxical bradycardia if dose <0.5 mg; tachycardia and hypertension with standard doses; delirium/agitation at higher doses; anticholinergic toxidrome
  • Special: Anticholinergic (blocks muscarinic receptors); first-line ACLS drug for symptomatic bradycardia; antidote for organophosphate/nerve agent poisoning (may require large cumulative doses); crosses BBB
Brand & Generic Names
  • Generic Name: atropine sulfate (systemic/ophthalmic)
  • Brand Names: AtroPen (auto-injector), Isopto Atropine (ophthalmic)
Medication Class

Anticholinergic

Pharmacology

Mechanism of Action:

  • Competitive antagonist at muscarinic acetylcholine receptors
  • Cardiac (M2): reduces vagal tone, increasing SA node firing and AV nodal conduction
  • Secretory/smooth muscle (M3): decreases salivary and bronchial secretions; reduces bronchial tone; decreases GI motility; may cause urinary retention
  • CNS penetration: central antimuscarinic effects at higher doses (agitation, delirium)

Pharmacokinetics (clinically relevant):

  • Onset: IV rapid (minutes); IM ~3–5 min
  • Duration: Cardiac effects ~30–60 min; antisialagogue effects up to ~4 h
  • Half-life: ~2–4 h in adults (longer in elderly)
  • Distribution: Large volume of distribution; crosses BBB and placenta
  • Metabolism: Hepatic metabolism
  • Elimination: Renal elimination of parent and metabolites
  • Special considerations: In organophosphate/nerve agent poisoning, large or continuous dosing may be required due to ongoing muscarinic stimulation and tissue redistribution
Indications
  • Symptomatic bradycardia from vagal excess (first-line per ACLS algorithms)
  • AV nodal block (e.g., Mobitz I) with symptoms/hemodynamic compromise
  • Antidote for organophosphate/carbamate insecticide or nerve agent poisoning (muscarinic toxidrome)
  • Premedication to mitigate vagal bradycardia during pediatric intubation in selected cases (less routine today)
  • Management of muscarinic adverse effects from cholinesterase inhibitors (e.g., neostigmine, pyridostigmine)
Conditions Treated
  • Symptomatic bradycardia
  • AV nodal block (Mobitz I) with hemodynamic compromise
  • Organophosphate/carbamate poisoning
  • Nerve agent exposure
  • Cholinergic crisis
Dosing & Administration

Available Forms:

  • Prefilled syringe: 1 mg/10 mL (0.1 mg/mL) IV/IO
  • Vials: 0.1, 0.4, or 1 mg/mL
  • Auto-injectors (AtroPen): 0.5 mg, 1 mg, 2 mg

Adult Dosing:

Indication Dose Notes
Symptomatic bradycardia 1 mg IV/IO; repeat every 3–5 min to total 3 mg Avoid doses <0.5 mg to prevent paradoxical bradycardia
Organophosphate/nerve agent poisoning 1–2 mg IV, then double every 3–5 min until secretions dry and ventilation improves Large cumulative doses common; may use infusion (0.02–0.08 mg/kg/h) after control
Auto-injector (field use) 0.5–2 mg IM per protocol based on weight/severity Multiple sequential devices may be needed for severe exposures

Pediatric Dosing:

  • Bradycardia: 0.02 mg/kg IV/IO (min 0.1 mg; max single dose 0.5 mg child, 1 mg adolescent); may repeat once. Max total: 1 mg child, 2 mg adolescent
  • Organophosphate poisoning: 0.02 mg/kg IV, then double every 3–5 min as needed
Contraindications

Contraindications:

  • Hypersensitivity to atropine
  • Note: In time-critical emergencies (bradycardia, OP poisoning), no absolute contraindications

Precautions:

  • Use caution in narrow-angle glaucoma, urinary retention/BPH, paralytic ileus
  • Severe ulcerative colitis/toxic megacolon
  • Myasthenia gravis (unless treating cholinergic crisis)
  • May precipitate tachyarrhythmias in ischemic heart disease or tachycardia syndromes; monitor closely
  • Heart transplant recipients may have poor/absent response due to denervation; consider isoproterenol or pacing
Pregnancy/Lactation: Crosses placenta and is excreted in breast milk; weigh risks/benefits for nonemergent indications.
Adverse Effects

Anticholinergic Effects:

  • Dry mouth/skin
  • Mydriasis/blurred vision, photophobia
  • Urinary retention
  • Constipation/ileus
  • Tachycardia
  • Flushing
  • Hyperthermia (decreased sweating)

CNS Effects:

  • Restlessness
  • Confusion
  • Delirium/hallucinations (dose-related; higher risk in elderly or high cumulative dosing)

Cardiac Effects:

  • Palpitations
  • SVT/VT (rare)
  • Paradoxical bradycardia with very low doses

Other:

  • Ophthalmic exposure can cause prolonged mydriasis and photophobia
Clinical Pearls
Bradycardia Treatment: Best for sinus bradycardia or AV nodal block (Mobitz I). In Mobitz II or complete heart block with wide QRS, move early to pacing or catecholamines.
Dosing: Give full adult doses (1 mg) to avoid paradoxical bradycardia; very small adult doses are counterproductive.
Organophosphate Poisoning: Endpoint is drying of secretions and improved ventilation—not heart rate. Massive cumulative doses may be required; infusion can maintain effect and reduce redosing gaps.
OP Poisoning Treatment: Treat muscarinic symptoms with atropine; give pralidoxime to regenerate acetylcholinesterase and benzodiazepines for seizures.
Pediatric Airway: Atropine as intubation premedication is no longer routine but remains reasonable in high-risk bradycardic infants or with succinylcholine—follow local protocols.
Transplant Hearts: Atropine often ineffective in heart transplant recipients; isoproterenol, theophylline, or pacing preferred.
Ocular Exposure: Prevent ocular exposure during IV use; avoid contacting conjunctiva with contaminated hands or tubing.
References
  • 1. Papadopoulos, J. (2008). Pocket guide to critical care pharmacotherapy. Humana Press.
  • 2. Medscape. (n.d.). Atropine: Drug monograph and dosing (systemic). Retrieved 2025-11-12, from https://reference.medscape.com/drug/atropen-atropine-343369
  • 3. DrugBank Online. (n.d.). Atropine (DB00572). Retrieved 2025-11-12, from https://go.drugbank.com/drugs/DB00572
  • 4. Medscape. (n.d.). Organophosphate toxicity: Treatment. Retrieved 2025-11-12, from https://emedicine.medscape.com/article/167726-overview
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