Atropine (antidote)

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Related FACEM curriculum (2022) learning objectives:

• ME 3.8.1.6(e) Principles of management of toxicological presentations including: Indications for antidotes
• ME 3.8.2.4 Identify the appropriate antidote or antivenom.

Presentations

• Atropine sulfate prefilled syringe: 0.1 mg/mL (10 mL).
• Atropine sulfate ampoules: 0.4 mg/mL, 0.5 mg/mL, 0.6 mg/mL, 1.2 mg/mL.

Toxicological Indications

• Poisoning impairing AV conduction (e.g., cardiac glycosides, beta-blockers, calcium channel blockers).
• Organophosphate and carbamate poisoning.

Contraindications

• Relative contraindications:
  • Closed-angle glaucoma.
  • Obstructive gastrointestinal disease.
  • Obstructive uropathy.

Mechanism of Action

• Competitive acetylcholine antagonist at muscarinic receptors.
• Reverses parasympathetic overstimulation from acetylcholinesterase inhibition.
• No activity at nicotinic receptors.

Pharmacokinetics

• Poor oral bioavailability; hepatic metabolism; 2–4 hour elimination half-life.
• Crosses blood–brain and placental barriers.
• ~50% excreted unchanged in urine.

Administration

General

• Ensure patient is in a monitored area with full resuscitative support available.

Organophosphate and Carbamate Poisoning

• Initial IV bolus: 1.2 mg.
• Repeat every 2–3 minutes, doubling dose until respiratory secretions dry.
• Large doses (up to 100 mg) and continuous infusion may be required in severe cases.

Drug-Induced Bradycardia with AV Conduction Blockade

• Initial IV bolus: 0.6 mg.
• Repeat 0.6 mg doses as needed up to 1.8 mg.

Therapeutic Endpoints

• Drying of respiratory secretions in organophosphate poisoning.
• Excessive dosing indicated by anticholinergic features.

Adverse Drug Reactions

• Anticholinergic poisoning symptoms: delirium, tachycardia, mydriasis, urinary retention.
  • Management: stop atropine, use benzodiazepines for delirium, and insert a urinary catheter.

Specific Considerations

• Pregnancy: No restrictions.
• Paediatric Dose: 20 micrograms/kg initial dose.
• Anticipate large atropine doses in organophosphate poisoning; procure sufficient stock early.

Pitfalls

• Inadequate dosing in organophosphate/carbamate poisoning.
• Excessive dosing causing iatrogenic anticholinergic poisoning.