Atropine is an anticholinergic agent which acts as a competitive antagonist at central and peripheral muscarinic receptors. It is used to treat organophosphate and carbamate toxicity, symptomatic bradycardia (e.g. in β-blocker toxicity), and chemical weapons nerve agent toxicity.

Cholinergic toxidrome in organophosphate toxicity

• A rapid loading protocol and infusion is used.
• 💊 Atropine 1.2 mg IV, double the dose q5min until target end points for atropinization reached, then start infusion; very high doses (up to 100 mg) may be required.
• 💊 Atropine 10-20% of total loading dose per hour IV infusion, usually 0.5-5 mg/hr.
• Titrate to atropinization target end points:
  • Clear chest, no auscultatory wheeze
  • HR > 80 bpm
  • Systolic BP > 80 mmHg
• Observe for signs of over-atropinization:
  • Confusion
  • Pyrexia
  • Absent bowel sounds

Cholinergic toxidrome excluding organophosphate toxicity

• 💊 Atropine 0.6 mg IV, double the dose q5min until target end points for atropinization reached; max cumulative dose 3 mg.
• Titrate to atropinization target end points:
  • Clear chest, no auscultatory wheeze
  • HR > 80 bpm
  • Systolic BP > 80 mmHg
• Observe for signs of over-atropinization:
  • Confusion
  • Pyrexia
  • Absent bowel sounds

Bradycardia (e.g. Beta Blocker Toxicity)

• 💊 Atropine 0.6 mg IV, q15min; max cumulative dose 3 mg.

Cholinergic toxidrome in organophosphate toxicity

• A rapid loading protocol and infusion is used.
• 💊👶 Atropine 0.05 mg/kg (up to 1.2 mg) IV, double the dose q5min until target end points for atropinization reached, then start infusion; very high doses may be required.
• 💊👶 Atropine 10-20% of total loading dose per hour IV infusion.
• Titrate to atropinization target end points:
  • Clear chest, no auscultatory wheeze
  • Resolution of symptomatic bradycardia
• Observe for signs of over-atropinization:
  • Confusion
  • Pyrexia
  • Absent bowel sounds

Cholinergic toxidrome excluding organophosphate toxicity

• 💊👶 Atropine 0.02 mg/kg (up to 0.6 mg) IV, double the dose q5min until target end points for atropinization reached; max cumulative dose 3 mg.
• Titrate to atropinization target end points:
  • Clear chest, no auscultatory wheeze
  • Resolution of symptomatic bradycardia
• Observe for signs of over-atropinization:
  • Confusion
  • Pyrexia
  • Absent bowel sounds

Bradycardia (e.g. Beta Blocker Toxicity)

• 💊👶 Atropine 0.02 mg/kg (up to 0.6 mg) IV; max cumulative dose 3 mg.

Pregnancy rating: A (AU/NZ)

Lactation: Small amounts excreted in breast milk

Renal impairment:

Hepatic impairment:

• Description of important/serious adverse effects, e.g.
• Serotonin syndrome:
• Systems e.g.
• GI:
• Resp:
• MSK: local phlebitis
• Frequency e.g.
• Common:

Mechanism of action:

Absorption:

• Oral bioavailability: variably reported between 50-95%
• GI tract absorption: From small intestine
• IM bioavailability: 50%
• Tmax:
  • IV: Almost immediate
  • Oral: 60 mins
  • IM: 11-30 mins
  • SC: 34 ± 23 mins
  • Inhaled: 15-114 mins

Distribution:

• Vd: 2-4 L/kg (large Vd; widely distributed in the body)
• Distribution t½ after IV: 1 min; rapid decline in serum concentration within first 10 mins
• Lipid solubility:
  • Crosses blood brain barrier
  • Crosses placenta
  • Excreted in breast milk in small amounts
• Protein binding: 14-22%

Metabolism: Hepatic metabolism - hepatic enzyme hydrolysis.

• Stereoselective metabolism: biologically active L-enantiomer metabolized, biologically inactive D-enantiomer excreted unchanged in urine.
• Metabolites: Tropine, noratropine, atropine-N-oxide, tropic acid.

Excretion:

• Elimination t½: 4 hrs
• Hepatic clearance: 519 ± 147 mL/min
• Renal clearance: 90% excreted in urine over 24 hours. 30-50% as unchanged drug.

Formulation:

Useful general references: