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ATROPINE

CLASS

Anti-cholinergic

PRESENTATION

Clear, colourless solution.

Formulations

  • 1ml vial, 600mcg, 600mcg/ml

INDICATIONS & DOSING

Bradycardia

  • Adult; 300-600mcg IV/IO/IM/subcut, repeat 3-5 minutes
  • Paediatric; 20mcg/kg IV/IO/IM/subcut, repeat 3-5 minutes

PRACTICALITIES

Administration

  • Drawn and administered neat

Incompatibilities

  • Adrenaline, thiopentone, heparin, metaraminol, sodium bicarbonate

Practice tips

  • Follow with a rapid saline flush and consider chest compressions to aid circulation of drug if circulation compromised 
  • Particularly efficacious when bradycardia is parasymapthetically driven (e.g. oculocardiac reflex)
  • Maximum dose due to limit in efficacy with complete parasympathetic blockade, not toxicity (adult ~3mg)
  • Avoid low dose which can cause paradoxical bradycardia via the Bezold-Jarisch reflex (adult <500mcg)

PHARMACOKINETICS

Onset

  • IV; 2-4 minutes 
  • IM; 15-50 minutes

Duration of action

  • IV/IM; maximum effect 20-60 minutes, duration up to 5 hours

Metabolism

Metabolised in the liver and tissues by hydrolysis to tropine and tropic acid which are renally excreted

Elimination

~30-50% of drug excreted unchanged renally

MECHANISM

Competitive antagonism of acetylcholine at central and peripheral muscarinic receptors. Inhibits effects of parasympathetic outflow.

DESIRED CLINICAL EFFECTS

Airway

  • Positive chronotropy, dromotropy, increase in cardiac output

Respiratory

  • Bronchodilation
  • Decrease in bronchial secretions

Gastrointestinal

  • Antisialagogue (less effective cf. hyoscine)
  • Reduces gastrointestinal tone, aiding procedural instrumentation
  • Anti-emetic

OTHER CLINICAL EFFECTS, ADVERSE EFFECTS & TOXICITIES

Respiratory

  • Increase in physiological dead space 

Cardiovascular

  • Paradoxical bradycardia (low dose, cardiac denervation post-transplant)
  • Tachycardia, precipitation of myocardial ischaemia
  • Dysrhythmias due to dromotropic effect 

Neurological

  • ‘Central anticholinergic syndrome’; excitatory (agitation, delirium, seizures) or depressive (sedation, coma)
  • Mydriasis, blurred vision 

Genitourinary

  • Urinary retention 

Other

  • Pyrexia in paediatric population due to inhibition of diaphoresis 

Antidote

  • Physostigmine

CONSIDERATIONS

Precautions

  • Ischaemic heart disease, myocardial ischaemia
  • Cardiac transplant (paradoxical bradycardia)
  • Elderly and other patients at high risk of delirium/cognitive impairment
  • Obstructive urinary tract disease
  • GI disease; obstructive, paralytic ileus/atony, infective
  • Myasthenia gravis; exacerbation 

Obstetric 

ADEC category A 

Drug interactions

  • Metoclopramide, antagonism
  • MAO-inhibitors; potential for hypertensive crisis
  • Oral anticholinergics; precipitation of central anticholinergic syndrome

REFERENCES

Drug information has been compiled from multiple sources including

  • Drugs in Anaesthesia and Intensive Care (Scarth & Smith)
  • Micromedex (IBM)
  • BJA Education (Oxford Academic)
  • Pharmacology for Anaesthesia and Intensive Care (Cambridge)
  • Australian Prescriber (NPS MedicineWise)

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