Antimuscarinic agent

  • Atropine is a tertiary amine alkaloid ester of tropic acid
  • Competitive, reversible muscarinic ACh receptor antagonist
    • Binding prevents release of IP3 (inositol triphosphate), DAG (diacyglycerol), and inhibition of adenylyl cyclase, which are caused by muscarinic agonists
  • Equipotent at M1, M2, M3 receptors
  • No significant nicotinic effect
Organ system effects
  • CNS:
    • Sedation
    • Delirium
    • Decreased tremor in Parkinson’s disease
  • Eye:
    • Mydriasis (pupillary constrictor muscle depends on muscarinic cholinoceptor activation)
    • Cyclopegia (weakened contraction of ciliary muscle)
  • CVS:
    • Initial bradycardia at lower doses (blocks prejunctional M1 receptors)
    • Tachycardia
  • Resp: bronchodilation and decreased secretions
  • GIT:
    • Decreased secretions
    • Decreased gastric emptying
    • Decreased gut motility
    • Increased intestinal transit time
  • GUT:
    • Relaxation of ureteric and bladder wall smooth muscle
    • Urinary retention
  • Skin: decreased sweating
  • Route of administration: IV, PO, nebulised, topical
  • Well absorbed orally
  • Significant levels in CNS within 30-60 minutes, wide Vd
  • Two phases of elimination:
    • Rapid: half-life 2 hours
    • Slow: half-life 13 hours
  • Hepatic metabolism and subsequent renal excretion:
    • 40% phase I and phase II metabolism
    • 60% unchanged
Clinical uses
  • Symptomatic bradyarrhythmias / bradycardia
  • Opthalmological: mydriatic and cyclopegic
  • Drying of secretions e.g. cholinergic nerve agonist, OP poisoning, palliative care
  • Traveller’s diarrhoea
Adverse effects
  • Extension of organ system effects, typical antimuscarinic effects
  • Glaucoma
  • Prostate hyperplasia
  • Gastric ulcers (slow gastric emptying thus worsen symptoms)
Further reading

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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