Antimuscarinics (Cardiac)

Antimuscarinics used for bronchodilation are covered under Antimuscarinics (Respiratory), whilst atropine is covered separately.

Antimuscarinics are as competitive, reversible antagonists of ACh at the muscarinic receptor. They are divided into:

  • Naturally occurring tertiary amines
    These can cross the blood-brain barrier, and have central effects.
    • Atropine
    • Hyoscine
  • Synthetic quaternary amines
    Do not cross the blood-brain barrier.
    • Glycopyrrolate
Property Glycopyrrolate Hyoscine
Class Quaternary amine. Muscarinic antagonist Tertiary amine
Uses Bradycardia, antisialagogue Antisialagogue, motion sickness
Presentation Clear, colourless solution at 200μ Incompatible with diazepam and thiopentone. Racemic, only L-isomer active
Route of Administration IV/IM PO, SC
Dosing 200-400μg 200-600μg
Absorption Minimal PO absorption - not used via this route. < 50% PO bioavailability
Distribution Crosses placenta but not BBB, VD VD
Metabolism Minimal hepatic hydrolysis Extensive metabolism by hepatic esterases
Elimination Renal of 85% unchanged drug Renal of metabolites
Resp Bronchodilation, antisialagogue Bronchodilation, greatest antisialagogue effect
CVS Initial bradycardia due to partial agonist effect. Reverses vagal causes of bradycardia, may cause tachycardia in doses >200μg. HR peaks at 3-9 minutes following administration. Least likely anticholinergic to cause tachycardia
CNS Most likely anticholinergic to cause central anticholinergic syndrome
MSK Anhydrosis
GIT Reduced oral and gastric secretions, and gastric motility Reduced oral and gastric secretions, and gastric motility
GU Difficult micturition


  1. Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.
  2. Petkov V. Essential Pharmacology For The ANZCA Primary Examination. Vesselin Petkov. 2012.
Last updated 2017-08-03

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