Pharm 101: Vecuronium

Class

Paralytic agent

Pharmacodynamics
  • Non-depolarising steroid neuromuscular blocking agent
  • At low doses, acts predominately as a competitive inhibitor of Acetylcholine (ACH) at nicotinic receptors
  • At higher doses, enters pore of ion channel causing more intense neuromuscular blockade
  • Also blocks pre-junctional Na channels which interferes with ACH mobilisation at nerve endings
Pharmacokinetics
  • IV use
  • Undergoes rapid initial distribution phase followed by slower elimination phase
  • Highly ionised therefore small volume of distribution 0.1L/kg
  • Onset of action: within 1 minute
  • Maximal effect at 3-5 minutes
  • Intermediate-acting: duration of action 20-35 minutes
  • Rapidly distributed to extracellular space
  • Metabolism: liver
  • Elimination: liver (75-90%) and kidney
Clinical uses
  • Rapid Sequence Induction (RSI)
    • Dose 0.1mg/kg
  • Clinical effects:
    • Initially motor weakness followed by skeletal muscles becoming flaccid and unexcitable to electrical stimulation
    • Larger muscles (e.g. abdominal, trunk, diaphragm) are more resistant to neuromuscular blockade and recover more rapidly than smaller muscles (e.g. facial, foot, hand)
    • Diaphragm is the last muscle to be paralysed
Sugammadex
  • Sugammadex is a modified cyclodextrin antidote used for rapid reversal of rocuronium and vecuronium
  • Binds tightly to rocuronium in a 1:1 ratio, and this complex is excreted unchanged in the urine
  • This decreases free plasma concentration and establishes a concentration gradient for rocuronium to diffuse away from the neuromuscular junction back into circulation for further binding to free sugammadex
  • Dosing varies for desired reversal effects:
    • 2mg/kg: reversal of shallow neuromuscular blockade
    • 4mg/kg: reversal of deeper blockade
    • 16mg/kg: immediate reversal following administration of single dose 1.2mg/kg rocuronium
  • Adverse effects:
    • Anaphylaxis in 0.3% of patients receiving 16mg/kg dosage
    • Hypersensitivity reactions are common
    • Bradycardia (may progress rapidly to cardiac arrest)
    • Coagulopathy: 25% elevation of APTT and PT/INR values lasting up to one hour
Precautions/contraindications
  • Enhanced neuromuscular blockade:
    • Myasthenia gravis
    • Aminoglycosides
  • Reduced neuromuscular blockade:
    • Corticosteroids
    • Phenytoin
  • Reduced clearance:
    • Hepatic failure
    • Advancing age
References
  • The Royal Children’s Hospital Melbourne. Parkville, Victoria, Australia. July 2017. Medication guidelines: Vecuronium
  • Katzung BG. Basic & Clinical Pharmacology. 14th ed. United States of America: McGraw-Hill Education; 2018. 476-484 p.
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MBBS CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

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