Pharm 101: Pancuronium

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
  • Long-acting: duration of action > 35 minutes
  • Metabolism: hepatic
  • Elimination: renal (80%)
Clinical uses of neuromuscular blocking drugs
  • Rapid Sequence Induction (RSI) to facilitate relaxation of pharyngeal and laryngeal muscles for intubation
  • 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
  • Surgical relaxation (especially for intra-abdominal and intra-thoracic procedures)
  • Control of ventilation in ventilatory failure due to pneumonia, COPD etc.
    • Reduce chest wall resistance i.e. improve thoracic compliance, decrease oxygen utilisation, and improve ventilator synchrony
Adverse effects
  • Moderate tachycardia and small increase in CO due to vagolytic action on cardiac muscarinic receptors
Precautions/contraindications
  • Enhanced neuromuscular blockade:
    • Myasthenia gravis
    • Aminoglycosides
  • Reduced neuromuscular blockade:
    • Corticosteroids
    • Phenytoin
  • Reduced clearance:
    • Renal failure
    • Advancing age
Further reading
References
  • Katzung BG. Basic & Clinical Pharmacology. 14e. 2018: 476-484
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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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