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

• Buttner R. Pharm 101: Rocuronium. LITFL
• Buttner R. Pharm 101: Vecuronium. LITFL
• Buttner R. Pharm 101: Suxamethonium. LITFL

References

• Katzung BG. Basic & Clinical Pharmacology. 14e. 2018: 476-484