Question 6

Describe the pharmacology of vecuronium, including factors that prolong its action of neuromuscular blockade.

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College Answer

Vecuronium is a commonly available and regularly used amino-steroid neuromuscular blocking agent. It is a level 1 drug in the 2017 syllabus. A simple template utilising the headings; pharmaceutics, PK, PD, uses in ICU and adverse reactions with associated relevant important facts would have scored well. Expected information regarding the factors prolonging neuromuscular blockade included electrolyte abnormalities, drug interactions and patient factors. Overall, the level of understanding and knowledge demonstrated in the answers was below an expected standard for a level 1 drug.


Name Vecuronium
Class Non-depolarising NMJ blocker
Chemistry Aminosteroid
Routes of administration IV or IM only
Absorption Poor absorption; minimal oral bioavailability
Solubility pKa=8.97; good water solubility
Distribution VOD= 0.2L/kg, 77% protein-bound
Target receptor Nicotinic acetylcholine receptors at the neuromuscular junction
Metabolism Perthaps 5% is metabolised; one of the metabolites has about 80% of the potency of the parent drug (3-desacetylvecuronium)
Elimination 30-40% is cleared by the liver and into the bile (good lipid solubility); another 30% is renally eliminated as unchanged drug
Time course of action Half-life 110 minutes
Mechanism of action Nondepolarising neuromuscular junction blocker (competitive antagonist of acetylcholine); by binding to the nicotinic acetylcholine receptor, this agent blocks the binding of acetylcholine, and prevents the cation channel from opening, thus preventing the depolarisation of the motor endplate.
Clinical effects Nondepolarising neuromuscular junction blockade; also:
- Minimal ganglionic effects
- Minimal vagolytic effect (slight increase in HR)
- Minimalsympathomimetic effect (slight increase in HR)
- Minimal histamine release (only slightly more than pancuronium)
Single best reference for further information Miller et al (1984)

Factors prolonging neuromuscular blockade:

  • Impaired clearance (renal or hepatic dysfunction, hypothermia)
  • Factors which increase the potency of vecuronium:
    • Factors that reduce the synthesis or storage of acetylcholine
      • Hemicholinium
      • Vesamicol
    • Factors that decrease acetylcholine release
      • Foetal/neonatal motor endplates
      • General anaesthetic agents (volatiles)
      • Regional local anaesthesia
      • Frusemide
      • Calcium channel blockers
      • Aminoglycosides
    • Factors that partially depolarise the motor endplate
      • Hypermagnesemia
      • Hypocalcemia
      • Hypokalemia
    • Factors that reduce the number of acetylcholine receptors, such as myasthenia gravis (for depolarising agents, this slows the onset)