Describe the pharmacology of vecuronium, including factors that prolong its action of neuromuscular blockade.
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:
Miller, Ronald D. "Vecuronium: A New Nondepolarizing Neuromuscular‐Blocking Agent; Clinical Pharmacology, Pharmacokinetics, Cardiovascular Effects and Use in Special Clinical Situations." Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy 4.5 (1984): 238-245.