Vecuronium, pancuronium and rocuronium Flashcards
What is vecuronium
Clean drug- doesn’t affect the CVS or release histamine.
Aminosteroidal
Chemical structure differs from pancuronium by a single methyl group making it a monoquaternary analogue
Presentation and uses of vec
Potentially unstable in solution. Presented as 10mg freeze-dried powder containing mannitol and Na hydroxide and is dissolved in 5ml water.
0.1mg.kg-1
Intubate at 90-120 seconds
Medium duration of action
Cardiovascular effects of vecuronium
No CV effects
What is critical illness myopathy?
Most frequently seen in critically ill patients in association with corticosteroids and/or muscle relaxants and may involve prolonged recovery
Kinetics of vecuronium
Like pancuronium, metabolised in the liver by de-acetylation to 3- and 17-hydroxy and 3,17 dihydroxy-vecuronium.
Lipid soluble (more than pan) and more excreted in the bile. May accumulate in infusion.
What is pancuronium?
A bisquaternary aminosteroidal compount
Presentation and uses of pancuronium
Colourless solution containing 4mg in 2ml and stored at 4 degrees.
0.1mg.kg-1 intubate at 90-150 seconds
Duration 45 mins
CVS effects of pancuronium
Tachycardia by blocking cardiac muscarinic receptors. Indirect sympathomimetic actions by preventing the uptake of noradrenaline at post-ganglionic nerve endings
Kinetics of pancuronium
10-40% plasma protein bound. Low volume of distribution.
35% metabolised in the liver by de-acetylation to 3- and 17-hydroxy and 3,17-hydroxy-pancuronium. Unchanged drug secreted in the urine and metabolites in the bile
How do NDMRs work?
Inhibit the action of ACh at the NMJ by binding competitively to the alpha subunit of the nicotinic ACh receptor (post junctional).
More than 70% of receptors need to be occupied by muscle relaxant before neuromuscular blockade can be detected.
Same characteristics of a phase 2 block.
Chemical groupings of NDMRs
Aminosteroid compounds- vec, roc, pan
Benzylisoquinolinium compounds- atracurium, mivacurium, tubocurarine
Unable to cross lipid membranes due to polar nature and so have a small volume of distribution.
Hydrolysed in the plasma or metabolised in the liver and excreted in urine or bile.
What is rocuronium?
Developed from vec and structurally different in 4 positions.
Rapid onset 60-90s due to low potency.
Low potency= higher dose. Higher number of molecules = greater conc gradient from the plasma to the NMJ so that diffusion is faster and onset time reduced.
Presentation of rocuronium
50mg in 5ml. 0.6mg.kg-1 100-120s. 0.9-1.2mg.kg = 60s
CVS effects of roc
Minimal. Tachy at increased dose
Kinetics of roc
Mainly excreted unchanged in the bile and to a lesser extent in the urine. Some de-acetylated metabolites may be produced. Duration of action may be prolonged in hepatic or renal failure.
