Neuromuscular Blocking Drugs Flashcards
What are the non-depolarizing isoquinoline derivatives?
- atracurium
- cisatracurium
- D-tubocurarine (off the market)
What are the non-depolarizing steroid derivatives?
- Pancuronium
- Rocuronium
- Vecuronium
What is the only depolarizing agent?
Succinylcholine
What are the reversal agents for NMBs?
- Edrophonium
- Pyridostigmine
- Neostigmine
- Sugammedex
What are reversal agents used for?
They are given post‐procedurally to reverse the residual effects of the paralytic agent and restore normal neuromuscular activity and tone.
What are the types of cholinergic receptors?
nicotinic receptors
and muscarinic receptors.
Where do paralytic agents act?
nicotinic M receptors found on post-synaptic skeletal muscle (the other type is the nicotinic N receptors- can be found on pre-synaptic terminal)
Describe the nicotinic acetylcholine receptor.
It is a multimeric ligand-gated ion channel for sodium influx into the cell, leading to depolarization
What must occur for the nicotinic acetylcholine receptor to activate?
2 molecules of Ach must bind
How are depolarizing paralytics different from non-depolarizing paralytics?
Non-depolarizers bind the receptor and prevent the opening of the receptor channel (thus preventing initial activation of muscle contraction) while depolarizing agents actually open the gate and causes persistent depolarization which prevents gate closure and repolarization
What is the result of depolarizing paralytics (i.e. succinylcholine)?
The initial, intense muscle contraction is replaced by flaccid paralysis from preventing repolarization to occur
How does a peripheral nerve stimulator (PNS) work?
It delivers 4 sequential stimuli at 2 Hz. Each stimuli causes release of Ach from synaptic vesicles. In the absence of neuromuscular blockade, the 4th twitch of the adductor polices muscle is as strong as the first. This is called ‘fade’
Only the first twitch is registered in a PNS when what percentage of receptors is bound?
85-90%
Which twitches can be seen when 70-8% of receptors are bound?
between 2-4
How are the non-depolarizing drugs metabolized?
rapid initial distribution into tissue with slower elimination and duration of action correlated closely with half life.
How are the non-depolarizing drugs eliminated?
more rapidly eliminated via liver than kidney
What is a potential downside of Atracurium?
it is intermediate acting with hepatic metabolism and Hofmann elimination which produced laudanosine, a metabolite linked to seizure
What are the advantages of Cisatracurium over atracurium?
it is less dependent on hepatic inactivation, thus producing less laudanosine and it also releases less histamine
How is succinylcholine eliminated?
broken down in situ by pseudocholinesterase enzyme (not present in synaptic cleft) (plasma) or by hydrolysis by butyrylcholinesterase (liver)
decreased pseudocholinesterase may be seen in older patients
How long does succinylcholine act?
only 5-10 minutes. However, Note the predisposition of some patients, with variant pseudocholinesterase activity, to experience prolonged drug action
When else has increased duration of action been seen in succinylcholine?
with ester-type anesthetic agents
What test can be performed to identify the extent of pseudocholinesterase activity?
Dibucaine test (inhibits normal enzyme by 80% and abnormal by only 20%)
Alternatively a simplified colorimetric screening test can be performed using the Acholest Test Paper, a substrate-impregnated test paper, a similar colorimetric reaction occurs
How are atracurium and cisatracurium eliminated? Tubocurarine?
spontaneously at site of action (tubocurarine is really mostly)
Which isoquinolone lasts longest? shortest?
longest- tubocurarine (50+ min)
shortest- atracurium (20-35 min)