Neuromuscular Blockers Flashcards
what are the only clinically useful nicotinic antagonists
skeletal muscle type nAChR’s (Nm)
what is the structure of all neuromuscular blocking drugs
analogues of acetylcholine
neuromuscular blockers are given by what route
IV
what is the difference between a non-depolarizing and a depolarizing block
non-depolarizing: nAChR antagonists
depolarizing: nAChR agonists
what are 2 considerations of neuromuscular blockers
animals fully conscious and no analgesia
in veterinary medicine, __________ is one of the most commonly used non-depolarizing neuromuscular blockers
atracurium
is atracurium a depolarizing or non-depolarizing neuromuscular blocker
non-depolarizing
what is the most common clinical use of atracurium
prevent eye movement during ocular surgery
what is a benefit of using atracurium during eye surgery
you can achieve complete muscle relaxation without the need for higher anesthetic doses, making it safer and a faster recovery
how does atracurium cause muscle relaxation
it competitively blocks AChRs at the NMJ
what are the pharmacokinetic considerations of atracurium
1) must be injected IV because it is highly polar (ionized)
2) duration of effect varies with dosage
3) usual recovery time (20min-30 min, sometimes 1h) follows last dose
what drugs can you use to reverse the effects of atracurium
neostigmine, pyridostigmine, edrophonium
what is a major consideration of using neuromuscular blockers that limits their use to in referral practices by board-certified veterinarians
can get dose-dependent respiratory paralysis
what is the order of paralysis of muscles when using neuromuscular blockers
1) extraocular
2) neck/face/hands/feet
3) abdomen/arms/legs
4) eye blink
5) respiratory and diaphragm
what is the order of recovery of muscles when using neuromuscular blockers
1) respiratory and diaphragm
2) eye blink
3) arms/legs/abdomen
4) face/neck/hands/feet
5) extraocular
what is the main depolarizing neuromuscular blocker
succinylcholine
how does succinylcholine cause paralysis
acts like a nicotinic agonist -> initial depolarization causes muscle contractions, then cannot repolarize so Na channels remain inactivated -> flaccid paralysis -> rapidly degraded by ACh esterase
what is the main clinical use of succinylcholine today
to help horses go down smoothly prior to euthanasia
what is the onset and duration of action of atracurium
3min; approx 45 min (dose-dependent)
what is the onset and duration of action of succinyl choline
less than 1 min; 90s
what is the role of muscle relaxants
decrease muscle tone/spasms without completely inhibiting voluntary contractions -> useful to alleviate muscle spasms associated with certain clinical conditions (IVDD, blocked cat…)
what are the 2 forms of muscle relaxants
centrally acting and peripherally acting
what are the 3 classes of centrally acting muscle relaxants
1) benzodiazepines (ex. Valium)
2) methocarbamol
3) guaifenesin
what is the peripherally acting muscle relaxant
dantrolene
how do benzodiazepines cause muscle relaxation
facilitate GABA activity in the CNS
what are 2 considerations of benzodiazepines
1) metabolism can be altered by other drugs
2) may cause CNS depression
what are the 3 main issues with methocarbamol
mechanism unknown, efficacy uncertain, contraindicated in renal diseases
what is the mechanism of action of guaifenesin
inhibits interneurons in motor reflexes
how is guaifenesin used
given IV with injectable anesthetics for induction
how does dantrolene work
inhibits Ca release from the SR
