Neuromuscular Blockers

Question 1

what are the only clinically useful nicotinic antagonists

Answer 1

skeletal muscle type nAChR’s (Nm)

Question 2

what is the structure of all neuromuscular blocking drugs

Answer 2

analogues of acetylcholine

Question 3

neuromuscular blockers are given by what route

Answer 3

IV

Question 4

what is the difference between a non-depolarizing and a depolarizing block

Answer 4

non-depolarizing: nAChR antagonists
depolarizing: nAChR agonists

Question 5

what are 2 considerations of neuromuscular blockers

Answer 5

animals fully conscious and no analgesia

Question 6

in veterinary medicine, __________ is one of the most commonly used non-depolarizing neuromuscular blockers

Answer 6

atracurium

Question 7

is atracurium a depolarizing or non-depolarizing neuromuscular blocker

Answer 7

non-depolarizing

Question 8

what is the most common clinical use of atracurium

Answer 8

prevent eye movement during ocular surgery

Question 9

what is a benefit of using atracurium during eye surgery

Answer 9

you can achieve complete muscle relaxation without the need for higher anesthetic doses, making it safer and a faster recovery

Question 10

how does atracurium cause muscle relaxation

Answer 10

it competitively blocks AChRs at the NMJ

Question 11

what are the pharmacokinetic considerations of atracurium

Answer 11

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

Question 12

what drugs can you use to reverse the effects of atracurium

Answer 12

neostigmine, pyridostigmine, edrophonium

Question 13

what is a major consideration of using neuromuscular blockers that limits their use to in referral practices by board-certified veterinarians

Answer 13

can get dose-dependent respiratory paralysis

Question 14

what is the order of paralysis of muscles when using neuromuscular blockers

Answer 14

1) extraocular
2) neck/face/hands/feet
3) abdomen/arms/legs
4) eye blink
5) respiratory and diaphragm

Question 15

what is the order of recovery of muscles when using neuromuscular blockers

Answer 15

1) respiratory and diaphragm
2) eye blink
3) arms/legs/abdomen
4) face/neck/hands/feet
5) extraocular

Question 16

what is the main depolarizing neuromuscular blocker

Answer 16

succinylcholine

Question 17

how does succinylcholine cause paralysis

Answer 17

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

Question 18

what is the main clinical use of succinylcholine today

Answer 18

to help horses go down smoothly prior to euthanasia

Question 19

what is the onset and duration of action of atracurium

Answer 19

3min; approx 45 min (dose-dependent)

Question 20

what is the onset and duration of action of succinyl choline

Answer 20

less than 1 min; 90s

Question 21

what is the role of muscle relaxants

Answer 21

decrease muscle tone/spasms without completely inhibiting voluntary contractions -> useful to alleviate muscle spasms associated with certain clinical conditions (IVDD, blocked cat…)

Question 22

what are the 2 forms of muscle relaxants

Answer 22

centrally acting and peripherally acting

Question 23

what are the 3 classes of centrally acting muscle relaxants

Answer 23

1) benzodiazepines (ex. Valium)
2) methocarbamol
3) guaifenesin

Question 24

what is the peripherally acting muscle relaxant

Answer 24

dantrolene

Question 25

how do benzodiazepines cause muscle relaxation

Answer 25

facilitate GABA activity in the CNS

Question 26

what are 2 considerations of benzodiazepines

Answer 26

1) metabolism can be altered by other drugs
2) may cause CNS depression

Question 27

what are the 3 main issues with methocarbamol

Answer 27

mechanism unknown, efficacy uncertain, contraindicated in renal diseases

Question 28

what is the mechanism of action of guaifenesin

Answer 28

inhibits interneurons in motor reflexes

Question 29

how is guaifenesin used

Answer 29

given IV with injectable anesthetics for induction

Question 30

how does dantrolene work

Answer 30

inhibits Ca release from the SR