Peripheral nervous system Neuromuscular junction

Question 1

Where is a drug acting when it interferes with synthesis, transport, and/or release of acetylcholine? (pre/post synaptic)

Answer 1

Presynpatic NMJ

NOT generally used in veterinary medicine

Question 2

What are some general characteristics of Neuromuscular blockers?

Answer 2

Developed from dart poisons
Paralyze all skeletal muscles
Consciousness is NOT affected
Quaterinary compounds

Question 3

Do neuromuscular blockers affect consciousness?

Answer 3

NO, patient cannot move but is still fully conscious and they have NO analgesic effects

Question 4

Is assisted ventilation required when using NMB?

Answer 4

YES, they paralyze all skeletal muscles

Question 5

What is a depolarizing (noncompetitive) NMB?

Answer 5

Succinylcholine

Question 6

What is phase I of succinylcholine?

Answer 6

Activation of nicotinic ACh receptors
Induces prolonged depolarization of the motor-end plate
There is NO complete repolarization which prevents stimulation by ACh
Muscle fasciculation (Flaccid paralysis)

Question 7

What is a phase II block of succinylcholine?

Answer 7

Nicotinic ACh receptors do NOT respond properly to ACh
Flaccid paralysis is prolonged

Generally want to AVOID this

Question 8

In what way are depolarizing blockers typically given?

Answer 8

IV, rarely IM

Very poor oral absorption

Question 9

What is the typical duration of a depolarizing blocker?

Answer 9

2-3 minutes

Question 10

What two species do depolarizing blockers work longer?

Answer 10

Dogs and ruminants

Question 11

What are some pharmacological effects of depolarizing blockers?

Answer 11

Skeletal muscles: Twitching followed by flaccid paralysis, may be painful

Other: Hyperkalemia, increased IOP due to contraction of ocular muscles, Transient bradycardia, Nicotinic ACh receptors at autonomic ganglia less sensitive than at NMJ

Question 12

What drug has clinical indications such as:

Facilitation of endotracheal intubation*
Muscle relazation during surgery (rare)

Answer 12

Succinylcholine

Question 13

In what situation should Succinylcholine never be used?

Answer 13

Should NEVER be used as an adjunct to euthanasia

Question 14

What are some adverse effects of Succinylcholine?

Answer 14

Apnea** ALWAYS use artificial respiration
Muscle fiber damage
Hyperkalemia
bradycardia
Increased arrhythmogenicity
Malignant hyperthermia

Question 15

Is there a specific reversal for Succinylcholine?

Answer 15

No specific reversal

Supportive care needed until metabolized
Anything that alters metabolism will prolong the affect (ex. exposure to irreversible cholinesterase inhibitors)

Question 16

What are some cautions for Succinylcholine?

Answer 16

Keep refrigerated to avoid spontaneous hydrolysis
Glaucoma or cardiac disease
Cholinesterase inhibitors

Question 17

What are some competitive (non-depolarizing) NMB?

Answer 17

Pancuronium
Atracurium
Vecuronium
Mivacurium
Rocuronium

Question 18

What is the mechanism of action for competitive NMBs?

Answer 18

Competitive antagonism with acetylcholine for nicotinic receptors at the motor-end plate

Question 19

In what ways are non-depolarizing blockers generally given?

Answer 19

IV, rarely IM

Question 20

What Non-depolarizing blockers are primarily metabolized by the liver, excreted by bile and urine?

Answer 20

Vecuronium, Rocuronium

Question 21

What non-depolarizing blocker undergoes spontaneous degradation in plasma?

Answer 21

Atracurium

Question 22

What is the pharmacokinetics of Pancuronium?

Answer 22

Most excreted unchanged by the kidney, some liver metabolism, minor bile excretion

Question 23

What is the main Pharmacological effect of Non-depolarizing blockers?

Answer 23

Flaccid paralysis

Question 24

What are some cautions when using non-depolarizing blockers?

Answer 24

May cause Histamine release in dogs and cats

Caution with liver/kidney disease