Muscle Relaxants

Question 1

What does Guaifenesin (GG) effect?

Answer 1

Effects the central nervous system but has an unknown mechanism of action other than depressing nerve impulses in the spinal cord.

Question 2

What is Guaifenesin (GG) used for?

Answer 2

Muscle relaxant used during anesthesia and during intubation.

Question 3

Guaifenesin (GG) mode of delivery?

Answer 3

IV infusion, dissolved in water, saline, or dextrose.

Question 4

Cautions when using Guaifenesin (GG)?

Answer 4

Transient hypotension (unlikely to be harmful) and solutions greater than 10% concentration can cause thrombophlebitis and hemolysis. 
*Can cross the placental barrier but not likely to effect fetus

Question 5

What drugs are commonly used with Guaifenesis (GG)?

Answer 5

Alpha - 2 agonist and ketamine

Question 6

What does Methocarbamol effect?

Answer 6

Effects the central nervous system but has an unknown mechanism of action other than neural inhibition of the spinal cord.

Question 7

Methocarbamol mode of delivery?

Answer 7

Can be oral or injectible

Question 8

What is Methocarbamol used for?

Answer 8

NOT used with Anesthesia.

Used to reduce muscular spasms in IVDD, urethral obstruction, toxins like tetanus.

Question 9

Cautions while using Methocarbamol?

Answer 9

irritating, mild sedation, salivation, and dark urine.

Question 10

What does Dantrolene effect?

Answer 10

Ryanodine receptor antagonist, inhibits Ca2+ release.

**Effects the peripheral nervous system

Question 11

What is Dantrolene used for?

Answer 11

Mainly used for the treatment of malignant hyperthermia (anesthetic induction problem causing muscle breakdown)

Question 12

Cautions while using Dantrolene?

Answer 12

Chronic use can cause hepatotoxicity and heart/respiratory problems.

Question 13

Neuromuscular blockers were originally used for?

Answer 13

Used for poison darts and derived from biological sources. Called ‘curare’

Question 14

What do neuromuscular blockers do?

Answer 14

Paralysis of all the skeletal muscles but animal is fully conscious. Ventilation is required because respiratory muscles are paralyzed.

Question 15

How are neuromuscular blockers typically delivered?

Answer 15

Parenterally, mainly given IV. They do not cross the BBB and have poor oral absorption.

Question 16

What are the two functional subclassifications of NMB?

Answer 16

Depolarizing and competitive

Question 17

What type of NMB is Succinylcholine?

Answer 17

Depolarizing (non-competitive) neuromuscular blockers.

Question 18

What is the mechanism of action of Succinylcholine?

Answer 18

Biphasic!
Phase I Block: ACh receptors are activated to prolong depolarization so that repolarization cant happen.
Phase II Block: Nicotinic receptors stay in an inactivated state and cant respond to ACh (flacid paralysis)

Question 19

What is the onset of action and duration of Succinylcholine?

Answer 19

Onset of action is one circulation time (30-60 seconds) and lasts several minutes before being hydrolyzed by PChE

Question 20

T/F Succinylcholine has a longer mechanism of action in ruminants and dogs.

Answer 20

True.
Ruminants have less PChE to hydrolyze the drug.

Dogs duration of action lasts 20 minutes.

Question 21

How are nicotinic receptors in the autonomic ganglia affected by Succinylcholine?

Answer 21

Effected but less sensitive than the NMJ but can cause hypertension, bradycardia, and increased ocular pressure.

Question 22

Clinical uses for Succinylcholine?

Answer 22

Facilitation of endotracheal intubation.

Not used for relaxation during surgery or to facilitate euthanasia (inhumane)

Question 23

Cations of using Succinylcholine?

Answer 23

Apnea, Muscle fiber damage, hyperkalemia, increased cardiac sensitivity, and no specific reversal agents.

Question 24

What drugs would prolong the effects of Succinylcholine?

Answer 24

Irreversible cholinesterase inhibitors (organophosphates) will slow hydrolysis.

Question 25

How do competitive (non-depolarizing) neuromuscular blockers work?

Answer 25

Competitive antagonists with ACh for nictonic receptors that will result in generalized flaccid paralysis.

Question 26

T/F Depolarizing NMBs are used more often than competitive NMB.

Answer 26

False.

Competitive NMBs are sometimes used for thoracic surgeries to allow control over thoracic wall.

Question 27

Competitive NMB effect on nicotinic receptors at ganglionic receptors ?

Answer 27

Blocks these receptors leading to hypotension, can cause histamine release, and possible tachycardia.

Question 28

Name 4 Competitive neuromuscular blockers?

Answer 28

Pancuronium, Atracurium, Vecuronium, and Rocuronium

Question 29

Effect of Pancuronium on the kidney and liver?

Answer 29

Significant amount is excreted unchanged in the urine (~40% in humans) and some is metabolized in the liver.

Question 30

Effect of Atracurium on the kidney and liver?

Answer 30

None. Undergoes spontaneous degradation in plasma (does NOT rely on hepatic or renal function for clearance).

Question 31

Effect of Vecuronium and Rocuronium on the kidney and liver?

Answer 31

Primarily metabolized by the liver and excreted in the bile and urine.

Question 32

What drugs do you give to reverse competitive NMB?

Answer 32

cholinesterase inhibitors (e.g. neostigmine, edrophonium) which may be combined with an antimuscarinic such as atropine or glycopyrrolate to block the muscarinic effects. Antimuscarinics may be avoided in equines due to the risk of colic.