Muscle relaxants

Question 1

Name the 3 Muscle relaxants (Anti-tremorigenic and sedating drugs)

Answer 1

 Methocarbamol
 Guaifenasin
 Dantrolene

Question 2

Site of action for muscle relaxants?

Answer 2

Peripheral
-Muscle cells- Dantrolene

Central
-Spinal cord- Guaifenesin + Methocarbamol

Question 3

Which drug is a peripherally acting muscle relaxant?

Answer 3

Dantrolene

Question 4

Mechanism of action for Dantrolene?

Answer 4

Peripherally acting muscle relaxant ( acts on the muscle cell)

Question 5

Does Dantrolene cross the BBB?

Answer 5

No

Question 6

Dantrolene is the drug of choice for

Answer 6

for treatment of malignant hyperthermia (hypermetabolic syndrome)

Question 7

What is hypermetabolic syndrome?

Answer 7

 Genetically determined idiosyncratic drug reaction

 Hypermetabolic reaction of skeletal m. –> rhabdomyolysis

 Life threatening hyperthermia, hyperkalemia, and cell death

 Shock, multiple organ dysfunction syndrome (MODS)

 OFTEN FATAL

Question 8

______ was part of this
dog’s treatment plan due to its
MUSCLE RELAXATION effects

Answer 8

Dantrolene

Question 9

Dantrolene is used for treatment of this infection

Answer 9

Tetanus (clostridium tetani) infection

Characterized by muscle rigidity & ↑ sympathetic tone

keep calm sedate, quiet, minimal noise, feeding tube, antibiotics

Prognosis (50% mortality)

Question 10

Which drugs are the centrally acting muscle relaxants?

Answer 10

Methocarbamol

Guaifenesen

Question 11

Methocarbamol mechanism of action?

Answer 11

Selective blockade of nerve impulse transmission in the
spinal cord

Crosses BBB

Question 12

Methocarbamol is approved in ____, _____, and ____ to reduce muscle spasm? (Tx of inflammatory or traumatic conditions)

Answer 12

dogs, cats, and horses

Question 13

Describe the route of administration for methocarbamol?

Answer 13

Rapid oral absorption

Relatively short half-life

(Shorter when given IV)

available as oral tablets or injectable$$ (irritating if given IM or SubQ)

Question 14

Main effects of methocarbamol?

Answer 14

Mild to moderate muscle relaxation patients do not require ventilation

Question 15

Clinical uses for methocarbamol?

Answer 15

• Intervertebral disk disease
• Tetanus
• Intoxication (tremorogenic)

(Less common but functional urethral obstruction)

(Crash cart drug)

Question 16

Side effects and adverse effects of methocarbamol?

Answer 16

 Sedation, salivation, weakness, lethargy, and ataxia.

 Caution using the injectable form with renal disease

 Cleared/excreted renally

 Avoid extravasation & administer IV injection slowly
(~2mL/minute)

 Check cost of IV injection, recently has been $$$

Question 17

Mechanism of action for guaifenesin?

Answer 17

 Intravenous centrally-acting muscle relaxant &
expectorant

 Acts mainly by blocking nerve impulse
transmission in the spinal cord, brain stem, & subcortical areas of the brain

 Crosses BBB

 Some sedative and analgesic effects

Question 18

Describe the onset of action and duration of guaifenesin?

Answer 18

 Rapid onset & short duration of action (10-20 minutes)

 Considered long-acting if used as part of an anesthetic induction & intubation protocol

Question 19

Clinical uses for guaifenesin?

What species is it approved in

Answer 19

Approved in horses

class 4 substance

 Combined for intubation and relaxation of pharyngeal & laryngeal muscles
(skeletal m.)

 Combination with ketamine and used in horses & cattle for procedural sedation

 Can be used in conjunction with Guaifenesin (GG) + Xylazine + Ketamine (“Triple Drip”)

Question 20

Precautions of using guaifenesin? Which species is more sensitive?

Answer 20

 High concentrations (≥ 10%) can cause hemolysis

 Cattle MORE SENSITIVE than horses

Question 21

______ is contraindicated in horses receiving guaifenesin.

Answer 21

Physostigmine