18. CENTRAL MUSCLE RELAXANT DRUGS

Question 1

which effect has central muscle relaxants on the cns?

Answer 1

• Causing decreased motor activity or paralysis of voluntary muscles without loss of consciousness.
• They do not inhibit other functions of CNS

Question 2

why are myorelaxants used?

Answer 2

• Central myorelaxants can activate the effect of anaesthetics drugs and combinations.
• They are also used to control certain spasmodic and painful disorders of skeletal (spinal) muscles.

Question 3

What are the effects of GUAIPHENESIN?

(Glycerol guaiacolate, Guaiacolglycerol ether)

Answer 3

Effect:
- It is a spinal interneuronal blocking agent

• It blocks polysynaptic but not monosynaptic reflexes.
• Exact mechanism is unknown. -
• It is effective against convulsion
• It paralyses limb muscles, respiratory muscles are generally unaffected.
• The consciousness is retained:→ sedatives must be applied (alpha2 -agonists, opioids, ketamine)

Secondary effect: expectorant (helps bring up mucus and other material from the lungs, bronchi, and trachea)

(A convulsion is a medical condition where body muscles contract and relax rapidly and repeatedly,)

Question 4

indications of guaiphensin:

Answer 4

Indications:

horses, cattle, sheep

– to adjunct anaesthesia dogs – strichnine poisoning (in pass)

Question 5

dosing of guaiphenesin:

Answer 5

Dosing:

• Due to low potency (50-100 mg/kg IV) and concentration large volume is required (infusion package)

Question 6

side-effect of guaiphenesin:

Answer 6

Side-effects:

• mild, at therapeutic dose slight decrease of (arterial) blood pressure.
• Only large doses cause respiratory depression.
• It causes haemolysis (concentration dependent), preferred 5% solution with 5% dextrose.

Question 7

pharmacokinetics of guaiphenesin:

Answer 7

Pharmacokinetics:

• Onset and elimination of action is fast, 2-4 and 60-80 min., respectively.
• Large distribution, crosses the placenta barrier.

Metabolism → conjugation with glucuronide → excration with urine.

Question 8

how does baclophen act?

Answer 8

• Acts as agonist at GABAB receptors in the brain and spinal cord, resulting in hyperpolarization of neurons due to increased K+ion conductance.
• Also inhibits neural function presynaptically, by reducing Ca2+ ion influx, and thereby reducing the release of excitatory neurotransmitters in both the brain and spinal cord.
• It may also reduce pain in patients by inhibiting the release of Substance P (SP) in the spinal cord as well (cf. opioids)

Question 9

Safety of baclophen:

Answer 9

Safety:

• Large therapeutic index.
• Clinical signs of toxicosis are vomiting, ataxia, and vocalization or disorientation, life-threatening signs are respiratory arrest, and seizures.

Question 10

indications of baclophen?

Answer 10

Spasm of skeletal muscles, rigidity, spinal cord injury and pain caused by injuries.

Baclophen has also been used extralabel in dogs to treat urinary retention by reducing urethral resistance.

Question 11

Why is Carisoprodol used?

Answer 11

• Is especially useful against various types of pain because of its analgesicsparing (potentiating) effect on opioid analgesics.
• Inactive in convulsion caused by strychnine.
• Is available by itself or mixed with Aspirin and in one preparation along with codeine and caffeine as well. (Problems with the use of combinations, dependence, abuse and side effects may occur.)

Question 12

how does methocarbamol act?

Answer 12

Acts on the internuncial neurones of the spinal cord. Reduces skeletal muscle hyperactivity without alteration in muscle tone. (Veterinary use?)