Skeletal Muscle Relaxants

Question 1

Central Muscle Relaxant

Answer 1

-act within the CNS
- They mainly depress the CNS

•GABA, (+):Diazepam
•GABA, (+):Baclofen
•A2(+):Tizanidine

Inhibit polysynaptic reflexes
•Mephensin
•Chlorzoxazone
•Thiocholchicoside

Question 2

Peripheral Muscle Relaxant

Answer 2

1. Directly Acting on the muscle
   •Dantrolene
   -#Ryanodine receptors in the ER
   -Used for
   Malignant hyperthermia
   Neuroleptic malignant syndrome
   S/E -Hepatotoxic
2. Neuro Muscular Junction blocker
   (NMJ #) (Indirectly Acting)

•Depolarizing muscle relaxants/
Non-competitive MR
•Non depolarizing muscle relaxants/
Competitive MR

Question 3

NMJ#
(Depolarizing MR/Non-competitive MR)

Answer 3

• Depolarizing MR/ Non-competitive MR:
  •Succinyl choline
• shortest acting MR (<5 min)
  -C/I in nerve & muscle injuries;
• Cause Severe Hyperkalemia
  -can preciptate malignant Hyperthermia
  -Fasciculations
  -Responsible for Post Operative Muscle
  Pain
  (Post operative muscle Rigidity is caused by Fentanyl group of drugs)

Question 4

NMJ#
(Non-Depolarizing/ Competitive MR)

Answer 4

•Tubocurarine (Curare)
-Do not cause post op muscle pain
-But it causes release of Histamine -causes
Severe bronchoconstriction
Hypotension

•Curium (release less H)
•Curonium (No H released)

Question 5

Curium drugs

Answer 5

-Release less H
•Atracurium
•Cis-atra curium
•Mivacurium (Shortest acting)
•Gantacurium
-Not yet approved by FDA
-Shortest and fastest acting(10 min)
NDMR

-Atracurium and Cis-atracurium undergo Hoffman’s elimination

Question 6

Curonium Drugs

Answer 6

-No histamine is released
•Pancuronium
•Pipecuronium
•Vecuronium
•Recuronium
•Rapacuronium

-MR of choice in a patient of Bronchial Asthma -Curonium drugs

Question 7

Hoffman’s Elimination

Answer 7

-Normally a drug is metabolized by liver
to become inactive or excreted by
kidney.
- Spontaneous, non-enzymatic
inactivation which occurs by molecular
rearrangement. This is called
Hoffman’s elimination Shown by
Atracurium & Cis-atracurium

•AtraCurium
-Releases Histamine
Some amount is metabolized by liver
also, which generates a metabolite
called Laudanosine. This metabolite
can cause Seizures

•Cis-Atracurium
-Negligible release of H. Undergo 100%
Hofmann elimination.
So, no risk of seizures

Question 8

Reversal agents (NMJ# Antagonists)

Answer 8

• used to reverse the action of NDMR
  after surgery
  •Neostigmine
  -Stimulate Nm Rec. Reverse the action
  of NDMR
  
  • M1 M2 M3 rec Prodces cholinergic S/E
    -To stop these S/E = Atropine

•Suggamadex
-Directly binds to muscle relaxant and
removes them from Nm receptor
-Selective Relaxnt Binding Agent (SRBA)
-Faster acting than neostigmine
-Higher risk of allergy