Skeletal Muscle Relaxatants and reversal agents

Skeletal Muscle Relaxants

So we have 2 types of muscle relaxants:-

Those which work on the CNS ( Central )

those who work on the muscle and their NM receptors (peripheral)

Central Muscle Relaxant

So to use center in material relaxants we need a drug which stimulates the receptors present in the CNS and such receptors are

•        GABA a receptors – Diazepam 
•     GABA b  receptors --- Baclofen 
•     alpha 2 receptors(acts like break )- tizanidine
•      Another group of centrally acting muscle relaxants are those which act by inhibiting the polysynaptic reflexes examples -Mephensin ,Chlorzoxazone, thiocolchicoside  
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Peripheral muscle relaxants

there are two types:-

 directly acting and indirectly acting

Directly acting:-

 they directly act on the muscles

directly acting-dantrolene :-works by blocking ryanodine receptor in endoplasmic reticulum from muscles

Ryanodine receptor-it is the same receptor which helps in the release of calcium ions from the endoplasmic reticulum

Indirectly acting or Neuromuscular blockers:-they block new impulses on the neuromuscular junction

Dantrolene--> blocks ryanodine receptor -> block calcium release --> muscle relaxation

dantrolene is used for  1.malignant hyperthermia

                                      2. neuroleptic malignant syndrome

dantrolene can also cause hepatotoxicity

Indirectly acting:-

(neuromuscular blockers)

the block now impulses on the neuromuscular junction

they work on neuromuscular junctions and neuromuscular receptors,

NM receptors have a property of optimal stimulation, that is , 

if they are stimulated more than necessary they develop muscle weakness and the same is observed if we provide less stimulation which also leads to muscle weakness

indirectly acting can be of two types:-

1.  depolarising(overstimulation) and 
2. non depolarising(competitive)

   

   Mechanism of depolarising and non depolarising muscle relaxant

   
   

Depolarising

So what does stimulate muscles , yes it's acetylcholi(AC H) so if we provide something with a longer name it will stimulate the muscle more such as succinylcholine sch

S--    shortest acting because it is metabolised by pseudocholinesterase there is a pharmacogenetic                 condition in which few people have low degree of pseudocholinesterase leading to longer than                required effect of succinylcholine

C --    contraindicated in Nerve and  muscle injury 

      cause it can lead to severe life threateninghyperkalemia

1.  nerve injury- spinal cord injury, paraplegia,  hemiplegia 
2. muscular injury-crush injury, burns, rhabdomyolysis

H- can precipitate malignant hyperthermia sch stimulates muscles a lot which can lead to fasciculations leading to postoperative muscle pain

question which drug can cause postoperative muscle pain?

Answer-succinylcholine

Question- which drug causes postoperative muscle rigidity?

Answer-opioid group like fentanyl group

Non depolarising 

directly inhibiting the neuromuscular receptors

D – Tubocurarine

• Doesn't cause postoperative muscle pain
• there is a problem which is that it releases histamines---the released histamines cause bronchoconstriction and hypo tension which leads to low BP

So in essence even if we want drugs like d-tubocurarine as it is not causing post operative muscle pain but we don’t want the histamine release to occur and so new drugs were developed

 

So there were two types of drugs developed

1.   curium(release less histamine)

a.   atracurium

b.   cis atracurium

c.   mivacurium(shortest acting)

2.   curonium(release no histamine at all)

a.   pancuronium

b.   pipecuronium

c.   vecuronium

d.   rocuronium

e.   rapacuronium

so if you want to give muscle accents to an asthmatic patient will give curoniums because we don't want any histamines to be released does leading two brown constructions

Hofffman’s elimination

atracurium and cis atracurium do not require kidney or liver to be inactivated they become inactive after sometimes and that spontaneous enzymatic inactivation of a drug by molecular rearrangement is hoffmans elimination

these are the muscle relaxants of choice in case of liver and kidney disease

 

 

Gantacurium

-shortest and fastest acting nondepolarizing muscle relaxant

 

Reversal agents

these are used to reverse the action of non depolarising muscle relaxants after surgery

1.   neostigmine

2.   suggamadex

 

 

 

 --- hey everyone , hope this short section on muscle relaxants was helpful , if you felt it was helpful, please leave a comment and share to those who might need this short note -- the fool