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Neuromuscular Blocker - NEET PG Anesthesia

Feb 15, 2023


Neuromuscular blocking agents, also known as muscle relaxants, play a crucial role in the field of anesthesia. Neuromuscular blockers are essential for various surgical procedures, as they allow for a patient to remain immobile and without pain during surgery. A good understanding of neuromuscular blockers is important for a comprehensive understanding of anesthesia and its role in surgical procedures.

In this blog post, we discuss this important anesthesia topic briefly for the NEET PG/NExT exam Preparation. Read on.

Acts on NMJ (Neuromuscular Junction)

Depolarizing Non - Depolarizing 
SuccinylcholineRest All 
Persistent / prolonged depolarization of Nc (Nicotinic cholinergic Receptor).Acts by Competitive antagonism.
Fasciculation is seen.
Postoperative myalgia may be seen.
Not reversed by the Neostigmine.
No post tetanic facilitation seen.
No fasciculations seen.
No myalgia seen.
Reversal by Neostigmine.
post tetanic facilitation seen.

Train of 4 Response

DepolarizingDefinitionNon - Depolarizing
MoAProlonged or persistent depolarization of nicotinic cholinergic receptor  Example Succinyl choline
Causes: Depolarization
Competitive inhibition

Fasciculation are seen-No Fasciculations
Lesser amplitude of contraction produced.-It will fade.
Post-operative myalgia-No Postoperative myalgia
Not reversed by Neostigmine -Reversed by Neostigmine
No post tetanic fasciculation seen -Post tetanic fasciculation seen
No train of 4 responses was seen.
A - Response by First stimulus.
B - Response by Last stimulus.
BA = TOF Ratio
TOF ratio = 1.Neuromuscular monitor is not used.
4 successive stimuli given at 2 Hz at the same interval of time i.e., 0.5 sec and of same amplitude.

In normal muscle it will produce 4 contractions.
TOF Ratio < 1
Neuromuscular monitor is used.


  • Mode of action
    • Prolonged depolarization of nicotinic cholinergic receptor
  • Fastest Onset: 30-45 seconds. 
  • Shortest Duration: 45 minutes. 
  • Metabolized by Pseudocholinesterase / Butyrylcholinesterase / Plasma Cholinesterase.
  • Suxamethonium Apnea 
    • Due to deficiency of Pseudocholinesterase or due to atypical pseudocholinesterase.
    • There is Prolonged Apnea. 
    • Management: Mechanical Ventilation (IPPV).
  • Two phases of block. 
    • Phase I block: Normal activity of Succinylcholine: TOF not seen in it.
    • Phase Il block: Desensitization block: Start resembling the property of Non – depolarizing block (competitive block): TOF seen in it. 

Also Read: Drugs for General Anesthesia - NEET PG Anesthesia

Side effects of Succinylcholine

  • Fasciculation, Post- Op Myalgia 
  • ↑ IOP, ↑ ICP , ↑ IGP 
  • ↑ Exaggerated hyperkalemia seen in conditions like 
    • Muscle Dystrophy 
    • Neuromuscular Disease 
    • Paraplegia
    • Burn
    • Trauma 
    • Stroke 
  • Bradycardia 
  • Can trigger Malignant Hyperthermia.
  • Due to all these side effects succinylcholine is not used routinely.

Used in the following condition

  • Rapid sequence induction and intubation- because of its fastest onset.
  • Very short general anesthesia, e.g. in Electroconvulsive therapy.
  • Difficult airway intubation attempt.

Also Read:  Alternative Airway Devices and Adjuncts - NEET PG Anesthesia

Non – Depolarizing NMB

  • Routinely used 
PancuroniumPipecuroniumLong Actingd- tubocurarineDoxacurium 
Rocuronium        M/c usedVecuronium Intermediate ActingAtracurium Cis-atracurium
Rapacuronium(Faster onset)Short ActingMivacurium (Shortest Duration)
No Histamine Release

CVS Stable 
-Histamine Release
CVS Unstable
BronchospasmBP ↓HR ↑Flushing
Metabolized by liver, kidney-Few drugs have unique Metabolism as given below


  • Non depolarizing NMB but it is an Oxime compound 
  • Benefits
    • Fast onset.
    • Duration very short. 
    • Metabolized by L – Cysteine.

Atracurium and Cis-atracurium

  • Metabolized by Hoffmann's degradation i.e., self-destruction of drug. Also metabolized by Nonspecific Ester hydrolysis. Produces by product Laudanosine: which is epileptogenic 

Important Information

  • Cis-atracurium > Atracurium
    • Because CVS stable.
    • More potent.
    • Less laudanosine production.
    • No histamine release.
  • Gantacurium (fastest & shortest) > Rapacuronium (Faster Onset 75 sec) > Rocuronium 90 sec (Mivacurium (Shortest Duration ), if Gantacurium is given in option go with it, but it not that much clinical use
    • So overall succinylcholine is fastest and shortest

Rest all have 3 – 5 min onset

Reversal Agents

  • Neostigmine + glycopyrrolate/atropine
    • Neostigmine is an indirect reversal agent; it acts by increasing the quantity of acetylcholine.
  • Sugammadex: Direct reversal agent for aminosteroids (rocuronium and vecuronium).
  • Calabadion: Direct reversal agent for all non depolarizing agents (still in inception phase, and not in the market).

Previous Year Questions

Q. Cis-atracurium is better than atracurium because? (NEET Jan 2019)

A. Less histamine release

B. Less half life

C. Low Drug Dose

D. Low cost

Q. A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery? (NEET Jan 2020)

A. Neostigmine

B. Carbachol

C. Succinylcholine

D. Physostigmine

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