Skeletal Muscle Relaxants (Including Neuromuscular Blockers)

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Neuromuscular blockers are essential adjuncts in anaesthesia, acting at the nicotinic acetylcholine receptors of the neuromuscular junction (NMJ) to induce muscle relaxation. Understanding their classification and unique pharmacokinetics is critical for surgical management.

Classification and Drug Profiles

Agent Details for Exam
Succinylcholine
(Depolarizing)
  • Ultra-short acting (duration 5-10 mins).
  • Acts as an ACh agonist, causing persistent depolarization.
  • Clinical Pearl: Causes fasciculations, increases intraocular/intragastric pressure, and is a trigger for Malignant Hyperthermia (MH).
Rocuronium
(Non-depolarizing)
  • Rapid onset, intermediate duration.
  • The agent of choice for Rapid Sequence Induction (RSI) when Succinylcholine is contraindicated.
Vecuronium
(Non-depolarizing)
  • Intermediate duration. Highly prized for cardiovascular stability, as it lacks significant autonomic side effects.
Atracurium / Cis-atracurium
(Non-depolarizing)
  • Intermediate duration.
  • Undergo Hofmann elimination (spontaneous breakdown at physiological pH and temperature).
  • Safe in renal/hepatic failure.
Pancuronium
(Non-depolarizing)
  • Long-acting.
  • Known to induce tachycardia due to vagolytic properties and sympathetic stimulation.
Dantrolene
(Direct-acting)
  • Acts by blocking calcium release from the sarcoplasmic reticulum.
  • The specific antidote for Malignant Hyperthermia.

High-Yield Clinical Pearls

  • Organ-Independent Elimination: Atracurium and Cis-atracurium are the go-to agents in patients with end-organ dysfunction (Renal/Hepatic failure).
  • Reversal Agents:
    • Non-depolarizers: Reversed by Acetylcholinesterase inhibitors (Neostigmine) to increase synaptic ACh.
    • Specific Reversal: Sugammadex selectively encapsulates Rocuronium and Vecuronium, providing rapid and reliable reversal.
  • Succinylcholine Contraindications: Strictly avoid in patients with:
    • Severe burns (>24h old) or crush injuries.
    • Denervation injuries (e.g., spinal cord injury).
    • Hyperkalemia.
    • Suspected neuromuscular disease (risk of massive K+ release).

Exam Reminder

Always distinguish between agents that rely on organ clearance (Vecuronium/Pancuronium) versus those that utilize organ-independent pathways (Atracurium/Cis-atracurium) for your exam questions.

For high-yield clinical resources and free medical questions, visit mymedschool.org.