Two Classes of Neuromuscular Block
Mechanism, onset characteristics, and reversal strategy
Competitive Antagonism
Nondepolarizing Block
  • Blocks nicotinic receptor — no channel opening
  • Membrane stays at resting potential
  • No fasciculations on onset
  • Train-of-four: fade (4th twitch weaker)
  • Reversed by anticholinesterases or sugammadex
  • Examples: rocuronium, vecuronium, pancuronium
Persistent Agonism
Depolarizing Block (Phase I)
  • Activates nicotinic receptor — holds membrane depolarized
  • Adjacent sodium channels become inactivated
  • Fasciculations precede flaccid paralysis
  • Train-of-four: no fade (uniform depression)
  • No reversal agent for phase I block
  • Only agent: succinylcholine
Key Reversal Distinction
Nondepolarizing — Reversible

Anticholinesterases (neostigmine) raise acetylcholine in the cleft, competing the drug off the receptor. Sugammadex encapsulates rocuronium and vecuronium directly.

Depolarizing Phase I — Not Reversible

Anticholinesterases would worsen block by prolonging succinylcholine action. Management is ventilatory support until succinylcholine is metabolized by pseudocholinesterase.