CNS (Skeletal muscle relaxant)

• Depolarizing/Non-competitive NMB


  Succinylcholine, Suxamethonium
• Succinylcholine


  • Only muscle relaxant in use today
  • Attaches to the nicotinic receptor
  • Acts like Ach to depolarize the junction
• Mechanism of action of Succinylcholine

  1. Phase 1: Continuous tetanic skeletal muscle contraction

  2. Phase 2: Flaccid Paralysis
• Succinylcholine


  • Injected IV
  • Short duration of action
  • Redistribution and rapid hydrolysis by plasma pseudocholinesterase
  • Useful when rapid endotracheal intubation is required during induction of anesthesia
  • Used during electroconvulsive shock treatment
• Non-depolarizing/Competitive NMB


  • Isoquinoline derivative: Curare (D-tubocurarine), Atracurium
  • Steroidal derivative: Pancuronium, Rocuronium, Vecuronium
• Atracurium


  • Releases histamine; metabolized to laudanosine (provoke seizures)
• Non-depolarizing (Competitive antagonists)


  • At lower doses: Competitively block Ach at the nicotinic receptors, Prevent depolarization of the muscle cell membrane and inhibit muscular contraction
  • At higher doses: Block the ion channels of the motor endplate, Muscle weakness
• Non-depolarizing (Competitive antagonists)


  • Effect can be reversed by Neostigmine and Edrophonium
• Manner of paralysis of non-depolarizing (Competitive antagonists)


  1. Small, rapidly contracting muscles of the face, eye (most susceptible)

  2. Fingers

  3. Limbs

  4. Neck

  5. Trunk muscles

  6. Intercostal muscles

  7. Diaphragm
• Non-depolarizing (Competitive antagonists)


  • Injected IV (occasionally IM)
  • Possess two or more quaternary amine in their ring structure (not effective orally)
  • Penetrate membranes very poorly
  • Do not enter Blood Brain Barrier
• Cholinesterase inhibitors


  Overcome the action of nondepolarizing neuromuscular blockers
• Halogenated hydrocarbon anesthetics (Desflurane)


  Enhance neuromuscular blockade by exerting a stabilizing action at the NMJ
• Aminoglycosides


  Inhibit Ach release from cholinergic nerves by competing with calcium ions
• Calcium channel blockers


  May increase the neuromuscular blockade