3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.3. Pharmacology
                  3.1.3.7. Neuromuscular blocking drugs
                      3.1.3.7.2. Non-depolarising NMBDs
 3.1.3.7.2.2. Intermediate-acting nondepolarising NMBDs 

Intermediate-acting nondepolarising NMBDs

[SH4:p231-241]

Long-acting vs intermediate-acting

Compared to long-acting nondepolarising NMBDs, intermediate-acting NMBDs:

  • More efficient clearance
  • More expensive
  • Similar onset rate of maximum neuromuscular blockade
    * Except for rocuronium
  • Approximately 1/3 the duration of action of long-acting nondepolarising NMBDs
  • 30-50% more rapid rate of recovery
  • Minimal to absent cumulative effects
  • Minimal to absent cardiovascular effects

The priming principle

For other intermediate-acting non-deploarising NMBDs, onset of action is accelerated by:

  • Inital small subparalysing dose (approximately 10% of the ED95)
  • Followed by the larger dose (2 to 3 times the ED95) in approximately 4 minutes

Mechanism of the priming principle

  1. Initial binding of spare receptors results in no observable clinical effects
  2. Subsequent deepening of the blockade

Reversal

NMJ blockade by intermediate-acting nondepolarising NMBDs are reliably antagonised by anticholinesterase within 20 minutes

 

Rapacuronium

[CEACCP 2004 Vol 4(1) "Pharmacology of neuromuscular blocking drugs"]

  • Withdrawn in USA in March 2001
    * Due to high incidence and severity of bronchospasm
  • Less potent
    --> Given in large doses
    --> Rapid onset of action
  • Short duration of action
  • Rapidly cleared by hepatic uptake and deacetylation
    * 3-desacetylrapacuronium has more potent NMJ blockade than the parent drugs
  • Causes histamine release
    --> Bronchospasm