Skeletal Muscle Relaxants : Must Know's

Skeletal Muscle Relaxants : Always asked invaluable points

1. Shortest acting SMR : Succinylcholine ( SCh)

2. Shortest acting Non-depolarising / Competitive SMR : Mivacurium

3. Fastest acting SMR : SCh (1-1.5 min).

4. Fastest acting ND-SMR : Rocuronium(1-2 min).

Rocuronium is an agent of intermediate duration but of rapid onset and lower potency. Its rapid onsets allows it to be used as an alternative to succinylcholine in rapid-induction anesthesia and in relaxing the laryngeal and jaw muscles to facilitate tracheal intubation

(* Note : Rapacuronium is the fastest acting ND/SMR, but due to it's broncho-constrictive side effects is withdrawn from the market, so in the question if 'Rocuronium' is not there go for Rapacuronium).

5. Longest acting SMR : Doxacurium

6. Most potent SMR: Doxacurium.

7. Least potent SMR : Gallamine.

8. Maximum histamine release : dTC (d-tubocurarine)

9. Minimum histamine release : Vecuronium.


NOTE : Succinylcholine, mivacurium, doxacurium, and atracurium also cause histamine release, but to a lesser extent unless administered rapidly. The ammonio steroids, pancuronium, vecuronium, pipecuronium, and rocuronium, have even less tendency to release histamine after intradermal or systemic injection. Histamine release typically is a direct action of the muscle relaxant on the mast cell rather than IgE-mediated anaphylaxis.

10. SMR undergoing Hoffmann elimination : Atracurium , Cisatracurium.

( The metabolite of Atracurium called Laudanosine can accumulate (theoretically/on prolonged use) to induce Seizures.



The benzylisoquinolines group that includes d-TC, Atracurium, Cis-atracurium, Doxacurium and Mivacurium- 'tend to release Histamine' : The least histamine releasing among this group is Cis-atracurium.

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