Ans. is 'c' i.e., Doxacurium o Amongst the given options doxacurium is longest acting (Duration of action 90-120 minutes),o Rocuronium (duration of action 30-60 minutes), Atracurium (duration of action 30-60 minutes) and vecuronium (duration of action 60-90 minutes) have shorter duration of action than doxacurium.Properties of NM Blockerso Longest acting Neuromuscular blocker - Pancuronium (duration of action 120-180 minutes). (Goodman & Gilman llth/e p. 222) (Note: In some books pipecuronium or Doxacurium have given as the longer activity),o Shortest and fastest acting neuromuscular blocker - Succinylcholine (suxamethonium) - duration of action 5-8 minutes.o Shortest acting competitive (nondepolarizing) neuromuscular blocker - Mivacurium (duration of action 12-18 minutes).o Fastest acting nondepolarizing blocker - Rocuronium (can be used for endotracheal intubation as an alternative to Sch).o Non-depolarizing neuro-muscular blockers can cause ganglion block, vagal block and Histamine release (different agents has different propensity).o Histamine release is caused by - D-TC (maximum tendency), succinylcholine, mivacurium, doxacurium, atracurium, tubocurarine - can cause bronchoconstriction.o Virtually no histamine release - Pancuroniumo Vagal block is caused by - Pancuronium, recuronium, Gallamine.o Maximal vagal block and tachycardia is caused by - Pancuronium (Previously it was gallamine, but it is not used now).o Vagal stimulation is caused by - succinylcholine (can cause bradycardia).o Ganglion block is caused by -d-Tc, Meiocurine, Alcuronium.o Maximum ganglion blockade is caused by - d-TC.o Ganglion stimulation is caused by - Succinylcholine.o Most commonly used muscle relaxant for routine surgery ->> vecuronium.o Most potent skeletal muscle relaxant - Doxacurium.o Least potent skeletal muscle relaxant - Succinylcholine (Gallamine was /east potent but it is not used now).o Least potent nondepolarising muscle relaxant - Rocuronium.o MR of choice for - intubation - Sch (1st choice), Rapacuroium (2nd choice), Rocuronium (3rd choice),o Mivacurium is the only non-depolarizing blocker that is metabolized by plasma cholinesterase.o Gallamine was the most nephrotoxic NM blocker - was contraindicated in renal failure. Due to its nephrotoxic and tetratogenic potential it has been withdrawn,o Recuronium produces pain on injection.o Succinylcholine is the muscle relaxant of choice for rapid endotracheal intubation. Rapacuronium and rocuronium are alternates.