<prompt> Which of the following is earliest and shortest acting skeletal muscle relaxant?RocuroniumVecuroniumAtracuriumSuxamethonium  <response>: D Suxamethonium Classification of non depolarising NM blocking drugs according to time from inj. to 90 recovery of twitch tension of adductor pollicis.1. Short acting: 10-20 min. -- Mivacurium2. Intermediate acting: 20-30 min.-- Atracurium, Vecuronium, Rocuronium3. Long acting: 30-60 mins.-- Alcuronium, Gallamine. SUXAMETHONIUM CHLORIDE Pharmacokinetics: Is two molecules of Ach linked back to back through the acetate methyl groups Dicholine ester of succinic acid. Provides profound relaxation with rapid onset of action 30-60 sec short duration of action 10 mins. Half life of drug is 2-4 mins. Rapid hydrolysis by pseudocholinesterase, an enzyme of liver plasma, initial metabolite Succinylmonocholine is weaker neuromuscular blocker, metabolised slowly to succinic acid choline. 90 of Suxamethonium given intravenously is destroyed 10 reaches Neuromuscular junction. Distribution limited to extracellular space. Succinylmonocholine can be prolonged by: Reduced quantity of normal enzyme; A typical form of Pseudocholinesterase. Low Pseudocholinesterase levels are seen in: Liver disease, Renal disease; Pregnancy; Phenelzine; Echothiophate; Cytotoxic drugs; Hexafluorine, Trimethaphan; Cancer; Ache inhibitors, Metoclopramide. Dibucaine, a local anaesthetic inhibits normal pseudocholinesterase activity by 80. Percentage of inhibition of pseudocholinesterase activity is termed the Dibucaine number Proportional to pseudocholin-esterase function. Shortest acting depolarization agent is Succinylcholine duration - 3 to 6 mm. Shortest acting non-depolarizing agent is - Mivacurium duration -12-20 min. 