<prompt> Which of the following is earliest and shortest acting skeletal muscle relaxant? NIMHANS March-2017 Post-MBBS, NIMHANS Pattern Re-exam March 2015; NIMHANS - 2014RocuroniumVecuroniumAtracuriumSuxamethonium  <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 neu- romuscular 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 pseudocholinesterase function. Shortest acting depolarization agent is succinylcholine duration - 3 to 6 mm. Shortest acting non-depolarizing agent is - Mivacurium duration -12-20 min. 