Which of the following is earliest and shortest acting skeletal muscle relaxant? (* NIMHANS March-2017 Post-MBBS, NIMHANS Pattern Re-exam March 2015; NIMHANS - 2014)

(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).