Shortest acting NM blocking agent is:

Ans. d (Mivacurium). (Ref. KDT, 6th ed., 345)Mivacurium is the shortest acting competitive blocker; does not need reversal. Dose and speed of injection related transient cutaneous flushing can occur due to histamine release. Fall in BP is possible, but change in HR is minimal. It is metabolized rapidly by plasma cholinesterases: prolonged paralysis can occur in pseudocho- linesterase deficiency.MEVA CURIUM# Among all nondepolarising muscle relaxants it has shortest duration of action.# An ideal M-relaxant for day care anesthesia.# Usually no reversal required.# Metabolised by Pseudocholinesterase enzyme (similar to succinyl choline)VECURONIUM# Excreted in bile# Not used in biliary obstruction# CARDIOVASCULAR stability, hence agent of choice in cardiac patients# Long term use results in polyneuropathy# Long acting, Non-depolarising muscle relaxant.# Duration of action about 20 min.# pH of solution 4. Stable for 24 hours at 25degC. (much more stable than Atracurium)# Dose 0. I mg/kg.# Onset of action 1-2 min.# Site of action is myoneural junction.PANCURONIUM# It is a non-depolarising, long acting muscle relaxant.# It is to be refrigerated.# It is a Quaternary amino Steroid, devoid of hormonal activity.# It has significant vagolytic effect producing tachycardia.# It causes least release of Histamine, hence a safe drug in asthma patients.# It causes Hypertension by releasing noradrenaline.# It does not cross Blood-Brain barrier.# It is five times more potent than d-tubocurare.# Dose is 0.08 to 0.1 mg/kg body weight.# Safe in patients susceptible to malignant hyperpyrexia.ATRACURIUM# Long acting non-depolarising Muscle relaxant# Muscle relaxant of choice in renal failure or anephric patients.# pH of solution is 3.5. Stored at 4 c. Duration of action doubled at 25degC.# Metabolism mainly by Hofmann elimination (a chemical degradation) and hydrolysis in plasma and elsewhere in body. Hence most preferred in patients with renal failure.# Major metabolite is Laudanosine, which is CNS- stimulant.Peripherally acting muscle relaxantsNeuromuscular blockers Long actingd-Tubocurarine, Pancuronium, Doxacurium,P ipecuronium.Intermediate actingVecuronium, Atracurium, cisracurium, Rocuronium, RapacuroniumShort actingMivacuriumDepolarizing NM blockersScoline (SCh., Suxamethonium), Decamethonium (C-10).Scoline is another short acting muscle relaxant.