Muscle Relaxants : Muscle Relaxants Slide 2: Muscle relaxant: Muscle relaxant is a term
usually used to refer to skeletal muscle relaxants (drugs), which act on the central nervous system (CNS) to relax muscles. These drugs are often prescribed to reduce pain and soreness associated with sprains, strains, or other types of muscle injury. Some examples of commonly prescribed skeletal muscle relaxant medications include carisoprodol (Soma), cyclobenzaprine (Flexeril), and metaxalone (Skelaxin), which are taken in tablet form. Muscle relaxant drugs are only available by prescription in the U.S. Definition of Muscle relaxant :- Slide 3: neuromuscular blocking drugs are sometimes used during the induction of general anesthesia or during insertion of an endotracheal (ET) tube. These muscle relaxants are given intravenously (through the bloodstream) and act directly on the muscles. Examples of muscle relaxants used during surgical procedures include succinylcholine (Anectine, Sucostrin), atracurium (Tracrium), and pancuronium (Pavulon). Other types of muscle relaxant drugs :- Muscle Relaxants : Muscle Relaxants What are they used for?
Facilitate intubation of the trachea
Facilitate mechanical ventilation
Optimized surgical working conditions Muscle Relaxants : Muscle Relaxants How skeletal muscle relaxation can be achieved?
High doses of volatile anesthetics
Administration of neuromuscular blocking agents
Proper patient positioning on the operating table Muscle Relaxants : Muscle Relaxants Muscle relaxants must not be given without adequate dosage of analgesic and hypnotic drugs
Inappropriately given : a patient is paralyzed but not anesthetized Muscle Relaxants : Muscle Relaxants How do they work?
Motor endplate of a muscle
Release of Acetylcholine (Ach)
Postsynaptic events Neuromuscular Junction (NMJ) : Neuromuscular Junction (NMJ) Binding of Ach to receptors on muscle end-plate : Binding of Ach to receptors on muscle end-plate Muscle Relaxants : Muscle Relaxants Depolarizing muscle relaxant
Nondepolarizing muscle relaxants
Long acting Depolarizing Muscle Relaxant : Depolarizing Muscle Relaxant Succinylcholine
What is the mechanism of action?
Physically resemble Ach
Act as acetylcholine receptor agonist
Not metabolized locally at NMJ
Metabolized by pseudocholinesterase in plasma
Depolarizing action persists > Ach
Continuous end-plate depolarization causes muscle relaxation Depolarizing Muscle Relaxant : Depolarizing Muscle Relaxant Succinylcholine
What is the clinical use of succinylcholine?
Most often used to facilitate intubation
What is intubating dose of succinylcholine?
Onset 30-60 seconds, duration 5-10 minutes Depolarizing Muscle Relaxant : Depolarizing Muscle Relaxant Succinylcholine
What is phase I neuromuscular blockade?
What is phase II neuromuscular blockade?
Resemble blockade produced by nondepolarizing muscle relaxant
Succinylcholine infusion or dose > 3-5 mg/kg Depolarizing Muscle Relaxant : Depolarizing Muscle Relaxant Succinylcholine
Does it has side effects?
Increase intraocular pressure
Increase intragastric pressure
Increase intracranial pressure
Malignant hyperthermia Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants What is the mechanism of action?
Compete with Ach at the binding sites
Do not depolarized the motor endplate
Act as competitive antagonist
Excessive concentration causing channel blockade
Act at presynaptic sites, prevent movement of Ach to release sites Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Long acting
Mivacurium Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Pancuronium
Onset 3-5 minutes, duration 60-90 minutes
Intubating dose 0.08-0.12 mg/kg
Elimination mainly by kidney (85%), liver (15%)
Side effects : hypertension, tachycrdia, dysrhythmia, Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Vecuronium
Analogue of pancuronium
much less vagolytic effect and shorter duration than pancuronium
Onset 3-5 minutes duration 20-35 minutes
Intubating dose 0.08-0.12 mg/kg
Elimination 40% by kidney, 60% by liver Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Atracurium
Onset 3-5 minutes, duration 25-35 minutes
Intubating dose 0.5 mg/kg
Side effects :
histamine release causing hypotension, tachycardia, bronchospasm
Laudanosine toxicity Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Cisatracurium
Isomer of atracurium
Metabolized by Hofmann elimination
Onset 3-5 minutes, duration 20-35 minutes
Intubating dose 0.1-0.2 mg/kg
Minimal cardiovascular side effects
Much less laudanosine produced Nondepolarizing Muscle Relaxants : Nondepolarizing Muscle Relaxants Rocuronium
Analogue of vecuronium
Rapid onset 1-2 minutes, duration 20-35 minutes
Onset of action similar to that of succinylcholine
Intubating dose 0.6 mg/kg
Elimination primarily by liver, slightly by kidney Alteration of responses : Alteration of responses Temperature
Drug interactions Alteration of responses : Alteration of responses Concurrent diseases
Myasthenic syndrome (Eaton-Lambert synrome)
Kidney diseases Alteration of responses : Alteration of responses Drug interactions
Neuromuscular locking drugs
Magnesium Antagonism of Neuromuscular Blockade : Antagonism of Neuromuscular Blockade Effectiveness of anticholinesterases depends on the degree of recovery present when they are administered
Onset 3-5 minutes, elimination halflife 77 minutes
Dose 0.04-0.07 mg/kg
Edrophonium Antagonism of Neuromuscular Blockade : Antagonism of Neuromuscular Blockade What is the mechanism of action?
Inhibiting activity of acetylcholineesterase
More Ach available at NMJ, compete for sites on nicotinic cholinergic receptors
Action at muscarinic cholinergic receptor
Increased intestinal tone Antagonism of Neuromuscular Blockade : Antagonism of Neuromuscular Blockade Muscarinic side effects are minimized by anticholinergic agents
Dose 0.01-0.02 mg/kg
glycopyrrolate Reversal of Neuromuscular Blockade : Reversal of Neuromuscular Blockade Goal : re-establishment of spontaneous respiration and the ability to protect airway from aspiration Slide 31: THANK YOU