skeletal muscle relaxants prof. hanan hagar. skeletal muscle relaxants are drugs used to induce...
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Skeletal muscle relaxants
Prof. Hanan Hagar
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Skeletal muscle relaxantsAre drugs used to induce muscle relaxation
Classification Peripherally acting (Neuromuscular
blockers). Centrally acting skeletal muscle relaxants
e.g. Baclofen - Diazepam Direct acting skeletal muscle relaxants
e.g. Dantrolene
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Neuromuscular blockers
Classification:
1) Competitive (non depolarizing blockers) 2) Depolarizing blockers
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Binding of Ach to receptors on muscle end-plate
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Neuromuscular Junction
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Uses of neuromuscular blockers Facilitate endotracheal intubation Facilitate endoscopy control convulsion electroshock therapy
in psychotic patient . Relieve of tetanus and epileptic convulsion. As adjuvant in general anesthesia to induce
muscle relaxation orthopedic surgery.
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Muscle Relaxants
Competitive (Nondepolarizing) muscle relaxants◦Short acting◦Intermediate acting◦Long acting
Depolarizing muscle relaxant ◦Succinylcholine
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Competitive NM blockers Long acting◦d-tubocurarine◦Pancuronium
Intermediate acting◦Atracurium◦Cisatracurium◦Vecuronium◦Rocuronium
Short acting◦Mivacurium
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Competitive NM blockers
Mechanism of Action Are competitive antagonists Compete with Ach for the nicotinic receptors
present in postjunctional membrane of motor
end plate.
No depolarization of postjunctional membrane
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Pharmacokinetics They are polar compounds◦ inactive orally & taken parenterally◦Do not cross placenta & CNS
Metabolism depend upon kidney or liver
Except
Mivacurium (degraded by acetylcholinesterase )
Atracurium (spontaneous degradation in blood)
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Pharmacological actions:
Skeletal muscle relaxation. They produce different effects on CVS Some release histamine and produce
hypotensiono d.Tubocurarine o Atracurium o Mivacurium
Others produce tachycardia ( H.R)o Pancuronium
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d – Tubocurarine
Long duration of action (1 - 2 hr) Eliminated by kidney 60% - liver 40%. Releases histamine that causes:
◦Bronchospasm
◦Hypotension
◦Tachycardia
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Atracurium As potent as curare (1.5) Has intermediate duration of action (30 min). Eliminated by non enzymatic chemical degradation in plasma (spontaneous hydrolysis
at body pH, Hofmann elimination). used in liver failure & kidney failure (drug of
choice). Liberate histamine (Transient hypotension)
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Mivacurium
Chemically related to atracurium Fast onset of action Metabolized by pseudo cholinesterases. Short duration of action (15 min). Longer duration in patient with liver disease
or genetic cholinesterase deficiency. Transient hypotension (due to histamine
release).
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Pancuronium
More potent than curare ( 6 times ). Excreted by the kidney ( 80 % ). Long duration of action. Side effects : hypertension, tachycardia
◦ NE release from adrenergic nerve
endings.
◦Antimuscarinic action (block
parasympathetic action)
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Vecuronium More potent than tubocurarine ( 6 times ).Metabolized mainly by liver.Intermediate duration of action.Has few side effects.
◦No histamine release.
◦No tachycardia.
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Depolarizing Neuromuscular Blockers
Mechanism of Action
combine with nicotinic receptors in
postjunctional membrane of neuromuscular
junction initial depolarization of motor end
plate muscle twitching Persistent
depolarization relaxation
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Succinylcholine (suxamethonium)
Pharmacological Actions
1. SK. muscle : initial contraction followed by
relaxation.
2. Hyperkalemia : Cardiac arrest.
3. Eye : intraocular pressure.
4. CVS : arrhythmia
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Pharmacokinetics
Fast onset of action (1 min.). Short duration of action (5-10 min.). Metabolized by pseudocholinesterase in plasma Half life is prolonged in◦Neonates◦Elderly◦Pseudcholinesterase deficiency (liver disease – malnutrition).
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Side Effects Hyperkalemia CVS arrhythmia IOP # glaucoma Can produce malignant hyperthermia May cause succinylcholine apnea due to
deficiency of pseudocholinesterase.
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Drug Duration Side effects NotesTubocurarine Long
1-2 hHypotension # Renal failure
Pancuronium Long1-2 h
Tachycardia # Renal failure
Atracurium Short30 min.
Transient hypotension
Histamine release
Spontaneous degradation
Used in liver and kidney failure
Vecuronium Short 40 min.
Few side effects # Liver failure
Mivacurium Short 15 min.
Similar to atracurium
Metabolized by pseudocholinesterase# Choline esterase
deficiency
Succinyl choline
Short10 min.
HyperkalemiaArrhythmiaIncrease IOP
# CVS Diseases# Glaucoma
# Liver disease
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Alteration of responses
Diseases ◦Myasthenia gravis◦Kidney failure◦Liver failure
Drug interactions◦Inhalation & Intravenous anesthetics◦Aminoglycosides antibiotics ◦Anticonvulsants◦Magnesium
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Is a rare inherited condition that occurs upon
administration of drugs as:◦general anesthesia e.g. halothane◦neuromuscular blockers e.g. suxamethonium
Inability to bind calcium by sarcoplasmic
reticulum in some patients due to genetic
defect Ca release, intense muscle spasm,
hyperthermia
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Spasmolytics
They reduce muscle spasm in spastic states
Baclofen: Centrally acting GABA agonist – acts on spinal cord. Diazepam (Benzodiazepines): Centrally acting facilitate GABA action on CNS. Dantrolene: direct action on skeletal muscles. Used in treatment of malignant hyperthermia
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Uses of spasmolytics They reduce muscle spasm in spastic states
produced by :
Spinal cord injury Cerebral stroke Cerebral palsy
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Dantrolene Mechanism of Action It interferes with the release of calcium from
its stores in skeletal muscles (sarcoplasmic reticulum).
It inhibits excitation-contraction coupling in the muscle fiber.
Uses Malignant Hyperthermia.Spastic states.IV, orally t ½ = 8 - 9 hrs.