Skeletal Muscle Relaxants
By
M.H.Farjoo M.D. , Ph.D.Shahid Beheshti University of Medical Science
M.H.Farjoo
Skeletal Muscle Relaxants
Introduction Classification Mechanism of Action Clinical Application Special Issues Adverse Effects (Depolarizing)
Spasmolytic Drugs Drug Pictures
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Classification of Muscle Relaxants
Nondepolarizing Tubocurarine Atracurium Rocuronium Pancuronium
Depolarizing Succinylcholine
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Mechanism of action of Skeletal Muscle Relaxants
Nondepolarizing Depolarizing
Phase I : Prolonged depolarization of muscle fiber Acetylcholinesterase inhibitors augment this
phase Phase II :
The channel desensitizes Later stage is identical to nondepolarizing drugs
Behaves like acetylcholine but more prolonged
1) Competitive blockade of nicotinic Ach receptor2) Can enter ion channel so cholinesterase inhibitors (neostigmine) can not antagonize them readily
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Clinical Application
Surgical Relaxation
Control of Ventilation
Treatment of Convulsions It has NO effect on the central processes involved
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Special issues in Skeletal Muscle Relaxants
Enhancing factors: Some antibiotic (aminoglycosides) Myasthenia gravis Advanced age (> 70 years)
Diminishing factors: Severe burns Upper motor neuron disease
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Adverse Effects of DEPOLARIZING drugs
Hyperkalemia
Increased Intragastric Pressure
Muscle PainSeen in heavily muscled patients
Seen in heavily muscled patients
1) Patients with burns, nerve damage or neuromuscular disease, closed head injury, and other trauma2) Can result in cardiac arrest
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Spasmolytic Drugs
Spasticity
To abolish spasticity
Increase in tonic stretch reflexes and flexor muscle spasms together with muscle weakness
Reduce the activity of fibers that excite the motoneuron
Enhance the activity of the inhibitory internuncial neurons
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Spasmolytic Drugs (Cont’d)
Diazepam Baclofen Tizanidine Dantrolene Botulinum Toxin Methocarbamol (Robaxin)
Acts at GABAB receptors
Is a congener of clonidine
1) Reduces skeletal muscle strength by interfering with excitation-contraction coupling2) Interferes with the release of Ca2+ through sarcoplasmic reticulum3) Used in malignant hyperthermia
1) Acts at GABAA synapses2) Its action is also mediated in the spinal cord
SummaryIn English
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