Skeletal muscle relaxants

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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