Muscle Relaxants

Chapter 6 Muscle Relaxants



I. Spasmolytics (Box 6-1)

• Certain chronic diseases (e.g., cerebral palsy, multiple sclerosis) and spinal cord injuries are associated with abnormally high reflex activity in neuronal pathways controlling skeletal muscles, resulting in painful spasms or spasticity.

A. Goals of spasmolytic therapy

1. Reduction of excessive muscle tone without reduction in strength

2. Reduction in spasm, which reduces pain and improves mobility

B. γ-Aminobutyric acid (GABA)-mimetics (see Box 6-1)

1. Baclofen (GABAB agonist)


a. Mechanism of action

• Interferes with release of excitatory transmitters in the brain and spinal cord

b. Uses

• Spasticity in patients with central nervous system (CNS) disorders, such as:

(1) Multiple sclerosis

(2) Spinal cord injuries


BOX 6-1 Spasmolytics



GABA-Mimetics


Baclofen


Diazepam



Other Relaxants


Botulinum toxin


Cyclobenzaprine


Dantrolene


Tizanidine



Maintenance intrathecal infusion can be administered via an implanted pump delivering the drug to a selective site of the spinal cord.


(3) Stroke

c. Adverse effects


(1) Sedation

(2) Hypotension

(3) Muscle weakness

2. Diazepam


a. Benzodiazepine, which acts on the GABAA receptor

b. Facilitates GABA-mediated presynaptic inhibition in the brain and spinal cord (see Chapter 7)


Diazepam acts on GABAA; baclofen acts on GABAB receptors.


C. Other relaxants (see Box 6-1)

1. Botulinum toxin (Botox)


a. Mechanism of action


(1) Type A toxin blocks release of acetylcholine (ACh) by degrading the SNAP-25 protein

(2) Inhibiting neurotransmitter release


Botox popular wrinkle remover


b. Uses


(1) Spasticity associated with cerebral palsy (pediatrics) or stroke (adults)

(2) Sialorrhea (excessive drooling)

(3) Facial wrinkles

(4) Cervical dystonia

(5) Strabismus

(6) Hyperhydrosis

(7) Migraine prophylaxis

2. Cyclobenzaprine


a. Relieves local skeletal muscle spasms, associated with acute, painful musculoskeletal conditions, through central action, probably at the brain-stem level

b. Ineffective in spasticity caused by CNS disorders, such as:


(1) Multiple sclerosis

(2) Spinal cord injuries

(3) Stroke

c. Sedating


Cyclobenzaprine is sedating.


3. Dantrolene


a. Mechanism of action


(1) Decreases the release of intracellular calcium from the sarcoplasmic reticulum

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Apr 8, 2017 | Posted by in PHARMACY | Comments Off on Muscle Relaxants

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