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Chapter 25
Drugs for Muscle Spasm and
Spasticity
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Drugs for Muscle
Spasm and Spasticity

Two groups of drugs that cause skeletal
muscle relaxation
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One group for localized muscle spasm
Other group for spasticity
Most produce their effects through actions in
the CNS (except dantrolene).
Groups are not interchangeable.
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Drugs for Muscle
Spasm and Spasticity
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
Muscle spasm: involuntary contraction of
muscle or muscle group
Causes
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Epilepsy
Hypocalcemia
Pain syndromes: adult and chronic
Trauma: localized skeletal muscle injury
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Drug Therapy of Muscle Spasm
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Treatment of spasm
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Physical measures
• Immobilization of affected muscle
• Cold compresses
• Whirlpool baths
• Physical therapy
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Drug Therapy of Muscle Spasm

Treatment of spasm
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Drug therapy
Analgesic anti-inflammatory (aspirin)
Centrally acting muscle relaxants
• Diazepam
• Tizanidine
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Centrally Acting Muscle Relaxants
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Mechanism of action (MOA) unclear – may
result from sedative properties of the drugs
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Diazepam
• MOA through enhancing effects of GABA
Tizanidine
• MOA through agonist action at presynaptic alpha2
receptors
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Centrally Acting Muscle Relaxants
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Therapeutic use
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Relieve local muscle spasm
Decrease local muscle pain
Increase range of motion
No studies to indicate superiority of one drug over
another
Drug selection prescriber preference and patient
response
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Centrally Acting Muscle Relaxants
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Adverse effects
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Generalized CNS depression
Hepatic toxicity
• Tizanidine (Zanaflex) and metaxalone (Skelaxin) can
cause damage.
• Chlorzoxazone (Paraflex) can cause hepatitis and
necrosis.

Physical dependence
• Abstinence syndrome
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Drugs for Spasticity

Spasticity
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
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Movement disorders of CNS origin
Most common causes: multiple sclerosis and
cerebral palsy
Characteristics include
• Heightened muscle tone
• Spasm
• Loss of dexterity
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Three Drugs for Spasticity
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Baclofen (Lioresal)
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Diazepam (Valium)
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Acts in the CNS
Acts in the CNS
Dantrolene (Dantrium)
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Acts directly on smooth muscle
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Baclofen (Lioresal)
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Mechanism
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Acts in the spinal cord
Suppresses hyperactive reflexes
Mechanism unknown
May mimic the action of GABA on spinal neurons
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Fig. 25-1. Structural similarity between baclofen and gamma-aminobutyric acid
(GABA).
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Baclofen (Lioresal)
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Therapeutic uses
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Multiple sclerosis, spinal cord injury, cerebral
palsy
NOT with stroke
Decreases flexor and extensor spasms
Suppresses resistance to passive movement
No direct effect on skeletal muscle
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Baclofen (Lioresal)
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Adverse effects
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No antidote for overdose
Gradual withdrawal over 1 to 2 weeks
• Abrupt intrathecal withdrawal: risk for rhabdomyolysis
CNS depressant
GI symptoms (nausea, constipation)
Urinary retention
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Diazepam (Valium)

Member of the benzodiazepine family
(see Chapter 34)
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Mechanism
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The only one labeled to treat spasticity
Acts in the CNS
Mimics action of GABA
Adverse effect

Sedation
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Dantrolene (Dantrium)
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Mechanism
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Acts directly on skeletal muscle
Suppresses the release of calcium from the
sarcoplasmic reticulum (SR)
Therapeutic uses


Spasticity associated with multiple sclerosis,
cerebral palsy, spinal cord injury
Malignant hyperthermia
• Potentially fatal condition caused by succinylcholine and
general anesthetics
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Dantrolene (Dantrium)
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Adverse effects
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Hepatic toxicity
Muscle weakness
Drowsiness
Diarrhea
Acne-like rash
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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