Table of
Contents
Definition
Skeletal muscle relaxants are drugs that relax
striated muscles (those that control the skeleton). They
are a separate class of drugs from the muscle relaxant
drugs used during intubations and surgery to reduce the
need for anesthesia and facilitate intubation.
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Purpose
Skeletal muscle relaxants may be used for relief of
spasticity in neuromuscular diseases, such as
multiple sclerosis, as well as for spinal cord
injury and stroke. They may also be used for
pain relief in minor strain injuries and control
of the muscle symptoms.
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Description
Muscle relaxants may be divided into
only two groups, centrally acting and peripherally
acting.
The centrally acting group, appears to act
on the central nervous system, and contains 9 drugs which
are chemically different.
- Flexeril (cyclobenzaprine)
- Maolate (chlorphenesin)
- Norflex (orphenadrine)
- Paraflex (chlorzoxazone)
- Robaxin
(methocarbamol)
- Skelaxin (metaxalone)
- Soma (carisoprodol)
- Valium (diazepam)
- Zanaflex (tizanidine)
All are used primarily
as an adjunct for rest in management of acute muscle
spasms associated with sprains. Muscle relaxation may
also be an adjunct to physical therapy in rehabilitation following stroke, spinal cord injury,
or other musculoskeletal conditions.
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Recommended
dosage
Dose varies with the drug, route of administration,
and purpose. There may be individual variations in
absorption that require doses higher than those usually
recommended, particularly with methocarbamol. Consult
specific references for further information.
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Precautions
All drugs in this class may cause sedation.
Diazepam may be addictive. It is a controlled
substance under federal law.
Tizanidine may cause low blood pressure, but this may
be controlled by starting with a low dose and increasing
it gradually. The drug may rarely cause liver damage.
Methocarbamol and chlorzoxazone may cause harmless
color changes in urine-orange or reddish-purple with
chlorzoxazone and purple, brown, or green with
methocarbamol. The urine will return to its normal color
when the patient stops taking the medicine.
Most drugs in this class are well tolerated.
Not all drugs in this group have been evaluated for
safety in pregnancy and breast feeding.
Diazepam is category D. All benzodiazepines
cross the placenta. Although the drugs appear to be safe
for use during the first trimester of pregnancy, use
later in pregnancy may be associated with cleft lip
and palate. Diazepam should not be taken while
breast feeding. Infants who were breast fed while their
mothers took diazepam were excessively sleepy and
lethargic.
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Interactions
Skeletal muscle relaxants have many potential drug
interactions. Individual references should be consulted.
Because these drugs cause sedation, they should be
used with caution with other drugs that may also cause
drowsiness.
The activity of diazepam may be increased by drugs
that inhibit its metabolism in the liver. These include:
Cimetidine: Contraceptives, oral, Disulfiram,
Fluoxetine, Isoniazid, Ketoconazole, Metoprolol,
Propoxyphene, Propranolol, and Valproic acid.
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Key Terms
- Central nervous system
- The brain and spinal cord.
- Intrathecal
- Introduced into or occurring in the space
under the arachnoid membrane which covers the
brain and spinal cord.
- Pregnancy category
- A system of classifying drugs according to
their established risks for use during
pregnancy. Category A: Controlled human studies
have demonstrated no fetal risk. Category B:
Animal studies indicate no fetal risk, but no
human studies, or adverse effects in animals,
but not in well-controlled human studies.
Category C: No adequate human or animal studies,
or adverse fetal effects in animal studies, but
no available human data. Category D: Evidence of
fetal risk, but benefits outweigh risks.
Category X: Evidence of fetal risk. Risks
outweigh any benefits.
- Sedative
- Medicine used to treat nervousness or
restlessness.
- Spasm
- Sudden, involuntary tensing of a muscle or a
group of muscles.
- Tranquilizer (minor)
- A drug that has a calming effect and is used
to treat anxiety and emotional tension.
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