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Guide to Prescription Muscle Relaxers

Muscle relaxants are widely used in the treatment of musculoskeletal conditions. Carisoprodol, cyclobenzaprine, and metaxalone are the most commonly prescribed medications for the management of musculoskeletal pain1.

All medications from this class target the brain, not the muscles, and have an insignificant, if any effect, at the muscle fiber level.

Dosage Quantity Pharmacy Price Shipping Buy
Carisoprodol 350 mg 30 tablets MPLLC.net $76 $18
Carisoprodol 350 mg 60 tablets MPLLC.net $79 $18
Carisoprodol 350 mg 90 tablets MPLLC.net $89 $18
Cyclobenzaprine 10 mg 30 tablets MPLLC.net $76 $18
Cyclobenzaprine 10 mg 60 tablets MPLLC.net $85 $18
Cyclobenzaprine 10 mg 90 tablets MPLLC.net $99 $18
Soma 350 mg 30 tablets MPLLC.net $79 $18
Soma 350 mg 60 tablets MPLLC.net $89 $18
Soma 350 mg 90 tablets MPLLC.net $111 $18

There are two categories of muscle relaxants: antispastic and antispasmodic agents.

The use of muscle relaxants continues to be a source of controversy among doctors, mainly because of their side effects. However, about 91% of physicians report using muscle relaxants.2

This guide presents a better understanding of the risks and benefits of most commonly used medications in this class.

List of muscle relaxants

Skeletal muscle relaxants (SMR) include:

Carisoprodol

Carisoprodol is a centrally acting skeletal muscle relaxant. It is metabolized to meprobamate, a schedule III controlled substance with a potential for drug dependence. Although carisoprodol is not a controlled substance, it has significant potential for physical or psychological dependence.

Side effects include dizziness, drowsiness, headache. Withdrawal symptoms may occur when carisoprodol is discontinued. When combined with benzodiazepines, pain killers, or other muscle relaxers, it may contribute to respiratory depression.

Carisoprodol is available as generic, and in various brand forms such as Soma, Vanadom.

Cyclobenzaprine

Cyclobenzaprine is the most well studied muscle relaxant and has been shown to be effective for various musculoskeletal conditions. Its chemical structure is similar to that of the tricyclic antidepressants. Therefore it has similar pharmacologic effects.

The sedative properties of cyclobenzaprine may benefit persons with insomnia caused by severe muscle spasms. Unlike other relaxers, cyclobenzaprine can be used on a longer-term basis.

Side effects include drowsiness, sedation, dry mouth, urinary retention, and increased intraocular pressure. It should be avoided in older patients and in persons with glaucoma.

Metaxalone

The exact mechanism of action of metaxalone is not fully understood, but its effect is presumed to be due to general depression of the central nervous system. It has no direct effect on the contractile mechanism of striated muscle, the motor endplate, or the nerve fiber. The advantages of metaxalone are low sedation, lack of abuse potential, and limited accumulation of the drug because of its short elimination half-life.

Common side effects include drowsiness, dizziness, headache, and nervousness. Paradoxic muscle cramps may also occur. Metaxalone may cause false-positive Benedict's tests.

Treatment with metaxalone may be expensive, as it is only available in brand form Skelaxin.

Methocarbamol (Robaxin)

Methocarbamol is a centrally acting muscle relaxant that suppresses spinal polysynaptic reflexes and has no direct effect on skeletal muscles.

Initially for the first 2 to 3 days, methocarbamol can be taken four times a day at a dosage of 1500 mg. For maintenance therapy, 1500 mg can be given three times per day.

Frequent side effects include drowsiness, dizziness, nausea, anorexia, headache, blurred vision, muscular discoordination. Use of this drug may cause black, brown, or green urine.

Tizanidine (Zanaflex)

Tizanidine is a centrally acting alpha-2-agonist that exerts its antispastic effect by causing presynaptic inhibition of motor neuron hyperactivity. It has a relatively quick onset of effect of 1-2 hours and a duration of only 3-6 hours. For this reason, tizanidine should be reserved for time-dependent activities.

Tizanidine should be prescribed through a gradual upward titration from an initial dose of 2 to 4 mg at bedtime up to the maximum of 8 mg three times per day. Tizanidine bedtime dose can provide an analgesic effect and improve sleep.

Orphenadrine (Norflex)

Orphenadrine is structurally related to diphenhydramine and has stronger anticholinergic and weaker sedative properties. It does not produce any direct effect on skeletal muscle, and its exact mode of action is unknown.

This drug has relatively long half-life, and the usual adult dosage is 100 mg twice per day.

Common side effects include drowsiness, dizziness, agitation, hallucinations, dry mouth, nausea, constipation, urinary retention.

Brief comparison of muscle relaxers
  Soma Watson Flexeril McNeil Skelaxin King
  Carisoprodol
Soma (Watson)
Cyclobenzaprine
Flexeril (McNeil)
Metaxalone
Skelaxin (King)
FDA approval date April 09, 1959 August 26, 1977 August 13, 1962
Pharmaceutical
Forms
350 mg tablets 5 mg, 10 mg tablets 800 mg tablets
FDA approved indications
  • relief of discomforts associated with acute, painful musculoskeletal conditions
  • relief of muscle spasm associated with acute, painful musculoskeletal conditions
  • relief of discomforts associated with acute, painful musculoskeletal conditions
Most common
side effects
  • drowsiness
  • dizziness
  • ataxia
  • tremor
  • agitation
  • drowsiness
  • dry mouth
  • dizziness
  • drowsiness
  • dizziness
  • headache
Less common
side effects
  • irritability
  • headache
  • depressive reactions
  • insomnia
  • nausea
  • vomiting
  • tachycardia
  • fatigue/tiredness
  • asthenia
  • nausea
  • constipation
  • dyspepsia
  • unpleasant taste
  • blurred vision
  • headache
  • nervousness
  • tachycardia
  • arrhythmia
  • nervousness
  • nausea
  • vomiting
  • gastrointestinal upset
Onset/ Duration of action Onset: 30 min
Duration: 4-6 hours
Onset: 1 hour
Duration: 12-24 hours
Onset: 30 min- 1 hour
Duration: 4- 6 hours
Generic avalability Yes Yes No

References

  • 1. Toth PP, Urtis J. Commonly used muscle relaxant therapies for acute low back pain: a review of carisoprodol, cyclobenzaprine hydrochloride, and metaxalone. Clin Ther. 2004 Sep;26(9):1355-67.
  • 2. Di Iorio D, Henley E, Doughty A. A survey of primary care physician practice patterns and adherence to acute low back problem guidelines. Archives Family Medicine 2000;9(10):1015–21.

Last updated: October, 2009