eMedExpert Home > Medications Facts > Cyclobenzaprine (Flexeril)

Cyclobenzaprine hcl is closely related to the first-generation tricyclic antidepressants, like amitriptyline and imipramine. It is a long-acting skeletal muscle relaxant which relieves muscle spasms and improves signs and symptoms such as pain, tenderness, limitation of motion, and restriction in activities of daily living.

The principal side effects of cyclobenzaprine are drowsiness, dry mouth or tongue, dizziness and bad taste.

Cyclobenzaprine after its synthesis in 1961 was found to have limited antidepressant action with no significant advantage over other tricyclic antidepressants. However it was found to act as a centrally acting muscle relaxant and has been widely used ever since.

Cyclobenzaprine was approved by the U.S. Food and Drug Administration in 1977 for the treatment of acute muscle spasms of local origin. Cyclobenzaprine is sold as a hydrochloride salt in a 10 mg non-scored tablet under the tradename Flexeril (Merck and Co.) or as a generic (Genera, Warner-Chilcott, Duramed, Mylan, Endogenerics, and Watson).

Once-a-day extended release formulation, Amrix, has been approved by the FDA in 2007 and is available in 15 and 30 mg capsules.

• adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions

A muscle spasm is an uncontrollable contraction of a muscle. Cyclobenzaprine only works to relieve muscle spasms caused by problems in the muscles. It is ineffective in muscle spasm due to central nervous system disease.

• Fibromyalgia1, 3
  Cyclobenzaprine may be helpful for sleep and pain control in fibromyalgia.
  The usual starting dose is 5-10 mg taken at bedtime. The dose may be increased to 20-30 mg, taken either at night or in divided doses during the day. Compared with amitriptyline, cyclobenzaprine is associated with better patient acceptance due to fewer side effects and more rapid onset of relief.
  Cyclobenzaprine has been studied in the treatment of fibromyalgia. In a study of 120 fibromyalgia patients, those receiving Cyclobenzaprine (10 to 40 mg) over a 12 week period had significantly improved quality of sleep and pain score. Interestingly, there was also a reduction in the total number of tender points and muscle tightness.
  A meta-analysis of cyclobenzaprine showed that it was superior to placebo for treating fibromyalgia but that it was not as effective as antidepressants.
• Tension headaches2
  In a 1972 double-blind study, 10 of 20 patients receiving cyclobenzaprine experienced a 50% or greater improvement in tension-type headache, compared with only 5 of 20 patients receiving placebo. The usual dose of cyclobenzaprine is 10 mg at bedtime.
• Insomnia
• Migraine

Advantages:

• Effective. Quick and lasting symptoms relief (back pain, neck pain, muscle spasms)
• No potencial for drug abuse and dependence.
• May be useful in patients with insomnia because of severe muscle spasms.
• Pregnancy category B. Cyclobenzaprine is considered to be safe during pregnancy.

Disadvantages:

• Sedation. Cyclobenzaprine commonly causes drowsiness and dizziness, which may interfere with your daily activity. Even if you take the drug just at bedtime, you may experience a hangover-like effect in the morning.
• Drug interactions. Life-threatening interactions with MAO inhibitors.
• Toxic potential similar to tricyclic antidepressants. Cyclobenzaprine shares the toxic potentials of the tricyclic antidepressants, including prolongation of conduction time, arrhythmias, and tachycardia.

Onset of action: 1 h.

Duration of action: 12 to 24 h.

Cyclobenzaprine is a muscle relaxant acting primarily on the central nervous system. It is structurally similar to Amitryptilline, differing by only one double bond. Cyclobenzaprine is a weak inhibitor of presynaptic norepinephrine and serotonin. Skeletal muscle relaxant activity is due to brainstem mediated inhibition of gamma motor neurons.

Cyclobenzaprine is eliminated quite slowly, with an effective half-life of 18 hours. It usually takes 4-5 days for drug to leave the system.

• Cyclobenzaprine (Flexeril) versus Other Medications

• 1. See S, Ginzburg R. Abstract Choosing a skeletal muscle relaxant. Am Fam Physician. 2008 Aug 1;78(3):365-70. Review. PubMed
• 2. Lance JW, Anthony M. No Abstract Cyclobenzaprine in the treatment of chronic tension headache. Med J Aust. 1972 Dec 16;2(25):1409-11.
• 3. Moldofsky H. Management of sleep disorders in fibromyalgia. Rheum Dis Clin North Am. 2002 May;28(2):353-65. PubMed

Published: October 05, 2008
Last updated: January 07, 2010