API: Cyclobenzaprine

What Is Cyclobenzaprine and How Does It Work?

Cyclobenzaprine hydrochloride is a tricyclic amine that is FDA-approved as a muscle relaxant to treat skeletal muscle spasms and the pain associated with acute musculoskeletal conditions. Although the exact mechanism of action is still under study, this drug is thought to work within the central nervous system at the brainstem level to reduce tonic somatic motor activity.1 Cyclobenzaprine is best used with a regimen of physical therapy and rest. The drug is also used off-label in the management of fibromyalgia.

For more information, including a MSDS sheet, please see PNA’s Cyclobenzaprine page.

Approved Indications

Acute Musculoskeletal Spasms: Cyclobenzaprine is approved as an adjunct therapy to physical therapy and rest in patients who suffer from spasms and associated symptoms, such as pain, tenderness, limited motion, and other restrictions in daily living.

Other Uses: Cyclobenzaprine is often prescribed off-label to ease pain and improve sleep in patients suffering from fibromyalgia.

Important Information: Cyclobenzaprine should only be used for short durations, up to 2-3 weeks, and should not be used to treat spasticity from cerebral or spinal cord disease, or due to cerebral palsy.

Side Effects and Drug Interactions

Common side effects in patients taking cyclobenzaprine include2:

  • Drowsiness, dizziness, and fatigue
  • Dry mouth or dry throat
  • Loss of appetite or nausea
  • Stomach pain
  • Diarrhea, constipation, or gas
  • Blurred vision
  • Muscle weakness

Patients who suffer from any of the following serious side effects should contact their pharmacist or physician immediately:

  • Rapid, pounding, or uneven heartbeats
  • Pain or heavy feeling in the chest
  • Pain that spreads to the arm or shoulder
  • Nausea, sweating, and general ill feeling
  • Sudden numbness or weakness, especially occurring on one side of the body
  • Sudden headache, confusion, problems with vision, speech, or balance
  • Light-headedness or fainting
  • Confusion, weakness, and lack of coordination
  • Stomach pain and low fever with loss of appetite
  • Dark urine or clay-colored stools
  • Jaundiced skin or eyes
  • Seizures
  • Unusual thoughts or behavior, or hallucinations
  • Easy bruising or bleeding and unusual weakness

Patients who are allergic to cyclobenzaprine who are currently taking a monoamine oxidase inhibitor (MAOI) or who suffer from heart conditions (including heart rhythm disorders, heart attacks or blocks, and congestive heart failure) or a thyroid disorder should not take this medication. Patients suffering from glaucoma, liver disease, an enlarged prostate, or who have trouble urinating should advise their physician before starting this medication.3

Medications known to have major interactions with cyclobenzaprine include MAOIs used within the past 14 days, and other drugs that raise serotonin levels (such as SSRIs, SNRIs, TCAs, tramadol, bupropion, meperidine, or verapamil). Use caution when co-administering cyclobenzaprine with anticholinergic drugs.4

Latest News and Research

Cyclobenzaprine was first synthesized in 1961 and initially was studied for its (limited) antidepressant activity. The drug was approved in 1977 to treat acute muscle spasms and has been in continual use since.5

More recently, cyclobenzaprine has been prescribed off-label for treatment of pain and insomnia in patients with fibromyalgia, a chronic musculoskeletal pain disorder that affects nearly 2% of the population in the U.S.6 Since fibromyalgia has no cure and limited management therapies, FDA approval of cyclobenzaprine for this indication would offer significant pain relief for patients. Perhaps as a side result of this research, at least one inventor has filed a patent on the use of cyclobenzaprine to prevent or treat fatigue stemming from different sleep disorders.7

New research is also being conducted into the use of cyclobenzaprine as a treatment for tinnitus, another condition that has no general class of treatment.8 Reduction of tinnitus has been observed with cyclobenzaprine alone and in conjunction with another drug and offers a lot of promise for drug development in that area.

Buying Guide

PNA is a recommended bulk supplier of Cyclobenzaprine and other APIs. You can learn more about Cyclobenzaprine here.

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Show 8 footnotes

  1. “Drug Bank: Cyclobenzaprine,” April 10, 2014, http://www.drugbank.ca/drugs/DB00924
  2. “Flexeril,” 2015, http://www.rxlist.com/flexeril-drug/patient-images-side-effects.htm
  3. “Cyclobenzaprine,” June 16, 2013, http://www.drugs.com/cyclobenzaprine.html
  4. “Cyclobenzaprine,” 2015, http://reference.medscape.com/drug/flexeril-amrix-flexmid-cyclobenzaprine-343338#5
  5. “Cyclobenzaprine- Rachel and Michaela,” January 22, 2013, https://prezi.com/h-vzojz2s5hj/cyclobenzaprine-rachel-and-michaela/
  6. “Treatment of Fibromyalgia With Cyclobenzaprine: A Meta-Analysis,” February 15, 2004, http://onlinelibrary.wiley.com/store/10.1002/art.20076/asset/20076_ftp.pdf?v=1&t=iibvzmrl&s=b27f62cffb3db389866e2b3f09cf12164e6b342d
  7. “Methods and compositions for treating fatigue associated with disordered sleep using very low dose cyclobenzaprine,” March 5, 2015, https://www.google.com/patents/US20150065581
  8. “Treatment of tinnitus with cyclobenzaprine: an open-label study,” 2012, http://europepmc.org/abstract/med/22541838