Cyclobenzaprine
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| Trade names | Amrix, Flexeril |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a682514 |
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| Routes of administration |
By mouth |
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| Pharmacokinetic data | |
| Bioavailability | 33% to 55% |
| Metabolism | major: CYP3A4, CYP1A2; minor: CYP2D6, N-demethylation |
| Biological half-life | 32 hours (range 8–37 hours; n=18) |
| Excretion | renal |
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| ECHA InfoCard | 100.005.588 |
| Chemical and physical data | |
| Formula | C20H21N |
| Molar mass | 275.387 g/mol |
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Cyclobenzaprine, sold under the brand name Flexeril among others, is a muscle relaxer medication used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions. It is the best-studied drug for this application. It has also been used off-label for fibromyalgia treatment.
As of 2015 the cost for a typical course of medication in the United States is less than US$25.
After sustaining an injury, painful muscle spasms may occur to stabilize the affected body part and prevent further damage. Cyclobenzaprine is used to treat such muscle spasms associated with acute, painful musculoskeletal conditions. It decreases pain in the first two weeks, peaking in the first few days, but has no proven benefit after two weeks. Since no benefit is proven beyond that, therapy should not be continued long-term. It is not useful for spasticity due to neurologic conditions such as cerebral palsy.
Cyclobenzaprine has also shown effectiveness in the treatment of fibromyalgia symptoms, with a report of 4.8 patients needing treatment for each (1) patient reporting pain reduction (but no change in fatigue or tender points). It may also be used along with other treatments for tetanus.
Meta-analysis studies have found significantly increased rates of drowsiness (38% of patients), dry mouth (24%), dizziness (10%), and adverse events of any kind in patients taking cyclobenzaprine versus placebo. Drowsiness and dry mouth appear to intensify with increasing dose.Dysphagia, a life threatening side-effect, may rarely occur.
The sedative effects of cyclobenzaprine are likely due to its antagonistic effect on histamine, serotonin, and muscarinic receptors. Agitation is a common side effect observed especially in the elderly. In general, the National Committee for Quality Assurance recommends avoiding the use of cyclobenzaprine in the elderly because of the potential for more severe side effects. Treatment protocols and support should follow the same as for any structurally related tricyclic, such as tricyclic antidepressants.
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Wikipedia