Cyclobenzaprine

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Cyclobenzaprine

Systematic (IUPAC) name
3-(5H-dibenzo[a,d]cyclohepten-5-ylidene)- N,N-dimethyl-1-propanamine
Identifiers
CAS number	303-53-7
ATC code	M03BX08
PubChem	2895
DrugBank	APRD00213
ChemSpider	2792
Chemical data
Formula	C20H21N
Mol. mass	275.387 g/mol
SMILES	eMolecules & PubChem
Pharmacokinetic data
Bioavailability	32.5% to 55%
Metabolism	hepatic
Half life	18 hours (range 8–37 hours; n=18)
Excretion	renal
Therapeutic considerations
Pregnancy cat.	Category B
Legal status	Unscheduled
Routes	PO (Per Oral)
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Cyclobenzaprine 10mg

Cyclobenzaprine is a drug^[1] that works in the central nervous system by altering the signals from the brain that cause muscles to tighten. It is marketed as Apo-Cyclobenzaprine (10 mg tablets) Flexeril (5 and 10 mg tablets), and also as Fexmid (7.5 mg tablet). Both Flexeril and Fexmid are available in generic form. Once-a-day extended-release formulation Amrix was approved by the U.S. Food and Drug Administration (FDA) in 2007 and is available in 15- and 30-mg capsules.^[2]

[edit] Mechanism of action

Cyclobenzaprine is structurally related to the first-generation tricyclic antidepressants such as imipramine and amitriptyline. The exact mechanism of action for cyclobenzaprine is unknown.

Current research appears to indicate that cyclobenzaprine has effects on the locus ceruleus, where it — like many tricyclic antidepressants — acts to inhibit the uptake of norepinephrine, resulting in increased transynaptic norepinephrine concentration. Tricyclic compounds with norepinephrine reuptake-inhibiting properties (e.g., amitriptyline) have been shown to exert analgesic effects in chronic nerve and muscle pain. Cyclobenzaprine also causes inhibition of descending serotonergic systems in the spinal cord by blocking 5-HT2A and 5-HT2C receptors.^[3] This action is thought to have an inhibitory effect on the alpha motor neurons in the ventral horn of the spinal cord, thereby resulting in decreased firing of alpha-motor neurons and a reduction in spinal mono- and polysynaptic reflexes.^[4]

[edit] Indications

Cyclobenzaprine is typically prescribed to relieve pain and muscle spasms. In usual circumstances, muscle spasms occur in an injury to stabilize the affected body part and prevent further damage. The spasm of the muscles can increase the pain level. It is believed that, by decreasing muscular spasm, pain is diminished. A common application would be that of a whiplash injury in a car accident. Muscle relaxants such as Cyclobenzaprine (Flexeril) and Orphenadrine Citrate (Norflex) have also 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. There was also a reduction in the total number of tender points and muscle tightness.

Like other tricyclic antidepressants, it is also prescribed off-label as a sleep-aid. The sedative effects of cyclobenzaprine are likely due to its antagonistic effect on histamine H1, serotonin 5-HT2A, and muscarinic acetylcholine receptors.

To avoid a possible upset stomach, it should be taken with food and a full glass of water.

[edit] Side-effects

Common side-effects include drowsiness, depression, headaches, severe dizziness, and blurred vision. Other side-effects are respiratory depression and decreased functionality in various muscles. Long-term use has been associated with vision damage. Another side-effect is dryness of the mouth.^[5] Agitation is a common side-effect observed especially in the elderly.^[6]

Because of potential for more severe side effects, this drug is on the list to avoid in the elderly. (See NCQA’s HEDIS Measure: Use of High Risk Medications in the Elderly, http://www.ncqa.org/Portals/0/Newsroom/SOHC/Drugs_Avoided_Elderly.pdf).

[edit] Interactions

Cyclobenzaprine has major contraindications with monoamine oxidase inhibitors (MAOIs). At least one study also found increased risk of serotonin syndrome when cyclobenzaprine was taken with duloxetine, an SSNRI.^[7]

Due to potential interactions, it is important to discuss the use of any of the following before taking them while using cyclobenzaprine:

• Alcohol
• Central nervous system (CNS) depressants (medicines that cause drowsiness) or
• Tricyclic antidepressants (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Pertofrane], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil]) The chance of side-effects may be increased
• Monoamine oxidase (MAO) inhibitors (furazolidone [e.g., Furoxone], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], selegiline [e.g., Eldepryl], tranylcypromine [e.g., Parnate]) Taking cyclobenzaprine while taking or within 2 weeks of taking MAO inhibitors may result in serious, life-threatening side-effects^[8].

[edit] Legality

Cyclobenzaprine is regulated in the U.S. for prescription use only. Cyclobenzaprine does not fall within most governmental guidelines as a controlled substance, however possession without a valid or current prescription may be illegal, depending upon various state and local laws.

[edit] Abuse

When used for illicit purposes, the drug is often referred to as "cyclone" or "mellow yellow." Users report mild to moderate drowsiness and relaxation as the primary effects. However, Cyclobenzaprine can induce moderate to severe anticholinergic effects at higher doses. At even higher doses, cyclobenzaprine may cause severe ataxia^[9].

[edit] Overdose

Cylobenzaprine overdose can be life-threatening due to intractable seizures and/or heart arrythmias. However, depending on the amount taken and on the many different factors unique to each individual, harmful overdose effects can occur. Note that the susceptibility to these potentially damaging effects is greatly increased when cyclobenzaprine is used in conjunction with other drugs, in particular central nervous system depressants and antidepressants. Use of cyclobenzaprine with an MAOI (monoamine oxidase inhibitor) could possibly result in fatality. A case of rhabdomyolysis (muscle breakdown) associated with its overdose has been reported in the scientific literature. This is a rare though potentially fatal complication. Treatment protocols and support should follow the same as for any tricyclic antidepressant.^[6]

[edit] Notes

[edit] External links

• Chabria Shiven B: Rhabdomyolysis: a manifestation of cyclobenzaprine toxicity
• Flexeril Label: "FLEXERIL (CYCLOBENZAPRINE HCl) Tablets" (PDF). Food and Drug Administration. 2003. http://www.accessdata.fda.gov/drugsatfda_docs/label/2003/17821se8-045_flexeril_lbl.pdf. Retrieved 2009-07-26.