cyclobenzaprine (Flexeril)
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Introduction
Tradename: Flexeril.
Indications
- muscle relaxant for short term management of muscle spasms
- ineffective in spasticity due to chronic neurologic disorders
- used for treatment of fibromyalgia
Dosage
Start 10 mg PO TID, max 60 mg/day
Tabs: 10 mg.
Sulingual: Tonmya (FDA-approved for fibromyalgia)[7]
Pharmacokinetics
- duration of action is 12-24 hours
- highly protein bound
- extensively metabolized by liver by cyt P450 1A2
- eliminated in the urine
- elimination 1/2life 1-3 days
elimination via liver
elimination via kidney
1/2life = 1-3 days
Adverse effects
- anticholinergic effects
- consider all adverse effects of amitriptyline
- other (< 1%)
- swelling of face & lips, clumsiness, tinnitus, dermatitis, hepatitis, syncope, urinary frequency, bloating, difficulty speaking, muscle weakness, hypotension, arrhythmias, asthenia, nervousness, rash, dyspepsia, dysgeusia (taste disturbance)
- risk of falls: baclofen, cyclobenzaprine > tizanidine
- risk of fracture: baclofen, cyclobenzaprine = tizanidine[6]
Drug interactions
- MAO inhibitors
- consider all interactions listed with amitriptyline
- any drug which inhibits cyt P450 1A2 can increase cyclobenzaprine levels
- any drug which induces cyt P450 1A2 can diminish cyclobenzaprine levels
- prevalence of depression is 61% among patients coprescribed gabapentin + cyclobenzaprine[5]
Mechanism of action
- centrally-acting muscle relaxant
- structurally related to tricyclic antidepressants (TCA)
- ineffective for muscle spasm due to CNS disease
More general terms
Additional terms
Component of
References
- ↑ The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996
- ↑ Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
- ↑ Kaiser Permanente Northern California Regional Drug Formulary, 1998
- ↑ Deprecated Reference
- ↑ 5.0 5.1 Qato DM, Ozenberger K, Olfson M Prevalence of Prescription Medications With Depression as a Potential Adverse Effect Among Adults in the United States. JAMA. 2018;319(22):2289-2298 PMID: https://pubmed.ncbi.nlm.nih.gov/29896627 https://jamanetwork.com/journals/jama/fullarticle/2684607
- ↑ 6.0 6.1 Hwang YJ, Chang AR, Brotman DJ, Inker LA, Grams ME, Shin JI. Baclofen and the risk of fall and fracture in older adults: A real-world cohort study. J Am Geriatr Soc. 2023 Nov 7. PMID: https://pubmed.ncbi.nlm.nih.gov/37933734 https://agsjournals.onlinelibrary.wiley.com/doi/abs/10.1111/jgs.18665
- ↑ 7.0 7.1 Gever J New Version of Old Drug OK'd for Fibromyalgia. Cyclobenzaprine in sublingual tablet marks first new fibromyalgia therapy approved in 15 years. MedPage Today. August 18, 2025 https://www.medpagetoday.com/rheumatology/fibromyalgia/117034