Cyclobenzaprine: Difference between revisions

Short-term relief of muscle spasm from acute musculoskeletal conditions (FDA; ≤2-3 weeks)0, Fibromyalgia (off-label, low-dose evening)0, Insomnia adjunct (off-label, low-dose)0

Pharmacy

Starting dose

IR 5 mg PO TID; titrate to 10 mg TID if needed. Amrix ER 15 mg PO once daily. Off-label insomnia / fibromyalgia: 5-10 mg PO at bedtime

Preparations

IR tablets 5, 7.5, 10 mg; Amrix ER capsules 15, 30 mg

US FDA Max

30 mg/day (IR or ER)

Pharmacology

Routes

Oral

Onset

~1 hour

Duration

12-24 hours (IR); 24 hours (Amrix ER)

Half-life

18 hours (IR); 32-33 hours (ER)^[1]

Bioavailability

~33-55% (IR); reduced by food^[1]

Pregnancy

Limited human data.^{[citation needed]}

Legal status

Rx-only in US. Not a controlled substance, distinguishing it from the carisoprodol alternative for muscle spasm^[1]

Purported mechanism

Structurally a tricyclic compound closely related to amitriptyline but FDA-approved as a muscle relaxant rather than an antidepressant. Centrally-acting via brainstem and supraspinal sites, reducing tonic somatic motor activity through noradrenergic descending pathways; the spinal cord is not the primary site of action. Substantial anticholinergic, H1 antihistaminergic, and α1-adrenergic antagonist activity accounts for sedation, dry mouth, and orthostatic adverse effects.0 Serotonin syndrome risk applies through the tricyclic-class identity when combined with SSRIs, SNRIs, MAOIs, tramadol, or other serotonergic agents. FDA labeling restricts to short-term use (≤2-3 weeks); evidence for prolonged use is limited^[1].

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 FDA Prescribing Information, Flexeril (cyclobenzaprine hydrochloride), Merck/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/017821s048lbl.pdf

[flexeril-label-1] 1.0 ^1.1 ^1.2 ^1.3 FDA Prescribing Information, Flexeril (cyclobenzaprine hydrochloride), Merck/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/017821s048lbl.pdf

[1]

@@ Line 1: / Line 1: @@
 {{MedTemplate
-| generic            = Cyclobenzaprine
+| generic           = Cyclobenzaprine
-| brand              = Flexeril
+| brand             = Flexeril (IR; brand discontinued in US, generic widely available), Amrix (ER)
-| structure          =
+| structure         =
-| classes            = Muscle relaxant
+| classes           = [[:Category:Skeletal muscle relaxants|Skeletal muscle relaxant (centrally-acting)]], [[:Category:Tricyclic-related compounds|Tricyclic-related compound]]
-| mechanism          = TCA-related; H1/alpha/muscarinic antagonist
+| uses              = <vote slug="acute-muscle-spasm-use">Short-term relief of muscle spasm from acute musculoskeletal conditions (FDA; ≤2-3 weeks)</vote>, <vote slug="fibromyalgia-low-dose-use">Fibromyalgia (off-label, low-dose evening)</vote>, <vote slug="insomnia-cyclobenzaprine-use">Insomnia adjunct (off-label, low-dose)</vote>
-| uses               =
+| starting_dose     = IR 5 mg PO TID; titrate to 10 mg TID if needed. Amrix ER 15 mg PO once daily. Off-label insomnia / fibromyalgia: 5-10 mg PO at bedtime
-| starting_dose      =
+| preparations      = IR tablets 5, 7.5, 10 mg; Amrix ER capsules 15, 30 mg
-| preparations       =
+| fda_max           = 30 mg/day (IR or ER)
-| routes             =
+| pill_id           =
-| onset              =
+| routes            = Oral
-| duration           =
+| onset             = ~1 hour
-| halflife           =
+| duration          = 12-24 hours (IR); 24 hours (Amrix ER)
-| bioavailability    =
+| halflife          = 18 hours (IR); 32-33 hours (ER)<ref name="flexeril-label">FDA Prescribing Information, Flexeril (cyclobenzaprine hydrochloride), Merck/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/017821s048lbl.pdf</ref>
-| pregnancy          =
+| bioavailability   = ~33-55% (IR); reduced by food<ref name="flexeril-label" />
-| legal              =
+| pregnancy         = Limited human data.{{citation needed}}
-| intro              =
+| legal             = [[USLegal:Prescription only|Rx-only]] in US. Not a controlled substance, distinguishing it from the carisoprodol alternative for muscle spasm<ref name="flexeril-label" />
-| pharmacokinetics   =
+| mechanism         = <vote slug="cyclobenzaprine-mech-claim">Structurally a tricyclic compound closely related to amitriptyline but FDA-approved as a muscle relaxant rather than an antidepressant. Centrally-acting via brainstem and supraspinal sites, reducing tonic somatic motor activity through noradrenergic descending pathways; the spinal cord is not the primary site of action. Substantial anticholinergic, H1 antihistaminergic, and α1-adrenergic antagonist activity accounts for sedation, dry mouth, and orthostatic adverse effects.</vote> '''Serotonin syndrome''' risk applies through the tricyclic-class identity when combined with SSRIs, SNRIs, MAOIs, tramadol, or other serotonergic agents. FDA labeling restricts to short-term use (≤2-3 weeks); evidence for prolonged use is limited<ref name="flexeril-label" />.
-| pharmacodynamics   =
-| indications        =
-| dosing             =
-| effects            =
-| contraindications  =
-| interactions       =
-| pregnancy_details  =
-| monitoring         =
-| counseling         =
-| anecdotes          =
-| seealso            =
-| references         =
 }}
-[[Category:Muscle_Relaxants]]
+== References ==
+<references />
+[[Category:Skeletal muscle relaxants]]
+[[Category:Tricyclic-related compounds]]

MDElliottMD (talk | contribs)

Latest revision as of 06:36, 23 May 2026

Experience

Problems

Titration strategies

Effects

Relevant anecdote

Relevant Literature

References