Brand and Other Names:Flexeril, Amrix, more...Fexmid
- Classes: Skeletal Muscle Relaxants
Dosing & Uses
Dosage Forms & Strengths
- 5 mg PO q8hr; may increase dose to 7.5-10 mg PO q8hr PRN
- 15 mg PO qDay; some patients may require up to 30 mg PO qDay
- Immediate-release tablet: 5 mg/day PO initially; titrate slowly upward and consider less frequent dosing
- Extended-release capsule not recommended in elderly, because of increased plasma levels (40%) and prolonged half-life (56%) compared with young adults
- Immediate-release tablet: 5 mg/day PO initially; titrate slowly and consider less frequent dosing
- Extended-release capsule: Not recommended in mild-to-severe hepatic impairment
- Not studied
Dosage Forms & Strengths
- <15 years: Safety and efficacy not established
- >15 years: 5 mg PO q8hr; may increase dose to 7.5-10 mg PO q8hr PRN
- <18 years: Safety and efficacy not established
- >18 years: 15 mg PO qDay; some patients may require up to 30 mg PO qDay
Serious - Use Alternative
Significant - Monitor Closely
Drowsiness (up to 39% immediate-release; 100% extended-release)
Dry mouth (21-32%)
Bad taste in mouth (1-6%)
Blurred vision (3%)
Cardiac dysrhythmia (rare)
Immune hypersensitivity reaction
Hypersensitivity to drug or formulation components
During the acute recovery phase of myocardial infarction and in patients with arrhythmia, heart block or conduction disturbances, or congestive heart failure
Concomitant use or within 14 days of discontinuing MAO inhibitors
Hyperpyretic crisis seizures and deaths have occurred in patients receiving cyclobenzaprine (or structurally similar tricyclic antidepressants) concomitantly with MAO inhibitors
Use only for short periods (2-3 wk)
Use caution in urinary retention, narrow-angle glaucoma or IOP, or concomitant use of other anticholinergic drugs
May cause drowsiness/dizziness; do not ingest alcohol or other CNS depressants; may impair ability to operate heavy machinery
May take with food to avoid stomach upset
Serotonin syndrome reported when coadministered with other drugs that increase serotonin (eg, SSRIs, SNRIs, TCAs, tramadol, bupropion, meperidine, verapamil, or MAO inhibitors [see also Contraindications])
Not effective for treatment of spasticity associated with cerebral/spinal cord disease or for pediatric cerebral palsy
Elderly patients may be more prone to adverse effects and require dose/frequency reduction
Use immediate release with caution in hepatic impairment; extended-release form not recommended with hepatic impairment
Pregnancy & Lactation
Pregnancy category: B
Lactation: Excretion in milk unknown; use with caution
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Mechanism of Action
Relieves local skeletal muscle spasm; clinical response similar to diazepam
Structurally related to cyclic antidepressants, and pharmacologic effects are similar, including reserpine antagonism, norepinephrine potentiation, potent peripheral and central anticholinergic effects, and sedation; reduces tonic somatic motor activity influencing alpha and gamma motor neurons
Onset: 1 hr
Duration: 12-24 hr
Peak plasma time: 7-8 hr
Peak plasma concentration: 15-25 ng/mL
Protein bound: 93%
Hepatic via CYP3A4, 1A2, and 2D6; may undergo enterohepatic recirculation
Half-life: 8-37 hours (immediate release); 32-33 hr (extended release)
Excretion: Urine, feces
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