Cyclobenzaprine

Pronunciation

(sye kloe BEN za preen)

U.S. Brand Names

Flexeril®

Synonyms

Cyclobenzaprine Hydrochloride

Generic Available

Yes

Canadian Brand Names

Apo-Cyclobenzaprine®; Flexeril®; Flexitec; Gen-Cyclobenzaprine; Novo-Cycloprine; Nu-Cyclobenzaprine

Use

Treatment of muscle spasm associated with acute painful musculoskeletal conditions

Use - Dental

Treatment of muscle spasm associated with acute temporomandibular joint pain

Pregnancy Risk Factor

Lactation

Excretion in breast milk unknown/not recommended

Contraindications

Hypersensitivity to cyclobenzaprine or any component of the formulation; do not use concomitantly or within 14 days of MAO inhibitors; hyperthyroidism; congestive heart failure; arrhythmias; acute recovery phase of MI

Warnings/Precautions

Cyclobenzaprine shares the toxic potentials of the tricyclic antidepressants and the usual precautions of tricyclic antidepressant therapy should be observed; use with caution in patients with urinary hesitancy, angle-closure glaucoma, hepatic impairment, or in the elderly. Do not use concomitantly or within 14 days after MAO inhibitors; combination may cause hypertensive crisis, severe convulsions. Safety and efficacy have not been established in patients <15 years of age.

Adverse Reactions

>10%:

Central nervous system: Drowsiness (29% to 39%), dizziness (1% to 11%)

Gastrointestinal: Xerostomia (21% to 32%)

1% to 10%:

Central nervous system: Fatigue (1% to 6%), confusion (1% to 3%), headache (1% to 3%), irritability (1% to 3%), mental acuity decreased (1% to 3%), nervousness (1% to 3%)

Gastrointestinal: Abdominal pain (1% to 3%), constipation (1% to 3%), diarrhea (1% to 3%), dyspepsia (1% to 3%), nausea (1% to 3%)

Neuromuscular & skeletal: Muscle weakness (1% to 3%)

Ocular: Blurred vision (1% to 3%)

Respiratory: Pharyngitis (1% to 3%)

<1% (Limited to important or life-threatening): Ageusia, agitation, anaphylaxis, angioedema, anorexia, arrhythmia, cholestasis, diplopia, facial edema, gastritis, hallucinations, hepatitis (rare), hypertonia, hypotension, insomnia, jaundice, liver function tests abnormal, malaise, palpitation, paresthesia, pruritus, psychosis, rash, seizure, tachycardia, thinking abnormal, tinnitus, tongue edema, tremor, urinary frequency, urinary retention, urticaria, vertigo, vomiting

Overdosage/Toxicology

Symptoms of overdose include troubled breathing, drowsiness, syncope, seizures, tachycardia, hallucinations, and vomiting. Following initiation of essential overdose management, treatment is supportive and symptomatic.

Drug Interactions

Substrate of CYP1A2 (major), 2D6 (minor), 3A4 (minor)

Anticholinergics: Because of cyclobenzaprine's anticholinergic action, use with caution in patients receiving these agents.

CNS depressants: Effects may be enhanced by cyclobenzaprine.

CYP1A2 inhibitors: May increase the levels/effects of cyclobenzaprine. Example inhibitors include amiodarone, ciprofloxacin, fluvoxamine, ketoconazole, norfloxacin, ofloxacin, and rofecoxib.

Guanethidine: Antihypertensive effect of guanethidine may be decreased; effect seen with tricyclic antidepressants.

MAO inhibitors: Do not use concomitantly or within 14 days after MAO inhibitors.

Tramadol: May increase risk of seizure; effect seen with tricyclic antidepressants and tramadol.

Ethanol/Nutrition/Herb Interactions

Ethanol: Avoid ethanol (may increase CNS depression).

Herb/Nutraceutical: Avoid valerian, kava kava, gotu kola (may increase CNS depression).

Stability

Store at room temperature 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F).

Mechanism of Action

Centrally-acting skeletal muscle relaxant pharmacologically related to tricyclic antidepressants; reduces tonic somatic motor activity influencing both alpha and gamma motor neurons

Pharmacodynamics/Kinetics

Onset of action: ~1 hour

Duration: 12-24 hours

Absorption: Complete

Metabolism: Hepatic via CYP3A4, 1A2, and 2D6; may undergo enterohepatic recirculation

Bioavailability: 33% to 55%

Half-life elimination: 18 hours (range: 8-37 hours)

Time to peak, serum: 3-8 hours

Excretion: Urine (as inactive metabolites); feces (as unchanged drug)

Dosage

Oral: Note: Do not use longer than 2-3 weeks

Adults: Initial: 5 mg 3 times/day; may increase to 10 mg 3 times/day if needed

Elderly: 5 mg 3 times/day; plasma concentration and incidence of adverse effects are increased in the elderly; dose should be titrated slowly

Dosage adjustment in hepatic impairment:

Mild: 5 mg 3 times/day; use with caution and titrate slowly

Moderate to severe: Use not recommended

Patient Education

Take exactly as directed. Do not increase dose or discontinue without consulting prescriber. Do not use alcohol, prescriptive or OTC antidepressants, sedatives, or pain medications without consulting prescriber. You may experience drowsiness, dizziness, lightheadedness (avoid driving or engaging in tasks that require alertness until response to drug is known); or urinary retention (void before taking medication). Report excessive drowsiness or mental agitation, chest pain, skin rash, swelling of mouth/face, difficulty speaking, ringing in ears, or blurred vision. Breast-feeding precaution: Breast-feeding is not recommended.

Dental Health: Effects on Dental Treatment

Key adverse event(s) related to dental treatment: Xerostomia and changes in salivation (normal salivary flow resumes upon discontinuation).

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

Drowsiness and dizziness are common; may cause nervousness or confusion

Mental Health: Effects on Psychiatric Treatment

Contraindicated with MAO inhibitors or within 14 days of MAO inhibitor; concurrent use with psychotropics may exacerbate the dry mouth and sedation commonly seen with cyclobenzaprine

Dosage Forms

Tablet, as hydrochloride: 10 mg

Flexeril®: 5 mg, 10 mg [film coated]

References

Ambre JJ, "Cyclobenzaprine Overdose," Ann Intern Med , 1985, 102(4):559-60.

Heckerling PS, Bartow TJ, "Paradoxical Diaphoresis in Cyclobenzaprine Poisoning," Ann Intern Med , 1984, 101(6):881.

Hucker HB, Stauffer SC, Albert KS, et al, "Plasma Levels and Bioavailability of Cyclobenzaprine in Human Subjects," J Clin Pharmacol , 1977, 17(11-12):719-27.

Linden CH, Mitchiner JC, Lindzon RD, et al, "Cyclobenzaprine Overdosage," J Toxicol Clin Toxicol , 1983, 20(3):281-8.

Spiller HA, Winter ML, Mann KV, et al, "Five Year Multicenter Retrospective Review of Cyclobenzaprine Toxicity," Vet Hum Toxicol , 1994, 36:370.

Theoharides TC, Harris RS, and Weckstein D, "Neuroleptic Malignant-Like Syndrome Due to Cyclobenzaprine?" J Clin Psychopharmacol , 1995, 15(1):79-81.

International Brand Names

Apo-Cyclobenzaprine® (CA); Ciclamil® (CL); Cycloflex® (IL); Flexeril® (CA); Flexiban® (AR, CR, GT, HN, IT, PA, SV); Flexitec (CA); Gen-Cyclobenzaprine (CA); Masterelax® (CL); Miosan® (BR); Novo-Cycloprine (CA); Nu-Cyclobenzaprine (CA); Reflexan® (CL); Tensamon® (CL); Tensiomax® (CL); Tensodox® (CL); Tonalgen® (CL); Yurelax® (ES)

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