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Cyclobenzaprine
Cyclobenzaprine is a centrally acting skeletal muscle relaxant1 and central nervous system depressant2 in the dibenzocycloheptene chemical class. First synthesized in 1961, it became available for human use in 1977.3 Structurally similar to tricyclic antidepressants such as amitriptyline,4 it differs by one double bond. It may cause drowsiness, dry mouth, dizziness,1 or, with extended-release capsules, irregular or abnormal heartbeats,4 and may potentiate some opioids.1
Dosage & Duration
Dosage
Doses are population estimates that vary widely between individuals.
Threshold~2 mg
Light2-5 mg
Moderate5-10 mg
Strong10-15 mg
Heavy15+ mg
Duration
Onset15-45 minutes
After Effects1-6 hours
Total6-12 hours
Subjective Effects
Subjective Effects not written up yet
Pharmacology
Pharmacodynamics
Cyclobenzaprine is a centrally acting skeletal muscle relaxant whose exact human mechanism remains unclear.5 Evidence from animal studies suggests supraspinal action in the brainstem, including reduced activity of efferent alpha and gamma motor neurons through inhibition of coeruleus-spinal or reticulospinal pathways.5 Cyclobenzaprine blocks serotonin and norepinephrine transporters6 and blocks several serotonin, adrenergic, histamine H1, and muscarinic acetylcholine receptors.
Pharmacokinetics
Oral bioavailability is approximately 33-55%,7 with peak plasma concentrations reached after about 4 hours. Cyclobenzaprine is extensively metabolized in the liver by oxidative N-demethylation, mainly through CYP3A4 and CYP1A2 and to a lesser extent CYP2D6, and by N-glucuronidation through UGT1A4 and UGT2B10; enterohepatic circulation also occurs. It has extensive tissue distribution, with a volume of distribution of about 146 L, and is approximately 93% plasma protein bound. The effective half-life is about 18 hours in young healthy subjects, increasing to 33.4 hours in elderly people and 46.2 hours with hepatic insufficiency. Most radiolabeled drug is excreted as metabolites, with 38-51% recovered in urine and 14-15% in feces, while about 1% is recovered unchanged in urine.
Interactions
Interactions not written up yet
An unlisted combination is an unknown one, not a safe one. Check a dedicated combination chart before mixing.
Tolerance
Tolerance not written up yet
Harm Potential
Addiction & Dependence
Psychological
TripSit classifies cyclobenzaprine as habit-forming, while reporting little recreational value when used alone.
Toxicity
| Species | Route | Value |
|---|---|---|
| mouse | oral | 338 mg/kg |
| rat | oral | 425 mg/kg |
Cyclobenzaprine overdose commonly causes tachycardia and can rarely produce irregular heart rhythms, cardiac arrest, or severe hypotension.8
Drowsiness is among the most common effects associated with cyclobenzaprine overdose; less frequent manifestations include confusion, hallucinations, tremor, agitation, and ataxia, while rare but potentially critical manifestations include seizures and neuroleptic malignant syndrome. Signs and symptoms of toxicity may develop rapidly after overdose.8
Dysphagia may rarely occur with cyclobenzaprine and is described as potentially life-threatening.
Psychosis Risk
Hallucinations may occur during cyclobenzaprine overdose.8 Confusion, delirium, and cognitive impairment have been reported particularly in elderly patients.
Seizure Risk
Seizures are rare but potentially critical complications of cyclobenzaprine overdose.8
History & Culture
Development and medical introduction
Cyclobenzaprine was first synthesized in 1961 and became available for human use in 197710 after initially being studied as a potential antidepressant because of its structural similarity to tricyclic antidepressants. Following approval, it remained a relatively popular
Legality
By Country
Prescription2
United StatesPrescription onlyFederal Food, Drug, and Cosmetic Act § 503(b), 21 U.S.C. § 353(b), read with the current FDA prescribing information for cyclobenzaprine hydrochloride tablets2072122
Current FDA prescribing information identifies cyclobenzaprine hydrochloride tablets as prescription drugs labeled ‘Rx Only’. Under 21 U.S.C. § 353(b), drugs subject to this requirement may be dispensed only on a licensed practitioner's prescription. This federal prescription-dispensing classification does not establish federal controlled-substance scheduling or determine separate state, district, territorial, tribal, or local rules.
CanadaPrescription onlyFood and Drugs Act, R.S.C. 1985, c. F-27, s. 29.1; Prescription Drug List: Human Use; Food and Drug Regulations, C.R.C., c. 870, ss. A.01.010 and C.01.04113141516171819
The federal Prescription Drug List for human use has listed cyclobenzaprine or its salts since 19 December 2013. The Food and Drug Regulations prohibit the sale of a prescription drug unless the seller is entitled under provincial law to dispense it and sells it under a received verbal or written prescription, or the sale falls under the section C.01.043 exception. This restriction governs sale and does not establish a general offence of ordinary possession.
References
Citations
Article Status
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