Cyclobenzaprine

Cyclobenzaprine
Clinical data
Trade names	Flexeril, Amrix, others
AHFS/Drugs.com	Monograph
MedlinePlus	a682514
License data	US DailyMed: Cyclobenzaprine;
Routes of; administration	By mouth
ATC code	M03BX08 (WHO) ;
Legal status
Legal status	US: ℞-only; In general: ℞ (Prescription only);
Pharmacokinetic data
Bioavailability	33–55%
Protein binding	93%
Metabolism	major: CYP3A4, CYP1A2; minor: CYP2D6, N-demethylation
Metabolites	Norcyclobenzaprine
Elimination half-life	32 hours (extended-release, range 8–37 hours), 18 hours (immediate release, range 8–37 hours)
Excretion	Kidney
Identifiers
	IUPAC name 3-(5H-dibenzo[a,d]cyclohepten-5-ylidene)-N,N-dimethyl-propan-1-amine;
CAS Number	303-53-7 ;
PubChem CID	2895;
IUPHAR/BPS	7152;
DrugBank	DB00924 ;
ChemSpider	2792 ;
UNII	69O5WQQ5TI;
KEGG	D07758 ;
ChEBI	CHEBI:3996 ;
ChEMBL	ChEMBL669 ;
CompTox Dashboard (EPA)	DTXSID0046933 ;
ECHA InfoCard	100.005.588
Chemical and physical data
Formula	C20H21N
Molar mass	275.395 g·mol−1
3D model (JSmol)	Interactive image;
	SMILES c3cc\2c(\C=C/c1c(cccc1)C/2=C/CCN(C)C)cc3;
	InChI InChI=1S/C20H21N/c1-21(2)15-7-12-20-18-10-5-3-8-16(18)13-14-17-9-4-6-11-19(17)20/h3-6,8-14H,7,15H2,1-2H3 ; Key:JURKNVYFZMSNLP-UHFFFAOYSA-N ;
	(verify)

Cyclobenzaprine, sold under several brand names including, historically, Flexeril, is a muscle relaxer used for muscle spasms from musculoskeletal conditions of sudden onset. It is not useful in cerebral palsy. It is taken by mouth.

Common side effects include headache, feeling tired, dizziness, and dry mouth. Serious side effects may include an irregular heartbeat. There is no evidence of harm in pregnancy, but it has not been well studied in this population. It should not be used together with MAOIs. How it works is unclear. In any case, it is known to inhibit serotonin and norepinephrine reuptake and to block serotonin, adrenergic, histamine, and muscarinic acetylcholine receptors. Chemically, it is very similar to tricyclic antidepressants like amitriptyline.

Cyclobenzaprine was approved for medical use in the United States in 1977. It is available by prescription as a generic medication. In 2022, it was the 45th most commonly prescribed medication in the United States, with more than 13 million prescriptions. It was not available in the United Kingdom as of 2012.