Title: Cyclobenzaprine
CAS Registry Number: 303-53-7
CAS Name: 3-(5H-Dibenzo[a,d]cyclohepten-5-ylidene)-N,N-dimethyl-1-propanamine
Additional Names: N,N-dimethyl-5H-dibenzo[a,d]cyclohepten-D5,g-propylamine; 5-(3-dimethylaminopropylidene)dibenzo[a,e]cycloheptatriene; 1-(3-dimethylaminopropylidene)-2,3:6,7-dibenzo-4-suberene; proheptatriene
Manufacturers' Codes: MK-130; Ro-4-1577; RP-9715
Molecular Formula: C20H21N
Molecular Weight: 275.39
Percent Composition: C 87.23%, H 7.69%, N 5.09%
Literature References: Prepn: GB 858187 (1961 to Hoffmann-La Roche); Villani et al., J. Med. Pharm. Chem. 5, 373 (1962); Winthrop et al., J. Org. Chem. 27, 230 (1962). Pharmacology: C. D. Barnes, W. L. Adams, Neuropharmacology 17, 445 (1978); N. N. Share, ibid. 721; and toxicology: J. Metysova et al., Arch. Int. Pharmacodyn. Ther. 144, 481 (1963). Metabolism: G. Belvedere et al., Biomed. Mass Spectrom. 1, 329 (1974); H. B. Hucker et al., Drug Metab. Dispos. 6, 184 (1978). Bioavailability: eidem, J. Clin. Pharmacol. 17, 719 (1977). Clinical studies: J. V. Basmajian, Arch. Phys. Med. Rehabil. 5, 58 (1978); B. R. Brown, J. Womble, J. Am. Med. Assoc. 240, 1151 (1978). Comprehensive description: M. L. Cotton, G. R. B. Down, Anal. Profiles Drug Subs. 17, 41-72 (1988).
Properties: bp1 175-180°. uv max: 224, 289 nm (log e 4.57, 4.02), (Villani et al.)
Boiling point: bp1 175-180°
Absorption maximum: uv max: 224, 289 nm (log e 4.57, 4.02), (Villani et al.)
Derivative Type: Hydrochloride
CAS Registry Number: 6202-23-9
Trademarks: Flexeril (Merck & Co.); Flexiban (Merck & Co.)
Molecular Formula: C20H21N.HCl
Molecular Weight: 311.85
Percent Composition: C 77.03%, H 7.11%, N 4.49%, Cl 11.37%
Literature References: Use as muscle relaxant: N. N. Share, FR 2100873 (1972 to Frosst), C.A. 78, 47801n (1973).
Properties: Crystals from isopropanol, mp 216-218°. Soly in water: >20 g/100 ml. Freely sol in water, methanol, ethanol; sparingly sol in isopropanol; slightly sol in chloroform, methylene chloride. Practically insol in hydrocarbons. uv max: 226, 295 nm (e 52300, 12000). LD50 in mice (mg/kg): 35 i.v., 250 orally (Metysova).
Melting point: mp 216-218°
Absorption maximum: uv max: 226, 295 nm (e 52300, 12000)
Toxicity data: LD50 in mice (mg/kg): 35 i.v., 250 orally (Metysova)
Therap-Cat: Muscle relaxant (skeletal).
Keywords: Muscle Relaxant (Skeletal).
Cyclobutane Cyclobutyrol Cyclobuxine D Cyclocumarol Cyclodrine

Cyclobenzaprine 3D.gif
Systematic (IUPAC) name
3-(5H-dibenzo[a,d]cyclohepten-5-ylidene)- N,N-dimethyl-1-propanamine
Clinical data
Trade names Amrix (former Flexeril)
AHFS/ monograph
MedlinePlus a682514
Pregnancy cat. Category B
Legal status Prescription only
Routes Oral
Pharmacokinetic data
Bioavailability 33% to 55% [1][2]
Metabolism hepatic
Half-life 18 hours (range 8–37 hours; n=18)
Excretion renal
CAS number 303-53-7 YesY
ATC code M03BX08
PubChem CID 2895
DrugBank DB00924
ChemSpider 2792 YesY
KEGG D07758 YesY
Chemical data
Formula C20H21N 
Mol. mass 275.387 g/mol
 YesY (what is this?)  (verify)

Cyclobenzaprine, brand names Amrix, Flexeril and Fexmid, is a muscle relaxant medication used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions.[3] It is the best-studied drug for this application,[4] it has also been used off-label for fibromyalgia treatment.[5] A new bedtime formulation of cyclobenzaprine is under development for the management of fibromyalgia syndrome.[6]