Cyclobenzaprine HCl (also known as MK130; Flexeril), the hydrochloride salt of Cyclobenzaprine, is a potent muscle relaxant by blocking pain sensations, used as a medication for the treatment of skeletal muscle spasms and associated pain in acute musculoskeletal conditions. Cyclobenzaprine has a 62 nM Ki value and binds to 5-HT2 receptors strongly. Cyclobenzaprine has a Ki value of 2900 nM when it binds to the 5-HT1 receptor. The administration of cyclobenzaprine at a dose of 1 mg/kg resulted in a decrease in the discharge rate of 16 out of 21 spontaneously active neurons; two neurons exhibited no response, and three neurons showed an increased rate.

Physicochemical Properties

Molecular Formula	C20H22CLN
Molecular Weight	311.85
Exact Mass	311.144
Elemental Analysis	C, 77.03; H, 7.11; Cl, 11.37; N, 4.49
CAS #	6202-23-9
Related CAS #	Cyclobenzaprine-d3 hydrochloride; 1184983-42-3; Cyclobenzaprine-13C,d3 hydrochloride; 1261394-10-8; Cyclobenzaprine-d6 hydrochloride; 2748492-38-6
PubChem CID	22576
Appearance	White to off-white crystalline powder
Boiling Point	405.9ºC at 760 mmHg
Melting Point	216-218ºC
Flash Point	9℃
LogP	5.355
Hydrogen Bond Donor Count	1
Hydrogen Bond Acceptor Count	1
Rotatable Bond Count	3
Heavy Atom Count	22
Complexity	365
Defined Atom Stereocenter Count	0
SMILES	Cl[H].N(C([H])([H])[H])(C([H])([H])[H])C([H])([H])C([H])([H])/C(/[H])=C1/C2=C([H])C([H])=C([H])C([H])=C2C([H])=C([H])C2=C([H])C([H])=C([H])C([H])=C/12
InChi Key	VXEAYBOGHINOKW-UHFFFAOYSA-N
InChi Code	InChI=1S/C20H21N.ClH/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;1H
Chemical Name	N,N-dimethyl-3-(2-tricyclo[9.4.0.03,8]pentadeca-1(15),3,5,7,9,11,13-heptaenylidene)propan-1-amine;hydrochloride
Synonyms	MK-130 HCl; Lisseril; Proeptatriene; MK130 hydrochloride; MK 130; Flexeril; Proheptatriene; Proheptatrien
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

Targets	5-HT2 receptor
ln Vitro	In vitro activity: Cyclobenzaprine is an antagonist and inhibitor of the 5-HT2 receptor; in certain articles, cyclobenzaprine hydrochloride was employed as the compound for cyclobenzaprine research. The monosynaptic reflex (MSR) enhancement caused by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) is inhibited by cyclobenzaprine. With a Ki value of 62 nM, cyclobenzaprine binds to 5-HT2 receptors very strongly. Cyclobenzaprine has a Ki value of 2900 nM when it binds to the 5-HT1 receptor.
ln Vivo	Cyclobenzaprine treatment raised the mono- and polysynaptic reflex amplitudes in rats receiving DOI therapy to roughly 150% of the control level. Cyclobenzaprine hydrochloride (300 µg/kg, i.v.) dramatically decreased the amplitude of mono- and polysynaptic reflex potentials in intact (nonspinalized) rats. The maximum effect of cyclobenzaprine was achieved within 15 minutes of administration, and this effect lasted for more than 60 minutes. Cyclobenzaprine inhibited the amplitudes of the mono- and polysynaptic reflexes by approximately 20% and 40%, respectively. 5-HT depletion significantly inhibited the depression of mono- and polysynaptic reflex potentials in intact rats induced by cyclobenzaprine hydrochloride (300 µg/kg, i.v.). In control rats, the mono- and polysynaptic reflex amplitudes were reduced to approximately 40–50% of the preadministration value 15 minutes after cyclobenzaprine was administered.
Enzyme Assay	Cyclobenzaprine Hcl is a depressant of the central nervous system (CNS) and a relaxant of skeletal muscle. Target: Receptor 2A of 5-HT Cyclobenzaprine is a central nervous system (CNS) depressant as well as a skeletal muscle relaxant. Cyclobenzaprine was believed to be an agonist of alpha 2-adrenoceptors that decreased the activity of descending noradrenergic neurons, hence reducing muscle tone. The alpha 2-adrenoceptor antagonists yohimbine and idazoxan did not block the dose-dependent reduction of the monosynaptic reflex amplitude caused by cyclobenzaprine. Cyclobenzaprine-induced monosynaptic reflex depression was not attenuated by noradrenergic neuronal lesions produced by 6-hydroxydopamine. Since clobenzaprine inhibits the serotonergic, not the noradrenergic, descending systems in the spinal cord, it has a muscle-relaxing effect. It is a 5-HT2 receptor antagonist.
Cell Assay	Cyclobenzaprine at a dose of 1 mg/kg reduced the discharge rate of 16 out of 21 spontaneously active neurons; two neurons did not respond, and three neurons showed an increase in the rate. Though it varied greatly, the decrease was always ≥ 25%. The decrease amounts were 100% in three cases. Under cyclobenzaprine, the cell response in every instance happened very soon after the MSR response.
Animal Protocol	C57BL/6 mice (8-10 weeks old) 1 mg/kg Intraperitoneal injection, daily, for 5 days
References	[1]. Eur J Pharmacol . 1996 Sep 5;311(1):29-35. [2]. Eur J Pharmacol . 2003 Jan 1;458(1-2):91-9.
Additional Infomation	Cyclobenzaprine hydrochloride is the hydrochloride salt of cyclobenzaprine. A centrally acting skeletal muscle relaxant, it is used in the symptomatic treatment of painful muscle spasm. It has a role as a muscle relaxant and an antidepressant. It contains a cyclobenzaprine. It derives from a hydride of a dibenzo[a,d][7]annulene. Cyclobenzaprine Hydrochloride is a centrally acting muscle relaxant, chemically similar to amitriptyline hydrochloride with antidepressant activity. The exact mechanism of action of cyclobenzaprine hydrochloride has not been fully determined. However, it primarily acts at the brain stem to reduce tonic somatic motor activity, influencing both gamma and alpha motor neurons. This leads to a reduction in muscle spasms. See also: Cyclobenzaprine (has active moiety).

Solubility Data

Solubility (In Vitro)

DMSO: 50~62 mg/mL (160.3~198.8 mM) Water: ~62 mg/mL (~198.8 mM) Ethanol: N/A

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.02 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL. Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 2: ≥ 2.5 mg/mL (8.02 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Solubility in Formulation 3: ≥ 2.5 mg/mL (8.02 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly. Solubility in Formulation 4: 110 mg/mL (352.73 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	3.2067 mL	16.0333 mL	32.0667 mL
	5 mM	0.6413 mL	3.2067 mL	6.4133 mL
	10 mM	0.3207 mL	1.6033 mL	3.2067 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.