Chlorzoxazone

Chlorzoxazone
Clinical data
Trade names	Lorzone, Paraflex, Muscol
AHFS/Drugs.com	Monograph
MedlinePlus	a682577
License data	US DailyMed: Chlorzoxazone;
Routes of; administration	By mouth
Drug class	Skeletal muscle relaxants
ATC code	M03BB03 (WHO) ;
Legal status
Legal status	US: ℞-only;
Pharmacokinetic data
Bioavailability	Well absorbed
Protein binding	13–18%
Metabolism	Hepatic
Elimination half-life	1.1 hours
Duration of action	3–4 hours
Excretion	urine (<1%)
Identifiers
	IUPAC name 5-chloro-3H-benzooxazol-2-one;
CAS Number	95-25-0 ;
PubChem CID	2733;
IUPHAR/BPS	2322;
DrugBank	DB00356 ;
ChemSpider	2632 ;
UNII	H0DE420U8G;
KEGG	D00771 ;
ChEBI	CHEBI:3655 ;
ChEMBL	ChEMBL1371 ;
CompTox Dashboard (EPA)	DTXSID9022813 ;
ECHA InfoCard	100.002.186
Chemical and physical data
Formula	C7H4ClNO2
Molar mass	169.56 g·mol−1
3D model (JSmol)	Interactive image;
	SMILES Clc2cc1c(OC(=O)N1)cc2;
	InChI InChI=1S/C7H4ClNO2/c8-4-1-2-6-5(3-4)9-7(10)11-6/h1-3H,(H,9,10) ; Key:TZFWDZFKRBELIQ-UHFFFAOYSA-N ;
	(verify)

Chlorzoxazone (INN) is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It can also be administered for acute pain in general and for tension headache (muscle contraction headache). It acts on the spinal cord by depressing reflexes. It is sold under the brand names Lorzone, Paraflex and Muscol and in combination form as Parafon Forte, a combination of chlorzoxazone and acetaminophen (paracetamol). Possible side effects include dizziness, lightheadedness, malaise, nausea, vomiting.^{[medical citation needed]} In rare cases, chlorzoxazone may cause severe liver dysfunction.^[3] On the other hand, chlorzoxazone may reduce the liver toxicity of acetaminophen by competitive inhibition.^[4]

It is available as a generic medication.^[5]

Like metaxalone, its mechanism of action is still in question. It is believed that metaxalone works by altering serotonin levels and acting as a mild MAO inhibitor.^{[medical citation needed]} The mechanism of action of chlorzoxazone is thought^{[by whom?]} to act on GABA_A and GABA_B receptors and voltage-gated calcium channels to a degree.^{[medical citation needed]} General central nervous system depression is the only currently accepted aspect to its medical benefits.^{[medical citation needed]} Elucidation of the exact mechanism of action is ongoing but there is limited study due to the existence of more effective, safe muscle relaxants (e.g., diazepam, cyclobenzaprine, tizanidine), greatly limiting the potential benefit of identifying novel compounds which share chlorzoxazone's mechanism of action.