Chemistry:Chlorzoxazone

Short description: Muscle relaxant

Chlorzoxazone

Clinical data
Trade names	Lorzone, Paraflex, Muscol
AHFS/Drugs.com	Monograph
MedlinePlus	a682577
License data	US DailyMed: Chlorzoxazone
Pregnancy category	US: N (Not classified yet)
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 Y
PubChem CID	2733
IUPHAR/BPS	2322
DrugBank	DB00356 Y
ChemSpider	2632 Y
UNII	H0DE420U8G
KEGG	D00771 Y
ChEBI	CHEBI:3655 Y
ChEMBL	ChEMBL1371 Y
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) Y Key:TZFWDZFKRBELIQ-UHFFFAOYSA-N Y
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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, and liver dysfunction. When used with acetaminophen it has added risk of hepatotoxicity.

It is available as a generic medication.

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. The mechanism of action of chlorzoxazone is thought to act on GABA_A and GABA_B receptors and voltage-gated calcium channels to a degree. General central nervous system depression is the only currently accepted aspect to its medical benefits. 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.

See also

• Zoxazolamine

Further reading

• "Chlorzoxazone inhibit contraction of rat thoracic aorta". Eur J Pharmacol 545 (2–3): 161–6. 2006. doi:10.1016/j.ejphar.2006.06.063. PMID 16859676. 
• "Effect of high-dose aspirin on CYP2E1 activity in healthy subjects measured using chlorzoxazone as a probe". J Clin Pharmacol 46 (1): 109–14. 2006. doi:10.1177/0091270005282635. PMID 16397290. 
• "Chlorzoxazone metabolism is increased in fasted Sprague-Dawley rats". J Pharm Pharmacol 58 (1): 51–61. 2006. doi:10.1211/jpp.58.1.0007. PMID 16393464. 

External links

• "Chlorzoxazone". Drug Information Portal. U.S. National Library of Medicine. https://druginfo.nlm.nih.gov/drugportal/name/chlorzoxazone. 
• Chloroxazone Safety Data Sheet
• D.F. Marsh, U.S. Patent 2,895,877 (1959)