U.S. Department of Health & Human Services Divider Arrow National Institutes of Health Divider Arrow NCATS

Details

Stereochemistry ACHIRAL
Molecular Formula C7H4ClNO2
Molecular Weight 169.565
Optical Activity NONE
Defined Stereocenters 0 / 0
E/Z Centers 0
Charge 0

SHOW SMILES / InChI
Structure of Chlorzoxazone

SMILES

ClC1=CC2=C(OC(=O)N2)C=C1

InChI

InChIKey=TZFWDZFKRBELIQ-UHFFFAOYSA-N
InChI=1S/C7H4ClNO2/c8-4-1-2-6-5(3-4)9-7(10)11-6/h1-3H,(H,9,10)

HIDE SMILES / InChI

Description
Curator's Comment: description was created based on several sources, including https://www.ncbi.nlm.nih.gov/mesh/68002753

Chlorzoxazone is a centrally acting central muscle relaxant with sedative properties. It is claimed to inhibit muscle spasm by exerting an effect primarily at the level of the spinal cord and subcortical areas of the brain where it inhibits multisynaptic reflex arcs involved in producing and maintaining skeletal muscle spasm of varied etiology. The clinical result is a reduction of the skeletal muscle spasm with relief of pain and increased mobility of the involved muscles. Chlorzoxazone is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. The mode of action of this drug has not been clearly identified, but may be related to its sedative properties. Chlorzoxazone does not directly relax tense skeletal muscles in man.

Originator

Curator's Comment: Marsh, D.F.; US. Patent 2,895,877; July 21, 1959; assigned to McNeil Laboratories, Inc.

Approval Year

Targets

Targets

Conditions

Conditions

ConditionModalityTargetsHighest PhaseProduct
Primary
CHLORZOXAZONE

Approved Use

INDICATIONS & USAGE SECTION Chlorzoxazone is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. The mode of action of this drug has not been clearly identified, but may be related to its sedative properties. Chlorzoxazone does not directly relax tense skeletal muscles in man.

Launch Date

1988
Cmax

Cmax

ValueDoseCo-administeredAnalytePopulation
15 μg/mL
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: HEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
12.2 μg/mL
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
5.2 μg/mL
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
3.45 μg/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
0.2 μg/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
6-HYDROXYCHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
5.1 μg/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered: QUERCETIN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
0.14 μg/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered: QUERCETIN
6-HYDROXYCHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
36.3 μg/mL
750 mg single, oral
dose: 750 mg
route of administration: Oral
experiment type: SINGLE
co-administered: ACETAMINOPHEN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
AUC

AUC

ValueDoseCo-administeredAnalytePopulation
43.5 mg × h/L
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: HEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
32.8 μg × h/mL
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
15.7 μg × h/mL
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
9.86 μg × h/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
0.95 μg × h/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
6-HYDROXYCHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
16.69 μg × h/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered: QUERCETIN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
0.64 μg × h/mL
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered: QUERCETIN
6-HYDROXYCHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
4084 μg × h/mL
750 mg single, oral
dose: 750 mg
route of administration: Oral
experiment type: SINGLE
co-administered: ACETAMINOPHEN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
T1/2

T1/2

ValueDoseCo-administeredAnalytePopulation
1.1 h
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: HEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
1.2 h
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
1.4 h
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
1.21 h
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
1.65 h
250 mg single, oral
dose: 250 mg
route of administration: Oral
experiment type: SINGLE
co-administered: QUERCETIN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
1.12 h
750 mg single, oral
dose: 750 mg
route of administration: Oral
experiment type: SINGLE
co-administered: ACETAMINOPHEN
CHLORZOXAZONE plasma
Homo sapiens
population: HEALTHY
age: ADULT
sex: MALE
food status: FASTED
Funbound

Funbound

ValueDoseCo-administeredAnalytePopulation
3.9%
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: HEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
4%
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
3.2%
500 mg single, oral
dose: 500 mg
route of administration: Oral
experiment type: SINGLE
co-administered:
CHLORZOXAZONE serum
Homo sapiens
population: UNHEALTHY
age: ADULT
sex: FEMALE / MALE
food status: FED
Overview

Overview

CYP3A4CYP2C9CYP2D6hERG

OverviewOther

Other InhibitorOther SubstrateOther Inducer



Drug as victim
PubMed

PubMed

TitleDatePubMed
ATP release triggered by activation of the Ca2+-activated K+ channel in human airway Calu-3 cells.
2004-03
Effects of cigarette smoking and carbon monoxide on chlorzoxazone and caffeine metabolism.
2003-11
Mechanism-based inhibition of human liver microsomal cytochrome P450 1A2 by zileuton, a 5-lipoxygenase inhibitor.
2003-11
GYKI-47261, a new AMPA [2-amino-3-(3-hydroxymethylisoxazole-4-yl)propionic acid] antagonist, is a CYP2E1 inducer.
2003-11
CYP2E1 regulation by benzene and other small organic chemicals in rat liver and peripheral lymphocytes.
2003-09-15
Simultaneous determination of aspirin and isosorbide 5-mononitrate in formulation by reversed phase high pressure liquid chromatography.
2003-08-21
Maintenance of liver functions in rat hepatocytes cultured as spheroids in a rotating wall vessel.
2003-08-02
Phorbol ester induces CYP2E1 in astrocytes, through a protein kinase C- and tyrosine kinase-dependent mechanism.
2003-08
Effects of glucose on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate.
2003-08
CYP2E1 activity before and after weight loss in morbidly obese subjects with nonalcoholic fatty liver disease.
2003-08
Rates of metabolism of chlorzoxazone, dextromethorphan, 7-ethoxycoumarin, imipramine, quinidine, testosterone and verapamil by fresh and cryopreserved rat liver slices, and some comparisons with microsomes.
2003-08
Characterization of vectorial chloride transport pathways in the human pancreatic duct adenocarcinoma cell line HPAF.
2003-08
Differential inhibition of human cytochrome P450 enzymes by epsilon-viniferin, the dimer of resveratrol: comparison with resveratrol and polyphenols from alcoholized beverages.
2003-07-18
Effects of recombinant human growth hormone on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate.
2003-06-06
Diterpene quinone tanshinone IIA selectively inhibits mouse and human cytochrome p4501A2.
2003-06
Functional characterization of three human cytochrome p450 2E1 variants with amino acid substitutions.
2003-06
How useful is the "cocktail approach" for evaluating human hepatic drug metabolizing capacity using cytochrome P450 phenotyping probes in vivo?
2003-06
Effects of acute renal failure on the pharmacokinetics of chlorzoxazone in rats.
2003-06
Cytochrome P450 expression and testosterone metabolism in the liver of deer.
2003-05-01
Construction and assessment of models of CYP2E1: predictions of metabolism from docking, molecular dynamics, and density functional theoretical calculations.
2003-04-24
Kinetic study of alkaline induced hydrolysis of the skeletal muscle relaxant chlorzoxazone using ratio spectra first derivative spectrophotometry.
2003-04
The cytochrome P-450 isoenzyme CYP2E1 in the biological processing of industrial chemicals: consequences for occupational and environmental medicine.
2003-04
Cytochrome P450 2E1 genotype and the susceptibility to antituberculosis drug-induced hepatitis.
2003-04
Lipopolysaccharide-mediated modulation of cytochromes P450 in Stat1 null mice.
2003-04
Isozyme-specific induction of low-dose aspirin on cytochrome P450 in healthy subjects.
2003-03
Pharmacokinetics of intravenous chlorzoxazone in rats with dehydration and rehydration: effects of food intakes.
2003-03
Hepatic cytochrome P450 2E1 activity in nondiabetic patients with nonalcoholic steatohepatitis.
2003-03
Metabolism of chloroform in the human liver and identification of the competent P450s.
2003-03
Study of the fragmentation mechanism of protonated 6-hydroxychlorzoxazone: application in simultaneous analysis of CYP2E1 activity with major human cytochrome P450s.
2003-02-01
Unexpected down-regulation of the hIK1 Ca2+-activated K+ channel by its opener 1-ethyl-2-benzimidazolinone in HaCaT keratinocytes. Inverse effects on cell growth and proliferation.
2003-01-31
Determination of 6-hydroxychlorzoxazone and chlorzoxazone in porcine microsome samples.
2003-01-25
Stimulatory effects of chlorzoxazone, a centrally acting muscle relaxant, on large conductance calcium-activated potassium channels in pituitary GH3 cells.
2003-01-03
Essential requirements for substrate binding affinity and selectivity toward human CYP2 family enzymes.
2003-01-01
Diabetes mellitus increases the in vivo activity of cytochrome P450 2E1 in humans.
2003-01
Validated HPLC method for determination of chlorzoxazone in human serum and its application in a clinical pharmacokinetic study.
2002-12
Potentiation of 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123)-induced liver toxicity by ethanol in guinea-pigs.
2002-12
Evaluation of cytochrome P450 probe substrates commonly used by the pharmaceutical industry to study in vitro drug interactions.
2002-12
Conformational changes in nitric oxide synthases induced by chlorzoxazone and nitroindazoles: crystallographic and computational analyses of inhibitor potency.
2002-11-26
Monolithic silica rod liquid chromatography with ultraviolet or fluorescence detection for metabolite analysis of cytochrome P450 marker reactions.
2002-11-25
[Simultaneous determination of three probe drugs by reversed-phase high performance liquid chromatography].
2002-11
Phenotype distribution and gender-related differences of CYP2E1 activity in a Chinese population.
2002-11
Inhibition of cytochrome P450 2E1 by propofol in human and porcine liver microsomes.
2002-10-01
Cytochrome P450 2E1 expression induces hepatocyte resistance to cell death from oxidative stress.
2002-10
Plasma levels of TNF-alpha and IL-6 are inversely related to cytochrome P450-dependent drug metabolism in patients with congestive heart failure.
2002-10
Metabolizing enzyme localization and activities in the first trimester human placenta: the effect of maternal and gestational age, smoking and alcohol consumption.
2002-10
Watercress has no Importance for the elimination of ethanol by CYP2E1 inhibition.
2002-09
Cytochrome P450 2E1 and 3A activities do not differ between Mexicans and European Americans.
2002-09
Cytochrome P450 phenotypic ratios for predicting herb-drug interactions in humans.
2002-09
Mechanism of aerobic transformation of carbon tetrachloride by poplar cells.
2002
Fondaparinux sodium is not metabolised in mammalian liver fractions and does not inhibit cytochrome P450-mediated metabolism of concomitant drugs.
2002
Patents

Sample Use Guides

One tablet three or four times daily. If adequate response is not obtained with this dose, it may be increased to one and one-half tablets (750 mg) three or four times daily. As improvement occurs dosage can usually be reduced.
Route of Administration: Oral
Chlorzoxazone did not affect the tension of the rat thoracic artery rings at rest, but relaxed the precontraction induced by 1 uM noradrenaline in an endothelium independent manner. Preincubation with chlorzoxazone also antagonized the contraction induced by 1 uM noradrenaline or 25 mM KCl.
Name Type Language
Chlorzoxazone
INN   JAN   MART.   MI   ORANGE BOOK   USP   USP-RS   VANDF   WHO-DD  
INN  
Official Name English
PARAFLEX
Preferred Name English
CHLORZOXAZONE [MART.]
Common Name English
chlorzoxazone [INN]
Common Name English
Chlorzoxazone [WHO-DD]
Common Name English
CHLORZOXAZONE [USP-RS]
Common Name English
5-Chloro-2-benzoxazolinone
Systematic Name English
STRIFON
Brand Name English
CHLORZOXAZONE [JAN]
Common Name English
CHLORZOXAZONE [USP IMPURITY]
Common Name English
CHLORZOXAZONE [MI]
Common Name English
CHLORZOXAZONE [ORANGE BOOK]
Common Name English
PARAFON
Brand Name English
CHLORZOXAZONE [VANDF]
Common Name English
CHLORZOXAZONE [USP MONOGRAPH]
Common Name English
2(3H)-BENZOXAZOLONE, 5-CHLORO-
Systematic Name English
Classification Tree Code System Code
LIVERTOX NBK548137
Created by admin on Mon Mar 31 21:27:42 GMT 2025 , Edited by admin on Mon Mar 31 21:27:42 GMT 2025
NDF-RT N0000175737
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WHO-VATC QM03BB53
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WHO-ATC M03BB03
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WHO-VATC QM03BB03
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WHO-ATC M03BB53
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NDF-RT N0000175730
Created by admin on Mon Mar 31 21:27:42 GMT 2025 , Edited by admin on Mon Mar 31 21:27:42 GMT 2025
WHO-ATC M03BB73
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NCI_THESAURUS C29696
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WHO-VATC QM03BB73
Created by admin on Mon Mar 31 21:27:42 GMT 2025 , Edited by admin on Mon Mar 31 21:27:42 GMT 2025
Code System Code Type Description
ECHA (EC/EINECS)
202-403-9
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PRIMARY
EPA CompTox
DTXSID9022813
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PRIMARY
MESH
D002753
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PRIMARY
FDA UNII
H0DE420U8G
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PRIMARY
DAILYMED
H0DE420U8G
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PRIMARY
IUPHAR
2322
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PRIMARY
CAS
95-25-0
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PRIMARY
EVMPD
SUB06215MIG
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PRIMARY
WIKIPEDIA
CHLORZOXAZONE
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PRIMARY
RXCUI
2410
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PRIMARY RxNorm
ChEMBL
CHEMBL1371
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PRIMARY
CHEBI
3655
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PRIMARY
INN
748
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PRIMARY
MERCK INDEX
m3471
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PRIMARY Merck Index
RS_ITEM_NUM
1130505
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PRIMARY
SMS_ID
100000081896
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PRIMARY
NCI_THESAURUS
C28926
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PRIMARY
DRUG CENTRAL
626
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PRIMARY
PUBCHEM
2733
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PRIMARY
DRUG BANK
DB00356
Created by admin on Mon Mar 31 21:27:42 GMT 2025 , Edited by admin on Mon Mar 31 21:27:42 GMT 2025
PRIMARY