Chlorzoxazone

Summary

Chlorzoxazone (CHEMBL1371) is an approved small-molecule muscle relaxant (ATC M03BB53) targeting KCNN2 and KCNN4.

At a glance

• Status: Approved (max clinical phase 4)
• Modality: Small molecule
• ATC class: M03BB53 (+2 more)
• Targets: 2 (KCNN2, KCNN4)
• Clinical trials: 6
• Chemistry: 169.56 Da · C7H4ClNO2

Identifiers

Drug identity and classification

Field	Value
ChEMBL ID	CHEMBL1371
Name	Chlorzoxazone
Type	Small molecule
Max phase	4
FDA approved	yes
PubChem CID	2733
ChEBI	CHEBI:3655
ATC	M03BB53, M03BB03, M03BB73
Molecular formula	C7H4ClNO2
Molecular weight	169.56
InChIKey	TZFWDZFKRBELIQ-UHFFFAOYSA-N

SMILES: C1=CC2=C(C=C1Cl)NC(=O)O2

IUPAC name: 5-chloro-3H-1,3-benzoxazol-2-one

ChEBI definition: A member of the class of 1,3-benzoxazoles that is 1,3-benzoxazol-2-ol in which the hydrogen atom at position 5 is substituted by chlorine. A centrally acting muscle relaxant with sedative properties, it is used for the symptomatic treatment of painful muscle spasm.

Pharmacological roles (ChEBI): muscle relaxant, sedative.

Also known as: Chlorzoxazone, Clorzoxazona, NSC-26189, Paraflex, Parafon, Parafon forte dsc, Parafon-forte, Strifon, Strifon forte dsc, chlorzoxazone, SID11110945, SID11110946

Patent coverage: 4,741 distinct patent families (16,752 SureChEMBL compound mentions), from 3 matched compound structure(s). Mentions count patents naming the compound (not distinct inventions), so promiscuous / reference molecules inflate the mention figure — families are the dedup metric.

Targets

Targets

Primary targets (GtoPdb curated mechanism): the Cancer dependency column is the DepMap CRISPR fitness signal (% of screened cell lines dependent on the target).

Gene	Target	Action	pAffinity	Cancer dependency	UniProt
KCNN2	KCa2.2		4.1	0%	Q9H2S1
KCNN4	KCa3.1	Agonist	4	0.2%	O15554

Broader ChEMBL bioactivity targets: 11 (assay-derived). Sample: Prelamin-A/C, RecQ-like DNA helicase BLM, Thrombopoietin, Alpha-2A adrenergic receptor, Thyrotropin receptor, Nitric oxide synthase 1, Cytochrome P450 1A2, Nitric oxide synthase 1, Nitric oxide synthase, inducible, Nitric oxide synthase 3.

Bioactivity

ChEMBL activities: 10 potent at pChembl ≥ 5 of 15 total. Top 30 by potency (10 = 0.1 nM, 6 = 1 µM):

Target	pChembl	Type	Value	Unit	Activity ID
LMNA	7.4	Potency	39.8	nM	CHEMBL_ACT_3661605
LMNA	7	Potency	100	nM	CHEMBL_ACT_3655224
THPO	6.9	Potency	125.9	nM	CHEMBL_ACT_4809423
THPO	6.9	Potency	125.9	nM	CHEMBL_ACT_5070434
CYP1A2	6.4	AC50	398.1	nM	CHEMBL_ACT_6042809
P29476	5.55	IC50	2794	nM	CHEMBL_ACT_7690581
CYP1A2	5.3	AC50	5012	nM	CHEMBL_ACT_6007966
ADRA2A	5.28	AC50	5200	nM	CHEMBL_ACT_25221024
TSHR	5.1	Potency	7943	nM	CHEMBL_ACT_3913404
NOS3	5.06	IC50	8700	nM	CHEMBL_ACT_87266

Target pathways

Aggregated over 2 target gene(s): KCNN2, KCNN4.

Top Reactome pathways

7 total, by targets touching each:

Pathway	Targets	Genes
Neuronal System	2	KCNN2, KCNN4
Ca2+ activated K+ channels	2	KCNN2, KCNN4
Potassium Channels	2	KCNN2, KCNN4
Sensory processing of sound	1	KCNN2
Sensory processing of sound by outer hair cells of the cochlea	1	KCNN2
Acetylcholine inhibits contraction of outer hair cells	1	KCNN2
Sensory Perception	1	KCNN2

Dominant GO biological processes

GO term	Targets
potassium ion transport	2
potassium ion transmembrane transport	2
monoatomic ion transport	2
monoatomic ion transmembrane transport	2
membrane repolarization during atrial cardiac muscle cell action potential	1
regulation of potassium ion transmembrane transport	1
monoatomic cation transmembrane transport	1
immune system process	1
calcium ion transport	1
cell volume homeostasis	1
defense response	1
stabilization of membrane potential	1
macropinocytosis	1
phospholipid translocation	1
saliva secretion	1

Indications & clinical

Indications

0 indications (0 at ChEMBL trial phase 4).

Clinical trials

Total trials: 6.

Phase distribution

Phase	Trials
PHASE4	4
PHASE1	2

Top trials by phase / activity

NCT	Phase	Status	Title
NCT07109882	PHASE4	RECRUITING	Effectiveness of Chlorzoxazone Versus Orphenadrine Citrate in Alleviating Bruxism Pain
NCT01342341	PHASE4	COMPLETED	Placebo-Controlled Cross Over Trial of Chlorzoxazone Intake
NCT01933542	PHASE4	COMPLETED	The Effect of Chlorzoxazone on Moderate to Severe Postoperative Pain After Spine Surgery
NCT02405104	PHASE4	COMPLETED	Chlorzoxazone in Hip and Knee Arthroplasty
NCT03103568	PHASE1	COMPLETED	A Study to Investigate the Potential Influence of Nitisinone on the Metabolism and the Transport of Other Drugs in Healthy Volunteers
NCT05257447	PHASE1	COMPLETED	Pharmacokinetic and Bioequivalence Comparison of Baclofen and Chlorzoxazone Administered Individually or Concurrently

Clinical evidence (CIViC)

No CIViC predictive evidence (expected for non-precision-medicine drugs).

Pharmacology

Pharmacogenomics

No CPIC/DPWG dosing guideline or drug-level clinical/variant annotations in PharmGKB for this molecule.

Related molecules

Related molecules

Molecules sharing ≥1 of this drug’s curated primary targets, merged from two biobtree sources and ranked by shared-target count, then clinical phase: ChEMBL clinical-stage candidates (development phase ≥2) and PubChem drug-class bioactivity (approved / known drugs acting on the target). Deduplicated by drug name; the drug’s own salt forms are excluded. Note: for a drug with few primary targets a shared-target match can reflect off-target / promiscuous binding rather than the same therapeutic mechanism — the phase ordering surfaces bona-fide therapeutics first.

5 molecules share ≥1 primary target. Top 5 by shared-target count:

Molecule	Source	Status	Shared targets
CLOTRIMAZOLE	ChEMBL + PubChem	Phase 4 (approved)	KCNN4
SENICAPOC	ChEMBL	Phase 3	KCNN4
CEPHARANTHINE	ChEMBL	Phase 2	KCNN2
Riluzole	PubChem	Approved	KCNN4
Tubocurarine	PubChem	Approved	KCNN2