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Title: Chlorzoxazone  
Author: World Heritage Encyclopedia
Language: English
Subject: Thiocolchicoside, Styramate, Flopropione, Lorbamate, Cyclarbamate
Collection: Benzoxazoles, Carbamates, Chloroarenes, Muscle Relaxants, Organochlorides
Publisher: World Heritage Encyclopedia


Systematic (IUPAC) name
Clinical data
Trade names Parafonforte
Routes of
Pharmacokinetic data
Bioavailability well absorbed
Protein binding 13–18%
Metabolism hepatic
Biological half-life 1.1 hr
Excretion urine (<1%)
CAS Registry Number  YesY
ATC code M03
PubChem CID:
DrugBank  YesY
ChemSpider  YesY
Chemical data
Formula C7H4ClNO2
Molecular mass 169.565 g/mol

Chlorzoxazone (INN) is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It acts on the spinal cord by depressing reflexes. It is sold under the trade names 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. Used with acetaminophen it has added risk of hepatoxicity, which is why the combination is not recommended. It can also be administered for acute pain in general and for tension headache (muscle contraction headache).


Chlorzoxazone synthesis: Mcneilab Inc, David F Marsh. U.S. Patent 2,895,877

Chlorzoxazone, 5-chloro-2-benzoxazolione, is synthesized by a hetercyclization reaction of 2-amino-4-chlorophenol with phosgene.


  • D.F. Marsh, U.S. Patent 2,895,877 (1959).
  • PARAFON DSC (chlorzoxazone) tablet, Daily Med, U.S. National Library of Medicine

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