New Drug Approvals

Home » GENERICS » Chlorzoxazone




Read all about Organic Spectroscopy on ORGANIC SPECTROSCOPY INTERNATIONAL 


Recent Posts

Blog Stats

  • 3,993,191 hits

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 2,735 other followers

add to any




Chlorzoxazone; Paraflex; Chlorzoxazon; Myoflexin; Solaxin; 95-25-0;


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. (From Martindale, The Extra Pharmacopoea, 30th ed, p1202)

Property Value Source
melting point 191-191.5 Marsh, D.F.; US. Patent 2,895,877; July 21, 1959; assigned to McNeil Laboratories, Inc.

Marsh, D.F.; US. Patent 2,895,877; July 21, 1959; assigned to McNeil Laboratories, Inc.

Chlorzoxazone (Paraflex) 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 as Muscol or 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.


The Chlorzoxazone with CAS registry number of 95-25-0 is also known as 2-Benzoxazolol, 5-chloro-. The IUPAC name is 5-Chloro-3H-1,3-benzoxazol-2-one. It belongs to product categories of Oxazole&Isoxazole; Intermediates & Fine Chemicals; Pharmaceuticals. Its EINECS registry number is 202-403-9. In addition, the formula is C7H4ClNO2 and the molecular weight is 169.57. This chemical should be stored in sealed containers in cool, dry place and away from oxidizing agents.

Physical properties about Chlorzoxazone are: (1)ACD/LogP: 2.19; (2)# of Rule of 5 Violations: 0; (3)ACD/LogD (pH 5.5): 2.19; (4)ACD/LogD (pH 7.4): 2.15; (5)ACD/BCF (pH 5.5): 27.16; (6)AACD/KOC (pH 7.4): 340.79; (7)#H bond acceptors: 3; (8)#H bond donors: 1; (9)#Freely Rotating Bonds: 0; (10)Index of Refraction: 1.603; (11)Molar Refractivity: 39.18 cm3; (12)Molar Volume: 114 cm3; (13)Surface Tension: 50 dyne/cm; (14)Density: 1.486 g/cm3; (15)Flash Point: 157.5 °C; (16)Enthalpy of Vaporization: 60.3 kJ/mol; (17)Boiling Point: 336.9 °C at 760 mmHg; (18)Vapour Pressure: 5.58E-05 mmHg at 25 °C.

Preparation of Chlorzoxazone: it is prepared by reaction of 5-chloro-2-hydroxy-benzamide. The reaction needs reagents iodobenzene diacetate, KOH and solvent methanol at the temperature of 0 °C. The yield is about 68%.


Systematic (IUPAC) name
Clinical data
Trade names Parafonforte
AHFS/ monograph
MedlinePlus a682577
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 95-25-0 Yes
ATC code M03BB03
PubChem CID: 2733
DrugBank DB00356 Yes
ChemSpider 2632 Yes
KEGG D00771 Yes
ChEBI CHEBI:3655 Yes
Chemical data
Formula C7H4ClNO2
Molecular mass 169.565 g/mol


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.


Follow New Drug Approvals on

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 2,735 other followers


DR ANTHONY MELVIN CRASTO, Born in Mumbai in 1964 and graduated from Mumbai University, Completed his Ph.D from ICT, 1991,Matunga, Mumbai, India, in Organic Chemistry, The thesis topic was Synthesis of Novel Pyrethroid Analogues, Currently he is working with GLENMARK LIFE SCIENCES LTD, Research Centre as Principal Scientist, Process Research (bulk actives) at Mahape, Navi Mumbai, India. Total Industry exp 30 plus yrs, Prior to joining Glenmark, he has worked with major multinationals like Hoechst Marion Roussel, now Sanofi, Searle India Ltd, now RPG lifesciences, etc. He has worked with notable scientists like Dr K Nagarajan, Dr Ralph Stapel, Prof S Seshadri, Dr T.V. Radhakrishnan and Dr B. K. Kulkarni, etc, He did custom synthesis for major multinationals in his career like BASF, Novartis, Sanofi, etc., He has worked in Discovery, Natural products, Bulk drugs, Generics, Intermediates, Fine chemicals, Neutraceuticals, GMP, Scaleups, etc, he is now helping millions, has 9 million plus hits on Google on all Organic chemistry websites. His friends call him Open superstar worlddrugtracker. His New Drug Approvals, Green Chemistry International, All about drugs, Eurekamoments, Organic spectroscopy international, etc in organic chemistry are some most read blogs He has hands on experience in initiation and developing novel routes for drug molecules and implementation them on commercial scale over a 30 PLUS year tenure till date June 2021, Around 35 plus products in his career. He has good knowledge of IPM, GMP, Regulatory aspects, he has several International patents published worldwide . He has good proficiency in Technology transfer, Spectroscopy, Stereochemistry, Synthesis, Polymorphism etc., He suffered a paralytic stroke/ Acute Transverse mylitis in Dec 2007 and is 90 %Paralysed, He is bound to a wheelchair, this seems to have injected feul in him to help chemists all around the world, he is more active than before and is pushing boundaries, He has 9 million plus hits on Google, 2.5 lakh plus connections on all networking sites, 90 Lakh plus views on dozen plus blogs, 233 countries, 7 continents, He makes himself available to all, contact him on +91 9323115463, email, Twitter, @amcrasto , He lives and will die for his family, 90% paralysis cannot kill his soul., Notably he has 33 lakh plus views on New Drug Approvals Blog in 233 countries...... , He appreciates the help he gets from one and all, Friends, Family, Glenmark, Readers, Wellwishers, Doctors, Drug authorities, His Contacts, Physiotherapist, etc

Personal Links

View Full Profile →



Follow my blog with Bloglovin The title of your home page You could put your verification ID in a comment Or, in its own meta tag Or, as one of your keywords Your content is here. The verification ID will NOT be detected if you put it here.
%d bloggers like this: