Chlorzoxazone Explained

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. In rare cases, chlorzoxazone may cause severe liver dysfunction.^[1] On the other hand, chlorzoxazone may reduce the liver toxicity of acetaminophen by competitive inhibition.^[2]

It is available as a generic medication.^[3]

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

• Dong DL, Luan Y, Feng TM, Fan CL, Yue P, Sun ZJ, Gu RM, Yang BF . Chlorzoxazone inhibits contraction of rat thoracic aorta . European Journal of Pharmacology . 545 . 2-3 . 161–166 . September 2006 . 16859676 . 10.1016/j.ejphar.2006.06.063 .
• Park JY, Kim KA, Park PW, Ha JM . Effect of high-dose aspirin on CYP2E1 activity in healthy subjects measured using chlorzoxazone as a probe . Journal of Clinical Pharmacology . 46 . 1 . 109–114 . January 2006 . 16397290 . 10.1177/0091270005282635 . 20092326 .
• Wan J, Ernstgård L, Song BJ, Shoaf SE . Chlorzoxazone metabolism is increased in fasted Sprague-Dawley rats . The Journal of Pharmacy and Pharmacology . 58 . 1 . 51–61 . January 2006 . 16393464 . 1388188 . 10.1211/jpp.58.1.0007 .

External links

• Web site: Chlorzoxazone . U.S. National Library of Medicine . Drug Information Portal .
• Chloroxazone Safety Data Sheet
• D.F. Marsh, (1959)

Notes and References

1. Book: LiverTox . Chlorzoxazone . National Institute of Diabetes and Digestive and Kidney Diseases . 2017-01-30 . 31643467 . https://www.ncbi.nlm.nih.gov/books/NBK548137/ . 2024-05-10.
2. Pingili RB, Vemulapalli S, Gadamsetty MV, Presingu D, Katuri R, Rachamsetty V, Kilaru NB . Chlorzoxazone reduced the paracetamol-induced toxicity via competitive inhibition of CYP2E1-mediated metabolism . Future Journal of Pharmaceutical Sciences . 9 . 1 . 2023-04-17 . 2314-7253 . 10.1186/s43094-023-00484-2 . free.
3. Web site: Competitive Generic Therapy Approvals . U.S. Food and Drug Administration (FDA) . 29 June 2023 . 29 June 2023 . 29 June 2023 . https://web.archive.org/web/20230629233651/https://www.fda.gov/drugs/generic-drugs/competitive-generic-therapy-approvals . live .