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. Conversely, chlorzoxazone may reduce the liver toxicity of acetaminophen by competitive inhibition.
It is available as a generic medication.
Pharmacology The mechanism of action of chlorzoxazone is thought to be primarily as an opener of BKCa, SKCa and IKCa calcium-activated potassium channels.Liu YC, Lo YK, Wu SN. Stimulatory effects of chlorzoxazone, a centrally acting muscle relaxant, on large conductance calcium-activated potassium channels in pituitary GH3 cells. Brain Res. 2003 Jan 3;959(1):86-97. Masi A, Narducci R, Mannaioni G. Harnessing ionic mechanisms to achieve disease modification in neurodegenerative disorders. Pharmacol Res. 2019 Sep;147:104343. Ferraguto C, Piquemal-Lagoueillat M, Lemaire V, Moreau MM, Trazzi S, Uguagliati B, Ciani E, Bertrand SS, Louette E, Bontempi B, Pietropaolo S. Therapeutic efficacy of the BKCa channel opener chlorzoxazone in a mouse model of Fragile X syndrome. Neuropsychopharmacology. 2024 Dec;49(13):2032-2041. A Technical Guide to the Cellular Effects of Chlorzoxazone on Intracellular Calcium Signaling 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 Flindokalner (BMS-204352) Zoxazolamine
References
Further reading
External links
Chloroxazone Safety Data Sheet D.F. Marsh, (1959)