chlorzoxazone chlorzoxazone 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, and liver dysfunction. used with acetaminophen it has added risk of hepatotoxicity. chlorzoxazoneclinical datatrade nameslorzone, paraflex ,muscolahfs/drugs.commonographmedlineplusa682577license data us dailymed: chlorzoxazone routes ofadministrationby mouthatc codem03bb03 (who) legal statuslegal status us: ℞-only pharmacokinetic databioavailabilitywell absorbedprotein binding13–18%metabolismhepaticelimination half-life1.1 hr duration of action 3-4 hrs.excretionurine (<1%)identifiers iupac name 5-chloro-3h-benzooxazol-2-one cas number95-25-0 ypubchem cid2733iuphar/bps2322drugbankdb00356 ychemspider2632 yuniih0de420u8gkeggd00771 ychebichebi:3655 ychemblchembl1371 ycomptox dashboard (epa)dtxsid9022813 echa infocard100.002.186 chemical and physical dataformulac7h4clno2molar mass169.56 g·mol−13d model (jsmol)interactive image smiles clc2cc1c(oc(=o)n1)cc2 inchi inchi=1s/c7h4clno2/c8-4-1-2-6-5(3-4)9-7(10)11-6/h1-3h,(h,9,10) ykey:tzfwdzfkrbeliq-uhfffaoysa-n y (verify) it is available as a generic medication. 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 & 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 (ex. diazepam, cyclobenzaprine, tizanidine), greatly limiting the potential benefit of identifying novel compounds which share chlorzoxazone's mechanism of action.