Chlorzoxazone


Concise Prescribing Info
Indications/Uses
Painful muscle spasm associated w/ musculoskeletal conditions.
Dosage/Direction for Use
Adult : PO Initial: 500 mg 3-4 times/day, may reduce to 250 mg 3-4 times/day. Max: 750 mg 3-4 times/day.
Dosage Details
Oral
Painful muscle spasm associated with musculoskeletal conditions
Adult: Initially, 500 mg 3-4 times daily, subsequently reduce to 250 mg 3-4 times daily if improvement occurs. Max: 750 mg 3-4 times daily.
Hepatic Impairment
Contraindicated.
Administration
Should be taken with food.
Contraindications
Hepatic impairment.
Special Precautions
Patient w/ history of liver disease, porphyria. Pregnancy.
Adverse Reactions
Significant: Elevated liver enzymes (i.e. ALT, AST, bilirubin, alkaline phosphatase).
Nervous: Drowsiness, dizziness, headache, light-headedness, malaise, overstimulation.
GI: Anorexia, nausea, vomiting, heartburn, abdominal distress, constipation, diarrhoea.
Hepatic: Jaundice.
Genitourinary: Urine discolouration.
Dermatologic: Rashes, petechiae, ecchymosis, urticaria, pruritus.
Potentially Fatal: Rarely, hepatocellular toxicity.
Patient Counseling Information
This drug may cause CNS depression, if affected, do not drive or operate machinery. This drug may cause orange or reddish-purple urine colouration.
MonitoringParameters
Monitor LFT periodically; assess signs or symptoms of hepatotoxicity.
Overdosage
Symptoms: Nausea, vomiting, diarrhoea, dizziness, drowsiness, headache, light-headedness, malaise, sluggishness, loss of muscle tone, decreased or absent deep tendon reflexes, hypotension, resp depression. Management: Supportive treatment. Employ gastric lavage or induce emesis, followed by admin of activated charcoal. Maintain adequate airway, assisted respiration, and may treat hypotension w/ cautious admin of vasopressor agent (e.g. norepinephrine), if necessary.
Drug Interactions
Enhanced CNS effect w/ other CNS depressants. Increased serum concentration w/ disulfiram, isoniazid.
Food Interaction
Enhanced CNS depression w/ alcohol.
Action
Description: Chlorzoxazone is a centrally acting skeletal muscle relaxant w/ sedative effects. It inhibits polysynaptic reflex arcs on the spinal cord and subcortical areas of the brain, thereby reducing skeletal muscle spasm w/ increased mobility of the muscle and relief of pain.
Onset: W/in 1 hr.
Duration: 3-4 hr.
Pharmacokinetics:
Absorption: Rapidly and completely absorbed from the GI tract. Time to peak plasma concentration: Approx 1-2 hr.
Metabolism: Rapidly metabolised in the liver by CYP2E1 enzyme via glucuronidation to an inactive metabolite, 6-hydroxychlorzoxazone.
Excretion: Via urine (mainly as glucuronide metabolite, <1% as unchanged drug). Elimination half-life: Approx 1 hr.
Chemical Structure

Chemical Structure Image
Chlorzoxazone

Source: National Center for Biotechnology Information. PubChem Database. Chlorzoxazone, CID=2733, https://pubchem.ncbi.nlm.nih.gov/compound/Chlorzoxazone (accessed on Jan. 21, 2020)

Storage
Store between 20-25°C.
MIMS Class
ATC Classification
M03BB03 - chlorzoxazone ; Belongs to the class of oxazol, thiazine, and triazine derivative agents. Used as centrally-acting muscle relaxants.
References
Anon. Chlorzoxazone (Briggs Drugs in Pregnancy and Lactation). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 22/03/2017.

Anon. Chlorzoxazone. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 23/02/2017.

Buckingham R (ed). Chlorzoxazone. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 23/02/2017.

Chlorzoxazone Tablet (Actavis Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 23/02/2017.

McEvoy GK, Snow EK, Miller J et al (eds). Chlorzoxazone. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 23/02/2017.

Disclaimer: This information is independently developed by MIMS based on Chlorzoxazone from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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