Chlorzoxazone

Oral
Painful muscle spasm associated with musculoskeletal conditions

Contraindicated.

Should be taken with food.

Hepatic impairment.

Patient w/ history of liver disease, porphyria. Pregnancy.

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.

This drug may cause CNS depression, if affected, do not drive or operate machinery. This drug may cause orange or reddish-purple urine colouration.

Monitor LFT periodically; assess signs or symptoms of hepatotoxicity.

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.

Enhanced CNS effect w/ other CNS depressants. Increased serum concentration w/ disulfiram, isoniazid.

Enhanced CNS depression w/ alcohol.

Description:
Mechanism of Action: 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.

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

Store between 20-25°C.

Muscle Relaxants

M03BB03 - chlorzoxazone ; Belongs to the class of oxazol, thiazine, and triazine derivative agents. Used as centrally-acting muscle relaxants.

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.