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Chlorzoxazone

Chlorzoxazone Chlorzoxazone
Chlorzoxazone Chlorzoxazone

Chlorzoxazone is used to relieve pain and stiffness caused by muscle strains and sprains. 

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Introduction

Chlorzoxazone is used to relieve pain and stiffness caused by muscle strains and sprains. It is a skeletal muscle relaxant that is used to treat discomfort caused by muscle spasms. It is indicated as an adjunct to rest, physical therapy and other measures for the relief of discomfort associated with acute painful musculoskeletal conditions.

Pharmacological class: Muscle Relaxant

Indications

  • Acute painful musculoskeletal conditions
  • Muscle relaxant

Pharmachologic action

Chlorzoxazone inhibits degranulation of mast cells, subsequently preventing the release of histamine and slow-reacting substance of anaphylaxis (SRS-A), mediators of type I allergic reactions. Chlorzoxazone may also reduce the release of inflammatory leukotrienes. It may act by inhibiting the calcium and potassium influx which would lead to neuronal inhibition and muscle relaxation. Chlorzoxazone acts primarily at the level of the spinal cord and subcortical areas of the brain, where it inhibits multisynaptic reflex arcs involved in producing and maintaining skeletal muscle spasms.

Dosage

Adult Dose for Muscle Spasm: 250 to 750 mg orally, 3 to 4 times a day.

Pharmacokinetics

T max of chlorzoxazone is 1 to 2 hours. It is rapidly metabolized in the liver and is excreted in the urine, primarily in a conjugated form as the glucuronide. Less than 1% of chlorzoxazone is excreted in the urine as an unchanged drug. The half-life of the drug is about 60 minutes.

Contraindications

  • Contraindicated in patients with known intolerance to the chlorzoxazone

Drug interaction

  • Lomitapide, when administered concomitantly with chlorzoxazone may increase the risk of liver problems
  • Concomitant intake of propoxyphene together with chlorzoxazone causes dizziness, drowsiness, confusion, and difficulty in concentrating
  • Using buprenorphine together with chlorzoxazone can lead to serious side effects such as respiratory distress, coma, or even death
  • Using sodium oxybate together with chlorzoxazone increases risk of drowsiness, dizziness, lightheadedness, confusion, depression, low blood pressure, slow or shallow breathing, impairment in thinking, judgment and motor coordination

Side effects

Common (affecting between 1 in10 to 1 in 100):

  • Dizziness
  • Drowsiness

 

Uncommon (affecting 1 in 100 to 1 in 1000):

  • Diarrhea
  • Throwing Up Feel
  • Headache
  • Heart burn
  • Incomplete or Infrequent Bowel Movements
  • Irritation of Stomach or Intestines

 

Very rare (affecting less than 1 in 10,000):

  • Abnormal Liver Function Tests
  • Anemia
  • Stomach/Intestine Bleeding
  • Deficiency of Granulocytes
  • Giant Hives
  • Hepatitis caused by Drugs
  • Hives
  • Itching
  • Life Threatening Allergic Reaction
  • Rash
  • Abnormal Urine Color
  • Confused
  • Hemorrhage Under the Skin
  • Memory Loss
  • Numbness and TinglingSmall Red-Purple Spots on the Skin

Precautions

  • Avoid in patients that are allergic to chlorzoxazone
  • Avoid using chlorzoxazone in patients suffering from liver disease
  • Chlorzoxazone may cause drowsiness so avoid its use during driving

Clinical evidence

One hundred and ten patients were randomly assigned to 500 mg oral chlorzoxazone or placebo in this blinded study of patients having spine surgery under general anesthesia. In the 4 h trial period analgesia consisted of IV patient-controlled analgesia (morphine bolus 2.5 mg). Primary outcome was pain during mobilization (visual analogue scale) 2 h after the intervention. Secondary outcomes were pain at rest, opioid consumption, nausea, vomiting, sedation and dizziness. For pain during mobilization 2 h after intervention, there was no significant difference between groups: 51 (21) vs. 54 (25) mm in the chlorzoxazone and placebo groups, respectively, mean difference 3 mm (95% CI -8 to 10), P = 0.59. For pain during mobilization and at rest (wAUC 1-4 h), there were no significant differences between groups. There was no significant difference in total IV morphine use 0-4 h: median 10 (7-21) vs. 13 (5-19) mg in the chlorzoxazone and placebo groups, respectively, P = 0.82. No analgesic effect of single-dose chlorzoxazone was demonstrated in patients with acute pain after spine surgery. Based on these findings, chlorzoxazone cannot be recommended for immediate treatment of acute pain after such procedures1

References

    1. Acta Anaesthesiol Scand. 2016 Sep;60(8):1152-60
    2. http://www.drugbank.ca/drugs/DB00356
    3. http://www.rxlist.com/parafon-forte-drug/overdosage-contraindications.htm
    4. https://www.nlm.nih.gov/medlineplus/druginfo/meds/a682577.html
    5. http://www.drugs.com/drug-interactions/chlorzoxazone.html

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