Chlorzoxazone

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DRUGS
Chlorzoxazone

Chlorzoxazone is used to relieve pain and stiffness caused by muscle strains and sprains. It is a skeletal muscle relaxant use 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.

Introduction

Chlorzoxazone is used to relieve pain and stiffness caused by muscle strains and sprains. It is a skeletal muscle relaxant use 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

Pharamcological 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 also may reduce the release of inflammatory leukotrienes. It may act by inhibiting calcium and potassium influx which would lead to neuronal inhibition and muscle relaxation. The drug 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 spasm.

Dosage

Adult Dose for Muscle Spasm

250 to 750 mg orally 3 to 4 times a day.

Pharmacokinetics

Tmax 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 unchanged drug. The t ½ is about 60 min.

Contraindications

  • Contraindicated in patients with known intolerance to the Chlorzoxazone.

Drug Interactions

  • 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)

  • Dizzy

  • Drowsiness

Uncommon (affecting 1 in 100 to 1 in 1000)

  • Diarrhea

  • Vomiting

  • Head Pain

  • 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

  • Bleeding of Stomach or Intestines

  • Granulocytes deficiency

  • Giant Hives

  • Hepatitis caused by drugs

  • Hives

  • Itching

  • Life Threatening Allergic Reaction

  • Rash

  • Abnormal Urine Color

  • Confused

  • Hemorrhage under Skin

  • Memory loss

  • Numbness and Tingling

  • Small Reddish-Purple Skin Spots

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.

 

Clinic Evidence

Total 110 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

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