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Chlorzoxazone is used
to relieve pain and stiffness caused by muscle strains and sprains.
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
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.
Adult Dose for Muscle Spasm: 250 to 750 mg orally, 3 to 4 times a day.
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.
Common (affecting between 1 in10 to 1 in 100):
Uncommon (affecting 1 in 100 to 1 in 1000):
Very rare (affecting less than 1 in 10,000):
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
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