indication

For the relief of discomfort associated with acute painful musculoskeletal conditions.

pharmacology

Chlorzoxazone, a synthetic compound, inhibits antigen-induced bronchospasms and, hence, is used to treat asthma and allergic rhinitis. Chlorzoxazone is used as an ophthalmic solution to treat conjunctivitis and is taken orally to treat systemic mastocytosis and ulcerative colitis. Chlorzoxazone is also a centrally-acting agent for painful musculoskeletal conditions. Data available from animal experiments as well as human study indicate that chlorzoxazone acts primarily at the level of the spinal cord and subcortical areas of the brain where it inhibits multisynaptic reflex a.c. involved in producing and maintaining skeletal muscle spasm of varied etiology. The clinical result is a reduction of the skeletal muscle spasm with relief of pain and increased mobility of the involved muscles.

mechanism of 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. Chlorzoxazone may act by inhibiting calcium and potassium influx which would lead to neuronal inhibition and muscle relaxation. Data available from animal experiments as well as human study indicate that 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 spasm

toxicity

Oral, mouse: LD₅₀ = 440 mg/kg; Oral, rat: LD₅₀ = 763 mg/kg; Symptoms of overdose include diarrhea, dizziness, drowsiness, headache, light-headedness, nausea, and vomiting.

biotransformation

Chlorzoxazone is rapidly metabolized in the liver and is excreted in the urine, primarily in a conjugated form as the glucuronide.

route of elimination

Chlorzoxazone is rapidly metabolized and is excreted in the urine, primarily in a conjugated form as the glucuronide.

drug interactions

Disulfiram: Disulfiram may increase the serum level of chlorzoxazone by decreasing its metabolism. Monitor for changes in the therapeutic and adverse effects of chlorzoxazone if diltiazem is initiated, discontinued or dose changed.

Triprolidine: The CNS depressants, Triprolidine and Chlorzoxazone, may increase adverse/toxic effects due to additivity. Monitor for increased CNS depressant effects during concomitant therapy.