Chlorzoxazone

May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks that require mental alertness (eg, operating machinery or driving).

Rare, serious (including fatal) idiosyncratic and unpredictable hepatocellular toxicity has been reported with use. Discontinue immediately if early signs/symptoms of hepatic toxicity arise (eg, fever, rash, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, jaundice). Also discontinue if elevated liver enzymes (eg, AST, ALT, alkaline phosphatase, bilirubin) develop.

Use caution in patients with known allergies or a history of allergic reactions to drugs; if sensitivity (itching, redness, urticaria) occurs, discontinue therapy. Concurrent drug therapy issues:

Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information. Dosage form specific issues:

Some dosage forms may contain sodium benzoate/benzoic acid; benzoic acid (benzoate) is a metabolite of benzyl alcohol; large amounts of benzyl alcohol (≥99 mg/kg/day) have been associated with a potentially fatal toxicity ("gasping syndrome") in neonates; the "gasping syndrome" consists of metabolic acidosis, respiratory distress, gasping respirations, CNS dysfunction (including convulsions, intracranial hemorrhage), hypotension and cardiovascular collapse (AAP 1997; CDC 1982); some data suggests that benzoate displaces bilirubin from protein binding sites (Ahlfors 2001); avoid or use dosage forms containing benzyl alcohol derivative with caution in neonates. See manufacturer's labeling.