Last updated: October 6, 2014
Trade Names: Parafon Forte
Drug Class: Skeletal muscle relaxant, centrally acting
Preparations: 500-mg caplet; 250-mg tablet
Dose: Usual dose, 250–500 mg three to four times daily; to as high as 750 mg three to four times daily
Indications: Relief of muscle spasm. Questionable efficacy and potentially serious adverse effects including fatal hepatotoxicity limit indications.
Mechanism of Action: Acts via spinal cord and subcortical regions to decrease muscle tone
Contraindications: Hypersensitivity to chlorzoxazone, impaired liver function, avoid in elderly
Monitoring: LFTs periodically with long-term use
Pregnancy Risk: C
Common: Drowsiness, lightheadedness, allergy, rash, nausea, cramps
Less common: Hematologic toxicity (aplastic anemia, leukopenia), unpredictable fatal hepatotoxicity
Drug Interactions: CNS depressants have increased effect.
Patient Instructions: It may cause drowsiness. Avoid alcohol.
Clinical Pharmacology: Rapid absorption; hepatic metabolism and renal excretion of metabolites