ChlorzoxazoneRx

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

Adverse Effects
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

Cost: $$