Chlorzoxazone

# Chlorzoxazone ## Overview - **Classification**: Centrally acting skeletal muscle relaxant - **Mechanism**: Acts on the spinal cord and subcortical areas of the brain, inhibiting polysynaptic reflex arcs. This leads to skeletal muscle relaxation. ## Primary Indications 1. **Muscle Spasm** - Associated with acute, painful musculoskeletal conditions 2. **Adjunct Therapy** - Used with rest, physical therapy, and other measures ## Adult Dosing ### Standard Dosing **Muscle Spasm** - **Dose**: **250 mg** to **750 mg** - **Frequency**: Three to four times daily (TID/QID) - **Route**: Oral - **Duration**: Short-term, as needed for acute symptoms ### Dose Adjustments - **Renal Impairment**: Use with caution. No specific dose adjustment guidelines; monitor for increased side effects. - **Hepatic Impairment**: Use with extreme caution or avoid. Chlorzoxazone is metabolized by the liver. - **Elderly Patients**: Start with lower doses (e.g., **250 mg** TID) due to increased sensitivity and potential for CNS effects. Monitor closely. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Safety and efficacy **not established**. - **Frequency**: Not recommended. - **Maximum**: Not applicable. - **Special Notes**: Use is contraindicated due to lack of data and potential for toxicity. ### Infants (1-12 months) - **Dose**: Safety and efficacy **not established**. - **Frequency**: Not recommended. - **Maximum**: Not applicable. ### Children (1-12 years) - **Dose**: Safety and efficacy **not established**. - **Frequency**: Not recommended. - **Maximum**: Not applicable. ### Adolescents (13-18 years) - **Dose**: Safety and efficacy **not established**. - **Maximum**: Not recommended for routine use. If considered in rare cases, use adult dosing with extreme caution and clinical justification. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to chlorzoxazone or any component. - **Absolute**: Pre-existing liver disease or hepatic impairment. - **Relative**: History of drug-induced liver injury. ### Common Adverse Effects - **Common (1-10%)**: Drowsiness, dizziness, lightheadedness. - **Common (1-10%)**: Nausea, gastrointestinal upset, heartburn. - **Common (1-10%)**: Malaise, agitation. - **Serious but Rare**: Hepatotoxicity (idiosyncratic, potentially fatal). - **Serious but Rare**: Angioedema, anaphylaxis. ### Key Drug Interactions - **CNS Depressants**: Enhanced sedative effects (e.g., alcohol, opioids, benzodiazepines). - **Other Hepatotoxic Drugs**: Increased risk of liver injury; monitor LFTs closely. ## Monitoring & Follow-up - **Before Treatment**: Assess liver function (baseline LFTs) if risk factors are present or for prolonged use. - **During Treatment**: Monitor for signs/symptoms of hepatotoxicity (jaundice, dark urine, malaise, abdominal pain). - **Clinical Signs**: Assess sedation, dizziness, and GI upset. ## Clinical Pearls - 💡 **Tip 1**: Take with food or milk to minimize GI upset. - 💡 **Tip 2**: May cause urine to turn orange or purplish-red; this is a harmless metabolite. - 💡 **Tip 3**: Warn patients about potential drowsiness and dizziness; avoid driving or operating machinery until effects are known. - 💡 **Tip 4**: Not recommended for long-term use; best for acute, short-term muscle spasms. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.