How to Use Chlorzoxazone (Muscle Relaxant)
Chlorzoxazone should be used as an adjunct to rest, physical therapy, and other measures for short-term relief of discomfort associated with acute, painful musculoskeletal conditions. 1
Dosage and Administration
- Standard adult dosage: 500 mg orally 3-4 times daily
- Take with food to minimize gastrointestinal upset
- Duration of therapy should be limited to short-term use (typically 2-3 weeks)
- Avoid abrupt discontinuation; taper gradually if used for more than a few days
Mechanism of Action
Chlorzoxazone is a centrally acting skeletal muscle relaxant. While its exact mechanism of action has not been clearly identified, it may be related to its sedative properties. It's important to note that chlorzoxazone does not directly relax tense skeletal muscles 1.
Indications
Chlorzoxazone is specifically indicated for:
- Acute painful musculoskeletal conditions
- Short-term relief of muscle spasms
- As part of a comprehensive treatment plan that includes rest and physical therapy
Precautions and Monitoring
Hepatotoxicity Risk
- Monitor for signs of liver dysfunction (jaundice, dark urine, right upper quadrant pain)
- Chlorzoxazone has been associated with hepatotoxicity that is generally reversible but can be serious 2
- Consider baseline liver function tests before starting therapy in high-risk patients
Central Nervous System Effects
- Sedation is a common side effect; caution patients about driving or operating machinery
- All skeletal muscle relaxants are associated with central nervous system adverse effects, primarily sedation 2
Drug Interactions
- Avoid combining with other CNS depressants (benzodiazepines, opioids, alcohol)
- May interact with midazolam and other CYP3A substrates 3
- Use caution when combining with other medications metabolized by CYP2E1 or CYP1A2 4
Pharmacokinetics
- Absorption: Rapidly absorbed from the gastrointestinal tract
- Peak plasma concentration (Cmax): Reached in approximately 1-2 hours
- Metabolism: Primarily metabolized in the liver by CYP2E1 and CYP1A2 to 6-hydroxychlorzoxazone 4
- Elimination half-life: Approximately 1.5 hours 5
Important Considerations
Limited duration: Skeletal muscle relaxants should be used for short-term relief of acute low back pain, not for chronic conditions 2
Not first-line therapy: Consider acetaminophen or NSAIDs as first-line options for musculoskeletal pain before using muscle relaxants 2
Avoid in liver disease: Use with caution or avoid in patients with history of liver disease due to risk of hepatotoxicity 6
Pregnancy and lactation: Limited data available; use only if benefits outweigh potential risks
Elderly patients: Start with lower doses due to increased risk of sedation and falls
When to Discontinue
- If no improvement after 1 week of therapy
- If signs of hepatotoxicity develop (jaundice, elevated liver enzymes)
- If intolerable side effects occur (excessive sedation, allergic reactions)
- After resolution of acute musculoskeletal symptoms
Remember that chlorzoxazone is intended for short-term use as part of a comprehensive treatment approach that includes physical therapy and other non-pharmacological measures.