Metaxalone: Use and Dosage
Metaxalone is a centrally acting skeletal muscle relaxant typically prescribed at 800 mg three to four times daily for acute musculoskeletal pain, with a maximum daily dose of 3200 mg. 1
Mechanism and Clinical Applications
Metaxalone is a centrally acting muscle relaxant used primarily for the relief of discomfort associated with acute, painful musculoskeletal conditions. While its exact mechanism of action is not fully understood, it appears to have effects on the central nervous system rather than directly on skeletal muscle.
Primary Indications:
- Relief of discomfort from acute, painful musculoskeletal conditions
- Adjunct to rest, physical therapy, and other measures for the relief of muscle spasm
Dosing Recommendations
Standard Adult Dosing:
- Initial dose: 800 mg orally three times daily
- Maintenance dose: 800 mg three to four times daily
- Maximum daily dose: 3200 mg
Special Populations:
- Elderly patients: Start with lower doses (400-800 mg three times daily)
- Hepatic impairment: Dose reduction recommended due to significant impairment in drug elimination 1
- Renal impairment: Dose reduction recommended due to potential drug accumulation 1
Administration Considerations
Metaxalone should be taken with food to enhance bioavailability. Taking with food increases peak plasma concentration and reduces time to reach peak concentration, potentially improving efficacy.
Safety and Monitoring
Cardiovascular Effects:
- May cause bradycardia and hypotension 1
- Use with caution in patients with cardiac conditions
- Consider less-sedating alternatives for patients with cardiovascular disease 1
Central Nervous System Effects:
- Sedation and drowsiness are common side effects
- Can potentiate CNS depression when used with other sedatives or alcohol
- May interfere with pyridostigmine bromide effects (contraindicated in myasthenia gravis) 1
Drug Interactions:
- Avoid concurrent use with alcohol and other CNS depressants
- Potential serotonergic effects at supratherapeutic concentrations when combined with SSRIs 2
- The Society for Perioperative Assessment and Quality Improvement recommends holding metaxalone on the day of surgical procedures due to cardiovascular effects 1
Efficacy Considerations
A randomized, placebo-controlled trial comparing ibuprofen plus metaxalone versus ibuprofen plus placebo for acute low back pain found that adding metaxalone to ibuprofen did not significantly improve functioning or pain compared to ibuprofen alone by one week after treatment 3. This suggests that metaxalone may have limited additional benefit when used with NSAIDs for acute low back pain.
Toxicity and Overdose
Metaxalone overdose can lead to serious complications:
- Toxic concentrations have been reported at levels above 10 mg/L 4, 5
- Fatal cases have been reported with blood concentrations of 39 mg/L and above 4
- Overdose symptoms may include severe CNS depression, respiratory depression, and cardiovascular effects
Clinical Pearls
- Monitor for signs of sedation and advise patients about potential impairment when driving or operating machinery
- Metaxalone should be used for short-term treatment (2-3 weeks) rather than long-term management
- Non-pharmacological approaches (physical therapy, heat/cold therapy) should be incorporated into treatment plans
- Consider discontinuing if no improvement is seen after 2-3 weeks of therapy
When prescribing metaxalone, always balance the potential benefits against risks, particularly in elderly patients or those with comorbid conditions that may increase vulnerability to adverse effects.