Skeletal Muscle Relaxant


Skeletal Muscle Relaxant, Methocarbamol, Robaxin, Chlorzoxazone, Parafon Forte, Metaxalone, Skelaxin, Orphenadrine, Orphengesic Forte, Norflex

  • See Also
  1. Antispastic Muscle Relaxant
  2. Cyclobenzaprine (Flexeril)
  • Contraindications
  • Efficacy
  1. More effective than Placebo, but less effective than first-line agents such as NSAIDs
  2. "Muscle relaxants" do not directly relax Muscles (most of effect is likely sedation)
  • Precautions
  1. Maximize Analgesics (NSAIDs and Acetaminophen) as they are generally more effective
  2. Dose as needed and primarily at night to assist sleep (primary effect is sedation)
  3. Limit to adjunctive (primarily bedtime use) in Acute Low Back Pain (and avoid in Chronic Low Back Pain)
  4. Avoid concurrent use of CNS Depressants (e.g. Alcohol, Benzodiazepines, Opioids)
    1. Risk of respiratory depression and death
  • Agents
  • Preferred
  1. Cyclobenzaprine (Flexeril) 5 mg (up to 10 mg) orally at bedtime up to three times daily
    1. Best studied of all antispasmodic agents, appears consistently effective, and is inexpensive
    2. Anticholinergic adverse effects (related to Tricyclic Antidepressants)
  2. Methocarbamol (Robaxin) 750 to 1500 mg four times daily
    1. Significantly less expensive than Flexeril
    2. Warn about Urine Color change
  • Agents
  • Higher risk of Adverse Effects
  1. Chlorzoxazone (Parafon Forte) 250-750 mg 3-4 times daily
    1. Risk of liver abnormalities and GI upset
  2. Metaxalone (Skelaxin) 800 mg 3-4 times daily
    1. Risk of liver, hematologic abnormalities and GI upset
    2. Less effective and expensive
  3. Orphenadrine (Norflex) 100 mg twice daily
    1. Risk of Tachycardia, hematologic abnormalities and GI upset
  4. Orphenadrine with 770 mg Aspirin and 60 mg Caffeine (Orphengesic Forte)
    1. Very expensive ($25/tab) rebranding of an older Muscle relaxant
    2. Unclear if any Muscle relaxant is indicated (low efficacy) and risk of falls and Fractures in older adults
    3. Aspirin adds additional bleeding risk including Gastrointestinal Bleeding
    4. (2020) presc lett 27(9): 51
  • Agents
  • Higher risk of dependence
  1. Carisoprodol (Soma) 350 mg up to four times daily
    1. Schedule IV drug in U.S. as of January 2012
    2. Risk of transient neurologic changes, serious Allergic Reactions, Substance Abuse, and fatal Overdoses
    3. Metabolized to Meprobamate, a Sedative and FDA controlled substance similar to Barbiturates
    4. See Carisoprodol Poisoning
  2. Benzodiazepines
    1. Diazepam (Valium) 2-10 mg orally 3-4 times daily