Comparison of Muscle Relaxants: Eperisone vs. Orphenadrine vs. Chlorzoxazone
Based on current evidence, none of these three muscle relaxants demonstrates superior efficacy, but eperisone appears to have a better safety profile with fewer adverse effects compared to orphenadrine and chlorzoxazone. 1
Efficacy Considerations
General Efficacy
- Current guidelines indicate that there is no compelling evidence that any skeletal muscle relaxant is superior to another in terms of efficacy 2
- All three medications are considered "so-called muscle relaxants" that do not directly relax skeletal muscle and have nonspecific effects on pain relief 2
Clinical Applications
- These medications may relieve skeletal muscle pain, but their effects are nonspecific and not related to actual muscle relaxation 2
- They should not be prescribed with the mistaken belief that they relieve muscle spasm 2
- For true muscle spasm, benzodiazepines or baclofen may be more appropriate choices 2
Safety Profiles
Orphenadrine
- Has anticholinergic properties that can cause sedation and other central nervous system effects 2
- Listed in the American Geriatrics Society Beers Criteria as potentially inappropriate for older adults due to anticholinergic effects 2
Chlorzoxazone
- Associated with hepatotoxicity that is usually reversible and mild 2
- A recent randomized trial showed no analgesic effect of single-dose chlorzoxazone in patients with acute pain after spine surgery 3
Eperisone
- Shows comparable efficacy to other muscle relaxants but with significantly fewer side effects (5% vs. 21.25% for thiocolchicoside in comparative studies) 1
- Primarily causes minor gastrointestinal side effects rather than CNS depression 1
Special Populations
Older Adults
- Muscle relaxants increase the risk of falls in older persons 2
- The American Geriatrics Society Beers Criteria specifically cautions against skeletal muscle relaxants in older adults 2
- If a muscle relaxant is necessary in older adults, the lowest effective dose should be used for the shortest duration possible 2
Patients with Hepatic/Renal Impairment
- Chlorzoxazone should be used with caution in patients with liver disease due to its association with hepatotoxicity 2
- For patients with renal or hepatic failure, benzylisoquinoline muscle relaxants (atracurium/cisatracurium) are recommended over these options 2
Algorithm for Selection
First, determine if a muscle relaxant is truly needed:
- Consider whether pain is actually due to muscle spasm
- Try acetaminophen or NSAIDs first if appropriate 2
If a muscle relaxant is necessary:
For patients with normal hepatic/renal function and low risk of falls:
- Eperisone is preferred due to better safety profile 1
For older adults or those at risk of falls:
- Avoid all three if possible 2
- If necessary, use eperisone at the lowest effective dose for shortest duration
For patients with liver concerns:
- Avoid chlorzoxazone 2
- Consider eperisone with appropriate monitoring
Duration of treatment:
- Limit treatment to short-term relief (≤21 days) 4
- Reassess efficacy and side effects regularly
Important Cautions
- These medications are not recommended for chronic pain management 2
- Evidence for efficacy is limited by poor methodologic design in many studies 2
- The sedative effects of muscle relaxants can impair driving and other activities requiring alertness 5
- There is no evidence supporting long-term use of these medications 6
Monitoring Recommendations
- Monitor for adverse effects, particularly drowsiness, dizziness, and anticholinergic effects
- In patients with hepatic impairment, monitor liver function when using chlorzoxazone
- Assess efficacy regularly to determine if continued use is warranted
Remember that these medications should be used as part of a comprehensive pain management strategy, and their use should be limited to short-term treatment when possible.