Use of Long-term Muscle Relaxants
QUESTION: What is the evidence for the use of long-term skeletal muscle relaxants in the treatment of chronic low back pain?
ANSWER: Chronic low back pain affects 60% to 80% of adults in the United States and is the second most common reason for physician office visits.1 Skeletal muscle relaxants are commonly used as adjuvant therapy to treat acute lower back pain. In fact, studies have reported that 91% of physicians say they prescribe muscle relaxants for low back pain, though only for a few days to weeks for acute treatment.2,3
Skeletal muscle relaxants are a broad class of pharmacological agents used for the treatment of muscle spasticity, although many of these agents cause a high degree of sedation. Evidence for the use of tizanidine (Zanaflex) and cyclobenzaprine (Flexeril) has shown benefit as short-term treatment agents, whereas evidence for the use of baclofen and dantrolene (Dantrium) in acute treatment is limited, and none exists for carisoprodol (Soma) or chlorzoxazone. Potential adverse effects from the long-term use of skeletal muscle relaxants include sedation, addictive potential, and hepatotoxicity. Evidence for acute treatment for each of these drugs is less than a month.4
The most evidence for the use of skeletal muscle relaxers in treating low back pain is with the use of cyclobenzaprine.5 One small study showed that cyclobenzaprine plus naproxen resulted in a significant decrease in muscle spasms and tenderness compared to naproxen alone.6 Evidence for the use of tizanidine comes from a Cochrane review, which showed that the combination of tizanidine plus analgesics provided better pain relief and a decrease in muscle spasms compared to analgesics alone.3 Based on this evidence, the recommendation of the Cochrane review is that skeletal muscle relaxers might help, though there is little evidence to support that these drugs become the standard of treatment for chronic back pain. Additionally, these studies demonstrate the efficacy of skeletal muscle relaxers for up to 14 days after symptom onset, and the evidence for long-term use is lacking.
The future may hold some answers as to the safety and efficacy of using skeletal muscle relaxants for long-term use but in the treatment of other medical conditions. A few ongoing studies are researching the use of long-term cyclobenzaprine ER in migraine prophylaxis and fibromyalgia and baclofen ER for chronic multiple sclerosis.7-9
However skeletal muscle relaxants are used, the data supporting their efficacy in chronic low back pain is controversial and very limited. Only a select group of patients may benefit from the use of these agents, and of those who use them long-term, many will experience adverse effects, particularly sedation. Therefore, the use of these medications should be evaluated on a risk of adverse effects vs. the potential, yet unproven, benefit of using skeletal muscle relaxants for the treatment of chronic low back pain.
St. John’s Hospital
McKenzie C. Ferguson, PharmD, BCPS
Assistant Professor, Pharmacy Practice
Drug Information & Wellness Center
Southern Illinois University Edwardsville