Highlights of contraindications, adverse effects, and drug interactions for these drugs are listed in Many of the studies evaluating the effectiveness of skeletal muscle relaxants are hampered by poor methodologic design, including incomplete reporting of compliance, improper or no mention of allocation concealment, not utilizing intention-to-treat methods, and inadequate randomization.1718 Nonetheless, skeletal muscle relaxants have been evaluated in systematic reviews and meta-analyses.
Some evidence appears to support nonbenzodiazepine skeletal muscle relaxants, such as carisoprodol, cyclobenzaprine, orphenadrine (Norflex), and tizanidine (Zanaflex), for acute low back pain.1718 Randomized controlled trials involving metaxalone have not been conducted since the 1970s.
In general, all of the drugs were shown to have some benefit.18 The limitations of published comparison trials include using unvalidated scales to measure outcomes, involving small numbers of participants, and often not reporting adverse effects of studied medications. Cyclobenzaprine hydrochloride effect on skeletal muscle spasm in the lumbar region and neck: two double-blind controlled clinical laboratory studies.
Caution is advised when prescribing skeletal muscle relaxants in older patients Allergy-type reactions may occur after the first to fourth dose; may be mild (e.g., cutaneous rash) or more severe (e.g., asthma attack, angioneurotic edema, hypotension, or anaphylactic shock); antihistamines, epinephrine, or corticosteroids may be needed The table contains only selected highlights about these medications.
The authors also described several limitations of the meta-analysis including inadequate blinding, heterogeneity among studies, and the presence of publication bias.27 Overall, studies appear to be consistent, with cyclobenzaprine having greatest benefit within the first few days of treatment rather than at one or two weeks.1827Skeletal muscle relaxants have also been studied as adjunctive therapy to analgesics in treating acute low back pain.
In one open-label study (20 patients), the addition of cyclobenzaprine to naproxen (Naprosyn) resulted in a statistically significant decrease in muscle spasm and tenderness compared with naproxen alone.28 A Cochrane review analyzed three high-quality trials (560 total patients) that showed tizanidine plus analgesics was more effective in providing pain relief and decreasing muscle spasm than analgesics alone.17 Conversely, one low-quality open-label study (867 patients) comparing cyclobenzaprine alone (5 mg three times daily) versus combination with ibuprofen (Motrin; either 400 or 800 mg three times daily) showed that, although all groups improved at seven days, there was no statistical difference in outcomes among the groups.29 Nonetheless, the use of combination therapy has been supported in quickening recovery,17 with minimal overall risk of adverse effects (relative risk [RR] = 1.34; 95% confidence interval [CI], 0.67 to 2.67].20Cyclobenzaprine has also been studied in treating fibromyalgia.
One fair-quality study showed no difference between metaxalone and placebo.19 Limited evidence exists to support the use of skeletal muscle relaxants in chronic low back pain.1720 Benzodiazepines have been effective for short-term use compared with placebo, but the basis of this recommendation stemmed from trials involving tetrazepam, which is not available in the United States.2126 One meta-analysis evaluated 14 studies comparing cyclobenzaprine with placebo for back and neck pain.27 The trials included were of less than 14 days' duration.
Cyclobenzaprine was found to be moderately more effective than placebo, but had more central nervous system adverse effects.