Cyclobenzaprine is used as an adjunct to rest and physical therapy for the relief of muscular spasm associated with acute, painful musculoskeletal conditions. Skeletal muscle relaxants generally appear to be more effective than placebo in providing symptomatic relief of acute low back pain, but are associated with a high incidence of adverse effects. Although comparative studies are limited, available data suggest that various skeletal muscle relaxants generally have similar efficacy for such use. Acute low back pain usually is a benign and self-limiting condition that improves spontaneously over time; if pharmacologic therapy is required, an analgesic agent such as acetaminophen or a nonsteroidal anti-inflammatory agent (NSAIA) generally is recommended as first-line therapy for most patients. Skeletal muscle relaxants (alone or in combination with analgesics) may be used as an option for short-term relief of acute low back pain; however, the possibility of adverse effects, particularly adverse CNS effects, should be considered. In general, skeletal muscle relaxants should be used with caution after weighing the potential risks against the benefits in individual patients.
Efficacy of cyclobenzaprine hydrochloride 10 mg initially was established in 8 controlled clinical studies comparing cyclobenzaprine, diazepam, and placebo for their effect on muscle spasm, local pain and tenderness, limitation of motion, and restriction in activities of daily living. Improvement in patients receiving cyclobenzaprine was substantially greater than in those receiving diazepam in 3 studies and was comparable to diazepam in the remaining 5 studies.
Efficacy of cyclobenzaprine hydrochloride 5 mg was evaluated in 2 controlled clinical studies; in one study patients received cyclobenzaprine hydrochloride 5 or 10 mg or placebo 3 times daily, and in the second study patients received 2.5 or 5 mg of the drug or placebo 3 times daily. In both studies, efficacy of cyclobenzaprine hydrochloride 5 mg was substantially greater than placebo for patient-assessed primary end points (i.e., global impression of change, medication helpfulness, and relief from starting backache) by the seventh day of treatment. In addition, cyclobenzaprine 5 mg was substantially more effective than placebo for a physician-assessed secondary end point (reduction in presence and extent of palpable muscle spasm). In the study comparing cyclobenzaprine 5 or 10 mg 3 times daily with placebo, both dosages of the drug were substantially more effective than placebo by the third or fourth day (48-72 hours after the first dose of medication) of treatment. The only efficacy-related difference between the 2 dosages was in onset of patient-rated relief from starting backache, which occurred after the third or fourth dose in patients receiving 5 mg but after the first 2 doses in patients receiving 10 mg. In the second study, the 2.5 mg dosage of cyclobenzaprine was no more effective than placebo.
Analysis of data from controlled studies indicates that an effective dosage of cyclobenzaprine may produce clinical improvement whether or not sedation occurs. A subanalysis of data from patients in both studies who received either cyclobenzaprine hydrochloride (5 mg 3 times daily) or placebo and did not report somnolence demonstrated a meaningful treatment effect for all primary efficacy variables for the 5-mg dose despite the absence of somnolence in these patients. The manufacturer states that no well-controlled clinical studies have been performed to determine whether cyclobenzaprine will enhance the clinical effects of aspirin or other analgesics or vice versa when such combinations are used to manage acute musculoskeletal conditions.
Some data suggest that cyclobenzaprine may be useful for the treatment of fibrositis. Cyclobenzaprine is ineffective in the treatment of spasticity associated with cerebral or spinal disease or in children with cerebral palsy.