Cyclobenzaprine hydrochloride is a muscle relaxant that is effective in improving
muscle spasm, reducing local
pain and tenderness, and increasing range of motion in acute, painful musculoskeletal conditions. Sedation is the most common adverse event associated with its use at the usual dosage of 10 mg TID. Studies in healthy adults suggest that a lower dose may produce less sedation. Because
cyclobenzaprine's duration of action is 4 to 6 hours, reducing the dosing frequency to 10 mg BID would create a potentially painful untreated interval between doses. The alternative is administration of a lower dose (eg, 5 or 2.5 mg) TID.
OBJECTIVE: In 2 randomized, double-blind, placebo-controlled, parallel-group trials conducted at primary care centers in the United States, adult patients with acute painful
muscle spasm of the lumbar or cervical region were randomly assigned to receive treatment with 2.5, 5, or 10 mg
cyclobenzaprine TID or placebo for 7 days (study 1:
cyclobenzaprine 5 or 10 mg TID or placebo; study 2:
cyclobenzaprine 2.5 or 5 mg TID or placebo). The primary efficacy measures were patient-rated clinical global impression of change, medication helpfulness, and relief from starting
backache. Neither study included a nonsteroidal anti-inflammatory
drug (
NSAID) as an active control. Although physicians frequently prescribe an
analgesic or
NSAID in addition to
cyclobenzaprine, these studies were not designed to assess whether adding
cyclobenzaprine provides a benefit over that of an
analgesic.
RESULTS: One thousand four hundred five patients (737 study 1; 668 study 2), two thirds with
low back pain and one third with
neck pain, were randomized to treatment. Their mean age was 42 years, and approximately 89% were white. In both studies, patients receiving
cyclobenzaprine 5 or 10 mg had significantly higher mean scores on the primary efficacy measures compared with those receiving placebo (study 1-P</=0.001
cyclobenzaprine 5 and 10 mg vs placebo, all measures at visits 2 and 3; study 2-P</=0.03
cyclobenzaprine 2.5 mg vs placebo, relief from starting
backache on day 3 only;
cyclobenzaprine 5 mg vs placebo, patient-rated clinical global impression of change, medication helpfulness, and relief from starting
backache at visit 3 or day 7 only). On day 7, significantly more patients receiving
cyclobenzaprine 5 or 10 mg reported relief compared with placebo recipients (P < 0.05 all
cyclobenzaprine groups vs placebo). Onset of relief was apparent within 3 or 4 doses of the 5-mg regimen. In the subanalysis of the proportion of responders in the pooled 5-mg groups who did and did not report
somnolence, a meaningful treatment effect was observed on all primary efficacy variables in patients who did not report
somnolence, suggesting that efficacy was independent of sedation.
Cyclobenzaprine was well tolerated.
Somnolence and dry mouth, the most common adverse effects, were mild and dose related. Overall, >/= 1 adverse event was reported in 54.1%, 61.8%, and 35.4% of patients receiving
cyclobenzaprine 5 or 10 mg or placebo, respectively, in study 1 and by 43.9%, 55.9%, and 35.4% of patients receiving
cyclobenzaprine 2.5 or 5 mg or placebo, respectively, in study 2. Adverse events were the primary reason for discontinuation of treatment in the
cyclobenzaprine 5- and 10-mg groups in both studies. In study 2, ineffectiveness of
therapy was the main reason for discontinuation of
therapy in the group receiving
cyclobenzaprine 2.5 mg.
CONCLUSIONS: