Cyclobenzaprine for the treatment of myofascial pain in adults.

BACKGROUND: Myofascial pain (MP) is a painful condition characterized by pain transmitted from trigger points (TP) within myofascial structures (in the muscles), local or distant from the pain. TPs can produce a characteristic pattern of irradiated pain or autonomic symptoms when stimulated. Cyclobenzaprine, a muscle relaxant that suppresses muscle spasm without interfering with muscle function, is used in clinical management of MP to improve quality of sleep and reduce pain.

OBJECTIVES: To assess efficacy and safety of cyclobenzaprine in treating MP.

SEARCH STRATEGY: The Pain Palliative and Supportive Care Review Group's Specialised Register, CENTRAL, PubMed, EMBASE, LILACS and Scielo were searched in February 2009.

SELECTION CRITERIA: All RCTs and quasi-RCTs reporting use of cyclobenzaprine for treating MP with pain assessment as a primary or secondary outcome.

DATA COLLECTION AND ANALYSIS: Two review authors independently screened studies identified, extracted data, assessed trial quality and analyzed results.

MAIN RESULTS: We identified two studies with a total of 79 participants. One study, with 41 participants, compared cyclobenzaprine with clonazepam and with placebo. Participants taking cyclobenzaprine had some improvement of pain intensity compared to those on clonazepam, mean difference (MD) -0.25 (95% CI, -0.41 to -0.09; P value 0.002) and placebo, MD -0.25 (95% CI, 0.41 to -0.09; P value 0.002). The other study, with 38 participants, compared cyclobenzaprine with lidocaine infiltration. Thirty days after treatment there were statistically non-significant differences between comparison groups, favoring lidocaine infiltration, for the mean for global pain, MD 0.90 (95% CI -0.35 to 2.15, P value 0.16), and for the mean for pain at digital compression, MD 0.60 (95% CI -0.55 to 1.75, P value 0.30). There were no life-threatening adverse events associated with the medications.

AUTHORS' CONCLUSIONS: There was insufficient evidence to support the use of cyclobenzaprine in the treatment of MP. We identified only two small studies in which a total of 35 participants were given cyclobenzaprine, and it was not possible to estimate risks for benefits or harms. Further high quality RCTs of cyclobenzaprine for treating MP need to be conducted before firm conclusions on its effectiveness and safety can be made. Experts in this area should elect cut-off points for participants to identify whether a patient has achieved a clinically relevant reduction of pain (primary outcome), so that their results can be combined easily into future versions of this review.