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Cyclobenzaprine is a muscle relaxant and as a class, the skeletal muscle relaxants (SMRs) include a diverse number of drugs that do not share many similarities other than their intended purpose. This makes it difficult to identify any one drug as the “best muscle relaxant”.

In comparison trials, no single skeletal muscle relaxant has been proven to be superior to another muscle relaxant. The most widely studied agent is cyclobenzaprine, with demonstrated efficacy for various musculoskeletal conditions but with significant sedation.

In a trial of cyclobenzaprine versus carisoprodol in patients with acute back pain and spasms there were no significant differences for pain, muscle stiffness, activity impairment, sleep impairment, tension, or relief scores compared to baseline. In this head-to-head trial dry mouth was more frequent with cyclobenzaprine (38% vs. 10%) and dizziness less frequent (8% vs. 26%). Withdrawal rates due to adverse events were equal (8%) 1.

Low back pain and Muscle spasm

The results of the randomized study2 demonstrated that patients with muscle spasm associated with acute low back strain benefited from the use of combination therapy with naproxen and cyclobenzaprine.

Two groups of 20 patients each, with mild to moderate acute low back pain with associated muscle spasm of ten days' duration or less, were treated with a combination of cyclobenzaprine and naproxen or naproxen alone in a randomized, 14-day open-label trial. Combination therapy was associated with less objective muscle spasm and tenderness and greater motion of the lumbosacral spine. Resolution of functional deficits and pain were faster with combined therapy. Combination therapy was associated with more side effects, due primarily to drowsiness from the cyclobenzaprine.

• Cyclobenzaprine (Flexeril) Facts

• 1. Rollings HE, Glassman JM, Soyka JP. Management of acute musculoskeletal conditions - Thoracolumbar strain or sprain: A double-blind evaluation comparing the efficacy and safety of carisoprodol with cyclobenzaprine hydrochloride. Curr Ther Res. 1983;34(6):917-928.
• 2. Borenstein DG, Lacks S, Wiesel SW. Cyclobenzaprine and naproxen versus naproxen alone in the treatment of acute low back pain and muscle spasm. Clin Ther. 1990 Mar-Apr;12(2):125-31. PubMed

Published: March 31, 2008
Last updated: April 25, 2011