Breaking a Vicious Circle?
Abstract & Commentary
By Allan J. Wilke, MD, MA, Professor and Chair, Department of Integrative Medicine, Ross University (Bahamas) Limited, Freeport, Grand Bahama, The Bahamas. Dr. Wilke reports no financial relationship to this field of study.
Synopsis: Adding a muscle relaxer to an NSAID added no benefit in acute neck strain.
Source: Khwaja SM, et al. Comparison of ibuprofen, cyclobenzaprine or both in patients with acute cervical strain: A randomized controlled trial. CJEM 2010;12:39-44.
The theory behind adding a muscle relaxant to a nonsteroidal anti-inflammatory drug (NSAID) in acute muscle strain goes like this: When muscles (for instance, neck muscles in a whiplash injury) are strained, they reflexly go into spasm, which causes more pain. This sets up a positive feedback loop (or, in layman's terms, a vicious circle). The NSAID reduces the pain, and the muscle relaxant reduces the spasm, so the sum should be greater than the parts. Or so goes the theory. A Cochrane review of the use of cyclobenzaprine (CBP) for myofascial pain concluded that there was insufficient evidence to support its use.1 A trial of CBP plus ibuprofen (IBU) vs CBP alone did not show a difference when treating adults with neck or back pain plus spasm.2 A meta-analysis of CBP for back pain found it to be modestly effective, but had greater adverse effects.3
These researchers from Stony Brook University randomized 61 adult patients who presented to their suburban emergency department with neck pain within 24 hours of a fall or a motor vehicle collision to one of three treatment groups. All medications were to be taken by mouth three times daily for 7 days or until pain was relieved. All patients received an initial dose of IBU 800 mg. They excluded pregnant women and patients who had a contraindication to the study drugs or who could not tolerate them. Patients and their physicians were blind to group assignment.
In addition to the usual demographic data, the patients kept a daily log of pain (measured on a 100-mm visual analog scale) and use of acetaminophen (APAP) and ice packs for rescue. They also recorded any adverse side effects, such as nausea, vomiting, or dizziness, and when they were able to resume their normal daily activities.
The three groups were similar. The patients' average age was 34 years. They were predominantly women (58%) and white (72%). Initially, the average pain score was 52.8 mm. All 3 groups got better over time, and there was a trend for Group 3 to have a greater average reduction in pain, but this did not reach statistical significance. There were nonsignificant trends for the IBU groups to use less APAP and to resume their normal daily activities sooner; 70% in Group 1, 38% in Group 2, and 65% in Group 3 returned to normal activities after one day. There was a trend (again, not statistically significant) for the groups receiving CBP to have more adverse drug effects.
Commentary
In this small study, only pain reduction reached statistical significance. Perhaps the study was underpowered and had the investigators enrolled more subjects, their findings would have reached statistical significance. It's difficult to say since there were no power calculations. That there were more adverse side effects is not surprising, since CBP is structurally similar to the tricyclic antidepressants and has strong anticholinergic properties. It should be used with caution in people who are elderly or who might be harmed by its sedative effects. The current study did not show a benefit for adding CBP to IBU, nor did it conclusively show more adverse events. There was, however, the added expense of drug purchase. "First, do no harm" tips the balance in favor of withholding its use in this circumstance.
References
1. Leite FM, et al. Cyclobenzaprine for the treatment of myofascial pain in adults. Cochrane Database Syst Rev 2009;(3):CD006830.
2. Childers MK, et al. Low-dose cyclobenzaprine versus combination therapy with ibuprofen for acute neck or back pain with muscle spasm: A randomized trial. Curr Med Res Opin 2005;21:1485-1493.
3. Browning R, et al. Cyclobenzaprine and back pain: A meta-analysis. Arch Intern Med 2001;161:1613-1620.
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