Cyclobenzaprine hydrochloride has the most recent and largest clinical trials demonstrating its benefit, but carisoprodol, diazepam and metaxalone also appear to be effective.
In 1989 researches compared the effectiveness of cyclobenzaprine (Flexeril) alone with diflunisal (Dolobid), placebo, and a combination of cyclobenzaprine and diflunisal in the treatment of acute low back pain and spasm. During the ten-day study period, the combined treatment group demonstrated significantly superior improvements in global ratings on day four, but not on day two or seven. This study suggested some effectiveness of combined analgesic and muscle relaxant therapy when utilized early in the initial week of pain onset.
Another study compared the effects of combined cyclobenzaprine and naproxen (Naprosyn) with naproxen alone and also found combination therapy to be superior in reducing tenderness, spasm, and range of motion in patients with low back pain and spasm.
Cyclobenzaprine and carisoprodol were compared in the treatment of patients with acute thoracolumbar pain and spasm rated moderate to severe and of no longer than seven days duration. Both drugs were effective, without significant differences between the treatment groups. Significant improvements were noted in physician rated mobility and in patients' visual analogue scores on follow up days four and eight. While 60% of patients experienced side effects in the form of drowsiness or fatigue, these differences were not significantly different between treatment groups and only eight percent of patients from each group discontinued treatment.
In an attempt to determine the mechanism of action of carisoprodol in the treatment of low back pain, a study was carried out comparing its effectiveness to that of a sedative medication butabarbital, and a placebo. Carisoprodol was significantly more effective in providing both pain relief and improvements in range of motion. The results of this study suggest that the effects of carisoprodol are not secondary to its sedative effects alone. In addition to the skeletal muscle-relaxing effects, carisoprodol also produces weak anticholinergic, antipyretic, and analgesic effects.
In an earlier study, diazepam (Valium) was found to offer no significant subjective or objective benefit, when compared to placebo, in patients treated for low back pain. Carisoprodol (Soma) was found to be superior to diazepam in the treatment of patients with "at least moderately severe" low back pain and spasm of no longer than seven days duration. In this study, the overall incidence of adverse reactions was higher in the diazepam treated group but was not of statistical significance.
