Fibromyalgia patients who took dextromethorphan experienced temporary reductions in the intensity of pain associated with minor repetitive physical contact -- a common characteristic of the poorly understood disease.
Researchers say the findings may have broader implications for the treatment of a host of chronic pain conditions. But they added that patients should definitely not self-medicate with over-the-counter drugs containing dextromethorphan.
Staud characterized the pain-relieving impact of the drug as "moderate." But he added that dextromethorphan or similarly acting medications may prove to be important additions to current treatments for fibromyalgia and other conditions involving heightened pain sensitivity.
Constant, Chronic Pain
It is estimated that as many as 10 million Americans have fibromyalgia -- a baffling disease that strikes mostly women and is characterized by pervasive pain, stiffness, fatigue, and muscle tenderness.
While the cause of fibromyalgia remains unknown, it is now thought that a mechanism known as central sensitization plays a major role in the disease. The theory is that the brain and spinal cord magnify pain signals to abnormally high levels.
Fibromyalgia patients often experience pain to stimuli that are not normally perceived as painful, such as a pat on the back. The pain can get worse with repeated contact.
Dextromethorphan has been shown to block the action of chemicals that relay pain to the spinal cord. It works by blocking a receptor known as N-methyl-D-aspartate or NMDA, which responds to these pain-transmitting chemicals. For this reason, Staud and colleagues evaluated the drug for pain control in fibromyalgia.
They found that people with fibromyalgia treated with dextromethorphan experienced moderate improvement in pain associated with repeated physical contact compared with those who got placebo treatments.
Better Drugs Needed
Staud tells WebMD that pharmaceutical researchers are working to develop more effective drugs that target the NMDA receptor with fewer side effects than the medications that are now available.
He estimates that these drugs could be commercially available within three to five years and could eventually be major players in pain control.
NMDA-receptor blockers like dextromethorphan have already been shown to improve pain control when given with morphine and other widely used opium-based medications. The hope is that combining the two drugs will allow a lower dose of the opioids to be used to control pain. Fibromyalgia expert Laurence Bradley, PhD, agrees that more research is needed before doctors or their patients turn to dextromethorphan for
"It would be a disservice to start to recommend that either patients or physicians begin experimenting right away with dextromethorphan, because I think there are some important questions about how to minimize the side effects [of the drug]," he says.