Why Fibromyalgia Pain Won't Let Up - And Which Drugs Might Help
By Donna Rae Siegfried
A new study explains why people with the chronic pain of fibromyalgia don’t respond as well as other people to strong pain medication, such as the opioids hydrocodone (Vicodin) or oxycodone (OxyContin).
What Goes Wrong
Apparently, the brains of people with fibromyalgia have fewer receptors for opioid medications, according to the study by researchers in the division of rheumatology at the University of Michigan Medical School in Ann Arbor. Fewer opioid receptors in the brain mean fewer places for the medicine to bind and, therefore, less opportunity for it to ease pain.
Easing pain is more difficult in people who are depressed, too, and this study helps explain that aspect, as well. “The people with fibromyalgia who had more depression than others with the disease were the ones with the fewest available opioid receptors, especially in the part of the brain that affects mood and emotional response to pain," says researcher and rheumatologist Daniel Clauw, MD, executive director of the University of Michigan's Chronic Pain and Fatigue Research Center.
Fewer opioid receptors were available because they were busy binding endorphins (feel-good hormones) produced by the body to relieve its own pain, explains Dr. Clauw. “The body can't produce enough endorphins to overcome the pain, yet the opioid medication can't take effect,” he says.
"There is a small subset of patients who will benefit from opioids, so I would never say 'don’t ever use them,'" says Dr. Clauw, who was one of the study authors. "Opioids should not be considered first or second line therapy for people with fibromyalgia, but they can be reserved for people who have failed to respond to other therapies," he says.
What Might Go Right
So if opioids won't work, what medications will? The newest crop of treatments includes anti-convulsant (or anti-seizure) and antidepressant medications.
Why anti-convulsants? Because those drugs work on the central nervous system (CNS) – the brain and spinal cord – fibromyalgia is thought to be a disorder of the CNS, rather than of the joints. People with fibromyalgia may abnormally process pain signals that flow through the CNS, says Dr. Clauw. Pain is felt in the muscles and tender spots throughout the body, but may originate in the CNS.
Gabapentin (Neurontin)
In a 2007 study, 150 people with fibromyalgia who took 1,200 to 2,400 mg of gabapentin every day for 12 weeks not only had less pain, but also experienced better sleep and less fatigue. Neurontin is FDA-approved for treating the pain of shingles, but some doctors prescribe it for those who have fibromyalgia.
Pregabalin (Lyrica)
Prior to its FDA approval for fibromyalgia last summer, Lyrica had been FDA-approved for treating seizures and the pain of shingles, as well as the nerve pain associated with diabetic neuropathy. For fibromyalgia, Lyrica decreases pain – by 48 percent in one study of people who took the 450-mg daily dose – and improves functioning in daily activities by helping people get more refreshing sleep.
Duloxetine (Cymbalta)
Already FDA-approved for treating depression and the nerve pain caused by diabetes, Cymbalta is now up for FDA approval for use in people with fibromyalgia. In one study, a 60-mg daily dose of duloxetine reduced the number of tender points and alleviated pain by about 50 percent. Results have been stronger in women than in men, but it is unclear why.
Milnacipran
Known in Europe as the antidepressant drug Ixel, milnacipran is not yet FDA-approved in the U.S. A recent phase III study shows that a daily dose of 100 or 200 mg diminished pain by at least 30 percent and improved cognitive and physical function.
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