New treatment for fibromyalgia: duloxetine

A study demonstrates the effectiveness of the antidepressant duloxetine to improve symptoms and relieve pain. Fibromyalgia is a chronic disabling musculoskeletal disorder. Nearly six times more common in women than in men, fibromyalgia is characterized by generalized body pain and muscle tenderness, often accompanied by headaches, sleep disturbances and fatigue. While its cause remains a mystery, fibromyalgia has been linked to abnormalities in the neurotransmitters of the brain, serotonin and norepinephrine, key chemicals for mood and widely recognized for their role in depression. Not all patients with fibromyalgia, however, have depression or respond to antidepressants.

Studies of the treatment of other types of antidepressant drugs, including selective serotonin reuptake inhibitors and tricyclic agents, have had mixed results. A new and different antidepressant, duloxetine, works by inhibiting the reuptake of serotonin and norepinephrine. In a recent clinical trial conducted for the treatment of fibromyalgia, it was shown that one of the largest duloxetines ever used reduces pain and improves a variety of disease symptoms significantly and safely. The results, published in the September 2004 issue of Arthritis & Rheumatism, offer the promise of relief for women with fibromyalgia. “Our results suggest that duloxetine improves pain and sensitivity, the hallmarks of fibromyalgia,” says Lesley M. Arnold, MD, who coordinated the research at 18 centers, including the University of Cincinnati School of Medicine, Faculty of Medicine of the Indiana University and Harvard School of Medicine. “The effect of duloxetine in reducing pain,” says Dr. Arnold, “seems to be independent of its effect on mood.”

To evaluate the effectiveness of duloxetine in the range of symptoms, the researchers recruited 207 patients, all meeting the criteria of the American College of Rheumatology for fibromyalgia. Like most people with this disease, the majority of participants, 89 percent, were women. 87 percent of the subjects were Caucasian and the average age was 49 years. A little over a third of the patients (38 percent) had been diagnosed with depression. Randomly, patients were prescribed one of two treatments for a 12-week course. Approximately half, 104 people, received 60 milligrams of duloxetine twice a day. The remaining 103 patients received a placebo. Both groups were evaluated and qualified, using the Fibromyalgia Impact Questionnaire and other standard measures, to improve their condition. In various measures of the disease, from generalized pain to fatigue and hypersensitivity, fibromyalgia patients treated with duloxetine improved significantly compared to those treated with placebo. One of the most drastic changes was the reduction in the number of tender points (places in the body where it hurts to touch) and the increase in the pain threshold of pressure.

Women with or without depression receiving duloxetine benefited emotionally and physically, reporting improvements in general mood, ability to function and general enjoyment of life. For the 23 men in the study, however, duloxetine did little to change their condition. Although the researchers reported some evidence of improvement in the sensitive spot measures among men treated with duloxetine compared to their counterparts treated with placebo, it was not statistically significant. “The reasons for the sex differences in the response are unclear,” observes Dr. Arnold. “Because the male subgroup was small, reflecting the much higher prevalence of fibromyalgia in women, the results of the study may not be generalizable for all men with fibromyalgia. There may also be sexual differences in fibromyalgia that affect the response to treatment. ” As Dr. Arnold points out, more research is needed on larger samples not only of men but also of other groups with fibromyalgia to evaluate the effectiveness of duloxetine. Duloxetine (Cymbalta®) is indicated by the FDA for the treatment of major depressive disorder and is not indicated for the treatment of fibromyalgia.

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