A drug commonly used to treat Parkinson's disease may also ease the pain of fibromyalgia.

A new study found that most people with fibromyalgia who took Mirapex in addition to their other medications experienced a significant decrease in pain. About eight in 10 reported some improvement in pain, and more than four in 10 reported a 50 percent or more improvement in their pain symptoms.

Fibromyalgia is a chronic condition that produces symptoms including muscle pain, fatigue, and sleep disturbances. The cause of fibromyalgia is unknown, and current treatments, such as antidepressants, muscle relaxants, and pain relievers, are designed to ease the symptoms rather than address the cause of the disease.

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New Target for Fibromyalgia Treatment?

But researchers say new findings suggest that the pain associated with fibromyalgia may be caused by abnormal signal processing in the brain and central nervous system. Therefore, targeting how the nervous system sends pain signals to the brain and then how the brain interprets those messages may offer a new avenue for fibromyalgia treatment.

Mirapex is part of a class of drugs known as dopamine receptor agonists that targets this pathway. The drug stimulates the production of the brain transmitter dopamine and is believed to inhibit sensory responses like pain.

The results appear in the August issue of Arthritis & Rheumatism.

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Mirapex May Ease Fibromyalgia Pain

In the study, researchers randomly assigned 60 people with fibromyalgia to take gradually increasing doses of Mirapex or a placebo every evening for 14 weeks.

About 50 percent of the patients had severe fibromyalgia; they required narcotic painkillers and/or were disabled from their condition.

Researchers allowed the participants to continue to take whatever treatments they were already using for their condition at the start of the study, but they were not allowed to start new treatments during the study.

Most of the 11 participants who did not complete the study were eliminated for starting a new treatment. None withdrew due to side effects caused by the medication.

Of the 49 who completed the study, those treated with Mirapex reported a significant decrease in pain compared with the placebo group. For example:

42 percent of the Mirapex group had a 50 percent or more decrease in pain vs. 14 percent of the placebo group. 82 percent of people taking Mirapex noted some improvement in pain vs. 57 percent of the placebo group. The Mirapex group also saw more improvement in function and fatigue.

Researchers say the drug was well-tolerated, and the most common side effects of the drug were weight loss and nausea. The fibromyalgia patients did not suffer from hallucinations and sleep attacks commonly reported by people taking Mirapex for Parkinson's disease.

Researchers say the results of this preliminary study suggest further study of Mirapex in the treatment of fibromyalgia pain is warranted to determine its long-term risks and benefits.

Mirapex is co-marketed by Pfizer, a WebMD sponsor.

By Jennifer Warner, reviewed by Michael W. Smith, MD

SOURCES: Holman, A. Arthritis & Rheumatism, August 2005; vol 52: pp 2495-2505. News release, Wiley InterScience.