Anticonvulsant medication gabapentin effective for fibromyalgia pain

New research supported by the National Institutes of Health's National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) shows that the anticonvulsant medication gabapentin, which is used for certain types of seizures, can be an effective treatment for the pain and other symptoms associated with the common, often hard-to-treat chronic pain disorder, fibromyalgia.

In the NIAMS-sponsored, randomized, double-blind clinical trial of 150 women (90 percent) and men with the condition, Lesley M. Arnold, M.D., director of the Women's Health Research Program at the University of Cincinnati College of Medicine, and her colleagues found that those taking gabapentin at dosages of 1,200 to 2,400 mg daily for 12 weeks displayed significantly less pain than those taking placebo. Patients taking gabapentin also reported significantly better sleep and less fatigue. For the majority of participants, the drug was well tolerated. The most common side effects included dizziness and sedation, which were mild to moderate in severity in most cases.

NIAMS Director Stephen I. Katz. M.D., Ph.D., remarked that While gabapentin does not have Food and Drug Administration approval for fibromyalgia, I believe this study offers additional insight to physicians considering the drug for their fibromyalgia patients. Fibromyalgia is a debilitating condition for which current treatments are only modestly effective, so a study such as this is potentially good news for people with this common, painful condition."

Fibromyalgia is a chronic disorder characterized by chronic, widespread muscle pain and tenderness, and is frequently accompanied by fatigue, insomnia, depression, and anxiety. It affects three million to six million Americans, mostly women, and can be disabling.

The precise cause of fibromyalgia in not known, but research suggests it is related to a problem with the central nervous system's processing of pain. As with some other chronic pain conditions, people with fibromyalgia often develop a heightened response to stimuli, experiencing pain that would not cause problems in other people. Yet, unlike many other pain syndromes, there is no physical evidence of inflammation or central nervous system damage.

Although gabapentin has little, if any, effect on acute pain, it has shown a robust effect on pain caused by a heightened response to stimuli related to inflammation or nerve injury in animal models of chronic pain syndromes. Researchers have suspected that it might have the same effect in people with fibromyalgia. The new research, published in the April 2007 edition of Arthritis & Rheumatism, indicates the suspicions were correct.

Although the researchers cannot say with certainty how gabapentin helps reduce pain, Dr. Arnold says one possible explanation involves the binding of gabapentin to a specific subunit of voltage-gated calcium channels on neurons. "This binding reduces calcium flow into the nerve cell, which reduces the release of some signaling molecules involved in pain processing," she says.

How gabapentin improves sleep and other symptoms is less clear, and there are probably different mechanisms involved in fibromyalgia symptoms. "Gabapentin improved sleep, which is an added benefit to patients with fibromyalgia who often report unrefreshing or disrupted sleep," Dr. Arnold says.

What is important is that people with fibromyalgia now have a potential new treatment option for a condition with few effective treatments. "Studies like this give clinicians evidence-based information to guide their treatment of patients," says Dr. Arnold.