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Gabapentin (Neurontin) Eases Chronic Pain in Fibromyalgia
June 13, 2007
Judith Groch, Senior Writer, MedPage Today
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco
For treating the chronic pain and other symptoms of fibromyalgia, the
anticonvulsant gabapentin (Neurontin) proved safe and effective,
researchers here reported.
In a 12-week randomized, double-blind clinical trial, patients
taking gabapentin displayed significantly less pain, better sleep, and
less fatigue than placebo controls, Lesley M. Arnold, M.D., of the
University of Cincinnati, and colleagues reported in the April issue of
Arthritis and Rheumatism.
However, the drug had no effect on acute pain points or depression, the researchers reported.
Although gabapentin, which was used off-label for fibromyalgia, 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, Dr. Arnold
said.
Studies have also found the drug to have a substantial analgesic
effects on diabetic neuropathy, postherpetic neuralgia, migraine, and
other neuropathic pain conditions, as well as beneficial effect on
sleep and restless legs syndrome. On the basis of these findings, the
researchers suspected that gabapentin might also ease fibromyalgia
pain.
The study, supported by the National Institute of Arthritis and
Musculoskeletal and Skin Diseases, included 150 mainly white
fibromyalgia patients (90% women). Of these, 75 took gabapentin at
dosages of 1,200 to 2,400 mg daily for 12 weeks, while there were 75
placebo controls.
The study was conducted at three outpatient research centers in the U.S., from September 2003 to January 2006.
The mean pain severity scores, measured by the Brief Pain Inventory
(BPI), decreased in both groups but more so among the gabapentin
patients (P = 0.015). The estimated difference between groups at week
12 was - 0.92 (95% confidence interval -1.75, -0.71).
Of the gabapentin-treated patients, 51% achieved a response at the endpoint compared with 31% of the placebo patients.
Gabapentin compared with placebo also significantly improved the BPI
average pain interference score, as well as a series of other scores.
These included the Fibromyalgia Impact Questionnaire total score, the
Clinical Global Impression of Severity Improvement, the Patient Global
Impression of Improvement, the Medical Outcomes Study (MOS), the Sleep
Problems Index, and the MOS Short Form 36 vitality score.
However, the drug had no effect on acute pressure-point
pain or depression (the Montgomery Asberg Depression Rating Scale), the
researchers reported. Overall, the drug was well-tolerated. Of the 150
patients, 19 dropped out due to adverse events, with no significant
difference between the treatment groups. The gabapentin patients
reported dizziness, sedation, lightheadedness, and weight gain
significantly more often that did the placebo-treated patients.
Notably, the researchers said, there was no significant difference in
weight change in the two groups as measured in the clinic, although
edema may have explained some of the patients' perceptions. Most
treatment adverse events, they reported, were mild to moderate in
severity.
The pathophysiology of fibromyagia is unknown, but
evidence suggests that it is associated with aberrant central nervous
system pain processing, the researchers said.
The drug appears to be effective in reducing abnormal
hypersensitivity induced by inflammatory responses or nerve injury. Yet
unlike many other pain syndromes, there is no physical evidence of
inflammation or CNS damage. One possible explanation, Dr. Arnold said,
is that gabapentin's effects involve binding to a specific subunit of
voltage-gated calcium channels on neurons. This binding, she said,
reduces calcium flow into the nerve cell, which reduces the release of
some signaling molecules involved in pain processing.
In discussing the study's limitations, the researchers
said that because the study was short, the results may not generalize
to longer treatment periods, and long-term efficacy should be studied
in future clinical trials.
Also, because the study was relatively small, they said
it may have lacked the power to detect potentially relevant differences
between the groups. Finally, they wrote that the results may not apply
to patients with some comorbid psychiatric disorders, such as bipolar
disorder, or to patients with other painful musculoskeletal disorders.
"In this, the first randomized, placebo-controlled
study to evaluate gabapentin in the treatment of fibromyalgia, the
results demonstrated that gabapentin, taken for up to 12 weeks, is
effective and safe in the treatment of pain and other symptoms
associated with fibromyalgia," Dr. Arnold concluded.
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