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Gabapentin

Gabapentin (brand name: Neurontin^®) is an anticonvulsant medication indicated in the treatment of epilepsy and neuropathic pain. Gabapentin is known for having a relatively mild side-effect profile, and passes through the body unmetabolized. more...

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Gabapentin is similar in structure to the neurotransmitter GABA but is not believed to act on the same brain receptors. Its exact mechanism of action is unknown, but its therapeutic action on neuropathic pain is thought to involve voltage-gated calcium ion channels.

Clinical uses

Gabapentin has also been used in the treatment of bipolar disorder. However, its off-label use for this purpose is increasingly controversial. Some claim gabapentin acts as a mood stabilizer and has the advantage of having fewer side-effects than more conventional bipolar drugs such as lithium and valproic acid. Some small, non-controlled studies in the 1990s, most sponsored by gabapentin's manufacturer, suggested that gabapentin treatment for bipolar disorder may be promising. However, more recently, several larger, controlled, and double-blind studies have found that gabapentin was no more effective than (and in one study, slightly less effective than) placebo, and the manufacturer has even halted its own studies regarding gabapentin and bipolar disorder. Despite this scientific evidence against the efficacy of gabapentin in the treatment of bipolar disorder, many psychiatrists continue to prescribe it for this purpose.

Gabapentin has also been used off label in the treatment of anxiety disorders such as social anxiety disorder and obsessive-compulsive disorder, in treatment-resistant depression, and for insomnia. Gabapentin may be effective in reducing pain and spasticity in multiple sclerosis.

In addition to its use in mood disorders, gabapentin was approved by the FDA for treating postherpetic neuralgia (neuropathic pain following shingles).

Marketing of gabapentin

Gabapentin is best known under the brand name Neurontin manufactured by Pfizer . In October 2004, FDA approved a generic equivalent to Neurontin made by Israeli firm Teva. Neurontin is one of Pfizer’s best selling drugs, and was one of the 50 most prescribed drugs in the United States in 2003. However, in recent years Pfizer has come under heavy criticism for its marketing of Neurontin, facing allegations that behind the scenes Pfizer marketed the drug for at least a dozen supposed uses for which the drug had not been FDA approved. By some estimates, so-called off-label prescriptions account for roughly 90% of Neurontin sales. While off-label prescriptions are common for a number of drugs and are perfectly legal (if not always appropriate), marketing for off-label uses of a drug is strictly illegal. In 2004, Pfizer agreed to pay a $430 million settlement for the illegal marketing of Neurontin for off-label purposes, and further legal action is pending.

Pfizer has developed a successor to gabapentin, called pregabalin (being marketed as Lyrica®). Structurally related to gabapentin, Pregabalin is effective for neuropathy pain assciated with diabetes and shingles, and for the treatment of epilepsy and seizures.

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Gabapentin reduces hot flushes - Tips from Other Journals - Author Abstract
From American Family Physician, 9/1/03 by Anne D. Walling

Approximately 75 percent of postmenopausal women and 40 percent of perimenopausal women experience hot flushes with the associated symptoms of sleep and mood disturbance and decreased quality of life. Hormone therapy effectively relieves symptoms of hot flushes, but it is now associated with increased rates of heart and breast disease and other adverse effects. Gabapentin has been noted to relieve hot flushes in patients during tamoxifen or leuprolide therapy. Guttuso and colleagues studied the ability of gabapentin to relieve the frequency and severity of hot flushes in postmenopausal women.

They recruited 59 healthy postmenopausal women who reported at least seven hot flushes daily. Women were excluded if they had less than 12 months of amenorrhea; had taken hormones or tamoxifen within two months; had changed intake of clonidine, raloxifene, or any antidepressant medication in the past month; or were taking gabapentin or a calcium channel antagonist medication. After screening, the women were randomly assigned to receive gabapentin (300 mg three times daily) or an identical-looking placebo. Patients recorded hot flushes in a diary and had follow-up visits after two, four, and 12 weeks of treatment. Assessments included sleep quality, mood, quality of life, and global impression of change measures. Adverse events also were recorded.

In the 54 women who completed the double-blind study, those assigned to the gabapentin group recorded a 45 percent decrease in mean hot flush frequency and a 54 percent reduction in mean hot flush composite score. The corresponding scores for the placebo group were 29 and 31 percent, respectively. The change was apparent after the first week of therapy and was not significantly altered by adjustment for baseline variables. Two thirds of women treated with gabapentin reported a more than 50-percent reduction in hot flush composite score, compared with 38 percent of those treated with placebo. Although 15 women treated with gabapentin reported at least one adverse effect, only four withdrew from the study because of adverse effects. The most common adverse effects were somnolence (20 percent), dizziness (13.3 percent), and rash (6.7 percent). Sleep quality initially improved in women treated with gabapentin, but by week 12, there was no significant difference between the groups. Measures of mood, general health, vital signs, and weight change were not significantly different between the groups.

The authors conclude that low-dose gabapentin effectively relieved hot flushes in postmenopausal women, and they call for larger studies to confirm their findings.

Guttuso T Jr, et al. Gabapentin's effects on hot flashes in postmenopausal women: a randomized controlled trial. Obstet Gynecol February 2003;101:337-45.

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