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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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Does gabapentin improve restless legs syndrome? - Patient Oriented Evidence That Matters: practice recommendations from key studies
From Journal of Family Practice, 4/1/03 by Brett H. Foreman

Garcia-Borreguero D, Larrosa O, del la Llave Y, Verger K, Masramon X, Hernandez G. Treatment of restless legs syndrome with gabapentin. A double-blind, cross-over study. Neurology 2002; 59:1573-1579.

* PRACTICE RECOMMENDATIONS

Gabapentin (Neurontin) improves symptoms in patients suffering with restless legs syndrome. In this study, the average daily dose was 1800 mg, with one third of total daily dosage taken at 12 PM and the remaining two thirds at 8 PM. The retail cost would be approximately $6/day.

Nearly half of the patients taking gabapentin reported adverse effects (primarily malaise and somnolence symptoms), but none stopped the medication. Gabapentin avoids the common complication of augmentation (a worsening of symptoms in the course of therapy) seen with older dopaminergic medications. It is unclear if gabapentin has any advantage over newer dopaminergic medications such as pergolide, pramipexole, and ropinirole, which also appear to cause less augmentation. (1)

* BACKGROUND

Restless legs syndrome is characterized by an uncomfortable sensation in the legs, typically occurring prior to sleep, or which may awaken the patient from sleep. Iron deficiency is a major risk factor for restless legs syndrome.

* POPULATION STUDIED

The patients in this study met criteria for restless legs syndrome established by the International Restless Legs Syndrome Study Group. The 24 patients, from Madrid, Spain, consisted of 8 men and 26 women with a mean age of 55 [+ or -] 11.6 years. Patients with iron deficiency were included, except those with ferritin levels below 20 mcg/mL. The authors did not explain how patients were recruited, but the study was performed at a Sleep Disorders Unit.

* STUDY DESIGN AND VALIDITY

This was a randomized, double-blind crossover study. Patients were randomized through a computer-generated code to 1 of 2 treatment groups. Each group received either gabapentin or placebo for a 6-week period. Following a 1-week washout period, each group was given the alternative treatment for an additional 6 weeks. Gabapentin was started at 600 mg/day with a maximum dose of 2400 mg/day. The treating physicians had the opportunity to increase, decrease, or maintain the dosage every 2 weeks.

Patient symptoms were rated at baseline and every 2 weeks using the International Restless Legs Syndrome Study Group Rating Scale, Pittsburgh Sleep Quality Index, the Clinical Global Impression of Change, and polysomnography. No patients had been treated previously with gabapentin or dopaminergic medications. Iron was not administered during the study.

This study was well done, with appropriate attention to patient symptoms and response to treatment. There was concealed allocation of subjects. It may have been difficult to maintain blinding when so many of the treatment patients had side effects. We do not know how the study patients compare with the general population.

The limited number of participants and short treatment periods decrease the study's power to detect uncommon adverse reactions. The unfamiliar scoring scales used for analysis make it difficult to discern whether the improvements represent a clinically significant benefit. Three patients did not complete the study for various reasons, none of which was related to side effects.

* OUTCOMES MEASURED

The primary outcome was the change between baseline and week 6 on the restless legs syndrome rating scale. The secondary outcome measures were patient global impression of change at week 6, Pittsburgh Sleep Quality Index, and effects of both treatments on sleep architecture.

* RESULTS

The restless legs syndrome rating scale scores were lower in the gabapentin group than in the placebo group. The mean baseline score was 20 points (out of 40) and the mean posttreatment score in the gabapentin group was 9.5 [+ or -] 1.35 points, compared with 17.9 [+ or -] 1.35 points in the placebo group (P<.001). Differences in treatment groups were observed by week 4 (P<.01).

The secondary outcomes of the patient global impression of change, Pittsburgh Sleep Quality Index, and total sleep time were all improved with gabapentin. Patients with higher initial symptom scores benefited more from treatment than those with lower scores. Gabapentin improved both sensorial and motor symptoms and main sleep outcomes.

Nearly 48% of patients taking gabapentin and 20.8% taking placebo (P<.05) reported adverse effects. Commonly reported effects were malaise, abdominal pain, somnolence, headache, and dyspepsia. No significant differences existed in the rate of individual adverse effects between groups.

REFERENCE

(1.) Clark M. Restless legs syndrome. J Am Board Fam Pract 2001; 14:368-374.

Brett H. Foreman, MD, and Lee Chambliss, MD, MSPH, Moses Cone Family Practice Residency, Greensboro, NC. E-mail: Brett.Foreman@mosescone.com.

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