Gabapentin: Definition from Answers.com Mobile

Gabapentin

Key Terms: Bipolar disorder, Diabetic neuropathy, Multiple sclerosis, Postherpetic neuralgia.

Definition

Gabapentin is indicated to be used in combination with other anti-seizure (anticonvulsant) drugs for the management of partial seizure types. Gabapentin should not be used alone for the treatment of seizures unless the patient cannot tolerate other anticonvulsant drugs. This medication can also be used for the treatment of certain syndromes associated with nerve (neuropathic) pain (diabetic neuropathy, postherpetic neuralgia), pain associated with multiple sclerosis, neuropathic cancer pain, trigeminal neuralgia, and bipolar mood disorder. Gabapentin is also known as Neurontin.

Description

Gabapentin was introduced in 1994 as an anticonvulsant medication. Other medications in the anticonvulsant class include phenytoin, carbamazepine, phenobarbital, valproic acid, topiramate, and lamotrigine. Gabapentin's structure is similar to that of gamma-aminobutiric acid (GABA), which is a chemical found in the central nervous system (brain and spinal cord) that decreases firing of neurons leading to a decrease in seizure activity. Despite this structural similarity, gabapentin does not interact with GABA receptors and its exact mechanism of action for either epilepsy or pain is not known.

Gabapentin is a relatively recent addition to the arsenal of drugs used in the treatment of neuropathic pain. Traditionally, tricyclic antidepressants (amitriptyline, nortriptyline, desipramine) have been used as first-line agents. It takes one to three weeks for either gabapentin or tricyclic antidepressants (TCAs) to provide relief of pain after starting treatment. Gabapentin appears to be a safer agent to use than TCAs, especially in elderly patients and patients on multiple other medications. One of the disadvantages of gabapentin over TCAs is its higher cost.

Recommended Dosage

Adults and Children Over 12 Years of Age

Management of Partial Seizure Types

Therapy should be started at a dose of 300 mg, three times daily. The dose can be increased to 1,800 mg/day in three divided doses. Some patients may need even higher doses to control their seizures. Doses up to 3,600 mg per day have been well tolerated in research studies.

Treatment of Neuropathic Pain

Dosages of 300-3,600 mg/day have been effective in research studies. However, optimal dosage appears to be 1,200-2,400 mg/day divided in three doses.

Treatment of Bipolar Disorder

Optimal dose has not been well established. Doses up to 4,800 mg/day have been used.

Children Less Than 12 Years of Age

Dosage varies due to the child's size, weight, and extent of condition. Parents should ask their physician about appropriate dosage levels for their child.

Administration

To minimize side effects, the first dose should be taken at bedtime. Capsules should not be chewed or crushed. Patients should avoid taking antacids (Mylanta, Maalox) at the same time as gabapentin. Doses should be taken at even intervals, and if a dose is missed, it should be taken as soon as remembered. However, double-doses can be hazardous and should be avoided.

Precautions

Gabapentin should be used with caution by breast-feeding mothers, children under 12 years of age (because of a lack of safety and efficacy studies in this population), and patients with impaired kidney function.

Gabapentin has resulted in fetal abnormalities in mice, rats, and rabbit offsprings. There are no current studies on gabapentin use in pregnant women. This drug should only be used during pregnancy if potential benefits justify the risk to the baby.

This medication should not be discontinued suddenly because of the possibility of increased frequency of seizures. Gabapentin doses should be decreased gradually over a period of at least one week.

Gabapentin may cause drowsiness and dizziness. Alcoholic beverages may intensify these effects and their intake should be limited. Patients should use caution when driving, operating dangerous machinery, or performing activities requiring alertness.

A patient experiencing any of the following should contact their physician or pharmacist immediately:

mental or mood changes
tingling or numbness of hands or feet
swelling of ankles
vision problems
fever or unusual bleeding

Side Effects

This medication is usually well tolerated. Nervous system side effects are the most common, including drowsiness, dizziness, unsteadiness when walking, fatigue, and vision changes (double-vision, blurred vision). These side effects appear to be dose-related, and some patients may develop tolerance to these effects after the first several weeks of therapy. If these side effects persist or worsen, a physician should be notified. Other side effects that occur less frequently are irritability, dyspepsia, mood changes, memory loss, difficulty concentrating, slurred speech, and impotence. Elderly patients may be more sensitive to the side effects of gabapentin.

Interactions

One of the advantages of gabapentin is that it is not broken down in the body and does not have a lot of drug interaction. Antacids may interfere with the absorption of this medication in the body; they should be taken at least two hours apart. Gabapentin does not effect other commonly used anticonvulsants (for example, phenytoin, carbamazepine, valproic acid, and phenobarbital).

—Olga Bessmertny, Pharm.D.