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Gabapentin

Definition

Gabapentin is an anti-seizure medication. It is sold in the United States under the trade name Neurontin.

Purpose

Gabapentin is used in combination with other antiseizure (anticonvulsant) drugs to manage partial seizures with or without generalization in individuals over the age of 12. Gabapentin can also be used to treat partial seizures in children between the ages of three and 12. Off-label uses (legal uses not specifically approved by the United States Food and Drug Administration [FDA]) include treatment of severe, chronic pain caused by nerve damage (such as occurs in shingles, diabetic neuropathy, multiple sclerosis, or post-herpetic neuralgia). Studies are also looking at using gabapentin to treat bipolar disorder (also known as manic-depressive disorder).

Description

Brain cells normally transmit nerve impulses from one cell to another by secreting chemicals known as neurotransmitters.

Gabapentin is chemically related to a naturally occurring neurotransmitter called GABA (gamma-amino butyric acid). The actual mechanism of action by which gabapentin acts in the brain to control seizures and treat pain is not known, although it appears to alter the action of nerve cells.

Gabapentin was approved for use in the United States in 1993. A liquid formulation was approved for use in 2000. Use in children ages three to 12 was also approved by the FDA in 2000.

Gabapentin is available in 100-, 300-, and 400-mg capsules; in 600- and 800-mg tablets; and in a liquid solution containing 250 mg per 5 ml.

Recommended dosage

People over the age of 12 should be started on 300 mg gabapentin taken three times a day. The dose can be increased up to a total of 1,800 mg per day. In some instances, doses of up to 3,600 mg per day have been tolerated.

Children should receive a dosage of 10–15 mg per kg of body weight per day, divided into three equal doses.

Chronic pain may be treated with 300–3,600 mg per day, divided into three equal doses.

When gabapentin is used for bipolar disorder, the starting dose is usually 300 mg taken at bedtime. Depending on the patient's response, the dose can be increased every four to seven days. Many people receive maximum therapeutic benefit at 600 mg per day, although some people have required up to 4,800 mg per day.

Precautions

Women who are breast-feeding and people who have decreased kidney functioning should discuss the risks and benefits of this drug with their physician. Women who are or wish to become pregnant will also require a careful assessment of the risks and benefits of gabapentin.

Patients should not suddenly discontinue gabapentin, as this can result in an increased risk of seizures. If the medication needs to be discontinued, the dosage should be reduced gradually over a week.

Until an individual understands the effects that gabapentin may have, he or she should avoid driving, operating dangerous machinery, or participating in hazardous activities. Alcohol should be avoided while taking gabapentin.

Side effects

Patients who experience the following side effects of gabapentin should check with their doctor immediately. These include more common side effects, such as unsteadiness, clumsiness, and uncontrollable back-and-forth eye movements or eye rolling. Less common side effects include depression, irritability, other mood changes or changes in thinking, and decreased memory. Rare side effects include pain in the lower back or side, difficulty urinating, fever and/or chills, cough, or hoarseness.

Children under age 12 who have the following more common side effects should also check with their doctor immediately: aggressive behavior, irritability, anxiety, difficulty concentrating and paying attention, crying, depression, mood swings, increased emotionality, hyperactivity, suspiciousness or distrust.

Multiple side effects often occur when a patient starts taking gabapentin. While these side effects usually go away on their own, if they last or are particularly troublesome, the patient should consult a doctor. More common side effects that occur when first starting to take gabapentin include blurred or double vision, muscle weakness or pain, swollen hand, feet, or legs, trembling or shaking, and increased fatigue or weakness. Less common side effects that occur when initiating gabapentin treatment include back pain, constipation, decreased sexual drive, diarrhea, dry mouth and eyes, frequent urination, headache, indigestion, low blood pressure, nausea, ringing in the ears, runny nose, slurred speech, difficulty thinking and sleeping, weight gain, twitching, nausea and/or vomiting, weakness.

Interactions

Antacids can decrease gabapentin levels in the blood. They should be taken at least two hours before taking gabapentin.

Resources

BOOKS

Ellsworth, Allan J. Mosby's Medical Drug Reference. St. Louis, MO: Mosby, Incorporated, 1999.

Mosby's Drug Consult. St. Louis, MO: Mosby, Incorporated, 2002.

Rosalyn Carson-DeWitt, M.D.