Topiramate

Definition

Topiramate is an anticonvulsant indicated for the control of seizures in the treatment of epilepsy (a neurological dysfunction in which excessive surges of electrical energy are emitted in the brain) and Lennox-Gastaut syndrome (a disorder which causes seizures and developmental delays).

In psychiatry, topiramate may also be used in the treatment of bipolar affective disorders .

Purpose

Topiramate is thought to decrease and balance the abnormal electrical activity within the brain that may trigger seizures. While topiramate controls some types of seizures associated with epilepsy, there is no known cure for the disorder.

In patients with bipolar disorders, topiramate stabilizes mood without producing a euphoric feeling or inducing manic episodes.

Description

In the United States, topiramate is sold under the brand name Topamax.

Topiramate is most commonly prescribed to treat patients who do not respond to other anticonvulsant medications, or is part of a combination of anticonvulsant medications used to treat intractable seizures. Although the precise mechanisms by which it exerts its therapeutic effects in epilepsy and other seizure disorders are unknown, topiramate has three specific seizure-reducing actions:

• topiramate decreases nerve-cell excitation by blocking targeted neurotransmitters from binding to certain receptors in the brain.
• topiramate blocks sodium channels in nerve cells, thus decreasing excessive nerve-cell firing.
• topiramate increases the availability of GABA, (gammaaminobutyric acid), a neurotransmitter that inhibits nerve-cell excitation in the brain.

Recommended dosage

Topiramate is taken by mouth in tablet or sprinkle form. Topiramate is available in strengths of 25 mg, 100 mg, and 200 mg tablets, along with 15 mg and 25 mg sprinkle capsules. Patients usually take topiramate twice daily. Typical total daily doses are usually between 200 milligrams (mg) to 400 mg for treatment of seizure disorders. For the treatment of bipolar disorders, dosages vary.

Beginning a course of treatment which includes topiramate requires a gradual dose-increasing regimen. The prescribing physician determines the proper beginning dosage and may raise a patient's daily dosage gradually over the course of several weeks. It may take several weeks to realize the full seizure-reducing benefits of topiramate.

A double dose of topiramate should not be taken to make up for a missed or forgotten dose. If a daily dose is missed, it should be taken as soon as possible. However, if it is almost time for the next dose, the missed dose is skipped. When discontinuing treatment with topiramate, physicians typically direct patients to gradually taper their daily dosages. Stopping the medicine suddenly may cause seizures to return or occur more frequently.

In the treatment of bipolar disorders, persons should not stop taking topiramate without consulting the prescribing physician. Stopping the medicine suddenly may cause seizures, or severely and suddenly alter a patient's mood.

Precautions

Topiramate is not habit-forming. A physician should be consulted before combining topiramate with certain non-prescription medications. Patients should avoid alcohol and CNS depressants (medicines that can make one drowsy or less alert, such as antihistimines, sleep medications, and some pain medications) while taking topiramate. Because topiramate may cause drowsiness, persons should not drive or operate heavy machinery until they know how they will react to the drug.

Persons taking topiramate, particularly those with predisposing factors, should maintain an adequate fluid intake in order to minimize the risk of kidney stone formation. Approximately 1.5% of people taking topiramate develop kidney stones.

Topiramate may not be suitable for persons with a history of liver or kidney disease, mental illness, high blood presure, angina (chest pain), irregular heartbeats, or other heart problems. Before beginning treatment with topiramate, patients should notify their physician if they consume a large amount of alcohol, have a history of drug use, are pregnant or planning on becoming pregnant.

Topiramate may inhibit perspiration, causing body temperature to increase. Persons taking topiramate are at a greater risk for heat stroke , and should use caution during strenuous exercise , prolonged exposure during hot weather, and while using saunas or hot tubs.

Topiramate may cause birth defects. Use effective birth control while taking topiramate. Patients who become pregnant while taking topiramate should contact their physician immediately.

Side effects

Patients and their physicians should weigh the risks and benefits of topiramate before beginning treatment. Topiramate is usually well tolerated, but may cause a variety of usually mild side effects. Dizziness and drowsiness are the most frequently reported side effects of topiramate. Other possible side effects include:

• double vision
• tingling or prickly feeling of the extremeties
• language problems described as "trouble finding the right word"
• loss of appetite and nervousness (in children)

Many of these side effects disappear or occur less frequently during treatment as the body adjusts to the medication. However, if any symptoms persist or become too uncomfortable, the prescribing physician should be consulted.

Other, uncommon side effects of topiramate can lead to serious complications. A person taking topiramate who experiences any of the following symptoms should immediately contact their physician:

• blurred vision and eye pain
• extreme mood or mental changes
• shakiness or unsteady walking
• kidney stones
• difficulty breathing
• chest pain
• irregular heartbeat
• faintness or loss of consciousness

Interactions

Topiramate may have negative interactions with some antihistimines, antidepressants, antibiotics, and monoamine oxidase inhibitors (MAOIs). Other medications such as diazepam (Valium), phenobarbital (Luminal, Solfoton), nefazodone, metronidazole, acetazolamide (Diamox), lanoxin (Digoxin, Digitek), phenytoin (Dilantin), primidone , and propranolol (Inderal) may also need to be adjusted and closely monitored if taken with topiramate. Topiramate, like many other anticonvulsant medications, may decrease the effectiveness of oral contraceptives (birth control pills).

Resources

BOOKS

Devinsky, Orrin. Epilepsy: Patient and Family Guide, 2nd. ed. Philadelphia: F. A. Davis Co., 2001.

Weaver, Donald F. Epilepsy and Seizures: Everything You Need to Know. Toronto: Firefly Books, 2001.

OTHER

Ortho-McNeil Pharmaceuticals. "Information for People Taking TOPAMAX®." Topamax. (April 4, 2004). <http://www.topamax.com/patients/index.htm>.

"Topiramate." Medline Plus. National Library of Medicine. (April 4, 2004). <http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a697012.html>.

ORGANIZATIONS

American Epilepsy Society. 342 North Main Street, West Hartford, CT 06117-2507. <http://www.aesnet.org>.

Epilepsy Foundation. 4351 Garden City Drive, Landover, MD 20785-7223. (800) 332-1000. <http://www.epilepsyfoundation.org>.

Adrienne Wilmoth Lerner