Anticonvulsants

Definition

Anticonvulsants are a class of drugs indicated for the treatment of various types of seizures associated with seizure disorders such as epilepsy , a neurological dysfunction in which excessive surges of electrical energy are emitted in the brain, and other disorders.

Some anticonvulsants are indicated for other medical uses. Some hydantoins , such as phenytoin, are also used as skeletal muscle relaxants and antineuralgics in the treatment of neurogenic pain . Some anticonvulsants and antiepileptic drugs (AEDs) are used in psychiatry for the treatment of bipolar disorders (manic-depression).

Purpose

Although there is no cure for the disorder, anticonvulsants are often effective in controlling the seizures associated with epilepsy. The precise mechanisms by which many anticonvulsants work are unknown, and different sub-classes of anticonvulsants are thought to exert their therapeutic effects in diverse ways. Some anticonvulsants are thought to generally depress central nervous system (CNS) function. Others, such as GABA inhibitors, are thought to target specific neurochemical processes, suppress excess neuron function, and regulate electrochemical signals in the brain.

Description

There are several sub-classes and types of anticonvulsants. They are marketed in the United States under a variety of brand names.

• Barbiturates, including Mephobarbital (Mebaral), Pentobarbital (Nembutal), and Phenobarbital (Luminol, Solfoton).
• Benzodiazepines, including Chlorazepate (Tranxene), Clonazepam (Klonopin), and Diazepam (Valium).
• GABA Analogues, including Gabapentin (Neurontin) and Tiagabine (Gabitril).
• Hydantoins, including Ethotoin (Peganone), Fosphentyoin (Mesantoin), and Phenytoin (Dilantin).
• Oxazolidinediones, including Trimethadione (Tridione).
• Phenyltriazines, including Lamotrigine (Lamictal).
• Succinamides, including Ethosuximide (Zarontin), Methsuximide (Celontin), and Phensuximide (Milontin).
• Other anticonvulsants, including Acetazolamide (Diamox), Carbamazepine (Carbatrol, Tegretol), Felbamate (Felbatol), Levetiracetam (Keppra), Oxcarbazepine (Trileptal), Primidone (Mysoline), Topiramate (Topamax), Valproic acid (Depakene, Depakote), and Zonisamide (Zonegran).

A physician prescribes anticonvulsant medication, or a combination of anticonvulsant medications, according to seizure type and pattern in individual patients. Some anti-convulsant medications are not appropriate for pediatric patients under 16 years of age.

Recommended dosage

Anticonvulsants are available in oral suspension (syrup), injectable, capsule, tablet, and sprinkle forms, depending on the type of medication. Not all anticonvulsants will be available in all forms. Anticonvulsants are prescribed by physicians in varying daily dosages, depending on the age, weight, and other health concerns of the individual patient, as well as the severity and frequency of their seizures.

It is important to follow the prescribing physicians directions carefully as each individual anticonvulsant medication has its own recommended daily dosages and dose schedule. Some anticonvulsants are taken in a single daily dose; others are taken in divided, multiple daily doses. A double dose of any anticonvulsant medication should not be taken. If a dose is missed, it should be taken as soon as possible. However, if it is within four hours of the next scheduled dose, the missed dose should be skipped. Taking an anticonvulsant at regular intervals and at the same time each day enables consistent levels of the medication to be maintained in the bloodstream, and results in more effective seizure control.

In general, initiating any course of treatment which includes anticonvulsants requires a gradual dose-increasing regimen. Adults and children typically take a smaller daily dose for the first two weeks. Daily dosages of anti-convulsant medication may then be slowly titrated, or increased over time until adequate seizure control is achieved using the lowest dose possible.

When ending a course of treatment of anticonvulsant, physicians typically taper the patient's daily dose over a period of several weeks. Suddenly stopping treatment including anticonvulsants may cause seizures to return or occur with greater frequency. Patients taking anticonvulsants drugs for the treatment of pain or bipolar disorders may experience also have seizures, even if they have never had them before, if they suddenly stop taking the medication.

Precautions

Each anticonvulsant medication may have its own precautions, counter-indications, and side-effects. However, many are common to all anticonvulsant medications.

Consult the prescribing physician before taking any anticonvulsant with non-perscription medications. Patients should avoid alcohol and CNS depressants (medications that make one drowsy or tired, such as antihistimines, sleep medications, and some pain medications) while taking anticonvulants. Anticonvulsants can exacerbate the side effects of alcohol and other medications. Alcohol may also increase the risk or frequency of seizures.

Anticonvulsants may not be suitable for persons with a history of stroke , anemia, thyroid, liver, depressed kidney function, diabetes mellitus, severe gastro-intestional disorders, porphyria, lupus , some forms of mental illness, high blood presure, angina (chest pain), irregular heartbeats, and other heart problems.

Before beginning treatment with anticonvulsants, patients should notify their physician if they consume a large amount of alcohol, have a history of drug use, are nursing, pregnant, or plan to become pregnant.

Physicians generally advise the use of effective birth control while taking many anticonvulsant medications. Patients taking anticonvulsants should be aware that many anticonvulsants may increase the risk of birth defects. Furthermore, many anticonvulsant medications are secreted in breast milk. Patients who become pregnant while taking any anticonvulsant should contact their physician immediately to discuss the risks and benefits of continuing treatment during pregnancy and while nursing.

Some anticonvulsants may be prescribed for children. However, children may experience increased side effects. Research indicates that some children who take high doses of some anticonvulsants (such as hydantoins) for an extended period of time may experience mild learning difficulties or not perform as well in school.

Side effects

In some patients, anticonvulsants may produce usually mild side effects. Headache , nausea, and unusual tiredness and weakness are the most frequently reported side effects of anticonvulsants. Other general side effects of anticonvulsants that do not usually require medical attention include:

• mild coordination problems
• mild dizziness
• abdominal pain or cramping
• sinus pain
• sleeplessness or nightmares
• change in appetite
• mild feelings of anxiety
• feeling of warmth
• tingling or prickly feeing on the skin, or in the toes and fingers
• mild tremors
• diarrhea or constipation
• heartburn or indigestion
• aching joints and muscles or chills
• unpleasant taste in mouth or dry mouth

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 perscribing physician should be consulted.

Other, uncommon side effects of anticonvulsants can be serious or may indicate an allergic reaction. A patient taking any anticonvulsant who experiencs one or more of the following symptoms should contact the prescribing physician immediately:

• rash or bluish, purplish, or white patches on the skin
• jaundice (yellowing of the skin and eyes)
• bloody nose or unusual bleeding
• hallucinations (seeing visions or hearing voices that are not present)
• sores in the mouth or around the eyes
• ringing or vibrations in the ears
• depression or suicidal thoughts
• mood or mental changes, including excessive fear, anxiety, hostility
• severe tremors
• prolonged numbness in the extremeties
• general loss of motor skills
• persistent lack of appetite
• altered vision
• frequent or burning urination
• difficulty breathing
• chest pain or irregular heartbeat
• faintness or loss of consciousness
• persistant, severe headaches
• persistant fever or pain.

Interactions

Anticonvulsants may have negative interactions with some antacids, anticoagulants, antihistimines, antidepressants, antibiotics, pain killers (including lidocaine) and monoamine oxidase inhibitors (MAOIs). Other medications such as amiodarone, diazoxide, phenybutazone, sulfonamides (sulfa drugs), corticosteroids, sucralfate, rifampin, and warfarin may also adversely react with anti-convulsants.

Some anticonvulsants should not be used in combination with other anticonvulsants. (For example, phenytoin (a hydantoin) when used with valproic acid, another anticonvulsant, may increase the seizure frequency). However, several anticonvulsant medications are indicated to be used in conjunction with or suppliment other anti-convulsants. If advised and carefully monitored by a physician, a course of treatment including multiple seizure prevention medications can be effective and safe.

Most anticonvulsants decrease the effectiveness of contraceptives that contain estrogens or progestins, including oral contraceptives (birth control pills), progesterone implants (Norplant), and progesterone injections (Depo-Provera).

Resources

BOOKS

Masters, Roger D., Michael T. McGuire. The Neurotransmitter Revolution. Southern Illinois University Press, 1994.

Mondimore, Francis Mark. Bipolar Disorder: A Guide for Patients and Families. Baltimore: The Johns Hopkins University Press, 1999.

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

Wyllie, Elaine. The Treatment of Epilepsy: Principles and Practice. New York: Lippincott, Williams & Wilkins, 2001.

PERIODICALS

Feely, Morgan. "Drug treatment of epilepsy." BMJ 318 (9 January 1999): 106–109.

"Risk of birth defects with anticonvulsants evaluated." Psychopharmacology Update 12, no. 5 (May 2001): 3.

OTHER

"Seizure Medicines." Epilepsy.com. <http://www.epilepsy.com/epilepsy/seizure_medicines.html> (May 1, 2004).

ORGANIZATIONS

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

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

Adrienne Wilmoth Lerner