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Hydantoin anticonvulsants are most commonly used in the treatment of seizures associated with epilepsy , a neurological dysfunction in which excessive surges of electrical energy are emitted in the brain. Some hydantoins, such as phenytoin, are also indicated for use as skeletal muscle relaxants and in the treatment of severe nerve pain , as in trigeminal neuralgia .


While hydantoins control the seizures associated with epilepsy, there is no known cure for the disorder. The precise mechanisms by which hydantoins work are unknown, but they are thought to exert their therapeutic effect by depressing abnormal neuronal discharges in the central nervous system (CNS).


For the treatment of seizures, hydantoins may be used alone or in combination with other anti-epileptic drugs (AEDs) or anticonvulsants. However, the use of multiple anticonvulsants and AEDs should be carefully monitored by the prescribing physician. Phenytoin, mephenytoin, ethotoin, and fosphenytoin are the individual hydantoin anticonvulsants. They are marketed under several brand names, including Cerebyx, Dilantin, Mesantoin, Peganone, and Phentek.

Recommended dosage

Hydantoins anticonvulsants are available in oral and injectable (phenytoin and fosphenytoin only) forms. Orally-administered hydantoins are available in the form of tablets, capsules, or oral suspension. Hydantoins are prescribed by physicians in varying daily dosages.

Some hydantoin anticonvulsants are taken in divided daily doses, twice daily. Others are administered in a single daily dose. A double dose of any hydantoin should not be taken. If a dose is missed, it should be taken as soon as possible. However, if it is almost time for the next dose, the missed dose should be skipped.

It may take several weeks to realize the full benefits of hydantoins. Beginning any course of treatment including hydantoins requires a gradual dose-increasing regimen. Children and adults typically take a smaller daily dose for the first two weeks. Daily dosages of hydantoins may then be slowly increased over time. When ending a course of treatment that includes hydantoin anticonvulsants, physicians typically taper the patient's daily dose over a period of several weeks. Suddenly stopping treatment with hydantoins may cause seizures or pain to occur or return with greater frequency.


Persons taking hydantoins should consult the prescribing physician before taking non-perscription medications. Patients should avoid alcohol and CNS depressants (medications that make one drowsy such as antihistimines, sleep medications, and some pain medications) while taking hydantoins. These medications may increase the frequency and severity of the side effects of hydantoins. Hydantoins may also potentiate the action of alcohol, and alcohol can increase the risk or frequency of seizures.

Hydantoins may not be suitable for persons with a history of thyroid, liver, or kidney disease, depressed renal function, diabetes mellitus, porphyria, lupus , mental illness, high blood presure, angina (chest pain), or irregular heartbeats and other heart problems. Before beginning treatment with hydantoins, 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 usually advise women of child-bearing age to use effective birth control while taking hydantoin anticonvulsants. Many anticonvulsant medications, including hydantoins, have been shown to increase the risk of birth defects. Patients who become pregnant while taking hydantoins should contact their physician.

Some hydantoin anticonvulsant medications may be prescribed for children; however, children sometimes experience increased side effects. Research indicates that some children who take high doses of hydantoins for an extended period of time may experience mild learning difficulties or not perform as well in school.

Side effects

In some patients, hydantoins may produce some mild side effects. Drowsiness and dizziness are the most frequently reported side effects of anticonvulsants. Other general side effects of hydantoins that usually resolve without medical attention include:

  • mild coordination problems
  • constipation
  • muscle twitching
  • unpleasant taste in mouth or dry mouth
  • unusual or excessive hair growth on face or body.

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 hydantoins may indicate an allergic reaction or other potentially serious condition. A patient taking hydantoin who experiencs any of the following symptoms should contact their physician immediately:

  • rash, excessive bruising, or bluish patches on the skin
  • bleeding in the gums or mouth
  • ringing or vibrations in the ears
  • general loss of motor skills
  • severe lack of appetite
  • altered vision
  • difficulty breathing
  • chest pain or irregular heartbeat
  • faintness or loss of consciousness
  • persistent fever or pain


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

Some hydantoins should not be used with other anti-convulsants. For example, phenytoin (a hydantoin) when used with valproic acid (a non-hydantoin anticonvulsant) may increase the seizure frequency. However, some patients may use hydantoins with other seizure prevention medications if carefully monitored by a physician.

Hydantoins may decrease the effectiveness of contraceptives, including oral contraceptives (birth control pills), progesterone implants (Norplant), and progesterone injections (Depo-Provera).



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


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


"Anticonvulsants, Hydantoin (Systemic)." Medline Plus. National Library of Medicine. (April 20, 2004). <http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202052.html>.


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