Health Guide
Drug Guide

Anticonvulsant, hydantoin (Oral route, parenteral route)

Brand Names:

Dosage Forms:

Uses of This Medicine:

Hydantoin anticonvulsants are used most often to control certain convulsions or seizures in the treatment of epilepsy. Phenytoin also may be used for other conditions as determined by your doctor.

In seizure disorders, these medicines act on the central nervous system (CNS) to reduce the number and severity of seizures. Hydantoin anticonvulsants may also produce some unwanted effects. These depend on the patient's individual condition, the amount of medicine taken, and how long it has been taken. It is important that you know what the side effects are and when to call your doctor if they occur.

Hydantoin anticonvulsants are available only with your doctor's prescription.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, phenytoin is used in certain patients with the following medical conditions:

Before Using This Medicine:


Tell your doctor if you have ever had any unusual or allergic reaction to medicines in this group or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Some side effects, especially bleeding, tender, or enlarged gums and enlarged facial features, are more likely to occur in children and young adults. Also, unusual and excessive hair growth may occur, which is more noticeable in young girls. In addition, some children may not do as well in school after using high doses of this medicine for a long time.

Older adults

Some medicines may affect older patients differently than they do younger patients. Overdose is more likely to occur in elderly patients and in patients with liver disease.


Although most mothers who take medicine for seizure control deliver normal babies, there have been reports of increased birth defects when these medicines were used during pregnancy. It is not definitely known if any of these medicines are the cause of such problems.

Also, pregnancy may cause a change in the way hydantoin anticonvulsants are absorbed in your body. You may have more seizures, even though you are taking your medicine regularly. Your doctor may need to increase the anticonvulsant dose during your pregnancy.

In addition, when taken during pregnancy, this medicine may cause a bleeding problem in the mother during delivery and in the newborn. This may be prevented by giving vitamin K to the mother during delivery, and to the baby immediately after birth.


Ethotoin and phenytoin pass into the breast milk in small amounts. It is not known whether mephenytoin passes into breast milk. Be sure you have discussed the risks and benefits of the medicine with your doctor.

Other medicines

Using medicines in this class with any of the following medicines is not recommended. Your doctor may decide not to treat you with a medication in this class or change some of the other medicines you take.

Using medicines in this class with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Other interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Other medical problems

The presence of other medical problems may affect the use of medicines in this class. Make sure you tell your doctor if you have any other medical problems, especially:

Proper Use of This Medicine:

Because fosphenytoin is converted to phenytoin in the body, it has the same effects as those listed for phenytoin.

For patients taking the liquid form of this medicine:

For patients taking the chewable tablet form of this medicine:

For patients taking the capsule form of this medicine:

If this medicine upsets your stomach, take it with food, unless otherwise directed by your doctor. The medicine should always be taken at the same time in relation to meals to make sure that it is absorbed in the same way.

To control your medical problem, take this medicine every day exactly as ordered by your doctor. Do not take more or less of it than your doctor ordered. To help you remember to take the medicine at the correct times, try to get into the habit of taking it at the same time each day.


The dose medicines in this class will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

Missed dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

If you miss a dose of this medicine and your dosing schedule is:

If you miss doses for 2 or more days in a row, check with your doctor.


Keep out of the reach of children.

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Do not keep outdated medicine or medicine no longer needed.

Keep the liquid form of this medicine from freezing. Do not refrigerate.

Precautions While Using This Medicine:

Your doctor should check your progress at regular visits, especially during the first few months of treatment with this medicine. During this time the amount of medicine you are taking may have to be changed often to meet your individual needs.

Do not start or stop taking any other medicine without your doctor's advice. Other medicines may affect the way this medicine works .

This medicine will add to the effects of alcohol and other CNS depressants (medicines that may make you drowsy or less alert). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; other medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine.

Do not take this medicine within 2 to 3 hours of taking antacids or medicine for diarrhea. Taking these medicines and hydantoin anticonvulsants too close together may make the hydantoins less effective.

Do not change brands or dosage forms of phenytoin without first checking with your doctor. Different products may not work the same way. If you refill your medicine and it looks different, check with your pharmacist.

If you have been taking this medicine regularly for several weeks or more, do not suddenly stop taking it. Your doctor may want you to reduce gradually the amount you are taking before stopping completely.

Your doctor may want you to carry a medical identification card or bracelet stating that you are taking this medicine.

For diabetic patients:

Before you have any medical tests, tell the doctor in charge that you are taking this medicine. The results of some tests (including the dexamethasone, metyrapone, or Schilling tests, and certain thyroid function tests) may be affected by this medicine.

Before having any kind of surgery, dental treatment, or emergency treatment, tell the medical doctor or dentist in charge that you are taking this medicine. Taking hydantoin anticonvulsants together with medicines that are used during surgery or dental or emergency treatments may cause increased side effects.

This medicine may cause some people to become dizzy, lightheaded, drowsy, or less alert than they are normally. After you have taken this medicine for a while, this effect may not be so bothersome. However, make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert .

Oral contraceptives (birth control pills) containing estrogen or progestin, contraceptive progestin injections (e.g., Depo-Provera), and implant contraceptive forms of progestin (e.g., Norplant) may not work properly if you take them while you are taking hydantoin anticonvulsants. Unplanned pregnancies may occur. You should use a different or additional means of birth control while you are taking hydantoin anticonvulsants. If you have any questions about this, check with your health care professional.

For patients taking phenytoin or mephenytoin:

Side Effects of This Medicine:

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

More common
Bleeding, tender, or enlarged gums (rare with ethotoin)
burning, tingling, pain, or itching, especially in the groin following fosphenytoin injection
clumsiness or unsteadiness
continuous, uncontrolled back-and-forth and/or rolling eye movements may be sign of overdose
muscle pain
skin rash or itching
slurred speech or stuttering may be sign of overdose
sore throat
swollen glands in neck or underarms
trembling may be sign of overdose
unusual excitement, nervousness, or irritability
Bone malformations
burning pain at place of injection
chest discomfort
chills and fever
dark urine
frequent breaking of bones
joint pain
learning difficulties in children taking high doses for a long time
light gray–colored stools
loss of appetite
nausea or vomiting
pain of penis on erection
restlessness or agitation
slowed growth
stomach pain (severe)
troubled or quick, shallow breathing
uncontrolled jerking or twisting movements of hands, arms, or legs
uncontrolled movements of lips, tongue, or cheeks
unusual bleeding (such as nosebleeds) or bruising
unusual tiredness or weakness
yellow eyes or skin
Rare (with long-term use of phenytoin)
Numbness, tingling, or pain in hands or feet
Symptoms of overdose
Blurred or double vision
clumsiness or unsteadiness (severe)
confusion (severe)
dizziness or drowsiness (severe)
staggering walk
stuttering or slurred speech

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
dizziness (mild)
drowsiness (mild)
Less common
Diarrhea (with ethotoin)
enlargement of jaw
muscle twitching
swelling of breasts in males
thickening of lips
trouble in sleeping
unusual and excessive hair growth on body and face (more common with phenytoin)
widening of nose tip

Last Updated: 6/12/2013

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