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Some commonly used brand names are:

In the U.S.—

  • Celontin 2
  • Zarontin 1

In Canada—

  • Celontin 2
  • Zarontin 1


For quick reference, the following succinimide anticonvulsants are numbered to match the corresponding brand names.

This information applies to the following medicines:
1. Ethosuximide (eth-oh-SUX-i-mide)
2. Methsuximide (meth-SUX-i-mide)
‡ Generic name product may be available in the U.S.


  • Anticonvulsant—Ethosuximide; Methsuximide


Succinimide anticonvulsants are used to control certain seizures in the treatment of epilepsy. These medicines act on the central nervous system (CNS) to reduce the number and severity of seizures.

This medicine is available only with your doctor"s prescription, in the following dosage forms:

  • Oral
  • Ethosuximide
    • Capsules (U.S. and Canada)
    • Syrup (U.S. and Canada)
  • Methsuximide
    • Capsules (U.S. and Canada)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For succinimide anticonvulsants, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to anticonvulsant medicines. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Although succinimide anticonvulsants have not been shown to cause problems in humans, there have been unproven reports of increased birth defects associated with the use of other anticonvulsant medicines.

Breast-feeding—Ethosuximide passes into breast milk. It is not known whether methsuximide passes into breast milk. However, these medicines have not been reported to cause problems in nursing babies.

Children—Succinimide anticonvulsants are not expected to cause different side effects or problems in children than they do in adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults. Although there is no specific information comparing use of succinimide anticonvulsants in the elderly to use in other age groups, they are not expected to cause different side effects or problems in older people than they do in younger adults.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking succinimide anticonvulsants, it is especially important that your health care professional know if you are taking any of the following:

  • Central nervous system (CNS) depressants (medicines that cause drowsiness)—Using these medicines together may increase CNS depressant effects
  • Haloperidol (e.g., Haldol)—A change in the pattern and/or the frequency of seizures may occur; the dose of either medicine may need to be changed

Other medical problems—The presence of other medical problems may affect the use of succinimide anticonvulsants. Make sure you tell your doctor if you have any other medical problems, especially:

  • Blood disease or
  • Intermittent porphyria or
  • Kidney disease (severe) or
  • Liver disease—Succinimide anticonvulsants may make the condition worse

Proper Use of This Medicine

This medicine must be taken every day in regularly spaced doses as ordered by your doctor . Do not take more or less of it than your doctor ordered.

If this medicine upsets your stomach, take it with food or milk unless otherwise directed by your doctor.

Dosing—The dose of succinimide anticonvulsants 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 ethosuximide and methsuximide. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules or teaspoonfuls of syrup 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 taking a succinimide anticonvulsant .

  • For ethosuximide
  • For oral dosage form (capsules or syrup):
    • As an anticonvulsant:
      • Adults and children 6 years of age and over—To start, 250 milligrams (mg) twice a day. Your doctor may increase your dose gradually if needed. However, the dose is usually not more than 1500 mg a day.
      • Children up to 6 years of age—To start, 250 mg once a day. Your doctor may increase your dose gradually if needed. However, the dose is usually not more than 1000 mg a day.
  • For methsuximide
  • For oral dosage form (capsules):
    • As an anticonvulsant:
      • Adults, teenagers, and children—To start, 300 milligrams (mg) once a day. Your doctor may increase your dose gradually if needed. However, the dose is usually not more than 1200 mg a day.

Missed dose—If you miss a dose of this medicine, take it as soon as possible. However, if it is within 4 hours of your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—To store this medicine:

  • Keep out of the reach of children.
  • Store away from heat and direct light.
  • Do not store the capsule form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
  • Keep the liquid form of this medicine from freezing. Do not refrigerate.
  • Do not keep outdated medicine or medicine that is no longer needed. Be sure any discarded medicine is out of the reach of children.

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.

If you have been taking a succinimide anticonvulsant regularly, do not stop taking it without first checking with your doctor . Your doctor may want you to reduce gradually the amount you are taking before stopping completely. Stopping this medicine suddenly may cause seizures.

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 slow down the nervous system, possibly causing drowsiness). 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; 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 .

This medicine may cause some people to become drowsy or less alert than they are normally. 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 not alert . After you have taken this medicine for a while, this effect may lessen.

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 succinimide anticonvulsants together with medicines that are used during surgery or dental or emergency treatments may increase the CNS depressant effects.

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

For patients taking methsuximide :

  • Do not use capsules that are not full or in which the contents have melted, because they may not work properly.

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:

More common

Muscle pain; skin rash and itching; swollen glands; sore throat and fever

Less common

Aggressiveness; difficulty in concentration; mental depression; nightmares


Chills; increased chance of certain types of seizures; mood or mental changes; nosebleeds or other unusual bleeding or bruising; shortness of breath; sores, ulcers, or white spots on lips or in mouth; unusual tiredness or weakness; wheezing, tightness in chest, or troubled breathing

Symptoms of overdose

Drowsiness (severe); nausea and vomiting (severe); troubled breathing

Other 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. However, check with your doctor if any of the following side effects continue or are bothersome:

More common

Clumsiness or unsteadiness; dizziness; drowsiness; headache; hiccups; loss of appetite; nausea or vomiting; stomach cramps

Less common


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

Revised: 02/05/2001

The information contained in the Thomson Healthcare (Micromedex) products as delivered by is intended as an educational aid only. It is not intended as medical advice for individual conditions or treatment. It is not a substitute for a medical exam, nor does it replace the need for services provided by medical professionals. Talk to your doctor, nurse or pharmacist before taking any prescription or over the counter drugs (including any herbal medicines or supplements) or following any treatment or regimen. Only your doctor, nurse, or pharmacist can provide you with advice on what is safe and effective for you.

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