Zarontin (zuh-RON-tin) is a brand name used in the United States, Canada, the UK, Australia, and some other countries for a type of medicine called ethosuximide (eth-oh-SUX-i-mide). Zarontin is marketed in the United States by Parke-Davis (a division of Pfizer). The name or appearance may be different in various countries but usually the dose (measured in milligrams, abbreviated "mg") will be the same. These descriptions apply to the U.S. versions.

Please see package insert.


Updated: 16/10/2023

Brand Name(s)


Used to Treat

Childhood and Juvenile Absence Epilepsy
Absence Seizures
Atypical Absence Seizures


Zarontin 250mg

250-mg orange-colored gelatin capsule

Liquid Solution

250 mg/5 mL (raspberry-flavored)

Package Insert

Frequently Asked Questions

    How to take and store Ethosuximide?

    Follow the doctor's directions. Call if you have any questions. Ask the doctor what to do if you forget a dose. The way the medicine is taken depends, of course, on what form the doctor has prescribed.

    Capsules should be swallowed whole. Don't chew them or break them open. Store them at room temperature, protected from heat and out of the reach of children.

    For liquid Zarontin, use the same accurate measuring spoon every time so the dose will be correct. Like the capsules, Zarontin liquid (syrup) should be stored at room temperature. Be especially careful to protect it from freezing and keep it away from light and out of the reach of children.

    It's OK to take Zarontin either with food or without food, but many people find that stomach upset is less of a problem if they take it with meals.

    Be sure to take only the amount that the doctor prescribes. If you think you've taken a little too much (such as one or two extra capsules or an extra teaspoon of liquid), call your doctor for advice. For a larger overdose, call your local poison control center or emergency room right away unless you have special instructions from the doctor.

    Don't stop taking Zarontin or change the amount you take without talking to the doctor first. Serious problems sometimes occur when people stop taking Zarontin suddenly.

    What if I forget?

    In general, if you forget a dose, take it as soon as you remember. If it is almost time for the next dose, delay that dose for a few hours, instead of taking two doses very close together. Then go back to the regular schedule. If you're not sure about what to do, call the doctor's office for more advice.

    If you've been using Zarontin only once a day, you could wait about 12 hours between doses and then resume a 24-hour schedule the next day.

    Taking the right amount of seizure medicine on time every single day is the most important step in preventing seizures!

    How does Ethosuximide affect the brain?

    No one entirely understands exactly how Zarontin works to stop seizures. It is probably by helping to keep brain cells from working extra fast. Brain cells need to work (fire) at a certain rate to function normally. During a seizure, brain cells are forced to work much more rapidly than normal.

    How does the body digest Ethosuximide?

    After medicine is swallowed, it must be absorbed into the blood so it can move throughout the body. The process of absorbing, digesting, and excreting a medicine or food is called metabolism. The way the body metabolizes a particular medicine affects how often it must be taken. It also determines whether it will interact with other medicines or be affected by conditions such as liver disease.

    Like many other medicines, Zarontin is broken down (digested) in the liver. If the person also takes other medicines that are digested in the liver, things can get complicated. How well each medicine works and how quickly it leaves the body may be changed.

    This is why the doctor needs to know about everything that a person takes—not just prescription medicines but even things like vitamins, herbs, and aspirin! These things can affect how much Zarontin is prescribed.

    How well does the Ethosuximide work?

    Zarontin (ethosuximide) generally is used only for the brief staring spells known as absence seizures (formerly known as "petit mal" seizures). It is highly effective and safe for children who have the disorder known as childhood absence epilepsy. Zarontin is often the first choice of medication for children with this disorder.

    Doctors have studied large numbers of patients to find out how well Zarontin controls absence seizures. In one early study, 95% of patients had the number of seizures reduced by at least half, and about half the patients had them reduced by at least 90%.

    Some children who have absence seizures have more complicated disorders that are harder to treat and may not be outgrown. Zarontin also controls absence seizures in many of these children, but other seizure medicines often are needed to control other types of seizures.

    Zarontin can be used in combination with other seizure medicines for patients who have other kinds of seizures in addition to absences. No single combination of seizure medicines is perfect for everyone. Sometimes, a series of combinations must be tried before finding what is best for the individual patient.

    What are the most common side effects of Ethosuximide?

    Many people who take Zarontin don't have any trouble with side effects. The most common complaints (usually not too severe) are problems like upset stomach, loss of appetite, or diarrhea. These problems are usually mild and often they go away by themselves. If they are really bothersome, call the doctor. Usually reducing the amount of Zarontin or taking it with meals will help, but don't stop taking Zarontin or change the way it's taken unless the doctor says it's OK to do that.

    A few people become sleepy or dizzy when they take Zarontin, so those who have just started taking it should be careful during activities that might be dangerous, until they know how it affects them.

    Allergic reactions

    Some people who take Zarontin have a red rash within the first few weeks of taking it. If this happens, tell the doctor or nurse right away, to be sure that it's not the beginning of a serious problem. It's rare for the rash to be serious, but don't ignore it. It's often necessary to switch to a different seizure medicine.

    What are the most serious side effects of Ethosuximide?

    Serious reactions to Zarontin are very rare but everyone who takes this medicine should at least be aware of them because a very small number of people have died because of them.

    If you notice any of these symptoms, call your doctor right away, but don't stop using the Zarontin unless the doctor says so:

    • Rash
    • Sore throat, fever, sores in the mouth, or easy bruising (could mean a blood problem)
    • Fever, rash, arthritis, swelling in the lymph nodes (could mean an autoimmune disorder)
    • Depression, anxiety, or aggressiveness
    • Hallucinations, hearing "voices" or losing contact with reality

    A complete list of all reactions to Zarontin can be found in the package insert, but it is important to remember that most people who take it have none of these serious problems.

    On July 10, 2008, an advisory panel was convened by the Food and Drug Administration (FDA) to review data that the FDA had previously collected from drug studies showing an association between many of the antiepileptic drugs (AEDs) and suicidal ideation and behavior, which together are called suicidality. According to the FDA’s Alert, among the patients with epilepsy in these drug studies, 1 out of 1000 people taking the placebo (inactive substance) showed suicidality compared to approximately 3.5 out of 1000 people who took an AED. The FDA advisory panel voted to accept the FDA's data at its meeting on July 10.

        Taking antiepileptic medicines may increase the risk of having suicidal thoughts or actions;

    • Do not make any changes to the medication regimen without first talking with the responsible healthcare professional;
    • Pay close attention to any day-to-day changes in mood, behavior and actions. These changes can happen very quickly so it is important to be mindful of any sudden differences.

        Be aware of common warning signs that might be a signal for risk of suicide. Some of these are:

    •  Talking or thinking about wanting to hurt yourself or end your life
    •  Withdrawing from friends and family
    •  Becoming depressed or having your depression get worse
    •  Becoming preoccupied with death and dying
    •  Giving away prized possessions

    We again urge patients and families to contact their doctor before stopping an epilepsy medication because this may possibly lead to seizures and worsening of mood.

    Impact of Ethosuximide on bone health

    At this time there is no evidence to support that ethosuximide causes bone health problems. However, it might. It is essential that if you taking this medication, that one take supplemental calcium of 1000 milligrams per day. Talk to your doctor about bone health. He/She may decide to check Vitamin D levels and other tests to check for the impact of this drug on your bones.

    Who should not take Ethosuximide?

    The only people who definitely should not take Zarontin (ethosuximide) are those who are allergic to it or to other medicines in the same family, called succinimides. The other common medicine in this family is Celontin (methsuximide).

    People who have liver or kidney disease need to be extra cautious about taking Zarontin. Most of them can take it successfully, however, if they work with the doctor to determine the correct amount to take. That is why it is so important to make sure the doctor knows about any liver disease and about every kind of medicine in use.

    Can Ethosuximide be taken with other medicines?

    Sometimes one kind of medicine changes the way another kind of medicine works in the body. This is true not only for prescription medicines, but also for medicines you just pick up off the shelf at the store. It's also true for herbal products, vitamins, a few kinds of food, and even cigarettes!

    Any time a doctor suggests a new prescription, be sure to talk about what other medicines you are already using. If two kinds of medicine affect each other, the doctor may want to prescribe something else or change the amount to be taken.

    Zarontin is less likely than many other seizure medicines to interact with other medications, however. The most important thing to know is that the level of Zarontin in the blood is reduced if it is taken along with certain other seizure medicines. The amount of Zarontin taken may need to be increased if you start taking one of these medicines.

    The seizure medicines with this effect are:

    • Tegretol, Carbatrol (carbamazepine)
    • Dilantin, Phenytek (phenytoin)
    • Mysoline (primidone)
    • phenobarbital
    What are the effects of Ethosuximide on Children?

    Absence seizures in many children can be mostly or completely controlled by Zarontin, with few or no side effects. Controlling absence seizures is important to help children learn better in school and avoid injuries from accidents.

    The amount of Zarontin that a particular child takes will depend on the child's weight and whether any seizures or side effects are occurring. Each child is different, so follow the doctor's prescription carefully.

    Usually the doctor will recommend that the child take some Zarontin two or three times a day. If the child took it all at once, the amount in the body might be too high at first, causing side effects. Later it might be too low and the child could have more seizures.

    If a woman takes Ethosuximide during pregnancy will it hurt the baby?

    In the United States, the Food and Drug Administration (FDA) assigns each medication to a "Pregnancy Category" according to whether it has been proven to be harmful in pregnancy. Zarontin is listed in Pregnancy Category C. This means that women should be cautious, but sometimes the benefits may outweigh the risks. In fact, a large majority of women who use Zarontin during pregnancy have normal, healthy babies.

    All women who are capable of becoming pregnant should take at least 0.4 mg (400 mcg) of the vitamin called folic acid every day because it helps to prevent one type of birth defect. (The most well-known of these is spina bifida, in which the spinal cord is not completely enclosed.) If the doctor thinks a woman is at especially high risk, a much larger dose of folic acid—4 mg (4000 mcg) per day—may be recommended, beginning before the woman becomes pregnant.

    Women with epilepsy who are pregnant or thinking about becoming pregnant should talk to their doctor about their seizure medicines. Taking more than one seizure medicine may increase the risk of birth defects, so doctors sometimes gradually reduce the number or amount of seizure medicines taken by women planning for pregnancy. This is not done routinely, however, because it increases the risk of seizures. Some kinds of seizures can injure the baby, so women should not stop using seizure medicines or reduce the amount they take without their doctor's OK.

    About 20% to 35% of women have seizures more often during pregnancy because of changes in hormones or changes in how their seizure medicine is handled by the body. It is helpful for the doctor to check the levels of medicine in the blood regularly during pregnancy so that the dosage can be adjusted if necessary.

    Women taking Zarontin who are interested in breast-feeding their baby should talk to their doctor, because this medicine does pass through breast milk.

    What are the effects of Ethosuximide on Seniors

    Absence seizures are much more common in childhood, so not many seniors take Zarontin. To reduce side effects, the doctor probably will prescribe a low dose of Zarontin to start and then be very cautious about any increases. It's especially important for seniors to keep the doctor informed about any changes that they notice.

    What are the dose ranges for Ethosuximide?

    The best amount is the amount that completely controls seizures without causing troublesome side effects. It depends on many factors, which are different for every individual. Follow the doctor's directions. Call if you have any questions.

    No one should stop taking Zarontin or change the amount they take without talking to the doctor first. Stopping any seizure medicine all at once can cause very serious problems.

    Don't use more than the doctor prescribes. If a little extra (such as one or two extra capsules) is taken by accident, call the doctor for advice. For a larger overdose, call a poison control center or emergency room right away unless you have other specific directions from your doctor.

    Read the package insert of Ethosuximide

    In the United States, companies that manufacture medicines are required to publish certain kinds of information about each product. This document is commonly known as a “package insert” because it is usually included with each package of the medicine.

    You can also read these documents (also called "prescribing information") online. The U.S. package insert for Zarontin (ethosuximide) is found at:

    Some of the information may differ in other countries.

    To learn how to read and understand a package insert, see "How to read a package insert."


    Primary Generalized Epilepsy

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