Small Description (basic): 

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).

Used to treat: 

Forms (basic): 

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:

Dosing (basic): 

Please see package insert.

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 effect 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. The FDA has provided the following information for patients, family members, and caregivers at http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm100192.htm.

    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 Gabapentin 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.

What else is Ethosuximide used for?

Zarontin is not used to treat anything other than seizures in epilepsy.

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.

Special Concerns for Ethosuximide

Please see package insert.

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."

Small Description (adv): 

Zarontin is the brand name used in the United States, Canada, the UK, Australia, and some other countries for ethosuximide.

Large Description (adv): 

Zarontin has been used since about 1960 as a first-line medication for the treatment of generalized absence seizures.

Indications (adv): 

Zarontin is used to treat absence seizures, particularly in young children. It has no effect against (or may even worsen) partial and tonic-clonic seizures.

Forms (adv): 

Zarontin is marketed in the United States by Parke-Davis (a division of Pfizer). The name or appearance may differ in other places. These descriptions apply to the U.S. versions:

Dosing (adv): 

Please see package insert.

How to take and store Ethosuximide?

Zarontin can be taken either with food or without food, but many people find that stomach upset is less of a problem if the medicine is taken with meals.

Zarontin capsules should be swallowed whole, not chewed or broken open. They are stored at room temperature.

Remind patients using the syrup to use an accurate measuring device and to store it at room temperature, protected from freezing and away from light.

Remind all patients to keep Zarontin out of the reach of children.

Missed Doses

Advise patients to take a forgotten dose immediately. If it is almost time for the next dose, they should delay that dose for a few hours, instead of taking two doses very close together. Patients who take Zarontin only once a day could be advised to wait about 12 hours between doses and then resume a 24-hour schedule the next day.

Patients who often forget doses may benefit from using a special pillbox or watch with an alarm.

Mechanisms of actions of Ethosuximide

The exact mechanism of action of ethosuximide is not entirely understood. Ethosuximide inhibits NADPH-linked aldehyde reductase necessary for the formation of gamma-hydroxybutyrate, which has been associated with the induction of absence seizures. Ethosuximide also appears to inhibit the sodium-potassium ATPase system. Ethosuximide can decrease the burst firing of thalamocortical neurons. This action may explain the anti-absence activity of the drug.

Ethosuximide also has been shown to decrease non-inactivating Na currents in thalamocortical neurons, as well as blocking Ca dependent K channels.

It does not appear to alter brain GABA concentrations.

Clinical Pharmacology of Ethosuximide

Absorption
Peak plasma levels are reached in 3 to 5 hours for both children and adults if capsules are taken. The time is somewhat shorter if the syrup is used, but the total amount absorbed will be about the same. Absorption is virtually complete.

Some generic forms of ethosuximide are now available in the United States. They may not be exactly equivalent to Zarontin pharmacologically.

Distribution and metabolism
Ethosuximide is not bound to plasma proteins. It is distributed through total body water and metabolized in the liver.

The half-life of ethosuximide is about 30 to 40 hours in children and 50 to 60 hours in adults.

Because ethosuximide is metabolized in the liver, people with liver disease should be treated with great caution. They may have to be started at a lower dose and have their dosage increased more slowly.

Steady state
In children, steady state is reached after 6 days of taking a stable dose of Zarontin. For adults, the equivalent period is 12 days. A patient's dosage should not be increased until steady state has been reached (or some time later), so that the effects of the previous dosage can be assessed.

Efficacy of Ethosuximide

Zarontin (ethosuximide) generally is used only for absence seizures. It is highly effective and safe for treating childhood absence epilepsy, which occurs in 8% of children with epilepsy between ages 5 and 14 years. This disorder usually begins between ages 4 and 8 in children without previous brain disorders. Often there is a family history of the same disorder. These seizures almost always can be provoked in the office by having the child hyperventilate for a few minutes. Although these seizures usually will stop when the child gets older, children who have them need effective treatment to avoid learning problems and accidental injuries.

Zarontin is often the first-line medication for childhood absence epilepsy. 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, such as atypical absence or juvenile myoclonic epilepsy.These children may also have other types of seizures, are often older when the absence seizures begin, and have a different EEG pattern than children with typical childhood absence epilepsy. Zarontin is also effective in controlling absence seizures in many of these children, but other medications often are needed to control other types of seizures. Depakote and other valproate medications will control absence seizures, so it may be used instead of Zarontin. Some children do best with a combination of these two.

Zarontin can also be used in combination therapy for patients who have both absences and other kinds of seizures. No single combination of antiepileptic medications is perfect for everyone. Sometimes, a series of combinations must be tried before finding what is best for the individual patient. Adding Zarontin usually does not affect the level of other seizure medicines in the body, but some adjustment of the Zarontin dosage may be needed if other medications are added.

Common side effects of Ethosuximide

Dose-related side effects

In early studies of ethosuximide, a minority of subjects reported adverse effects. The most common adverse effects were gastrointestinal:

  • nausea
  • abdominal discomfort
  • vomiting
  • anorexia
  • diarrhea


These problems are usually mild. If they do not diminish within several days, a reduction in the dose of Zarontin may be required. Another effective technique to resolve such problems is to divide the daily dosage into smaller doses to be taken with meals.

Less common were other adverse effects:

  • drowsiness
  • dizziness
  • hiccups
  • behavioral changes (irritability, mood change, aggressiveness)


These effects generally respond to dose reduction.

Some children taking ethosuximide develop persistent headaches, which do not appear to be dose-related.

Other patients notice a pinkish or brownish discoloration of their urine. This is unlikely to represent a serious problem.

Idiosyncratic reactions

The most common idiosyncratic reaction to ethosuximide is a mild rash, which often disappears if the medication is stopped. Some patients need steroid therapy.

Serious Side effects of Ethosuximide

A small percentage of people who take ethosuximide experience serious reactions. Alert patients to call immediately if they notice any of the following symptoms:

  • Rash
  • Sore throat, fever, sores in the mouth, or easy bruising (blood dyscrasias)
  • Fever, rash, arthritis, swelling in the lymph nodes (systemic lupus erythematosus or lupuslike syndrome)
  • Depression, anxiety, or aggressiveness
  • Hallucinations, hearing "voices" or losing contact with reality (psychosis)

As with many seizure medicines, skin rashes (including the very rare Stevens-Johnson syndrome, which can be fatal) have been a problem for a small number of patients. Most rashes are much less serious and will disappear if ethosuximide is withdrawn.

Similarly, Zarontin carries a very small risk of blood abnormalities. Checking the blood cell count within 2 to 12 weeks after the Zarontin is started and every 4 to 12 months after that is often recommended, but reminding patients to report symptoms promptly is probably more effective in early recognition of blood disorders.

One effect that has been studied extensively is an allergic reaction to Zarontin that might bring about some of the symptoms and blood test results found in systemic lupus erythematosus (SLE). Sometimes patients with these symptoms have a lupuslike syndrome from which they fully recover when ethosuximide is stopped, though recovery may take some time.

Behavioral changes occasionally occur shortly after patients start taking Zarontin. Hallucinations, paranoia, and other signs of psychosis have been reported in a few patients, mostly adolescents or young adults with a history of previous emotional problems or psychiatric disease. These problems may be more likely if high doses are given.

Tests of liver and kidney function are also recommended. Zarontin should be given to patients with liver or kidney disease only with extreme caution.

A complete list of all reactions to Zarontin can be found in the package insert.

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. The FDA has provided the following information for patients, family members, and caregivers at http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm100192.htm.

    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

See package insert. 

Other Uses of Ethosuximide

Besides childhood absence epilepsy, Zarontin has shown itself to be effective against atypical absence seizures and absence status (at high levels). It is also a useful adjunctive medication for patients with juvenile myoclonic epilepsy and Lennox-Gastaut syndrome.

It also has shown efficacy in controlling negative myoclonus, a rare type of partial seizures seen in some epilepsy syndromes in children. Unlike the more common brisk jerks of positive myoclonus, negative myoclonus involves a brief loss of postural tone. This loss occurs at the same time as spike-and-wave complexes in the contralateral cerebral hemisphere.

Ethosuximide Contraindications

Patients who are allergic to succinimides should not take Zarontin. Besides ethosuximide, the other common succinimide is Celontin (methsuximide).

Ethosuximide should be administered with extreme caution to patients with known liver or kidney disease.

Ethosuximide Interactions with other medications

Zarontin is less likely than many other antiepileptic drugs to interact with other medications. Nevertheless, it's advisable to question patients or family members about the use of prescription and OTC medications, herbal products, vitamins, alcohol, and other substances when prescribing Zarontin. Usually all necessary medications can be used, but the dosages may need to be adjusted to achieve therapeutic levels.

Effects of Zarontin (ethosuximide) on other drugs

Zarontin has little effect on other medications. It may elevate blood levels of phenytoin (Dilantin, Phenytek) somewhat, but the clinical significance is unclear.

Effects of other drugs on Zarontin (ethosuximide)

Valproate (Depakote, Depakene, valproic acid) may slightly increase blood levels of ethosuximide, but it is unclear whether the effect is clinically significant. The combination of these two medications is often beneficial.

Administering ethosuximide along with isoniazid, ritonavir, or erythromycin may elevate serum levels of ethosuximide to a greater extent because of their inhibitory effects on enzymes responsible for its metabolism in the liver.

The level of ethosuximide is reduced if it is taken concurrently with enzyme-inducing medications, including:

  • carbamazepine (Tegretol, Carbatrol)
  • phenytoin (Dilantin, Phenytek)
  • primidone (Mysoline)
  • phenobarbital
  • rifampin

AED Interaction Sheets:

Seizure drugs are often affected by drug-drug interactions. Print these informative sheets for practical help.

Interaction sheet for ethosuximide (Zarontin)

Ethosuximide effects on Children

Ethosuximide has been used for many years to treat children with absence seizures. Side effects are usually mild, most often gastrointestinal upsets that can be minimized by taking doses with meals, up to three times a day.

The initial dose for patients 3 to 6 years of age is one capsule or one teaspoon of syrup (250 mg) per day. Children over 6 years can start with two capsules or two teaspoons of syrup (500 mg) per day. The dose thereafter must be individualized by small increments according to the patient's response. One useful method is to increase the daily dose by 250 mg every 4 to 7 days until control is achieved with minimal side effects.

The optimal daily dose for most children is 20 mg/kg. This dose has given average plasma levels within the accepted therapeutic range of 40 to 100 mcg/mL.

Ethosuximide and Pregnancy

The U.S. Food and Drug Administration (FDA) lists Zarontin in Pregnancy Category C. This indicates that caution is advised, but the benefits of the medication may outweigh the potential risks.

The babies of women taking antiepileptic drugs (AEDs) generally are more likely to have birth defects, although a large majority are normal. The risk of defects is higher for women who take more than one AED and for women with a family history of birth defects. The reasons for these differences are uncertain, since factors other than medication, such as genetics and seizures, also may play a role.

There is little solid evidence indicating whether particular AEDs are more teratogenic than others. We do know that ethosuximide crosses the placenta and plasma levels in neonates are similar to those of the mother.

Advise women who are capable of becoming pregnant to take 400 mcg (0.4 mg) of folic acid (folate) daily to help prevent neural tube defects. Women at high risk, such as those with a history of a neural tube defect in a previous pregnancy, should take 4000 mcg (4 mg) daily, beginning before they become pregnant.

About 20% to 35% of women have seizures more often during pregnancy because of changes in hormones or changes in how their medication is handled by the body. Check the blood levels of ethosuximide regularly during pregnancy so that the dosage can be adjusted as needed.

Ethosuximide appears in breast milk. Estimates are that a nursing infant might receive a dose of 13 to 38 mg per day. The effect of this dose on an infant is unknown. Discuss the options with women taking ethosuximide who are interested in breast-feeding, including staying with ethosuximide, switching to a different AED, or discontinuing their medication.

Ethosuximide effects on Seniors

Absence seizures are much more common in childhood, so not many seniors take Zarontin. As with most other medications, low initial doses and caution in titration is advised. Patients with reduced liver function must be treated with particular caution.

Some common side effects of Zarontin, such as drowsiness or dizziness, may exacerbate pre-existing problems of seniors, and their greater risk of injury from falls or other accidents makes this an area of concern.

Ethosuximide Dosing and titration

For children ages 3 to 6 years with absence seizures, the usual starting dose is 1 capsule or 1 teaspoon (5 mL) of the syrup per day. This is often given as half a teaspoon (2.5 mL) twice a day.

The initial daily dose for older children is often 2 capsules or 2 teaspoons of syrup, which can be increased after about a week.

Most children do best at about 20 mg/kg per day. The dose is usually divided, with doses given two or three times a day.

A therapeutic serum level of ethosuximide is generally considered to be 40-100 mcg/mL, but adjustments should depend on clinical response. Because Zarontin has a long half-life, blood levels do not fluctuate much, so the time when tests are done is not important. Levels in saliva are very similar to plasma levels and also can be used to monitor therapy.

Special Concerns for Ethosuximide

Please see package insert.

Ethosuximide Package insert

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."

Ethosuximide References for Professionals

Abstracts of articles related to Zarontin (ethosuximide) are available through PubMed, a service of the National Library of Medicine:

Here is a link to one article about Zarontin:

Browne TR, Dreifuss FE, Dyken PR, et al. Ethosuximide in the treatment of absence (petit mal) seizures Neurology 1975 Jun;25(6):515-24. PMID: 805382.