Ethosuximide / Zarontin

Zarontin (zuh-RON-tin) is the brand name used in the United States, Canada, the UK, Australia, and some other countries for the seizure medicine ethosuximide (eth-oh-SUX-i-mide).

Zarontin has been used since about 1960, almost entirely to treat absence seizures. It has no effect against (or may even worsen) myoclonic, partial, and tonic-clonic seizures.

No one entirely understands exactly how Zarontin works to stop seizures. It affects some neurotransmitters, but does not change GABA concentrations. It also reduces the tendency of neurons in certain parts of the brain to fire in bursts. This may explain how it prevents absence seizures.

How fast the body absorbs Zarontin depends on what form is taken. When capsules are used, the amount of medicine in the blood will be highest after 3 to 5 hours for both children and adults. The time is somewhat shorter if the syrup form is used, but the total amount absorbed will be about the same.

Zarontin is broken down (digested) in the liver. People with liver disease must be cautious about taking it. Other people also need to be careful if they take other medicines that are digested in the liver, as many are. The metabolism of each medicine may be affected, changing how quickly it works and leaves the body.

This is why the doctor needs to know about everything that a person takes—prescription drugs, over-the-counter medications, vitamins and other dietary supplements, and herbs. In most cases, all the medicines can be used if the amounts are adjusted to allow for these changes.

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, 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 someone else in the family has had the same disorder in the past. The diagnosis can be confirmed by detecting a particular EEG pattern during a seizure. (The EEG is normal at other times.) The doctor almost always can cause this kind of absence seizure to occur in the office by having the child hyperventilate (breathe especially fast or deeply) 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 choice of 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. They often are older when the absence seizures begin, and they 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 seizure medicines often are needed to control other types of seizures. Depakote or medicines related to it 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 with other seizure medicines for patients who have other kinds of seizures in addition to absences. 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.

In rare cases, Zarontin has been reported to worsen generalized tonic-clonic seizures.

Many people who take Zarontin (ethosuximide) don't report any side effects. Those who do most often complain of digestive problems:

nausea, upset stomach
vomiting
loss of appetite, weight loss
diarrhea


These problems are usually mild and often they go away by themselves. If they continue or are really bothersome, call the doctor. Usually reducing the amount of Zarontin prescribed or taking it with meals will help. Don't stop taking Zarontin or change the way it's taken without the doctor's guidance.

Other side effects are less common:

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


As with the other side effects, tell the doctor if these continue to be a problem. The doctor may suggest a lower dose of Zarontin.

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

People who have just started taking Zarontin (or who have just started taking a larger amount) should be careful during activities that might be dangerous, until they know whether they are having any side effects.

Be sure to read about the serious side effects so you will be aware of symptoms that might indicate the beginning of a serious reaction to Zarontin. These serious problems are very rare, but everyone who takes this medicine should at least be aware of 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.

Pregnancy Category C. This indicates that caution is advised, but the benefits of the medication may outweigh the potential risks.

The babies of women who take seizure medicines generally are more likely to have birth defects, although a large majority are normal. The risk is higher if the woman takes more than one medicine or has a family history of birth defects. Doctors are not sure how much of the added risk is caused by the medicines and how much is the result of factors such as genetics or seizures themselves.

Also, there is little specific information about whether particular seizure medicines are more likely to cause birth defects than others. We know that ethosuximide crosses freely from the mother into the baby during pregnancy, but we don't know much about its effects.

Women who are capable of becoming pregnant should take at least 400 mcg (0.4 mg) of folic acid (folate) daily to help prevent a type of birth defect called a neural tube defect. (The best-known of these is spina bifida, in which the spinal cord is not completely enclosed.) Women at high risk, such as those who have had a baby with this kind of 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. The doctor may recommend checking the level of medication in the blood regularly during pregnancy so that the dosage can be adjusted as needed.

Ethosuximide (Zarontin) 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. Women taking ethosuximide who are interested in breast-feeding should discuss their options with their doctor.