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Your child needs to take the medicine called ethosuximide (say: eth-oh-SUKS-i-mide) for his or her seizures or fits. This information sheet explains what ethosuximide does, how to take it, and what side effects or problems your child may have when he or she takes this medicine.

What is ethosuximide?

Ethosuximide is a medicine called an anticonvulsant. It is used to control and prevent certain types of seizures. It is often used to control and prevent absence seizures, also called petit mal seizures. (These are seizures that cause only a brief loss of awareness.)

You may also hear ethosuximide called by its brand name Zarontin. Ethosuximide is available as a tablet and liquid.

Before giving ethosuximide to your child…

Tell your doctor if your child has had an unusual or allergic reaction to succinimides or any component of the drug.

Talk with your doctor or pharmacist if your child has any of the following conditions. Precautions may need to be taken with this medicine if your child has:

  • kidney disease
  • liver disease

How should you give your child ethosuximide?

Follow these instructions when you give your child ethosuximide:

  • Give your child ethosuximide regularly, exactly as your doctor or pharmacist tells you to. Talk to your child's doctor before you stop giving this medicine for any reason. Abrupt withdrawal of ethosuximide can lead to a precipitation of seizures.
  • Give your child ethosuximide at the same time every day. Pick a time that is easy for you so that you do not miss doses.
  • Make sure you have enough ethosuximide for weekends, holidays, and vacations.
  • Have your child take ethosuximide with food or milk, if the medicine causes an upset stomach.

What should you do if your child misses a dose of ethosuximide?

If your child misses a dose of ethosuximide:

  • Give the missed dose as soon as you remember.
  • If you remember the missed dose within 4 hours of the next dose, skip the missed dose.
  • Give the next dose at the regular time.
  • Give your child only 1 dose at a time.

What are the possible side effects of ethosuximide?

Your child may have some of these side effects while he or she takes ethosuximide. Usually your child will not need to see a doctor about them. These side effects may go away as your child's body gets used to the ethosuximide. Check with your child's doctor if your child has any of these signs or symptoms and they do not go away or they bother your child:

  • loss of appetite
  • dizziness
  • drowsiness
  • headaches
  • irritable or unusual behaviour
  • upset stomach

Most of the following side effects are not common but they may be a sign of a serious problem. Call your child's doctor right away or take your child to the Emergency Department if your child has any of these signs:

  • a rash, itchy skin, or hives (raised, red, itchy, areas on the skin)
  • unusual tiredness or weakness
  • seizures that are new or get worse
  • unusual bleeding or bruising
  • fever, sore throat
  • problems breathing

What safety measures should you take when your child is using ethosuximide?

Ethosuximide may cause your child to be less alert. Have your child avoid activities that require him/her to be alert (for example riding a bicycle, rollerblading, contact sports). School work may be more difficult for your child to focus on so tell your child’s teacher that he/she is taking this medicine.

Check with your child's doctor or pharmacist before you give your child any other medicine, even medicine you can buy without a doctor’s order (prescription).

There are some medicines that should not be taken together with ethosuximide or in some cases the dose of ethosuximide or the other medicine may need to be adjusted. It is important that you tell your doctor and pharmacist if your child takes any other medications (prescription, over the counter, or herbal) including:

  • St. John’s Wort
  • Hydroxyzine (Atarax®)
  • Other anticonvulsants including phenytoin (Dilantin®) and valproic acid​ (Depakene®, Epival®)

What other important information should you know about ethosuximide?

Before your child has any kind of operation, even on the teeth, or an emergency treatment, tell the doctor or dentist that your child is taking ethosuximide.

Keep ethosuximide at room temperature in a dry place. Do not store in a bathroom. If the medication your child is taking is in a syrup formulation, protect it away from light.

Keep ethosuximide out of your child's sight and reach.

If your child takes too much of any medicine, call the Ontario Poison Centre at one of these numbers. These calls are free.

  • Call 416-813-5900 if you live in Toronto.
  • Call 1-800-268-9017 if you live somewhere else in Ontario.
  • If you live outside of Ontario, call your local Poison Information Centre.

Disclaimer: The information in this Family Med-aid is accurate at the time of printing. It provides a summary of information about ethosuximide and does not contain all possible information about this medicine. Not all side effects are listed. If you have any questions or want more information about ethosuximide, speak to your healthcare provider.   

Amelia Rodrigues, BScPhm, ACPR, RPh