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Overview: Ethosuximide is used to control certain types of seizures. Common side effects include nausea, vomiting, diarrhea, upset stomach, tiredness, dizziness, headache, and trouble focusing. Do not drive or do other activities that require alertness or coordination until you know how ethosuximide affects you. Tell your health care provider right away if you get a rash, sore throat, or a fever. If you have trouble swallowing capsules, ethosuximide is also available as an oral liquid.

Uses

What is ethosuximide used for?

Ethosuximide is commonly used to control certain types of seizures.

Ethosuximide may also be used for other conditions as determined by your health care provider.

How does ethosuximide work (mechanism of action)?

A seizure happens when electrical and chemical brain signals suddenly become too active. Ethosuximide works by helping calm down unusual brain activity to prevent seizures.

How is ethosuximide supplied (dosage forms)?

Brands and other names

  • Zarontin

Dosage forms and strengths

  • 250 mg oral capsules
  • 250 mg/5 mL oral solution

How should I store ethosuximide?

Ethosuximide should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect the oral liquid from light, and do not freeze.

Side Effects

What are the most common side effects of ethosuximide?

The most common side effects of ethosuximide are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Nausea, vomiting, or diarrhea
  • Upset stomach
  • Loss of appetite
  • Weight loss
  • Tiredness
  • Dizziness or lightheadedness
  • Headache
  • Trouble focusing
  • Feeling unsteady when standing or walking
  • Hiccups

There may be other side effects of ethosuximide that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of ethosuximide?

While less common, the most serious side effects of ethosuximide are described below, along with what to do if they happen.

Blood Disorders. Ethosuximide can cause blood disorders such as agranulocytosis, low platelet levels (thrombocytopenia), and low white blood cell levels (leukopenia). Call your health care provider right away if you have any of the following symptoms of blood disorders.

  • Fever
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or bleeding
  • Frequent infection
  • Sore throat
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking ethosuximide. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Kidney Damage. Kidney damage can happen when taking ethosuximide. Call your health care provider right away if you have any of the following symptoms of kidney damage.

  • Reduced need to pee
  • Swelling in your feet, ankles, or legs
  • Weakness or unusual tiredness
  • Trouble catching your breath or chest pain/pressure
  • Confusion
  • Nausea
  • Seizures

Lupus-like Symptoms. Ethosuximide can cause symptoms that look like a condition called lupus. Call your health care provider right away if you have any of the following symptoms.

  • Rash
  • Joint pain
  • Fever
  • Weakness or unusual tiredness
  • Swollen glands
  • Reduced need to pee
  • Pink, red, or brown pee
  • Swelling

Suicidal Thoughts and Actions. Ethosuximide may cause suicidal thoughts or actions in a small number of people. If you are about to harm yourself, call 911 or call or text 988, the Suicide & Crisis Lifeline. Call your health care provider right away if you have any of the following symptoms.

  • New or increased thoughts of suicide or death
  • Suicide attempt
  • New or increased feelings of anxiety, depression, or other unusual changes in mood or behavior

Severe Skin Reactions. Ethosuximide can cause severe skin reactions, called Stevens-Johnson syndrome (SJS), that can lead to death if not treated. If you have a rash, call your health care provider right away. Get emergency help if you have any of the following symptoms of SJS.

  • Painful red or purple skin that looks burned and peels off
  • Flat red rash or blisters on your skin, mouth, nose, and genitals
  • Red, painful, watery eyes
  • Flu-like symptoms including fever, chills, and muscle aches

Severe Allergic Reactions. Ethosuximide may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for drug reaction with eosinophilia and systemic symptoms. It is also sometimes called multiorgan hypersensitivity. This is a reaction that can affect multiple parts of the body including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Shortness of breath, trouble swallowing, or throat tightness
  • Swelling in your feet, ankles, or legs
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain
  • Dark-colored pee
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Warnings & Precautions

Who should not use ethosuximide?

Allergies to Ingredients. People who are allergic to any of the following should not take ethosuximide.

  • Ethosuximide
  • Zarontin
  • Any other medicine known as a succinimide, such as methsuximide
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific ethosuximide products they stock.

What should I know about ethosuximide before using it?

Do not take ethosuximide unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share ethosuximide with other people, even if they have the same condition as you. It may harm them.

Keep ethosuximide out of the reach of children.

Do not stop taking ethosuximide without talking to your health care provider. Stopping ethosuximide suddenly could lead to increased seizures and increase your risk of having status epilepticus, which is a seizure that lasts more than five minutes. If you need to stop taking ethosuximide, your health care provider can tell you how to slowly stop the medicine.

Use an accurate measuring device to measure your dose of ethosuximide oral liquid. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

Your health care provider will likely check lab work while you are taking this medicine to watch for signs of liver, kidney, and blood problems. Keep all appointments, including those for lab work, while you are taking this medicine. 

Ethosuximide can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how ethosuximide affects you.

What should I tell my health care provider before using ethosuximide?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if ethosuximide is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Blood disorders
  • Depression, mood problems, suicidal thoughts or behavior, or a history of any of these
  • Liver or kidney problems
  • Lupus

Other Medicines and Supplements. Ethosuximide may interact with other medicines and supplements. Before taking ethosuximide, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how ethosuximide could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take ethosuximide while you are pregnant or trying to get pregnant. If you become pregnant while taking ethosuximide, you can sign up for the North American Antiepileptic Drug Pregnancy Registry by calling 888-233-2334 or at www.aedpregnancyregistry.org. This registry collects safety information about the use of seizure medicines during pregnancy.

Breastfeeding. Ethosuximide passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take ethosuximide while breastfeeding.

Interactions

Does ethosuximide interact with foods or drinks?

There are no known interactions between ethosuximide and foods or drinks. 

Do not drink alcohol while taking ethosuximide. The risk of drowsiness and dizziness may be increased if you drink alcohol while taking ethosuximide.

Does ethosuximide interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss with your health care provider if you are using any of the following before taking ethosuximide.

  • Phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures
  • Divalproex sodium, valproate sodium (Depakote and others), or valproic acid, which is a medicine used for seizures and other conditions
  • Any medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, or medicines for anxiety

This may not be a complete list of medicines that can interact with ethosuximide. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much ethosuximide?

If you or someone else has used too much ethosuximide, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of ethosuximide?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.