Ethosuximide (Zarontin)

Miriam Calleja
Author: Miriam Calleja Medical Reviewer: Dr. Leila Khurshid Last updated:

Ethosuximide is an anticonvulsant used to control petit mal seizures, commonly called absence seizures. During treatment, patients should be observed for any mental health changes, as ethosuximide can cause the development of suicidal thoughts.

Ethosuximide brand names

Ethosuximide is sold under the brand names Esemide and Zarontin.

What is ethosuximide prescribed for?

Ethosuximide is a medication that is used to treat absence seizures. It is classified as an anticonvulsant and works by reducing the spread of electrical activity in the brain. This can help to prevent seizures from occurring or reduce their frequency and severity if they do occur.[1]

Absence seizures, or petit mal, cause a very brief – generally around ten to twenty seconds – loss of awareness during which the person is unresponsive and may stare straight ahead or blink. There may also be small movements such as finger rubbing, chewing motions, or lip smacking. Afterward, there is a rapid return to a normal level of alertness. The patient does not typically fall over during the episode, and they have no recollection of the time they were having the seizure.

This type of seizure is more common in children than in adults. While some children may outgrow this condition, others may develop full convulsions. If left untreated, the child can suffer from behavioral problems, social isolation, and learning challenges.[2]

Ethosuximide is usually considered a relatively safe and effective treatment option, but it is not suitable for everyone. Some people may experience adverse effects such as drowsiness, dizziness, or nausea.

How does ethosuximide work?

Ethosuximide is an anti-epilepsy medication used to treat absence seizures, that works by controlling electrical activity in the brain that can lead to these seizures thus reducing their frequency.[1]

The brain and nervous system are made up of nerve cells that send electrical signals to communicate with each other. During normal function, these signals are regulated. However, when the brain experiences electrical signals that are abnormally rapid or repetitive, it becomes overstimulated, and this results in seizures.[3]

How is ethosuximide usually taken?

Ethosuximide and Zarontin are available in capsule (250mg) or liquid form (250mg/5ml) to be taken orally. The dose is usually taken once or more daily at around the same time. When using the liquid, you should carefully measure the quantity with the specific measuring device (spoon, syringe, or cup) provided in the package rather than using a household spoon, as the latter will give an inaccurate dosage.

The dosage chosen by your doctor will depend on your or your child’s age, the severity of the condition, response to the first dose, response to treatment, blood levels of ethosuximide achieved during treatment, and any other medical conditions present. In the case of children, the dosage will also depend on their weight.

  • Ages 3-6: the initial dose is one teaspoon (250mg) per day
  • Ages 6-17: the initial dose is two teaspoons (500mg) per day
  • Ages 18 and older: the initial dose is 500mg per day

The dose is then increased in small increments according to response, e.g., an increase of 250mg every four to seven days until control of the absence of seizures is achieved while keeping the side effects to a minimum. The capsule should not be cut or crushed.

The dose for most children is 20mg/kg/day, and amounts rarely exceed 1.5 g daily in divided doses. However, when more than 1.5 g daily is needed, this will require further monitoring, even in adults. Zarontin may also be used with other medications when other forms of epilepsy are present.[4]

The medicine does not cure the condition but controls it, so it is essential to take the medication as directed by your doctor. However, taking too much (more than the prescribed dose), risks severe side effects.

Sudden cessation will worsen the seizures. And so, if you need to stop the medication due to side effects or other reasons, the doctor will guide you on decreasing the dose gradually.

How long does ethosuximide stay in your system?

The half-life of a medication is the time it takes for levels of the drug in the body to reduce by half. For example, the half-life of ethosuximide is about 60 hours, which means it can take up to 5 days for the drug to be eliminated entirely from the body. However, this may vary depending on individual factors such as age, kidney function, and liver function.[5]

Ethosuximide side effects

Ethosuximide can cause drowsiness. Until you know how this medicine affects you, you should not drive or use machinery, or do similar activities that may put you in danger if you are not alert.

It can also cause other side effects. Some common side effects of ethosuximide are:

  • Dizziness or lightheadedness
  • Fatigue (feeling tired)
  • Weight loss
  • Stomach problems: diarrhea, nausea, vomiting, indigestion, loss of appetite, or stomach pain
  • Hiccups
  • Loss of coordination
  • Headache
  • Trouble focusing
  • Hair growth in unusual places
  • Overgrowth of the gums

These may be mild and go away after a few days. However, you should consult your doctor or healthcare provider if they persist or worsen.

Serious side effects possible include:

  • Suicidal thoughts or actions, including thoughts about dying, and suicide attempts; panic attacks; new or worse depression; acting impulsively; mania (extreme increase in talking or actions); new or worse irritability; aggression, anger, or violence; and trouble sleeping.
  • Changes in mental health: alteration in moods and behavior as manifested by suspicious thoughts; hallucinations (where you see or hear something that isn’t there); and delusions.
  • Allergic reactions: Stevens-Johnsons syndrome (a life-threatening allergic reaction); hives, skin rash; trouble breathing; blistering skin; patchy or yellowing skin color; sores in the mouth, nose or around the eyes; swollen glands; and swelling of the lips, tongue or face.
  • Increase in the number or worsening of seizures, including grand mal seizures (also known as tonic-clonic fits),which can include muscle stiffness, loss of consciousness, involuntary moaning or crying, foaming at the mouth, jerking movements, and loss of bladder/bowel control.
  • Blood problems (can be life-threatening): persistent or frequent fever, swollen glands, and sore throat; persistent or frequent infections; bruising easily; nosebleeds or bleeding from the gums; red or purple spots on the skin; severe and unexplained weakness or tiredness.
  • The development of systemic lupus erythematosus (lupus, an autoimmune disease). Symptoms include inflamed and painful joints, muscle pain, low-grade fever, fatigue, chest pain with breathing, and skin rash.[6]

If you or your child experience any severe side effects, consult your doctor immediately. Do not stop taking/giving the medication until your doctor guides you.

Ethosuximide precautions

Those with certain health conditions may not be able to take ethosuximide or may need special supervision during their treatment:

  • Those with liver disease
  • Those with kidney disease
  • Those with grand mal seizures

Ethosuximide vs. pregnancy

The antiepileptic drug ethosuximide is not recommended during pregnancy as it may cause congenital disabilities. Therefore, you should warn your doctor if you get pregnant during treatment or are planning on trying for a baby. The drug is only used if its use justifies the potential risks. However, suppose you are taking the treatment and become pregnant. You should not stop the medication without consulting your doctor, as this may cause seizures and serious complications for you and your baby.

Ethosuximide passes through breastmilk and is not recommended during breastfeeding as it may cause effects in the breastfed infant. If you plan to breastfeed, consult your doctor to make the changes needed.[7]

Ethosuximide interactions

Ethosuximide has several serious drug interactions. If you are taking any of the following, or any other prescription drugs, over-the-counter medications, herbal preparations, or vitamins, warn your doctor or pharmacist before starting ethosuximide:

  • Alcohol
  • Other anticonvulsants, e.g., phenobarbital, phenytoin
  • Tricyclic antidepressants
  • Central nervous system (CNS) depressants, such as sedatives
  • Isoniazid (a drug for tuberculosis)
  • Valproic acid
  • Tramadol[8]

Ethosuximide storage

You should always keep ethosuximide in the container it came in. Keep both the liquid and capsules at room temperature, and never freeze. Medicines should be kept out of view and reach of children and pets. Store the medicine in a cool, dry place away from excessive heat, light, and moisture.

When the medicine is expired, or you no longer need it, do not flush it down the toilet or dispose of it in the garbage. Instead, ask your pharmacist the best way to dispose of it properly.

What to do if you overdose on ethosuximide

Symptoms of overdose may include:

  • Decreased alertness
  • Slowed breathing
  • Nausea and vomiting
  • Loss of consciousness leading to coma

When consuming alcohol with ethosuximide, you might inadvertently cause an overdose. This is because this combination causes more ethosuximide than usual in the blood. This will cause drowsiness and difficulty concentrating, which can lead to motor vehicle and other accidents. Some people also experience impaired judgment, thus putting themselves in danger (e.g., by having unprotected sex).

If you suspect that you or someone you know has taken an overdose, you should call the poison control helpline. If the person has collapsed, is unresponsive, has had a seizure, or has trouble breathing, then you should call emergency services.

  1. Zarontin (ethosuximide) dosing, indications, interactions, adverse effects, and more. (2022, February 21).
  2. Absence seizure—Symptoms and causes. (n.d.). Mayo Clinic. Retrieved 16 November 2022, from
  3. Zarontin (ethosuximide) dosing, indications, interactions, adverse effects, and more. (2022c, February 21).
  4. Zarontin Dosage Guide. (n.d.). Retrieved 16 November 2022, from
  5. Ethosuximide Monograph for Professionals. (n.d.). Retrieved November 16, 2022, from
  6. DailyMed – ZARONTIN- ethosuximide capsule. (n.d.). Retrieved November 24, 2022, from
  7. DailyMed – ZARONTIN- ethosuximide capsule. (n.d.). Retrieved November 24, 2022, from
  8. Ethosuximide Monograph for Professionals. (n.d.). Retrieved November 16, 2022, from
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Miriam Calleja
Author Miriam Calleja Writer

Miriam Calleja is a pharmacist with an educational background from the University of Malta and the European Medicines Agency.

Published: Nov 22nd 2022, Last edited: Oct 27th 2023

Dr. Leila Khurshid
Medical Reviewer Dr. Leila Khurshid PharmD, BCPS

Dr. Leila Khursid is a medical reviewer with a Doctor of Pharmacy degree and completed a PGY1 Pharmacy Residency from St. Mark's Hospital.

Content reviewed by a medical professional. Last reviewed: Nov 23rd 2022
Medical Reviewer Medical Reviewer:
Dr. Leila Khurshid
Last reviewed: Nov 23rd 2022 Dr. Leila Khurshid

PharmD, BCPS