Ethosuximide
Ethosuximide is an anticonvulsant medication used to control absence (petit mal) epilepsy.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 13 clinical label sets within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
Ethosuximide (Zarontin) is a seizure medicine for absence (petit mal) epilepsy, the brief staring spells common in children, and it works by quieting the spike-and-wave brain signals behind them; on the market since about 1960 and available as a generic, it is usually a first choice for this seizure type. Most people tolerate it reasonably well, and what they notice most is stomach upset or nausea, drowsiness and, oddly, hiccups. The thing to watch for is a rare but serious blood cell problem, so report fever, sore throat, or unusual bruising or bleeding right away, and get medical help at the first sign of a rash.
Clinical pearls
- Taking each dose with food or milk usually takes the edge off the nausea and stomach upset.
- It treats absence seizures only, so anyone who also has convulsive seizures usually needs another seizure medicine alongside it.
- Expect periodic blood counts and liver tests, plus level checks if valproic acid or phenytoin is also in the mix.
- Families should watch for new irritability, low mood or behavior changes, and report any thoughts of self-harm right away.
Patient information guide A plain-language walkthrough of Ethosuximide, written from its FDA label.
What Ethosuximide is used for
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Ethosuximide is an anticonvulsant (anti-seizure) medication approved to control absence (petit mal) epilepsy.
- Ethosuximide capsules and oral solution are indicated for the control of absence (petit mal) epilepsy.
- Zarontin capsules and oral solution are indicated for the control of absence (petit mal) epilepsy.
- Ethosuximide capsules and oral solution may be used alongside other anticonvulsant medications when other types of epilepsy occur together with absence epilepsy.
- Zarontin capsules and oral solution may be used alongside other anticonvulsant medications when other types of epilepsy occur together with absence epilepsy.
How Ethosuximide works
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Ethosuximide targets the abnormal burst of electrical signals in the brain that causes absence seizures — specifically the repetitive spike-and-wave pattern that produces brief blackouts or staring spells. It appears to work by calming activity in the motor cortex (the brain area controlling movement) and raising the brain's overall threshold for seizure activity, making it harder for a seizure to start. The result is a reduction in how often these seizure episodes occur.
Ethosuximide dosage
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Ethosuximide is taken by mouth and is available as a capsule or an oral solution. Dosing is always individualized — your prescriber will start at a low amount and increase it slowly (typically every four to seven days) until your seizures are well controlled with minimal side effects. Very high daily doses must only be taken under close medical supervision.
- Do not change your dose or stop taking ethosuximide without talking to your doctor first — stopping suddenly can trigger serious seizures.
- Your doctor may order periodic blood level tests to help find the best dose for you.
- If you miss a dose, follow the guidance on your prescription label or ask your pharmacist.
Dosing details from the FDA-approved label
From the Ethosuximide prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.
- Patients 3 to 6 years of age (initial dose)
- One teaspoonful (250 mg) per day for the solution
- One capsule (250 mg) per day for the capsules
- The dose thereafter must be individualized according to the patient's response
- Dosage should be increased by small increments
- One useful method is to increase the daily dose by 250 mg every four to seven days until control is achieved with minimal side effects
- Maximum: Dosages exceeding 1.5 g daily, in divided doses, should be administered only under the strictest supervision of the physician.
- Patients 6 years of age and older (initial dose)
- 2 teaspoonfuls (500 mg) per day for the solution
- 2 capsules (500 mg) per day for the capsules
- The dose thereafter must be individualized according to the patient's response
- Dosage should be increased by small increments
- One useful method is to increase the daily dose by 250 mg every four to seven days until control is achieved with minimal side effects
- Maximum: Dosages exceeding 1.5 g daily, in divided doses, should be administered only under the strictest supervision of the physician.
- Most pediatric patients (optimal dose)
- 20 mg/kg/day, which has given average plasma levels within the accepted therapeutic range of 40 to 100 mcg/mL
- Subsequent dose schedules can be based on effectiveness and plasma level determinations
- Absence (petit mal) epilepsy coexisting with other forms of epilepsy
- May be administered in combination with other anticonvulsants
Read the label’s full dosing text
DOSAGE AND ADMINISTRATION Ethosuximide capsules are administered by the oral route. The initial dose for patients 3 years to 6 years of age is one capsule (250 mg) per day; for patients 6 years of age and older, 2 capsules (500 mg) per day. The dose thereafter must be individualized according to the patient's response. Dosage should be increased by small increments. One useful method is to increase the daily dose by 250 mg every four to seven days until control is achieved with minimal side effects. Dosages exceeding 1.5 g daily, in divided doses, should be administered only under the strictest supervision of the physician. The optimal dose for most pediatric patients is 20 mg/kg/day. This dose has given average plasma levels within the accepted therapeutic range of 40 mcg/mL to 100 mcg/mL. Subsequent dose schedules can be based on effectiveness and plasma level determinations. Ethosuximide capsules may be administered in combination with other anticonvulsants when other forms of epilepsy coexist with absence (petit mal). The optimal dose for most pediatric patients is 20 mg/kg/day.
Read the full Dosage and Administration section on DailyMed →
Ethosuximide side effects
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The most common side effects of ethosuximide involve the stomach and nervous system:
Common side effects
- Nausea, vomiting, or stomach upset
- Loss of appetite or weight loss
- Drowsiness or fatigue
- Headache or dizziness
- Irritability or mood changes
- Hiccups
- Trouble concentrating
- Nausea, vomiting, stomach cramps, or upset stomach
- Diarrhea or abdominal pain
- Drowsiness, fatigue, or lethargy
- Irritability, hyperactivity, or trouble concentrating
- Sleep disturbances or night terrors
When to get medical help
- Call your doctor right away if you notice signs of infection — such as sore throat, fever, or unusual bruising or bleeding — as these may signal a serious blood cell problem
- Seek immediate medical help if a skin rash appears; stop taking ethosuximide at the first sign of rash unless your doctor tells you otherwise
- Get emergency help for symptoms of Stevens-Johnson syndrome: painful blistering or peeling skin, sores in the mouth or eyes
- Contact your doctor immediately if you develop fever, swollen lymph nodes, or facial swelling, especially with a rash — this may be a serious reaction called DRESS
- Tell your doctor if you notice new or worsening depression, unusual changes in mood or behavior, or any thoughts of self-harm or suicide
- Report signs of lupus (joint pain, butterfly-shaped facial rash, persistent fever) to your doctor
- Seek care right away if you develop signs of very low platelets: unusual bruising, tiny red or purple spots on the skin, or prolonged bleeding
More serious reactions — including severe skin rashes, blood cell problems, liver changes, and mood or behavior changes including suicidal thoughts — require immediate medical attention. See the Warnings section for details.
Ethosuximide warnings and precautions
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- Suicidal thoughts and behavior: Like all antiepileptic drugs, ethosuximide increases the risk of suicidal thinking or behavior. Patients, caregivers, and family should watch closely for new depression, unusual mood swings, or any thoughts of self-harm, and report them to a healthcare provider right away.
- Serious blood disorders: Ethosuximide has been linked to dangerous drops in blood cell counts — including severely low platelet counts (drug-induced immune thrombocytopenia) and other conditions — some fatal. Report fever, sore throat, unusual bruising, or bleeding to your doctor immediately. Regular blood counts are recommended.
- Severe skin reactions: Stevens-Johnson syndrome (painful blistering and skin peeling) and DRESS (a multi-organ allergic reaction with fever, rash, and swollen lymph nodes) have occurred and can be life-threatening. Stop ethosuximide at the first sign of a rash and seek care immediately.
- Liver and kidney effects: Ethosuximide can affect liver and kidney function. People with existing liver or kidney disease should use it with extra caution and regular monitoring.
- Systemic lupus erythematosus: Cases of this autoimmune condition have been reported with ethosuximide use.
- Pregnancy: Anticonvulsant drugs, including ethosuximide, have been associated with an increased risk of birth defects. However, stopping seizure medication during pregnancy carries its own serious risks. Discuss this carefully with your doctor.
- Breastfeeding: Ethosuximide passes into breast milk. Use during breastfeeding should only occur if the benefits clearly outweigh the risks, as discussed with your doctor.
Ethosuximide interactions
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Ethosuximide can interact with other seizure medications, affecting drug levels in the blood:
- Phenytoin: Ethosuximide may raise phenytoin blood levels, potentially increasing phenytoin's effects and side effects — monitoring may be needed.
- Valproic acid: This drug can either raise or lower ethosuximide blood levels unpredictably, so both medications need to be watched closely when used together.
- Other antiepileptic drugs: Periodic blood level checks of concurrently used seizure medications are recommended, as interactions are possible.
Interactions listed in the FDA-approved label
From the Ethosuximide prescribing information (“Drug Interactions”): what the manufacturer studied or reported to the FDA.
- Other antiepileptic drugs (concurrently administered): Ethosuximide may interact with concurrently administered antiepileptic drugs. Periodic serum level determinations of these drugs may be necessary.
- Phenytoin: Ethosuximide may elevate phenytoin serum levels. Periodic serum level determinations may be necessary.
- Valproic acid: Valproic acid has been reported to both increase and decrease ethosuximide levels. Periodic serum level determinations may be necessary.
Read the label’s full interactions text
Drug Interactions: Since Zarontin (ethosuximide) may interact with concurrently administered antiepileptic drugs, periodic serum level determinations of these drugs may be necessary (e.g., ethosuximide may elevate phenytoin serum levels and valproic acid has been reported to both increase and decrease ethosuximide levels).
Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.
Before taking Ethosuximide
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- Do not take ethosuximide if you have ever had an allergic reaction (hypersensitivity) to ethosuximide or other succinimide-type medications.
- Tell your doctor if you have liver or kidney disease — extra caution and regular monitoring are needed.
- If you are pregnant or trying to become pregnant, talk to your doctor about the risks and benefits; anticonvulsants have been associated with birth defects, but uncontrolled seizures also carry risks.
- If you are breastfeeding, discuss this with your doctor — ethosuximide is present in breast milk and its effects on nursing infants are not fully known.
- Tell your doctor about any personal or family history of depression, psychiatric conditions, or suicidal behavior.
- Make sure your doctor knows all other seizure or epilepsy medications you take, as dose adjustments or monitoring may be necessary.
Ethosuximide overdose
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Taking too much ethosuximide can cause nausea, vomiting, and central nervous system (CNS) depression — including coma and slowed breathing in severe cases. If an overdose is suspected, seek emergency medical care right away. Treatment may include measures to remove the drug from the body and general supportive care; hemodialysis (a kidney-filtering procedure) may be helpful in serious cases.
What Ethosuximide does in the body
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Ethosuximide suppresses the repetitive spike-and-wave electrical activity in the brain that is the hallmark of absence (petit mal) seizures. By depressing activity in the motor cortex and raising the central nervous system's threshold for convulsive stimulation, it reduces how frequently absence seizure episodes occur.
How to store Ethosuximide
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Store at 20°-25°C (68°-77°F) . Dispense in a tight, light-resistant container as defined in the USP. Protect from moisture.
Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
Supplements & herbs that interact with Ethosuximide
226 supplements and herbal products have documented interactions with Ethosuximide in the licensed clinical database we use. Most are manageable — but your pharmacist should know about everything you take, including vitamins and herbals.
- Major · 9
- Moderate · 179
- Minor · 38
Educational information from a licensed clinical database (Natural Medicines) — see our data sources & update cadence. Not medical advice: an interaction being documented does not mean it will happen to you; do not start or stop medications or supplements without professional guidance.
Nutrient depletion considerations
Ethosuximide has been associated with lower levels of 1 nutrient in the clinical literature. This does not mean a deficiency will occur — it means these may be worth discussing with your pharmacist or healthcare provider, especially with long-term use.
Educational information from a licensed clinical database (Natural Medicines) — not medical advice. Do not start or stop medications or supplements without professional guidance.
Ethosuximide: pharmacist answers to common questions
Quick, plain-English answers to the questions patients ask most about Ethosuximide — the kind of thing our pharmacy team would talk through with you at the counter.
What exactly does ethosuximide treat?
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How should I take ethosuximide, and does it matter if I take it with food?
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What side effects should I expect, and which ones mean I need to call a doctor right away?
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I've heard antiseizure drugs can affect mood. Should I be worried?
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Can I take ethosuximide with my other seizure medications?
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Is it safe to take ethosuximide during pregnancy or while breastfeeding?
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Is Ethosuximide available over the counter?
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When was Ethosuximide first available?
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Who makes Ethosuximide?
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Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
More about Ethosuximide on HelloPharmacist
Ethosuximide forms and strengths (how it comes)
Ethosuximide is available in 2 forms. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Capsule
How this form is used
- Ethosuximide capsules are used to control absence (petit mal) epilepsy
- Zarontin capsules are used to control absence (petit mal) epilepsy
- Ethosuximide capsules may be used together with other anticonvulsants when other types of epilepsy coexist with absence epilepsy
- Zarontin capsules may be used together with other anticonvulsants when other types of epilepsy coexist with absence epilepsy
- Ethosuximide capsules are taken by mouth; dosing starts low and is increased gradually based on your response
- Zarontin capsules are taken by mouth; dosing starts low and is increased gradually based on your response
- Very high daily doses of either product should only be taken under close physician supervision
- Your doctor may periodically check blood levels to help find the right dose for you
Oral solution
How this form is used
- Ethosuximide oral solution is used to control absence (petit mal) epilepsy
- Zarontin oral solution is used to control absence (petit mal) epilepsy
- Ethosuximide oral solution may be used together with other anticonvulsants when other types of epilepsy coexist with absence epilepsy
- Zarontin oral solution may be used together with other anticonvulsants when other types of epilepsy coexist with absence epilepsy
- Ethosuximide oral solution is taken by mouth using the measuring device provided; dosing starts low and is increased gradually
- Zarontin oral solution is taken by mouth; dosing starts low and is increased gradually based on your response
- Very high daily doses of either product should only be taken under close physician supervision
- Your doctor may periodically check blood levels to help find the right dose for you
Ethosuximide on the U.S. market: products, makers and brands
How Ethosuximide appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
9 companies list 12 Ethosuximide product records with the FDA, mostly as capsule, oral solution; the earliest marketing or approval year on record is 1960. Brand names on the directory include Zarontin; the rest are generics.
FDA-listed product records by dose form (tablet variants merged) — FDA National Drug Code Directory. Record counts are not sales or prescription volume.
Also listed with the FDA, not a patient dose form: Powder (2) — bulk drug substance sold to compounders/manufacturers and multi-item kits. These aren’t counted in the dose-form total above.
Share of FDA-listed product records by manufacturer — FDA National Drug Code Directory. Record counts are not sales or prescription volume.
How widely Ethosuximide is used (Medicaid data)
A general measure of how commonly Ethosuximide is prescribed, based on Medicaid — one of the largest public drug programs. The figure below is prescriptions filled in Q1–Q4 2025, summed across every form and brand of the drug.
Think of this as a proxy for how widely Ethosuximide is used, drawn from freely available public data. Medicaid is just one program — these numbers don’t include Medicare, other government coverage, or commercial and cash-pay prescriptions, so real-world use is higher than what’s shown here.
How commonly is Ethosuximide prescribed? Of the 1,601 medications we measure, Ethosuximide ranks #540 by Medicaid prescriptions — more than 66% of them.
Utilization by Ethosuximide product
Pick a product to see its own Medicaid numbers. Each chip is one clinical product — a specific strength & dosage form as defined by RxNorm — with brand-name and generic versions combined.
ethosuximide 250 MG Oral Capsule Most dispensed
Summed across the 4 of 15 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 197682
ethosuximide 50 MG/ML Oral Solution
Summed across the 3 of 7 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 251322
Shares are of the Medicaid prescriptions shown here. Product grouping follows RxNorm (the National Library of Medicine’s drug terminology), so “one product” means one strength & dosage form regardless of manufacturer. Dollar figures are gross Medicaid reimbursement before mandatory rebates — rebates (often large, especially for brand-name drugs) are confidential, so actual net cost to Medicaid is lower than shown.
Source: Medicaid State Drug Utilization Data (CMS), aggregated by generic ingredient — summed across every NDC (all brands, strengths, salt forms and dosage forms) of Ethosuximide, and across all states and both fee-for-service and managed-care claims. A general popularity signal; it excludes Medicare, commercial insurance and cash prescriptions, so it is not total U.S. use. Based on the 7 of 22 listed Ethosuximide NDCs with Medicaid activity.
Compare Ethosuximide products
A representative set of FDA-listed product records for Ethosuximide — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Capsule | ||||
| 250 mg | Oral | Bionpharma Inc. | ANDA | View NDC → |
| 250 mg | Oral | Bryant Ranch Prepack | ANDA | View NDC → |
| 250 mg | Oral | Chartwell RX, LLC | ANDA | View NDC → |
| 250 mg | Oral | Epic Pharma, LLC × 2 listings | ANDA | View NDC → |
| 250 mg | Oral | Parke-Davis Div of Pfizer Inc | NDA | View NDC → |
| 250 mg | Oral | Strides Pharma Science Limited | ANDA | View NDC → |
| 💊Oral solution | ||||
| 250 mg/5 mL | Oral | Chartwell Governmental & Specialty RX, LLC. | ANDA | View NDC → |
| 250 mg/5 mL | Oral | Chartwell RX, LLC | ANDA | View NDC → |
| 250 mg/5 mL | Oral | Mylan Pharmaceuticals Inc. | ANDA | View NDC → |
| 250 mg/5 mL | Oral | PAI Holdings, LLC dba PAI Pharma | ANDA | View NDC → |
| 250 mg/5 mL | Oral | Parke-Davis Div of Pfizer Inc | ANDA | View NDC → |
Showing 12 of 12 products — FDA National Drug Code Directory. See every product, package size and price: browse all 12 Ethosuximide NDCs →
Ethosuximide side effects reported to the FDA (FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Ethosuximide — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Ethosuximide in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
Ethosuximide FDA approval history
How Ethosuximide went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
Ethosuximide recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
The FDA’s enforcement reports list one Ethosuximide recall since July 2021. It is no longer listed as ongoing. A recall names specific lots from one company, so check the lot number on your own bottle rather than assuming every product is affected; your pharmacist can check whether your supply came from an affected lot.
- Ethosuximide Oral Solution USP 250 mg/5 mL, 16 fl oz (473 mL), Rx ONLY, Pharmaceutical Associates, Inc. Greenville, SC 29605, NDC 0121-0670-16 Lots: Lot: C9BC Exp. 31OCT2022 FDA record D-0723-2021 →
Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Sep 24, 2026.
RxNorm Concept Web — From Ingredient to Every Form and Strength
This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.
RxCUI 4135 2 dose forms · 2 strengths
Look up RxCUI 4135 in the RxCUI Atlas →
RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.
Ethosuximide supply and shortage status
Whether Ethosuximide is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
💵 What Ethosuximide costs pharmacies (NADAC benchmark)
The national average invoice price pharmacies pay for the drug itself, from CMS's NADAC survey (data as of Sep 30, 2026). This is a supply-cost benchmark — not a retail price and not what you'd pay at the counter.
| Form | Strength | Pharmacy acquisition benchmark | |
|---|---|---|---|
| Capsule · Oral | 250 mg | $1.31 per capsule | NDC details & price history |
Source: CMS National Average Drug Acquisition Cost (NADAC), a survey of retail pharmacy invoice prices. Benchmarks shown are the range across package sizes of a representative product for each form and strength — other manufacturers' products may differ.
Ethosuximide brand names
Ethosuximide is sold under one brand name in the FDA directory — Zarontin. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.
Who makes Ethosuximide: manufacturers and labelers
9 companies list Ethosuximide products with the FDA. By number of product records, the largest are Chartwell RX, LLC, Epic Pharma, LLC, Parke-Davis Div of Pfizer Inc. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.
Ethosuximide drug class (RxNorm)
Ethosuximide belongs to the Anti-epileptic Agent class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
Sources for this Ethosuximide page
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How this page is built
HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. Parke-Davis Div of Pfizer Inc is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →