Ethosuximide is an active pharmaceutical ingredient in the Succinimide Derivatives group (N03AD). The information below is compiled per regulator from the product labels on record, with direct links to the original documents.
GBOfficial regulatory label· revised October 10, 2025[1]
Pyknoleptic absences as well as complex and atypical absences - Myoclonic-astatic petit mal and myoclonic fits of adolescents (impulsive petit mal) if other medicinal products are not effective and/or are not tolerated
How to take
GB
CACanada· Health Canada
4 products
Uses
CAOfficial regulatory label· revised March 22, 2025[2]
ZARONTIN / ZARONTIN SYRUP (ethosuximide) is indicated for the control of absence (petit mal) epilepsy. 2 Recommended Dose and Dosage Adjustment). 2 Geriatrics No data are available to Health Canada. Caution should be exercised in dose selection for an elderly patient, recognizing the more frequent hepatic and renal dysfunctions.
How to take
USUnited States· FDA
1 product
Uses
USOfficial regulatory label· revised May 25, 2026[3]
INDICATIONS AND USAGE
Zarontin is indicated for the control of absence (petit mal) epilepsy.
How to take
US
Drug interactions
Known interactions involving Ethosuximide. Select one for details. This list is informational and not a complete interaction checker.
Showing 240 of 303. Type above to find a specific drug.
Interaction data compiled from DDInter (academic, CC-BY). Severity classification only - this is not a complete interaction checker and not medical advice.
Sources & citations
[1]MHRA (UK) · PL344240087 · revised October 10, 2025
[2]Health Canada (DPD) · 00022799 · revised March 22, 2025
[3]FDA DailyMed · 0e008f33-70a1-4b… · revised May 25, 2026 [PDF]
[4]OpenFDA adverse-event reports (US), 12 months ending June 4, 2026.
Information on this page is compiled from public regulatory records. Drugvu is not affiliated with any regulator or pharmaceutical manufacturer. This is not medical advice. Always consult a qualified healthcare professional.
Posology Adults, elderly patients and children over 6 years of age:
The treatment is started at a daily dose of 500 mg. Depending on the patient’s tolerance, the dose is increased every five to seven days in increments of max. 250 mg until the seizures are controlled by a daily dose of 1000- 1500 mg.
In an individual case, a daily dose of 2000 mg, taken in several single doses, may be required. The therapeutic plasma level of ethosuximide is normally between 40 and 100 μg/ml. However, the dose depends on the patient’s clinical response.
The half-life of ethosuximide in plasma is more than 24 hours so that the daily dose can be taken as a single dose provided the medicinal product is well tolerated. Higher daily doses should be taken in 2 or 3 single doses, however.
The probability of dose-dependent undesirable effects can be reduced by careful dosing (small initial dose at the start of treatment, gradual increase of dose) and by taking the medicinal product during or after meals. Anti-epileptic therapies are principally long-term therapies.
A specialist (neurologist, neuropaediatrician) should decide about the start, duration and discontinuation of ethosuximide on an individual basis. In general, reduction of the dose and discontinuation of the medicinal product should not be considered before the patient has been free from fits for 2-3 years.
The medicinal product must be discontinued by reducing the dose gradually over a period of one to two years. Children may be allowed to outgrow the dose per kg body weight instead of adjusting the dose according to their age, however, it must be ensured that the EEC findings do not deteriorate.
Special populations Haemodialysis patients Ethosuximide is dialysable. Haemodialysis patients therefore require a supplementary dose or a modified dose regimen. During a dialysis period of four hours, 39% to 52% of the dose taken is removed.
5 ml). The dose is increased gradually in small increments every few days until the fits are controlled. Children between 2 and 6 years The treatment is started at a daily dose of 250 mg (5 ml). The dose is increased gradually in small increments every few days until the fits are controlled.
The optimum daily dose for most children is 20 mg/kg. The maximum daily dose is 1000 mg. 1. Method of administration Ethosuximide is for oral use. The solution can be taken during or after meals. 5 ml steps) and an adapter for the oral syringe.
A single dose of the oral solution is drawn into the oral syringe up to the required level and transferred into a glass of water or mixed with milk pudding. Alternatively, the oral solution can directly be applicated into the mouth.
Afterwards, the patient should drink half a glass of water.
This is not medical advice. Consult a qualified healthcare professional.
Side effects & warnings
GBOfficial regulatory label· Adverse reactions· revised October 10, 2025[1]
4). Within the therapeutic dose range undesirable effects are common and have been observed in about 1/6 of patients. These are mainly nausea, vomiting, singultus and abdominal pain. Tabulated list of adverse reactions The frequency of possible undesirable effects is defined using the following convention: Very common (≥ 1/10) Common (≥ 1/100 to < 1/10) Uncommon (> 1/1,000 to < /100) Rare (> 1/10,000 to < 1/1,000) Very rare (< 1/10,000) Not known (frequency cannot be estimated from the available data) Blood and lymphatic system disorders Rare: Leucopenia*, agranulocytosis*, eosinophilia* Not known: In individual cases thrombocytopenia, aplastic anemia* and pancytopenia* have been observed.
Metabolism and nutrition disorders Uncommon:
Loss of weight, loss of appetite Psychiatric disorders Uncommon: Withdrawal, anxiety, sleep disturbances Rare: Paranoid and hallucinatory phenomena developing over days and weeks.
Nervous system disorders Uncommon:
Severe headache, ataxia, lethargy Not known: A few individual cases of dyskinesia have been reported for the period of the first 12 hours after start of the treatment; it disappeared soon after discontinuation of ethosuximide or the administration of diphenhydramine Respiratory, thoracic and mediastinal disorders Common to very common: Singultus Gastrointestinal disorders Common to very common: Nausea, vomiting, abdominal pain Uncommon: Diarrhea, constipation Skin and subcutaneous tissue disorders Rare: Lupus erythematosus of varying extent* Not known: Allergic skin reactions* such as exanthema, but also the severe generalized form of Stevens-Johnson syndrome* or drug reaction with eosinophilia and systemic symptoms (DRESS) may occur.
2) If undesirable effects occur which are independent of the dose taken and reversible, the medicinal product should be discontinued. They may reappear when the medicinal product is taken again. g. the performance in school of children and adolescents.
Reporting of suspected adverse reactions Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.
GBOfficial regulatory label· Warnings and precautions· revised October 10, 2025[1]
8), ethosuximide must be discontinued anddiphenhydramine administered by the intravenous route, if required. Special attention should be given to clinical symptoms of bone marrow damage (fever, angina, haemorrhage). It is recommended to check the blood count regularly (initially monthly, after one year every six months) to identify potential bone marrow damage.
At a leucocyte count of less than 3500/mm3 or a granulocyte ratio of less than 25%, the dose should be reduced or the therapy discontinued. The liver enzymes should also be checked regularly. 8, paranoid and hallucinatory symptoms, anxiety, agitation) may occur, therefore special caution is required when treating this group of patients with ethosuximide.
Suicidal ideation and behaviour Suicidal thoughts and behaviour have been reported in patients treated with anti- epileptics for various indications. A meta-analysis of randomised, placebo-controlled studies with anti-epileptics also showed a slightly increased risk for suicidal thoughts and behaviour.
The mechanism triggering this undesirable effect is unknown, and the data available do not exclude a potentially increased risk when taking ethosuximide. Therefore, patients should be monitored for the emergence of suicidal thoughts and behaviour, and an appropriate treatment should be considered.
Patients (and their caregivers) should be advised to seek medical help if symptoms of suicidal thoughts or behaviour occur. g. primidone or phenobarbital). Additional grand mal prophylaxis can be dispensed with only in the case of pyknoleptic absence epilepsies in children of school age.
Severe skin reactions Serious dermatologic reactions, including Stevens-Johnson Syndrome (SJS) and drug reaction with eosinophilia and systemic symptoms (DRESS), have been reported with ethosuximide treatment. SJS and DRESS can be fatal.
Patients appear to be at highest risk of these reactions early in the course of therapy, the onset of the reaction occurring in the majority of cases within the first month of treatment. Ethosuximide should be discontinued at the first appearance of signs and symptoms of severe skin reactions, such as skin rash, mucosal lesions, or any other sign of hypersensitivity.
This is not medical advice. Consult a qualified healthcare professional.
Who should not take it
GBOfficial regulatory label· Contraindications· revised October 10, 2025[1]
1.
This is not medical advice. Consult a qualified healthcare professional.
1 Dosing Considerations As with other anticonvulsants, it is important to proceed slowly when increasing or decreasing dosage, as well as when adding or eliminating other medication. Abrupt withdrawal of anticonvulsant medication may precipitate absence (petit mal) status.
Patients taking ethosuximide should be advised of the importance of adhering strictly to the prescribed dosage regimen. 2 Recommended Dose and Dosage Adjustment Initial dose: children aged 3 to 6 years, 250 mg daily; older patients, 500 mg daily in divided doses.
The dose thereafter must be individualized according to response and tolerance. g. increase daily dose by 250 mg every 4 to 7 days until control is Product Monograph Date: September 2022 ZARONTIN / ZARONTIN SYRUP Page 5 of 18 achieved with minimal side effects.
5 g in divided doses frequently controls seizures; however, it may be necessary to exceed this amount by slow increases and careful evaluation of patient’s response. 5 g daily, in divided doses, should be administered only under the strictest supervision of the physician.
The optimal dose for most children is 20 mg/kg/day. This dose has given average plasma levels within the accepted therapeutic range of 280 to 710 mol/L (40 to 100 g/mL). Subsequent dose schedules can be based on effectiveness and plasma level determinations.
Ethosuximide may be administered in combination with other anticonvulsants when other forms of epilepsy coexist with absence (petit mal). The optimal dosage for most children is 20 mg/kg/day. 4 Administration Ethosuximide can be taken with or without food.
Syrup:
Advise the patient to carefully measure the dose using a measuring device/spoon. A household spoon should not be used to avoid dosing errors. 5 Missed Dose In case of missed dose, the next dose should be taken as scheduled. A double dose should not be taken.
This is not medical advice. Consult a qualified healthcare professional.
Side effects & warnings
CAOfficial regulatory label· Adverse reactions· revised March 22, 2025[2]
5 Post-Market Adverse Reactions Gastrointestinal: Gastrointestinal symptoms occur frequently and include anorexia, vague gastric upset, nausea and vomiting, cramps, epigastric and abdominal pain, weight loss, and diarrhea. There have been reports of gum hypertrophy and swelling of the tongue.
Genitourinary: microscopic hematuria and vaginal bleeding.
Hemopoietic:
Leukopenia, agranulocytosis, pancytopenia, aplastic anemia, with or without bone marrow suppression, eosinophilia, and thrombocytopenia.
Integumentary:
Dermatologic manifestations which have occurred with the administration of ethosuximide have included urticarial, Stevens-Johnson syndrome (SJS), Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), systemic lupus erythematosus, and pruritic erythematous rashes.
Miscellaneous: myopia and hirsutism.
Nervous system:
Neurologic and sensory reactions reported during therapy with ethosuximide have included drowsiness, headache, dizziness, euphoria, hiccups, irritability, hyperactivity, lethargy, fatigue, and ataxia. Psychiatric or psychological aberrations associated with ethosuximide administration have included disturbances of sleep, night terrors, inability to concentrate, and aggressiveness.
These effects may be noted particularly in patients who have previously exhibited psychological abnormalities. There have been rare reports of paranoid psychosis, increased libido, and increased state of depression with overt suicidal intentions.
CAOfficial regulatory label· Warnings and precautions· revised March 22, 2025[2]
, Hematologic 07/2022 7 WARNINGS AND PRECAUTIONS, Skin 07/2022 TABLE OF CONTENTS Sections or subsections that are not applicable at the time of authorization are not listed. RECENT MAJOR LABEL CHANGES ..........................................................................................
2 TABLE OF CONTENTS ............................................................................................................ 2 PART I: HEALTH PROFESSIONAL INFORMATION ....................................................................
5 5 OVERDOSAGE............................................................................................................ 5 6 DOSAGE FORMS, STRENGTHS, COMPOSITION AND PACKAGING ................................ 5 7 WARNINGS AND PRECAUTIONS .................................................................................
1 Special Populations .................................................................................................. 1 Pregnant Women ...............................................................................................
This is not medical advice. Consult a qualified healthcare professional.
Who should not take it
CAOfficial regulatory label· Contraindications· revised March 22, 2025[2]
ZARONTIN / ZARONTIN SYRUP is contraindicated in patients who are hypersensitive to ethosuximide or to any ingredient in the formulation, including any non-medicinal ingredient, or component of the container. For a complete listing, see 6 DOSAGE FORMS, STRENGTHS, COMPOSITION AND PACKAGING.
ZARONTIN / ZARONTIN SYRUP should not be used in patients who are hypersensitive to succinimides or components of these products.
This is not medical advice. Consult a qualified healthcare professional.
Zarontin is administered by the oral route. The initial dose for patients 3 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. 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 to 100 mcg/mL. Subsequent dose schedules can be based on effectiveness and plasma level determinations.
Zarontin 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.
This is not medical advice. Consult a qualified healthcare professional.
Most-reported reactions to the US regulator (12 mo to June 4, 2026): 130 reports total. [4]
Off Label Use 39
Drug Ineffective 37
Seizure 30
Somnolence 16
Behaviour Disorder 15
Decreased Appetite 14
Status Epilepticus 14
Drug Ineffective For Unapproved Indication 12
Generalised Tonic-Clonic Seizure 12
Myoclonic Epilepsy 10
Bk Virus Infection 9
Epilepsy 9
Side effects & warnings
USOfficial regulatory label· Adverse reactions· revised May 25, 2026[3]
ADVERSE REACTIONS
Body As A Whole:
Allergic reaction, Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).
Gastrointestinal System:
Gastrointestinal symptoms occur frequently and include anorexia, vague gastric upset, nausea and vomiting, cramps, epigastric and abdominal pain, weight loss, and diarrhea. There have been reports of gum hypertrophy and swelling of the tongue.
Hemopoietic System:
Hemopoietic complications associated with the administration of ethosuximide have included leukopenia, agranulocytosis, pancytopenia, with or without bone marrow suppression, eosinophilia, and thrombocytopenia (see WARNINGS ).
Nervous System:
Neurologic and sensory reactions reported during therapy with ethosuximide have included drowsiness, headache, dizziness, euphoria, hiccups, irritability, hyperactivity, lethargy, fatigue, and ataxia. Psychiatric or psychological aberrations associated with ethosuximide administration have included disturbances of sleep, night terrors, inability to concentrate, and aggressiveness.
These effects may be noted particularly in patients who have previously exhibited psychological abnormalities. There have been rare reports of paranoid psychosis, increased libido, and increased state of depression with overt suicidal intentions.
Integumentary System:
Dermatologic manifestations which have occurred with the administration of ethosuximide have included urticaria, pruritic erythematous rashes, Stevens-Johnson syndrome, and hirsutism.
Special Senses:
Myopia .
Genitourinary System:
Vaginal bleeding, microscopic hematuria.
USOfficial regulatory label· Warnings and precautions· revised May 25, 2026[3]
WARNINGS
Blood Dyscrasias:
Blood dyscrasias, including some with fatal outcome, have been reported to be associated with the use of ethosuximide; therefore, periodic blood counts should be performed. , sore throat, fever) develop, blood counts should be considered at that point.
Drug-Induced Immune Thrombocytopenia:
Drug-induced immune thrombocytopenia (DITP) has been reported with ethosuximide. In the reported cases, the onset of symptoms occurred 1 to 3 weeks after initiation of ethosuximide; one patient had recurrence of symptoms within 1 day of a subsequent re-challenge with the drug.
In those cases in which the platelet count was specified, the nadir was 2,000 and 3,000/mm 3 . When DITP is suspected, discontinue Zarontin, monitor serial platelet counts, and treat as appropriate. If possible, assess the presence of drug-dependent antiplatelet antibodies.
Avoid future use of Zarontin in patients with history of ethosuximide-induced DITP.
Effects on Liver and Kidneys:
Ethosuximide is capable of producing morphological and functional changes in the animal liver. In humans, abnormal liver and renal function studies have been reported. Ethosuximide should be administered with extreme caution to patients with known liver or renal disease.
Periodic urinalysis and liver function studies are advised for all patients receiving the drug.
Systemic Lupus Erythematosus:
Cases of systemic lupus erythematosus have been reported with the use of ethosuximide. The physician should be alert to this possibility.
Suicidal Behavior and Ideation:
Antiepileptic drugs (AEDs), including Zarontin, increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.
This is not medical advice. Consult a qualified healthcare professional.
Who should not take it
USOfficial regulatory label· Contraindications· revised May 25, 2026[3]
CONTRAINDICATION
Ethosuximide should not be used in patients with a history of hypersensitivity to succinimides.
This is not medical advice. Consult a qualified healthcare professional.
Ethosuximide Key Pharmaceuticals 250 mg/5 ml oral solution contains sodium benzoate (E 211), propylene glycol (E 1520) and sodium. This medicine contains 5 mg of sodium benzoate in each 5 ml. Increase in bilirubinaemia following its displacement from albumin may increase neonatal jaundice which may develop into kernicterus (non-conjugated bilirubin deposits in the brain tissue).
This medicine contains 14 mg propylene glycol in each 5 ml. Coadministration with any substrate for alcohol dehydrogenase such as ethanol may induce serious adverse effects in neonates. This medicine contains less than 1 mmol sodium (23 mg) per 5 ml solution, that is to say essentially 'sodium-free'.
12 PATIENT MEDICATION INFORMATION ................................................................................ 13 Product Monograph Date: September 2022 ZARONTIN / ZARONTIN SYRUP Page 4 of 18 PART I: HEALTH PROFESSIONAL INFORMATION 1 INDICATIONS ZARONTIN / ZARONTIN SYRUP (ethosuximide) is indicated for the control of absence (petit mal) epilepsy.
2 Recommended Dose and Dosage Adjustment). 2 Geriatrics No data are available to Health Canada. Caution should be exercised in dose selection for an elderly patient, recognizing the more frequent hepatic and renal dysfunctions. 2 CONTRAINDICATIONS ZARONTIN / ZARONTIN SYRUP is contraindicated in patients who are hypersensitive to ethosuximide or to any ingredient in the formulation, including any non-medicinal ingredient, or component of the container.
For a complete listing, see 6 DOSAGE FORMS, STRENGTHS, COMPOSITION AND PACKAGING. ZARONTIN / ZARONTIN SYRUP should not be used in patients who are hypersensitive to succinimides or components of these products. 3 SERIOUS WARNINGS AND PRECAUTIONS BOX Serious Warnings and Precautions Blood […]
7) of suicidal thinking or behavior compared to patients randomized to placebo. 24% among 16,029 placebo-treated patients, representing an increase of approximately one case of suicidal thinking or behavior for every 530 patients treated.
There were four suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide. The increased risk of suicidal thoughts or behavior with AEDs was observed as early as one week after starting drug treatment with AEDs and persisted for the duration of treatment assessed.
Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed. The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed.
The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5–100 years) in the clinical trials analyzed.
Table 1 shows absolute and relative risk by indication for all evaluated AEDs. 9 The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications.
Anyone considering prescribing Zarontin or any other AED must balance the risk of suicidal thoughts and behavior with the risk of untreated illness. Epilepsy and many other illnesses for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior.
Should suicidal thoughts and behavior emerge during treatment, the prescriber needs to consider whether the emergence of these symptoms in any given patient may be related to the illness being treated. Patients, their caregivers, and families should be informed that AEDs increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of the signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm.
Behaviors of concern should be reported immediately to healthcare providers.
Serious Dermatologic Reactions:
Serious dermatologic reactions, including Stevens-Johnson syndrome (SJS), have been reported with ethosuximide treatment. SJS can be fatal. The onset of symptoms is usually within 28 days, but can occur later. Zarontin should be discontinued at the first sign of a rash, unless the rash is clearly not drug-related.
If signs or symptoms suggest SJS, use of this drug should not be resumed and alternative therapy should be considered.
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS):
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multi organ hypersensitivity, has occurred with Zarontin. Some of these events have been fatal or life-threatening. DRESS typically, although not exclusively, presents with fever, rash, lymphadenopathy and/or facial swelling, in association with other organ system involvement, such as hepatitis, nephritis, hematologic abnormalities, myocarditis, or myositis, sometimes resembling an acute viral infection.
Eosinophilia is often present. This disorder is variable in its expression, and other organ systems not noted here may be involved. g. fever, lymphadenopathy) may be present even though rash is not evident. If such signs or symptoms are present, the patient should be evaluated immediately.
Zarontin should be discontinued if an alternative etiology for the signs or symptoms cannot be established.
Usage in Pregnancy:
Ethosuximide crosses the placenta. Reports suggest an association between the use of anticonvulsant drugs by women with epilepsy and an elevated incidence of birth defects in children born to these women. Data are more extensive with respect to phenytoin and phenobarbital, but these are also the most commonly prescribed anticonvulsants; less systematic or anecdotal reports suggest a possible similar association with the use of all known anticonvulsant drugs.
Cases of birth defects have been reported with ethosuximide. The reports suggesting an elevated incidence of birth defects in children of drug-treated epileptic women cannot be regarded as adequate to prove a definite cause and effect relationship.
, genetic factors or the epileptic condition itself, may be more important than drug therapy in leading to birth defects. The great majority of mothers on anticonvulsant medication deliver normal infants. It is important to note that anticonvulsant drugs should not be discontinued in patients in whom the drug is administered to prevent major seizures because of the strong possibility of precipitating status epilepticus with attendant hypoxia and threat to life.
In individual cases where the severity and frequency of the seizure disorder are such that the removal of medication does not pose a serious threat to the patient, discontinuation of the drug may be considered prior to and during pregnancy, although it cannot be said with any confidence that even minor seizures do not pose some hazard to the developing embryo or fetus.
The prescribing physician will wish to weigh these considerations in treating or counseling epileptic women of childbearing potential. Ethosuximide is excreted in human breast milk. Because the effects of ethosuximide on the nursing infant are unknown, caution should be exercised when ethosuximide is administered to a nursing mother.
Ethosuximide should be used in nursing mothers only if the benefits clearly outweigh the risks.