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[Pharmacology](https://durgical.com/en/pharmacology/) · [Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

# Ethosuximide

A medicine for absence seizures, the brief staring spells of childhood. It blocks T-type calcium channels in the thalamus.

Updated 2026-11-01

- Class: [Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)
- Ion channel: T-type calcium channel (Cav3)
- ATC code: N03AD01
- WHO Model List of Essential Medicines

## Mechanism of action

Ethosuximide reduces the low-threshold T-type calcium currents of thalamic neurons. These currents drive the rhythmic thalamocortical firing behind the 3-per-second spike-and-wave pattern of absence seizures, so blocking them stops the lapses of awareness.

- Blocks T-type calcium channels in thalamic neurons
- Low-threshold calcium currents fall
- Thalamocortical rhythm of 3-per-second spike and wave stops
- Absence spells are prevented

## Pharmacokinetics

**Absorption**
Absorbed by mouth

**Distribution**
Little bound to plasma proteins; reaches the cerebrospinal fluid well

**Metabolism**
Mostly in the liver; about a quarter leaves unchanged in the urine

**Half-life**
About 40 to 50 hours in adults and about 30 hours in children

## Indications

- Absence (petit mal) seizures [Epilepsy and seizures →](https://durgical.com/en/conditions/epilepsy-and-seizures/)

## Adverse effects

### Common

- Nausea, stomach upset, loss of appetite and weight
- Drowsiness, headache and dizziness
- Hiccups
- Irritability or hyperactivity

### Serious (rare, important)

- Blood dyscrasias, some fatal
- Systemic lupus erythematosus
- More tonic-clonic seizures when used alone in mixed epilepsy
- Serious skin reactions

## Contraindications

- Hypersensitivity to succinimides

## Key interactions

**Valproate**
Can raise or lower ethosuximide levels

**Phenytoin**
Ethosuximide may raise phenytoin levels

**Alcohol and other sedatives**
More drowsiness

## What is monitored

- Periodic blood counts
- Liver and kidney tests
- Frequency of absence and tonic-clonic seizures

## Administration and safety

- Given by mouth as capsules or liquid
- Withdrawn gradually: stopping suddenly can trigger absence status

## Nursing care

- Teach parents to report fever, sore throat, bruising or bleeding
- Watch for joint pain or rash that could suggest lupus
- Teach parents to record staring spells and any convulsions

## Pregnancy and breastfeeding

It crosses the placenta and passes into breast milk; it is used in pregnancy only when the benefit justifies the risk.

## Memory aid

Ethosuximide: «Sux to have silent seizures» – succinimide for absence, via T-type calcium channels in the thalamus.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the target of ethosuximide?

T-type (low-threshold) calcium channels of thalamic neurons, which drive the spike-and-wave rhythm of absence seizures.

## What EEG pattern does ethosuximide suppress?

The 3-per-second generalized spike-and-wave discharges of absence seizures.

## Why is ethosuximide not used alone when a child also has tonic-clonic seizures?

It does not control tonic-clonic seizures and, used alone in mixed epilepsy, may make them more frequent.

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## Related drugs

- [Valproic acid](https://durgical.com/en/pharmacology/valproic-acid/)

## Related conditions

- [Epilepsy and seizures](https://durgical.com/en/conditions/epilepsy-and-seizures/)

[← Back to the class: Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Ethosuximide: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682327.html) (MedlinePlus (U.S. National Library of Medicine), 2017); [DailyMed - ETHOSUXIMIDE capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a4dbc665-4db1-4d0a-9630-5cd200ec4c82) (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 20 (McGraw Hill, 2023); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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