Pharmacology · 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
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 →
Adverse effects
Common
- Nausea, stomach upset, loss of appetite and weight
- Drowsiness, headache and dizziness
- Hiccups
- Irritability or hyperactivity
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- Withdrawn gradually: stopping suddenly can trigger absence status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.
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.
Related drugs
Related conditions
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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 (MedlinePlus (U.S. National Library of Medicine), 2017); DailyMed - ETHOSUXIMIDE capsule (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 (World Health Organization, 2025).
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Representative model, for educational purposes only.