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Antiepileptic — T-type Calcium Channel Blocker Pregnancy: Avoid if possible — limited teratogenicity data; supplement folate

Ethosuximide

Brand names: Emeside, Zarontin

Adult dose

Dose: 500 mg twice daily initially; increase by 250 mg every 5–7 days
Route: Oral
Frequency: Twice daily
Max: 2000 mg/day
Drug of choice for childhood absence epilepsy — blocks thalamic T-type calcium channels involved in spike-wave discharge generation. NOT effective for other seizure types. NICE first-line alongside valproate for absence seizures; preferred over valproate in girls of childbearing age.

Paediatric dose

Dose: 5 mg/day/kg
Route: Oral
Frequency: Twice daily
Max: 40 mg/kg/day
Children: start 5 mg/kg/day; increase by 5 mg/kg every 5–7 days to 20–40 mg/kg/day. Available as 250 mg/5 mL syrup (Emeside) for children.

Dose adjustments

Renal

No specific adjustment required.

Hepatic

Caution in hepatic impairment.

Paediatric weight-based calculator

Children: start 5 mg/kg/day; increase by 5 mg/kg every 5–7 days to 20–40 mg/kg/day. Available as 250 mg/5 mL syrup (Emeside) for children.

Clinical pearls

  • NETTLES trial (NEJM 2010): ethosuximide superior to valproate and lamotrigine for attentional effects in childhood absence epilepsy — first-line recommendation reinforced
  • Purely an absence seizure drug — no efficacy against tonic-clonic, focal, or myoclonic seizures. Add valproate if patient has mixed seizure types.
  • Preferred over valproate in females due to teratogenicity and PCOS risk of valproate

Contraindications

  • Hypersensitivity to succinimides
  • Porphyria

Side effects

  • GI disturbance (nausea, vomiting — take with food)
  • Anorexia
  • Hiccups
  • Headache
  • Behavioural changes
  • Rare: blood dyscrasias (agranulocytosis, aplastic anaemia)
  • Lupus-like syndrome (rare)

Interactions

  • Valproate (increases ethosuximide levels — reduce dose if combined)
  • Carbamazepine/phenytoin (reduce ethosuximide levels)

Monitoring

  • FBC (blood dyscrasias — if fever or malaise)
  • Drug levels if inadequate response or toxicity (target 40–100 mg/L)
  • Seizure diary

Reference: BNFc; BNF 90; NICE NG217; NETTLES Trial (NEJM 2010); BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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