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Antiepileptic — T-type Calcium Channel Blocker

Ethosuximide

Brand names: Emeside, Zarontin

Ethosuximide is an antiepileptic that is first-line specifically for absence seizures. It does not control tonic-clonic seizures, so additional cover may be needed where both seizure types coexist.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION 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. 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 …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-05-25. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It reduces low-threshold (T-type) calcium currents in thalamic neurons, which underlie the rhythmic discharges responsible for absence seizures.

Prescribing in practice

  • Rare but serious blood dyscrasias and severe skin reactions can occur — advise the patient to report a sore throat, fever, mouth ulcers, bruising or rash promptly.
  • Gastrointestinal upset (nausea, abdominal discomfort) and drowsiness are common, especially early in treatment.
  • It does not control tonic-clonic seizures; withdraw gradually rather than stopping abruptly.

Monitoring

Be alert to features of blood dyscrasia or serious skin reaction and investigate promptly; monitor seizure control, gastrointestinal tolerance, and mood or suicidal ideation as with all antiepileptics.

Counselling the patient

  • Seek medical advice urgently if you develop a sore throat, fever, mouth ulcers, unusual bruising or a rash.
  • Nausea and drowsiness are common at first and often settle — taking doses with food may help.
  • Do not stop the medicine suddenly.

Evidence & guidelines

First-line for absence seizures (NICE NG217).

Reference: NICE NG217; NETTLES Trial (NEJM 2010); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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