From the FDA Drug Label
DOSAGE AND ADMINISTRATION Zarontin is administered by the oral route. The initial dose for patients 3 to 6 years of age is one teaspoonful (250 mg) per day; for patients 6 years of age and older, 2 teaspoonfuls (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. The dosage and management of Zarontin (ethosuximide) for absence seizures is as follows:
- Initial dose: 250 mg per day for patients 3 to 6 years of age, and 500 mg per day for patients 6 years of age and older.
- Dose titration: Increase the daily dose by 250 mg every four to seven days until control is achieved with minimal side effects.
- Optimal dose: 20 mg/kg/day for most pediatric patients.
- Maximum dose: 1.5 g daily, in divided doses, under strict supervision of the physician 1.
From the Research
Zarontin (ethosuximide) is typically initiated at 250 mg twice daily for adults and adolescents with absence seizures, with gradual titration to an effective dose of 500-1500 mg daily divided into two doses, as supported by the most recent and highest quality study 2. The medication should be taken with food to minimize gastrointestinal side effects.
- Blood level monitoring is recommended, with therapeutic levels ranging from 40-100 μg/mL, as noted in earlier studies 3.
- Common side effects include nausea, dizziness, headache, and fatigue, which often diminish over time.
- Patients should be monitored for rare but serious adverse effects including blood dyscrasias, systemic lupus erythematosus, and behavioral changes, as reported in case studies 4. Treatment is typically long-term, with consideration for discontinuation after 2-3 years of seizure freedom, though this should be done gradually over 3-6 months to prevent seizure recurrence.
- Ethosuximide works by inhibiting T-type calcium channels in thalamic neurons, disrupting the thalamocortical circuits responsible for generating the 3 Hz spike-and-wave discharges characteristic of absence seizures, making it particularly effective for this seizure type with efficacy rates of approximately 70-80%, as demonstrated in clinical trials 5. The choice of ethosuximide as the initial treatment for absence seizures is supported by its superior effectiveness compared to lamotrigine, as shown in a large randomized controlled trial 2, and its favorable side effect profile compared to valproate, as noted in studies 5 and 6.