For children ages 3 to 6 years with absence seizures, the usual starting dose is 1 capsule or 1 teaspoon (5 mL) of the syrup per day. This is often given as half a teaspoon (2.5 mL) twice a day.

The initial daily dose for older children is often 2 capsules or 2 teaspoons of syrup, which can be increased after about a week.

Most children do best at about 20 mg/kg per day. The dose is usually divided, with doses given two or three times a day.

A therapeutic serum level of ethosuximide is generally considered to be 40-100 mcg/mL, but adjustments should depend on clinical response. Because Zarontin has a long half-life, blood levels do not fluctuate much, so the time when tests are done is not important. Levels in saliva are very similar to plasma levels and also can be used to monitor therapy.

• Algorithm for dosing ethosuximide (Zarontin)

Reviewed February 2004 by Barry Gidal, PharmD, epilepsy.com Editorial Board.