Absorption
Peak plasma levels are reached in 3 to 5 hours for both children and adults if capsules are taken. The time is somewhat shorter if the syrup is used, but the total amount absorbed will be about the same. Absorption is virtually complete.

Some generic forms of ethosuximide are now available in the United States. They may not be exactly equivalent to Zarontin pharmacologically.

Distribution and metabolism
Ethosuximide is not bound to plasma proteins. It is distributed through total body water and metabolized in the liver.

The half-life of ethosuximide is about 30 to 40 hours in children and 50 to 60 hours in adults.

Because ethosuximide is metabolized in the liver, people with liver disease should be treated with great caution. They may have to be started at a lower dose and have their dosage increased more slowly.

Steady state
In children, steady state is reached after 6 days of taking a stable dose of Zarontin. For adults, the equivalent period is 12 days. A patient's dosage should not be increased until steady state has been reached (or some time later), so that the effects of the previous dosage can be assessed.

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