Dose-related side effects
In early studies of ethosuximide, a minority of subjects reported adverse effects. The most common adverse effects were gastrointestinal:

• nausea
• abdominal discomfort
• vomiting
• anorexia
• diarrhea

These problems are usually mild. If they do not diminish within several days, a reduction in the dose of Zarontin may be required. Another effective technique to resolve such problems is to divide the daily dosage into smaller doses to be taken with meals.

Less common were other adverse effects:

• drowsiness
• dizziness
• hiccups
• behavioral changes (irritability, mood change, aggressiveness)

These effects generally respond to dose reduction.

Some children taking ethosuximide develop persistent headaches, which do not appear to be dose-related.

Other patients notice a pinkish or brownish discoloration of their urine. This is unlikely to represent a serious problem.

Idiosyncratic reactions
The most common idiosyncratic reaction to ethosuximide is a mild rash, which often disappears if the medication is stopped. Some patients need steroid therapy.

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