Zonisamide requires several daily doses and comes in capsule form.

How It Works
It is not clear how zonisamide prevents epileptic seizures.

Why It Is Used
Zonisamide has been approved for treatment of partial seizures in people older than 16. It is not approved for use in children younger than 16. It is used in combination with, not instead of, other antiepileptic medications.

How Well It Works
When added to treatment with other antiepileptic medications, zonisamide is sometimes effective in reducing partial seizures in people who have had trouble controlling their seizures with medication (medically refractory epilepsy).

Zonisamide may also be helpful in reducing generalized tonic-clonic seizures, myoclonic seizures, and infantile spasms. It has not been formally approved for these uses, however.

Side Effects
The most common side effects of zonisamide include:

Loss of appetite and weight loss.
Nausea.
Headache.
Agitation, irritability, decreased concentration, or confusion.
See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About
Side effects. Zonisamide seems to be well tolerated by most people. A small number of people taking the drug may develop kidney stones, and it may not be safe for people who have reduced kidney function. Zonisamide has been associated with more serious health problems in a few cases, including liver problems, blood problems (such as aplastic anemia), and a life-threatening rash (Stevens-Johnson syndrome). The risk of these problems is extremely low, however.

Cost. Like other new antiepileptic medications, zonisamide is expensive.

Other concerns. Zonisamide is a fairly new drug. For some people, it may produce side effects or carry risks, including an increased risk of birth defects, that are not fully known yet. It may also interact badly with carbamazepine, phenytoin, or phenobarbital. Report any unexpected side effects or problems to your doctor.

It may take time and careful, controlled adjustments by you and your doctor to find the combination, schedule, and dosing of medication to best manage your epilepsy. The goal is to prevent seizures while causing as few unwanted side effects as possible. Once the most effective medication program is determined, it is important that you follow it exactly as prescribed.