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Zonegran / Zonisamide

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1Zonegran / Zonisamide Empty Zonegran / Zonisamide on Wed Sep 30, 2009 10:19 am


Zonegran (ZAHN-uh-gran) is the brand name used in the United States for the seizure medicine zonisamide (zoh-NIH-sah-mide). In 2003, Zonegran was not available in Canada, the UK, or Australia.

Zonisamide was first used in Japan in 1972 to treat psychiatric diseases, and it has been widely used to treat epilepsy in Japan and Korea since at least 1990. The Food and Drug Administration (FDA) approved it for use in the United States in March 2000, suggesting that it be used along with other seizure medicines (as adjunctive or add-on therapy) in the treatment of partial seizures in adults.

Zonegran is used as an adjunctive (add-on) therapy for partial seizures (seizures that begin in a limited area of the brain) in adults with epilepsy. Research and experience with patients suggests that it also may be effective for other types of epilepsy and epilepsy syndromes, including:

Lennox-Gastaut syndrome
infantile spasms (West syndrome)
progressive myoclonic epilepsy (PME)

Zonegran (zonisamide) is chemically classified as a sulfonamide. It is not related to any other seizure medicines.

The precise way that it works to control seizures (what doctors call the "mechanism of action") is unknown. Possible mechanisms may have something to do with the fact that it blocks sodium channels (the route by which sodium ions move in and out of nerve cells) and certain calcium channels. These effects may stabilize the membranes of nerve cells in the brain and prevent them from all firing together in an uncontrolled surge.

Zonisamide also slightly inhibits the action of an enzyme called carbonic anhydrase. Some other substances that have this action are effective against certain types of seizures, but this effect is not thought to be a major contributing factor in the antiseizure activity of zonisamide.

Most people who take Zonegran don't report any side effects.
The others most often complain of:

sleepiness or fatigue
loss of appetite (it's not unusual to lose several pounds)
upset stomach
agitation or irritability

Most of these problems are mild to moderate.
During scientific studies in which some people took Zonegran in addition to their regular seizure medicine, and some people took an inactive substitute (a placebo) instead of Zonegran, only 17% of the patients taking Zonegran reported a problem with sleepiness (as did 7% of those taking the placebo). The other side effects were even less common. So you can see that side effects are not a problem for most people. You should be careful when you first start taking Zonegran, though, and make sure you don't have a problem with sleepiness when driving or doing anything else that might be dangerous.

Some other side effects mentioned even less often were:

poor coordination or tremor
speech problems
poor concentration
vision problems
If you notice problems like any of these while you are taking Zonegran, it's probably a good idea to discuss them with your doctor or nurse. Sometimes the doctor can help with these side effects by changing the prescription:

Reducing the overall dose
Changing the amount taken at certain times, such as taking a greater proportion at bedtime to reduce daytime sleepiness
Prescribing smaller doses, to be taken more often You shouldn't stop taking Zonegran or any other seizure medication without your doctor's advice.

People who have just started taking Zonegran (or who have just started taking a larger amount) should be careful during activities that might be dangerous, until they know whether they are having any side effects.

Approximately 1 in 20 people who take Zonegran have a red rash within the first few weeks of taking it. If this happens, tell the doctor or nurse right away, to be sure that it's not the beginning of a serious problem. It's rare for the rash to be serious, but don't ignore it. It's often necessary to switch to a different seizure medicine.

Pregnancy Category C and recommends that women who could possibly become pregnant should use effective birth control while using Zonegran. Recognizing that seizures in the mother also may be hazardous to a fetus, however, they conclude that the risks and benefits must be weighed in considering the use of Zonegran during pregnancy. Tell your doctor right away if you are pregnant or thinking about becoming pregnant.

The use of Zonegran (zonisamide) by pregnant women hasn't been fully studied, but there are serious concerns based on studies using animals. When it was given to pregnant mice, rats, and dogs early in pregnancy, there were high rates of fetal abnormalities, especially heart defects and skeletal malformations. After it was given to monkeys during certain stages of pregnancy, many of the fetuses died, possibly because of malformations. All of these effects occurred at doses (and blood levels in the mother) that were equivalent to the amounts used to treat epilepsy in humans, or sometimes even lower. There was also a higher rate of death among the offspring of rats who were given zonisamide late in their pregnancy.

In one study in Japan of 26 human pregnancies, there were 2 malformations affecting fetuses whose mothers were receiving zonisamide along with other seizure medicines, but none among 4 whose mothers were receiving only zonisamide. Based on this information, the researchers suggested that the risk may not be greater than for other seizure medicines, but such risk "cannot be neglected," especially if more than one medicine is being used. In general, the risk of birth defects is higher for women who take more than one seizure medicine and for women with a family history of birth defects.

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