Zonisamide for seizures: Uses and side effects

Anticonvulsants Prescription medicines Medication safety Medicine Seniors

The bottom line

Zonisamide is an anticonvulsant used for partial onset seizures. Common side effects of zonisamide include drowsiness, dizziness, confusion, headache, poor coordination, and difficulty with memory or finding words. Gastrointestinal symptoms and mood changes can occur. Serious skin and allergic reactions as well as abnormal laboratory findings are possible. Avoid alcohol and other central nervous system depressants when taking zonisamide.

Prevention Tips

Store zonisamide up, away, and out of reach of children.
Take as prescribed.
Do not take more than prescribed or more often than prescribed.
Shake liquid suspension well before each use.
Do not double your doses if you miss a dose.
Store at room temperature, away from heat and moisture. Do not put in direct sunlight.
Discuss possibility of food or drug interactions with your doctor or pharmacist. Herbal supplements may also interact with this medication so be sure to mention those as well if you take them.
Contact your doctor immediately if you develop rashes, skin swelling, fever, or swollen glands.
Do not stop this medication suddenly since this may cause your seizures to return.

This Really Happened

A 25-year-old woman with a history of seizures became drowsy and vomited after an overdose of 12.6 grams of zonisamide in a suicide attempt. On arrival in the emergency department 8 hours after ingestion she was very drowsy and continued to vomit. Vital signs were normal. An EKG showed QRS and QT interval widening and blood gases showed moderate lactic acidosis. She was intubated and activated charcoal was administered to minimize absorption.

Her level of consciousness improved within 8 hours and she was extubated. However, she remained very drowsy for 50 more hours with a brief period of myoclonus (sudden involuntary muscle spasms) and double vision. On day 3, her EKG was normal and her acidosis resolved. Laboratory analysis from the day of admission revealed a high plasma zonisamide concentration.

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What zonisamide prescribed for?

Zonisamide is prescribed for treatment of epilepsy in adults and children 16 years of age and older. It is considered a second-line therapy and is used in combination with other anti-epileptic drugs for the treatment of partial onset seizures (also called focal seizures). Off-label uses (not FDA approved) include prescribing it for other types of seizures (tonic-clonic, myoclonic), migraine prevention, neuropathic pain, alcohol dependence, and weight loss.

How does zonisamide work?

Zonisamide decreases abnormal electrical activity in the brain by blocking voltage-gated sodium and calcium channels. It also modulates neuronal inhibition by the neurotransmitter GABA and inhibits the enzyme carbonic anhydrase.

What are the side effects of zonisamide?

Common side effects of zonisamide include drowsiness, dizziness, confusion, headache, lack of coordination, trouble concentrating, and difficulty with memory or finding words. Other side effects include mood changes such as irritability, agitation, and depression. People may experience nausea, diarrhea, constipation, abdominal pain, and decreased appetite.

More serious effects include severe skin reactions, severe allergic reactions (such as swelling of face or throat), kidney stones, abnormal blood laboratory findings (such as metabolic acidosis, increased ammonia levels, aplastic anemia, or agranulocytosis), decreased sweating, and sudden blurred vision or secondary angle-closure glaucoma.

Is zonisamide a controlled substance?

No, zonisamide is not a controlled substance, but is available by prescription only. It is available as oral capsules (25, 50, 100 mg) and oral suspension. The capsule’s brand name is Zonegran and the oral suspension is Zonisade; generic formulations are also available.

What should I avoid while taking zonisamide?

When you are taking zonisamide, you should avoid alcohol and other depressants because of the increased risk of drowsiness and dizziness. Avoid driving or doing anything dangerous until you determine how this medication affects your coordination. Avoid becoming dehydrated since zonisamide can decrease sweating and increase body temperature.

Food and drug interactions include grapefruit, as well as drugs that cause acidosis or kidney stones such as bismuth subsalicylate (Pepto Bismol) or metformin. Avoid taking zonisamide if pregnant since zonisamide may cause birth defects; consult with your doctor about whether its benefits outweigh the risks. You should also avoid stopping zonisamide abruptly since this may cause seizures to return.

What should I do if someone accidentally takes zonisamide or takes too much zonisamide?

If someone accidentally takes a dose of someone else’s zonisamide or takes a double dose of their own zonisamide, severe toxicity is unlikely although there is increased risk of drowsiness, dizziness, and headache. Seek medical advice, especially if symptoms are present. Overdoses of zonisamide can cause more serious toxicity including severe drowsiness, abnormal gait, agitation, vomiting, decreased blood pressure, increased heart rate, and respiratory depression. Immediate medical attention is needed.

If someone swallows zonisamide or if you have a question about using zonisamide safely, use the webPOISONCONTROL^® online tool to get help, or call your poison center at 1-800-222-1222. Whether online or by phone, expert guidance is always free, confidential, and available 24 hours a day.