Zonegran (Zonisamide)

How does it work?

Zonegran capsules contain the active ingredient zonisamide, which is a medicine that is used to treat epilepsy. It works by stabilising electrical activity in the brain.

The brain and nerves are made up of many nerve cells that communicate with each other through electrical signals. These signals must be carefully regulated for the brain and nerves to function properly. When abnormally rapid and repetitive electrical signals build up and spread through the brain, the brain becomes over-stimulated and normal function is disturbed. This can result in seizures or fits.

Zonisamide prevents epileptic fits by preventing the excessive electrical activity in the brain. It is not fully understood how zonisamide works, but it is thought to act on sodium and calcium channels found on the nerve cells in the brain. Sodium needs to move into the nerve cells for an electrical signal to build up and then be passed on to other nerve cells. Zonisamide may prevent sodium from entering the nerve cells when they begin to fire abnormally rapid and repetitive electrical signals. This helps stabilise the electrical activity in the brain and prevent the excessive seizure-causing signals from spreading through the brain.

Zonisamide may also affect the activity of a neurotransmitter called GABA. Neurotransmitters are natural body chemicals that are stored in nerve cells. They are also involved in transmitting messages between the nerve cells. GABA is a neurotransmitter that acts as a natural 'nerve calming' agent. It helps keep the nerve activity in the brain in balance. Zonisamide may enhance the activity of GABA and so help calm the nerve activity in the brain.

Zonisamide is used as an add-on treatment for adults whose epilepsy has not been well controlled by other anti-epileptic medicines. It is used to prevent partial seizures, and partial seizures that spread to secondary generalised seizures.

What is it used for?

  • Epilepsy - used as an add-on therapy for adults with partial seizures with or without secondary generalisation.


  • This medicine may cause drowsiness or difficulty concentrating, particularly when first starting treatment or after a dose increase. If affected, you should take care when performing potentially hazardous tasks, such as driving or operating machinary.
  • It is important to drink plenty of water while taking this medicine, particularly in warm environments or when doing exercise. This is because zonisamide has been reported to reduce sweating on rare occasions and this could cause flushing and raised body temperature. Drinking water helps keep the body cool.
  • Zonisamide may increase the risk of kidney stones, particularly if you have a personal or family history of kidney stones, or if you are taking other medicines that can cause this side effect. Drinking plenty of water also reduces the risk of developing kidney stones. Consult your doctor if you get a sudden pain in your back or stomach, have pain on urinating, or notice blood in your urine, as this may be a sign of kidney stones.
  • This medicine can cause loss of appetite and weight loss. You should be weighed regularly during treatment. If you are losing too much weight, your doctor will ask you to increase the amount of food being eaten, or may prescribe dietary supplements.
  • There may be a small increased risk of suicidal thoughts and behaviour in people taking antiepileptic medicines such as zonisamide for any condition. For this reason, it is very important to seek medical advice if you, or someone else taking this medicine, experience any changes in mood, distressing thoughts, or feelings about suicide or self-harm at any point while taking this medicine. For more information speak to your doctor or pharmacist.
  • This medicine may very rarely cause serious skin rashes. For this reason you should consult your doctor if you develop a rash, skin peeling, itching, or other unexplained skin reaction while taking this medicine.
  • This medicine may very rarely cause a decrease in the normal amounts of blood cells in the blood. For this reason you should consult your doctor immediately if you experience any of the following symptoms: unexplained bruising or bleeding, purple spots, sore throat, mouth ulcers, high temperature (fever), feeling tired or general illness. Your doctor may want to take a blood test to check your blood cells.
  • This medicine may very rarely have side effects on the muscles. For this reason you should inform your doctor immediately if you experience any muscular symptoms such as pain, tenderness, cramps, or weakness while taking this medicine, particularly if it is accompanied by a fever or feeling generally unwell. Your doctor may need to check for side effects on the muscles by taking a blood test to measure the level of a compound called creatinine kinase in your blood.
  • If you have epilepsy it is important to take your medication regularly, as directed by your doctor, because missing doses can trigger seizures in some people. If you have trouble remembering to take your medicine you should ask your pharmacist for advice. You may find a pill reminder box helpful.
  • You should not suddenly stop taking this medicine without consulting your doctor, as this may result in your seizures returning or getting worse. If it is decided that you should stop taking this medicine, the dose should usually be reduced gradually at weekly intervals. Follow the instructions given by your doctor.

Use with caution in

  • Elderly people.
  • Decreased kidney function.
  • Decreased liver function.
  • People weighing less than 40 kg.
  • High levels of calcium in the urine.
  • Personal or family history of kidney stones.

Not to be used in

  • Allergy to medicines from the sulphonamide group, eg the antibiotic sulfamethoxazole.
  • The manufacturer has not studied the safety and efficacy of this medicine in children and adolescents under 18 years of age. It is not recommended for this age group.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • It is very important for women with epilepsy to talk to the doctor responsible for their epilepsy treatment about getting pregnant. Antiepileptic medicines are associated with an increased risk of developmental disorders and malformations in the baby. However, stopping antiepileptic treatment during pregnancy runs the risk of the mother having seizures, which can harm both the mother and the foetus. This risk may be higher than that from continuing the medication. It is important that all the risks and benefits of treatment are weighed up. Seek medical advice from your doctor.
  • The manufacturer of this medicine recommends that women who could get pregnant use contraceptives to avoid pregnancy both during treatment and for a month after stopping treatment with this medicine.
  • This medicine passes into breast milk. As this could be harmful to a nursing infant, this medicine should not be used by women who are breastfeeding. A decision must be made about whether to stop taking this medicine or to continue treatment and not breastfeed the child. It is important that all the risks and benefits are weighed up. Seek medical advice from your doctor. If you do breastfeed, you should not start until one month after stopping this medicine, as it takes this long for the medicine to be fully removed from the body.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.

  • Sleepiness.
  • Dizziness.
  • Loss of appetite.
  • Agitation.
  • Irritability.
  • Confusion.
  • Depression.
  • Shaky movements and unsteady walk (ataxia).
  • Memory problems.
  • Double vision.
  • Diarrhoea.
  • Nausea and vomiting.
  • Fever.
  • Weight loss.
  • Kidney stones.
  • Gallstones.
  • Disturbances in the normal levels of blood cells in the blood.
  • Inflammation of the pancreas (pancreatitis).
  • Skin reactions such as decreased sweating, rashes or itching.
  • Muscle disorder (rhabdomyolysis).

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

There may be an increased risk of developing kidney stones if this medicine is taken in combination with other medicines that can have this side effect, for example topiramate, acetazolamide.

If this medicine is taken in combination with other medicines that can reduce sweating and raise body temperature, for example topiramate or anticholinergic medicines, there may be an increased risk of raised body temperature and possibly heat stroke, particularly in warm weather.

The following medicines may decrease the amount of zonisamide in your blood. If you start or stop treatment with any of these while taking zonisamide your doctor may need to increase your dose of zonisamide, as they could make it less effective:

  • carbamazepine
  • phenobarbital
  • phenytoin
  • rifampicin.

It is recommended that people who are taking any antiepileptic medicines should avoid taking the herbal remedy St John's wort (Hypericum perforatum). This is because St John's wort may affect the level of antiepileptic medicines in the blood and could increase the risk of seizures.

Other medicines containing the same active ingredient

There are currently no other medicines available in the UK that contain zonisamide as the active ingredient.