Phenytoin for preventing seizures

This leaflet is for parents and carers about how to use this medicine in children. Our information may differ from that provided by the manufacturers, because their information usually relates to adults. Read this leaflet carefully. Keep it somewhere safe so that you can read it again.

Do not stop giving Phenytoin suddenly, as your child may have more seizures.

Name of medicine


Why is it important for my child to take Phenytoin?

It is important that your child takes phenytoin regularly so that they have fewer seizures.

What is Phenytoin available as?

  • Tablets: 100 mg
  • Capsules:  25 mg, 50 mg, 100 mg, 300 mg
  • Infatabs: 50 mg
  • Liquid medicine: 30 mg in 5 mL and 90 mg in 5 mL

Liquid medicine comes in several different strengths. Make a note of which one you usually have, and check that you have been given the right one each time.

When should I give Phenytoin

The Phenytoin is usually given twice each day. Give one dose in the morning and one in the evening. Ideally these times are 10–12 hours apart. For example, this could be between 7am and 8am and between 7pm and 8pm.

Your doctor may tell you to start by giving Phenytoin once a day until your child gets used to it. This is usually in the evening.

Give the medicine at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

How much should I give?

Your doctor will work out the amount of Phenytoin (the dose) that is right for your child. This is usually worked out from their weight. The dose will be shown on the medicine label.

When you first start giving Phenytoin to your child, you will probably give them a low dose, which may be increased bit by bit over a few days or weeks. This helps your child to get used to the medicine. Your doctor will explain what to do.

It is important that you follow your doctor’s instructions about how much to give.

How should I give Phenytoin?


  • Tablets should be swallowed with a glass of water, squash or juice. Your child should not chew the tablet.


  • Capsules should be swallowed with a glass of water, squash or juice. Your child should not chew the capsule.


  • Can be chewed or swallowed whole.

Liquid medicine

  • Shake the medicine well.
  • Measure out the right amount using an oral syringe or a medicine spoon. You can get these from your pharmacist. Do not use a kitchen teaspoon as it will not give the right amount.

When should the medicine start working?

It will take a few weeks for Phenytoin to work properly, so your child may still have seizures during this time. This is because the amount of medicine has to be increased slowly. Continue to give the medicine as you have been told to by your doctor.

What if my child is sick (vomits)?

  • If your child is sick less than 30 minutes after having a dose of Phenytoin, give them the same dose again.
  • If your child is sick more than 30 minutes after having a dose of Phenytoin, do not give them another dose. Wait until the next normal dose.

If your child is sick again, seek advice from your family doctor, nurse, pharmacist, or hospital. They will decide what to do based on your child’s condition and the specific medicine involved.

What if I forget to give it?

If you usually give it twice a day: If you remember up to 4 hours after you should have given a dose, give your child the missed dose. For example, if you usually give a dose at about 7am, you can give the missed dose at any time up to 11am. If you remember after that time, do not give the missed dose. Give the next dose as usual.

Never give a double dose of Phenytoin.

What if I give too much?

If you think you may have given your child too much Phenytoin, contact your doctor or local NHS services (details at end of leaflet) or take your child to hospital. Have the medicine container or packaging with you, even if it is empty. This will be useful to the doctor.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side effects).

Side effects you must do something about

If your child develops a blotchy red skin rash, contact your doctor straight away, as your child may be allergic to Phenytoin. The rash usually affects the whole body but may just affect the face. You may also see blisters in the mouth, and your child may have a high temperature (fever).

Other side-effects you need to know about

Phenytoin usually causes only mild side-effects, which should get better as your child’s body gets used to the medicine.

  • Your child may have difficulty with coordination or balance. They may feel sick (nausea) and their vision may be blurred or double. They may also be drowsy (sleepy). These effects should get better after about a week. If they don’t, contact your doctor.
  • A few children get a mild tremor (shakiness) of their fingers. This may happen after 2–3 weeks and usually goes away. If it doesn’t, contact your doctor.
  • The skin on your child’s face may look and feel coarse and become slightly hairy if they have been taking phenytoin for longer than 3–4 months. The skin will slowly return to normal after phenytoin is stopped.
  • Your child’s gums may start to get thicker if they have been taking phenytoin for longer than 4–6 months. Brushing the teeth for at least 2 minutes twice a day will help to reduce this effect, and the gums will return to normal after phenytoin is stopped. A dentist should check your child’s teeth every 6 months.
  • Your child’s bones may become slightly weaker if they have been taking phenytoin for more than a few years. This effect can be reduced if your child takes additional vitamin D supplements.
  • Your child may also get spots that look like acne. Keeping the face clean will help to reduce this.

There may sometimes be other side effects that are not listed above. If you notice anything unusual and are concerned, contact your doctor. You can report any suspected side effects to a UK safety scheme at

Can other medicines be given at the same time as Phenytoin?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.

Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal and complementary medicines.

Epilepsy and pregnancy

  • Pregnancy presents a risk to both the mother with epilepsy and her unborn baby. If your daughter has sex, it is essential that she uses adequate contraception to prevent an unplanned pregnancy.
  • If your daughter is worried that she may be pregnant, it is important that she sees her doctor as early as possible. Your daughter should keep taking her medication until she sees her doctor.

Phenytoin and pregnancy

  • Phenytoin may harm an unborn baby.
  • The oral contraceptive pill can be used safely in women or girls who are taking phenytoin.

Is there anything else I need to know about this medicine?

It is best that your child always has the same brand, strength and form (for example, tablet or capsule) of Phenytoin, because there are differences between them. Keep a record of which brand, strength and type of Phenytoin your child has. If you have any concerns or questions, speak with your child’s doctor or pharmacist.

  • Some other medicines used to treat epilepsy may affect how well Phenytoin works, or may cause side-effects. If you are worried about side-effects, or if your child seems to be having more fits, contact your doctor or epilepsy nurse.
  • Your doctor may want to measure the amount of Phenytoin in your child’s blood.

General advice about medicines

  • If your child seems to have more seizures than usual, contact your doctor or your epilepsy nurse.
  • If your doctor decides to stop a particular medicine, they will discuss this with you. You will usually reduce the dose bit by bit.
  • Try to give medicines at about the same times every day, to help you remember.
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses as you may do harm.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that you always have enough medicine. Order a new prescription at least 2 weeks before you will run out.
  • Make sure that the medicines you have at home have not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

Do not suddenly stop giving any medicines for seizures to your child. If you are worried, contact your doctor but carry on giving the medicine to your child as usual.

Do not change the dose of any medicine without talking to your doctor first.

If you think someone else may have taken the medicine by accident, contact your doctor straight away.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight.
  • It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information?

Your child’s doctor, pharmacist or nurse will be able to give you more information about Phenytoin and about other medicines used to treat epilepsy.

England: NHS 111

Tel 111

Scotland: NHS 24

Northern Ireland: NI Direct

Wales: NHS 111 Wales

Epilepsy Action

0808 800 5050

Epilepsy Society

Young Epilepsy

Copyright disclaimer

Version [2]. © NPPG, RCPCH and WellChild, all rights reserved. Review by January 2017.

The primary source for the information in this leaflet is the British National Formulary for Children. For details on any other sources used for this leaflet, please contact us through our website,

We take great care to make sure that the information in this leaflet is correct and up-to-date. However, medicines can be used in different ways for different patients. It is important that you ask the advice of your doctor or pharmacist if you are not sure about something. This leaflet is about the use of these medicines in the UK, and may not apply to other countries. The Royal College of Paediatrics and Child Health (RCPCH), the Neonatal and Paediatric Pharmacists Group (NPPG), WellChild and the contributors and editors cannot be held responsible for the accuracy of information, omissions of information, or any actions that may be taken as a consequence of reading this leaflet.