Phenobarbital for preventing seizures

This leaflet is about the use of phenobarbital to prevent epileptic seizures. (Seizures may also be called convulsions or fits.)

This leaflet has been written specifically about the use of this medicine in children. The information may differ from that provided by the manufacturer. Please read this leaflet carefully. Keep it somewhere safe so that you can read it again.

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

Name of drug

Phenobarbital
(This drug used to be known as phenobarbitone.)

Why is it important for my child to take this medicine?

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

What is phenobarbital available as?

  • Tablets: 15 mg, 30 mg, 60 mg; these tablets contain lactose
  • Liquid medicine (orange): 15 mg in 5 mL; this contains a high concentration of alcohol and is not suitable for children with epilepsy
  • Other liquid medicines that do not contain alcohol can be prepared specially by your pharmacist.

When should I give phenobarbital?

Phenobarbital is usually given twice a day: once in the morning and once in the evening. Ideally, these times are 10–12 hours apart, for example sometime between 7 and 8 am and between 7 and 8 pm. Your doctor may tell you to start by giving phenobarbital once a day until your child gets used to it. This is usually in the evening.

How much should I give?

Your doctor will work out the amount of phenobarbital (the dose) that is right for your child. The dose will be shown on the medicine label. When you first start giving phenobarbital to your child, you will give them a small amount and then increase the dose 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 it?

Phenobarbital for preventing seizuresTablets should be swallowed whole with a glass of water, milk or juice. Your child should not chew the tablet. You can crush the tablets and mix them with about 2 tablespoons of fruit juice or soft food (e.g. yogurt, honey or jam). Make sure your child swallows it all straight away, without chewing.

Phenobarbital for preventing seizuresLiquid medicine: Measure out the right amount using an oral syringe or 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 phenobarbital to work properly, so your child may still have seizures for a while. This is because the amount of medicine has to be increased slowly. Continue to give the medicine in the way that you have been told to.

What if my child is sick (vomits)?

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

What if I forget to give it?

  • If you remember within 4 hours, give your child the missed dose. For example, if you usually give a dose at 7 am, you can give the missed dose at any time up to 11 am.
  • If you remember after this time, do not give the missed dose. Wait until it is time to give the next normal dose.

Never give a double dose of phenobarbital.

What if I give too much?

If you think you may have given your child too much phenobarbital, contact your doctor or NHS Direct (0845 4647 in England and Wales; 08454 24 24 24 in Scotland) or take your child to hospital. Take the medicine packaging with you, even if it is empty. This will be useful to the doctor. Have the packaging with you if you telephone for advice.

Are there any possible side-effects?

We use medicines to make our children better, but sometimes they cause effects that we don’t want (side-effects).
Side-effects that you must do something about

If your child develops a red blistering skin rash, this is a serious reaction. Contact your doctor or epilepsy nurse straight away, or take your child to hospital. Your child may also have a fever (high temperature), be irritableand may be sick (vomit). Tell the doctor that your child is taking phenobarbital.

Other side-effects you need to know about

  • In the first 1–2 weeks of taking phenobarbital your child may be drowsy (sleepy), lethargic (tired and with little energy), clumsy or unsteady, and they may not be able to concentrate. These effects should get better as your child’s body gets used to the medicine.
  • Your child’s behaviour may change and they may become moody. They may be irritable, hyperactive (more active than normal, finding it hard to relax) or aggressive. Their sleep may be disturbed. If any of these things happens, talk to your doctor or epilepsy nurse, as the dose of phenobarbital may need to be changed. Do not change the dose yourself without talking to your doctor first.

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

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.
  • Some cough medicines and medicines for hay fever could make children drowsy (sleepy) if they are also taking phenobarbital. Check with a doctor or pharmacist before giving any of these medicines to your child.
  • It is important to check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal or 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 thinks that she may be pregnant, it is important that she sees your family doctor as early as possible. Your daughter should keep taking her medication until she sees her doctor.

Phenobarbital and pregnancy

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

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

  • Some other medicines used to treat epilepsy may affect how well phenobarbital 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 level of phenobarbital in your child’s blood if is doesn’t seem to be working properly, or if they are worried about side-effects.

General advice about medicines for seizures

Do not suddenly stop giving any of these medicines to your child, as they may have a seizure. If you are worried, talk to your doctor but carry on giving the medicine to your child as usual.

If your child seems to have more seizures than usual, contact your doctor or 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.

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

  • It is best that your child always has the same brand of each medicine, as there may be differences between brands. Keep a record of which medicines your child has.
  • Try to give medicines at about the same times every day, to help you remember.
  • Only give the medicine(s) to your child. Never give them to anyone else, even if their condition appears to be the same, as this could do harm.

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

  • 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.

Where I should 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 hospital doctor, epilepsy nurse or pharmacist will be able to give you more information about phenobarbital and other medicines used to treat epilepsy.


You can also get useful information from:


Publication Date

9/12/2011

Copyright Disclaimer

Version 1.3, February 2008 (January 2012). © NPPG, RCPCH and WellChild 2011, all rights reserved.
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, www.medicinesforchildren.org.uk
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.