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Phenytoin for epilepsy


Try to keep your regular doctor's appointments. Your doctor may need to test your blood to decide the correct dose for you.

You need to take phenytoin regularly. Do not stop taking it unless your doctor tells you to.

Different formulations and brands of phenytoin can act in a slightly different way in your body. Each time you collect a prescription, check to make sure your supply looks the same as you have had before. If not, please ask your pharmacist to check your prescription for you.

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About phenytoin

Type of medicine

An antiepileptic medicine

Used for

Epilepsy in children and adults; trigeminal neuralgia

Also called

Phenytoin sodium, Epanutin®

Available as

Tablets, capsules, chewable tablets and oral liquid medicine

If you have epilepsy, it means that you have had more than one unexplained fit, or seizure. A seizure is a short episode of symptoms caused by a burst of abnormal electrical activity in your brain. Different parts of the brain control different functions of your body, so the symptoms that occur during a seizure will depend on where the abnormal burst of electrical activity occurs. Symptoms that may occur during a seizure can affect your muscles, sensations, behaviour, emotions, consciousness, or a combination of these. The seizures can be prevented in most people by suitable antiepileptic medication. Phenytoin is a commonly used medicine. It works by stabilising the electrical activity of your brain, which prevents the seizures from occurring.

Phenytoin is also prescribed as a treatment for severe burning or stabbing pains in the face, a nerve pain called trigeminal neuralgia. This is because it can modify some types of pain. If you have been given phenytoin for this reason, ask your doctor if you have questions about your treatment.

Before taking phenytoin

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you (or your child if you are their carer) start taking phenytoin it is important that your doctor knows:

  • If you are pregnant, trying for a baby or breastfeeding.

  • If you have any problems with the way your liver works.

  • If you have a rare inherited blood disorder called porphyria.

  • If you have ever had an allergic reaction to a medicine.

  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

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How to take phenytoin

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about phenytoin and will provide you with a full list of the side-effects which you may experience from taking it.

  • Take phenytoin exactly as your doctor tells you to. Your dose will be printed on the label of the pack to remind you about what the doctor said. It is usual to start treatment on a low dose, and then for the dose to be increased gradually to a regular maintenance dose.

  • It is important you try to take your doses at the same times each day. Having a routine will help you to remember to take your doses regularly. Although phenytoin can be taken before a meal, it is better taken during or straight after a meal.

  • If you are taking phenytoin chewable tablets (Epanutin® Infatabs), you can chew the tablet to help you swallow or you can swallow the tablet in the usual way with a drink of water.

  • If you are taking phenytoin oral liquid medicine (Epanutin® suspension), make sure that you shake the bottle well before you measure out your dose.

  • If you forget to take a dose, take it as soon as you remember. If when you remember, it is nearly time for your next dose, take your next dose when it is due but leave out the missed dose. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • When you first start a new treatment for epilepsy there may be a change in the number or type of seizures you experience. Your doctor will advise you about this.

  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. You will need to have blood tests from time to time.

  • While you are being treated for epilepsy there is a small risk that you may develop mood changes, distressing thoughts and feelings about suicide. If this happens, you must tell your doctor about it straightaway.

  • People with epilepsy must stop driving at first. Your doctor will advise you about when it may be possible for you to start driving again. This will usually be after a year free of seizures.

  • Different formulations and brands of phenytoin can act in a slightly different way in your body. Because of this, it is important that you continue to take phenytoin from the same manufacturer as you have had before. So, each time you collect a prescription, check to make sure your supply looks the same and that the brand name is the same. If you are unsure, or if you have any questions about your prescription, please ask your pharmacist to check it for you.

  • If you drink alcohol, ask your doctor for advice. Your doctor may advise you not to drink alcohol while you are on this medicine because it can alter the amount of phenytoin in your body.

  • If you buy any medicines, check with a pharmacist that they are suitable for you to take with your antiepileptic medication. Some indigestion remedies can interfere with the amount of phenytoin in your body.

  • Many antiepileptic medicines can harm an unborn child. If you are a woman, make sure you have discussed with your doctor which types of contraception are suitable for you and your partner. Phenytoin can make oral contraceptives less effective. Your doctor will advise you on other types of contraception such as an intra-uterine device (IUD) and barrier methods. You should use effective contraception throughout treatment with phenytoin and for one month after stopping. If you want to have a family, discuss this with your doctor so that you can be given advice from a specialist before you become pregnant.

  • You need to take phenytoin regularly every day. Do not stop taking it unless your doctor tells you to stop. Stopping treatment suddenly can cause problems and your doctor will want you to reduce your dose gradually if this becomes necessary.

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Can phenytoin cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with phenytoin. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common phenytoin side-effects

What can I do if I experience this?

Feeling sick (nausea) or being sick (vomiting)

Stick to simple meals - avoid rich or spicy food


Eat a well-balanced diet and drink plenty of water each day

Feeling dizzy or sleepy; eyesight problems such as double vision

Do not drive and do not use tools or machines while affected


Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the headaches continue, let your doctor know


Let your doctor know about this as soon as possible, even if it is mild

Difficulty sleeping, numb or tingling feelings, lack of appetite, sore or swollen gums, facial changes, acne, increased hair growth, slurred speech, lack of concentration, and feeling confused, nervous, unsteady or shaky

If any of these become troublesome, let your doctor know

Important: your doctor will discuss with you the possibility that phenytoin can cause blood and skin disorders. Although these occur less commonly than the side-effects listed above, it is important that you contact your doctor straightaway if you experience any of the following symptoms:

  • A high temperature (fever), sore throat or swollen glands.

  • A severe skin rash.

  • Mouth ulcers.

  • Unexplained bruising or bleeding.

If you experience any other symptoms which you think may be due to phenytoin, speak with your doctor or pharmacist for further advice.

How to store phenytoin

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

MHRA - Reporting adverse reactions

Report suspected side effects to medicines, vaccines, e-cigarettes, medical device incidents, defective or falsified (fake) products to the Medicines and Healthcare products Regulatory Agency to ensure safe and effective use.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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