Phenytoin for epilepsy

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  • Keep your regular doctor's appointments. Your doctor may need to test your blood to decide the correct dose for you.
  • Do not stop taking phenytoin without speaking to your doctor first. Stopping taking it suddenly can cause problems.
  • If you develop a skin rash, fever, mouth ulcers, or unexplained bruising or bleeding, tell your doctor straightaway.
Type of medicine Anti-epileptic
Used for Epilepsy in children and adults
Trigeminal neuralgia
Also called Phenytoin sodium
Available as Tablets, capsules, chewable tablets, and oral liquid

If you have epilepsy, it means that you have had repeated seizures. 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 parts and functions of your body. Therefore, the symptoms that occur during a seizure 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. These seizures can be prevented by suitable anti-epileptic medication. Phenytoin works by stabilising the electrical activity of your brain, which prevents the seizures from occurring.

Phenytoin is also used in trigeminal neuralgia (severe burning or stabbing pains in your face), where other available treatments are unsuitable. 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.

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 the carer) start taking phenytoin it is important that your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you have liver problems.
  • If you have porphyria (a rare inherited blood disorder).
  • If you have ever had an allergic reaction to this or to any other medicine.
  • If you are taking any other medicines, including those available to buy without a prescription, herbal and complementary medicines.
  • Before you start this treatment, read the manufacturer's printed information leaflet from inside the pack. The leaflet will give you more information about the brand and form of phenytoin you have been given, and a full list of possible side-effects from taking it.
  • Take phenytoin exactly as your doctor has told you. Your doctor or pharmacist will tell you how much to take and when to take it. Your dose will also be on the label of your pack. You need to take phenytoin regularly every day to prevent the seizures from occurring.
  • When first starting this treatment, your doctor will give you a small dose and then gradually increase the dose. This allows your doctor to make sure that you have the dose that helps your condition and avoids any unwanted symptoms.
  • You may take phenytoin before, during or after a meal.
  • Phenytoin chewable tablets can be chewed before being swallowed or you can swallow them whole with a little water if you prefer.
  • If you are taking phenytoin oral liquid, make sure you shake the bottle well before you measure out your dose.
  • Try to take your doses of phenytoin at the same times each day. This will help you to avoid missing any doses.
  • If you do forget to take a dose, take it as soon as you remember unless it is nearly time for your next dose, in which case leave out the missed dose. Do not take two doses together to make up for a forgotten dose.
  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. You also will need to have blood tests from time to time.
  • 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.
  • People with epilepsy must stop driving at first. Your doctor will advise you about when it may be possible for you to resume driving again. This will usually be after a year free of seizures.
  • If you drink alcohol, ask your doctor for advice about taking phenytoin and alcohol. This is because alcohol can alter the amount of phenytoin in your body and may not be recommended for you.
  • 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 tablets/capsules 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 have any questions about your prescription, please ask your pharmacist to check it for you.
  • If you buy any medicines or herbal remedies, check with a pharmacist that they are suitable for you to take. This is because some medicines (such as indigestion remedies) and some herbal remedies (such as St John's wort) reduce the amount of phenytoin in your body and should be avoided.
  • If you are a woman using hormonal contraception ('the pill'), discuss this with your doctor. This is because phenytoin makes 'the pill' less effective and other methods of contraception will be more suitable for you. If you want to have a family, make sure you discuss this with your doctor well in advance of becoming pregnant. This is so that you can be given advice from a specialist before you become pregnant. If you become pregnant while you are taking phenytoin, you must tell your doctor straightaway.
  • While you are taking phenytoin, there is a small risk that you may develop mood changes or distressing feelings, and thoughts about suicide. If this happens, you must tell your doctor straightaway.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking phenytoin.
  • Do not stop taking this medicine unless your doctor tells you to do so. Stopping phenytoin suddenly can cause problems and your doctor will probably want you to reduce your dose gradually if this is necessary.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Common phenytoin side-effects What can I do if I experience this?
Feeling or being sick Stick to simple meals - avoid rich and spicy food
Constipation Eat a well-balanced diet and drink plenty of water each day
Feeling dizzy or sleepy If this happens, do not drive or use tools or machines
Headache Ask your pharmacist to recommend a suitable painkiller
Rash Let your doctor know about this as soon as possible, even if it is mild
Difficulty sleeping, numb or tingling sensations, loss of weight, sore or swollen gums, acne, increased hair growth, slurred speech, and feeling confused, nervous, unsteady, or shaky If any of these become troublesome, let your doctor know

Important: your doctor will have discussed with you the possibility of side-effects of this treatment that you must let your doctor know about. Contact your doctor straightaway if you experience any of the following:

  • A high temperature and a sore throat.
  • A severe skin rash.
  • Mouth ulcers.
  • You start bruising or bleeding easily.

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.
  • Never take more than the prescribed dose. If you suspect that someone has taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. 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.
  • Never 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.

Further reading & references

  • British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
1460 (v23)
Last Checked:
Next Review:
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