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What does it do?

Phenytoin is used to treat and prevent seizures.

How should you take it?

Take phenytoin regularly as directed with a glass of water.
Phenytoin Infatabs® may be chewed.
Measure phenytoin liquid carefully with an oral syringe or measuring spoon. Shake the bottle well before measuring each dose.

What if you forget a dose?

Take the missed dose as soon as possible and continue as directed.

Can you take other medicines?

Phenytoin can react with many medicines, sometimes with severe results.

Tell your pharmacist or doctor about all medicines or treatments that you may be taking including vitamins, herbal products or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Skin rash, skin peeling or blisters

Stop taking and see your doctor immediately

Suicidal thoughts

Reduced number of blood cells that fight infections or help your blood to clot - symptoms include: fever, chills, sore throat or generally feeling unwell, or easy or unusual bruising or bleeding

Symptoms of liver problems including: yellow skin or eyes, itching, dark urine, pale bowel motions, abdominal pain

Tell your doctor immediately

Agitation, confusion, loss of co-ordination/walking or handwriting problems, mood changes, slurred speech, trouble concentrating, unusual behaviour or thinking

Changes in vision

Enlarged, tender or bleeding gums

Tingling or numbness, tremor

Tell your doctor

Dizziness, drowsiness, headache

Body hair changes

Tell your doctor if troublesome

Stomach upset

Take with food

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • Tell your doctor if you have liver or blood problems, or diabetes.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • Some contraceptives may not work as well while you are taking phenytoin, and for 4 weeks after stopping. Discuss with your doctor or pharmacist.
  • Do not take calcium or antacids containing aluminium or magnesium within 2 hours of taking phenytoin.
  • Phenytoin can impair your ability to do tasks such as driving or using machines. Alcohol makes this worse. Discuss your risk with your health professional. (search NZTA - Are you safe to drive?)
  • You may need blood tests from time to time to make sure you are taking the right dose of phenytoin.
  • Long-term use of phenytoin may weaken your bones.
  • Do not stop taking phenytoin without talking to your doctor first, unless you have a skin rash (see Side Effects).

This leaflet contains important, but not all, information about this medicine.

Prepared by the PILs Committee at Christchurch Hospital, Canterbury District Health Board, New Zealand. October 2020

For more general information about this sheet annd its contents, see: What does a My Medicines sheet cover?

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About My Medicines

My Medicines Patient Information Leaflets (PILs) contain important, but not all, information about the medicines they describe.

For more information about the sheets, see: What does a My Medicines sheet cover?

My Medicines is developed by a team at the Canterbury District Health Board. Our team is made up of doctors, pharmacists, and a non-medical person to help us keep to plain language. We also discuss our information with specialist health professionals or groups when needed