Phenytoin

Sounds like 'FEN-eh-toe-in'

Key points about phenytoin

Phenytoin is used to control seizures by preventing or decreasing them.
It is an anti-seizure medication used in epilepsy or brain surgery.
Phenytoin is also called Dilantin® or Dilantin Infatabs®.
Find out how to take it safely and possible side effects.

HN 0891 mother and young son receiving counselling from pharmacist

Phenytoin is used to treat epilepsy by preventing or decreasing seizures. It’s also used to help prevent seizures during or after brain surgery. It works by stabilising the electrical activity in your brain and in this way reduces seizures. Read more about epilepsy.

In Aotearoa New Zealand phenytoin is available as:

chewable tablets (50 mg)
capsules (30 mg and 100 mg)
liquid.

The dose of phenytoin will be different for different people.
Your doctor will start you on a low dose, and increase your dose slowly over a few weeks.
Phenytoin is usually taken once or twice times a day.
Always take your phenytoin exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much phenytoin to take, how often to take it, and any special instructions.

Phenytoin is best taken with or after food.
Take your doses at the same times each day, usually 1 or 2 times a day.
For doses that are taken 2 times a day, take it once in the morning and once in the evening. Ideally, these times are 10 to 12 hours apart, for example, some time between 7 and 8 am and between 7 and 8 pm.
Phenytoin is available as chewable tablets, capsules and liquid.

Formulation	How to take it
Tablets	Chew the tablets before swallowing or you can swallow them with a glass of water.
Capsules	Swallow the capsules whole with a glass of water, milk or juice. Don't chew the capsules.
Liquid	Shake the bottle well before you measure out the dose. Measure the right amount using an oral syringe or medicine spoon. You can buy these from your pharmacy. Don't use a kitchen spoon as it won't give you the right amount. Read more tips on how to give medicines to babies and children.

Missed dose: If you forget to take your dose, take it as soon as you remember. But if your next dose is due anytime in the next 4 hours, skip the dose and just take the next dose at the usual time. Don't take double the dose.

Here are some things to know when you're taking phenytoin. Other things may be important as well, so ask your healthcare provider what you should know about.

The effects of phenytoin are not immediate. It may take 2 weeks before seizures are controlled.
Driving: Phenytoin can make you feel sleepy or blur your vision. Be careful when driving or using tools until you know how this medicine affects you.
Children: If phenytoin makes your child sleepy they need to be extra careful when they ride a bike, climb trees or do anything that could be dangerous until they know how this medicine affects them.
Other medicines: Phenytoin interacts with some other medicines (eg, the oral contraceptive pill, antidepressants and some antibiotics), herbal supplements (eg, St John’s Wort) and rongoā Māori. Check with your doctor or pharmacist before starting phenytoin or before starting any new medicines or supplements.
- Indigestion medicines: Don’t take indigestion medication (antacids) within 2 hours of taking phenytoin.
- Oral contraceptive pills: Some contraceptives may not work as well while you’re taking phenytoin, and for 4 weeks after stopping. You may need to change to an IUD device for contraception. Discuss this with your healthcare provider.
Contraception: Once you start taking phenytoin you must use reliable contraception(external link) every time you have sex, even if it's only occasionally. Your healthcare provider can advise you about reliable contraception options. When you stop phenytoin, it's still important to continue using contraception until at least 1 month after stopping.
Alcohol: Limit alcohol while you’re taking phenytoin. It can increase your chance of side effects such as dizziness.
Keep taking phenytoin regularly every day (see tips to help you remember to take your medicines regularly(external link)). Do not stop taking phenytoin suddenly (unless you have a skin rash) as this can cause problems. Talk to your healthcare provider before stopping.
Blood tests: You may need blood tests to make sure you’re taking the right amount of phenytoin.
Taking phenytoin for more than a few years can cause your bones to become slightly weaker so your doctor may prescribe vitamin D for you to take.
Breastfeeding: It's considered safe to breast feed your baby while taking medication for epilepsy. The baby will be exposed to small amounts of the medicine, but has been exposed to higher amounts during the pregnancy. Talk to your healthcare provider about this if you’re wanting to start breastfeeding.

If you are planning a pregnancy

If you or your partner would like to become pregnant, or plan a family, contact your doctor 6 to 12 months ahead of time so you can make a plan and discuss the best options for you.
If you have epilepsy, having seizures while you're pregnant can also harm your unborn child so it's important to keep taking anti-seizure medication.

If you're pregnant or think you might be pregnant

Keep taking your medicine at the right dose, and contact your healthcare provider straight away, tell them you think you're pregnant and make an urgent appointment to see them.

For more detailed information, see:

Like all medicines, phenytoin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects	What should I do?
Feeling sick (nausea) or being sick (vomiting) Stomach upset Constipation	These are common when starting phenytoin and may settle within a week or two. Try taking phenytoin with a full glass of water and at the same time as food. Tell your doctor if these bother you.
Feeling dizzy or light-headed Feeling sleepy, drowsy or tired Problems with your eyesight such as blurred vision or double vision	This is common when starting phenytoin and may settle within a week or two. Be careful when driving or using tools until you know how this medicine affects you. Read more epilepsy/seizures and driving(external link) Limit or avoid alcohol. Tell your doctor if these bother you.
Headache Unsteady on your feet Tremor	Tell your doctor.
Gum problems such as swollen gums or bleeding gums	This is common. Practice good dental hygiene – brush and floss regularly, and visit your dentist regularly. Read more about how to take care of your teeth. Tell your dentist you're taking phenytoin.
More hair growth on face, chest and back	This is common. Tell your doctor if this bothers you.
Changes in mood, such as low mood, feeling down, feeling depressed	Tell your doctor. If you have any thoughts of harming yourself tell your doctor immediately or ring Healthline on 0800 611 116.
Signs of an allergic reaction such as skin rash, mouth ulcers, bruising, fever	Tell your doctor immediately or ring Healthline on 0800 611 116.
Signs of problems with your liver such as severe tummy pain, yellowing of the eyes and skin, dark urine.	This is rare. Tell your doctor immediately or ring Healthline on 0800 611 116.