Phenytoin

What is phenytoin?

Phenytoin is used to control and prevent certain types of seizures. It works by calming the brain.

You may hear phenytoin called by its brand name, Dilantin. Phenytoin comes as a chewable tablet, capsule, liquid, or injection form.

Before giving phenytoin to your child?

Tell your child's doctor if your child has:

• allergies to phenytoin, fosphenytoin, or hydantoins
• heart disease

Talk with your child's doctor or pharmacist if your child has any of the following conditions. Precautions may need to be taken with this medicine if your child has:

• diabetes mellitus (high blood sugar)
• kidney disease
• liver disease
• porphyria, a problem with enzymes that make red blood cells

How should you give your child phenytoin?

• Give phenytoin exactly as your child's doctor or pharmacist tells you. Talk to your child's doctor before you stop giving this medication for any reason.
• You may give phenytoin with food or milk, but be consistent. Always give phenytoin with food or milk or always give it on an empty stomach.
• If your child is taking chewable tablets, encourage your child not to swallow them whole. Instead, the chewable tablets may be chewed, crushed, or mixed with food.
• If your child is taking liquid phenytoin, shake the bottle well before using and measure out each dose with the special spoon, dropper, or syringe that the pharmacist gave you.
• If your child has a feeding tube, the liquid or capsule forms of phenytoin may be used. For liquid phenytoin, stop tube feeding 1 to 2 hours before giving phenytoin. Flush the feeding tube with water before and after giving phenytoin. Restart tube feeding 1 to 2 hours after giving phenytoin.

What should you do if your child misses a dose of phenytoin?

• Give the missed dose as soon as you remember.
• If it is almost time for the next dose, skip the missed dose. Give the next dose at the regular time.
• Do not give your child 2 doses to make up for 1 missed dose.

How long does phenytoin take to work?

Your child may start feeling better after several days of taking phenytoin, but it may take several weeks to see the full effect.

What are the possible side effects of phenytoin?

Your child may have some of these side effects while they take phenytoin. Check with your child's doctor if your child continues to have any of these side effects and they do not go away, or if they bother your child:

• dizziness, headache, or inability to think clearly
• feeling tired, weak, or sleepy
• difficulty sleeping
• nausea or vomiting (throwing up)
• difficulty having a bowel movement (constipation)
• change in balance or coordination
• shakiness
• red, swollen, tender, or bleeding gums
• increased growth of facial or body hair

Most of the following side effects are not common, but they may be a sign of a serious problem. Call your child's doctor right away or take your child to Emergency if your child has any of these side effects:

• skin rash or itching
• severe dizziness, drowsiness, nausea, or vomiting
• unsteady walking
• slurred speech
• blurred vision
• unusual eye movements
• unexplained sore throat, fever, joint pain, or bruising
• unusual behaviour
• worsening seizures

What safety measures should you take when your child is using phenytoin?

There are some medicines that should not be taken together with phenytoin, or in some cases the dose of phenytoin or the other medicine may need to be adjusted. It is important that you tell your doctor and pharmacist if your child takes any other medications (prescription, over-the-counter, or herbal), including:

• birth control pills
• carbamazepine (Tegretol)
• cimetidine (Tagamet)
• corticosteroids
• fluoxetine (Prozac)
• lamotrigine (Lamictal)
• phenobarbital
• valproic acid (Depakene, Epival)
• voriconazole (Vfend)
• warfarin (Coumadin)

Blood levels of phenytoin may be checked routinely. On the day that your child is having a level checked, do not give the next dose until the blood has been drawn.

It is important to keep all appointments with the doctor in order that your child's response to the medication be monitored.

Before your child has any medical tests or procedures (including dental treatment), tell the doctor or dentist in charge that your child is taking phenytoin.

To help prevent problems with your child's gums, practice good dental hygiene. Brush and floss your child's teeth regularly and carefully, and massage the gums. Make sure your child sees a dentist regularly, and tell the dentist that they are taking phenytoin.

Phenytoin may make your child dizzy, drowsy, or less alert than normal, especially at the beginning of therapy. Have your child avoid tasks or activities that require alertness until you see how phenytoin affects them. Tell your child's teacher that they are taking this medication.

Phenytoin may cause your child's urine to turn a pinkish-red or brown colour. This is harmless.

Oral contraceptives (birth control pills) may not work properly if they are taken together with phenytoin. This should be discussed with the doctor.

Keeping a record of your child's seizures, behaviour, and school performance can help to identify the best dose of this medication for your child.

What other important information should you know about phenytoin?

• Keep a list of all medications your child is on and show the list to the doctor or pharmacist.
• Do not share your child's medicine with others. Do not give anyone else's medicine to your child.
• Make sure you always have enough phenytoin to last through weekends, holidays, and vacations. Call your pharmacy at least 2 days before your child runs out of medicine to order refills.
• Keep phenytoin at room temperature in a cool, dry place away from sunlight. Do NOT store it in the bathroom or kitchen. Store injectable doses of phenytoin as directed by your child's pharmacist.
• Do not keep any medicines that are out of date. Check with your pharmacist about the best way to throw away outdated or leftover medicines.

Keep phenytoin out of your child’s sight and reach and locked up in a safe place. If your child takes too much phenytoin, call your local Poison Information Centre at one of these numbers. These calls are free. 

• Call 1-844 POISON-X, or 1-844-764-7669, from anywhere in Canada except Quebec.
• Call 1-800-463-5060 if you live in Quebec.