Usage
Phenytoin is an anti-epileptic drug used to control several seizure types and can be prescribed with other anti-epileptics. It is also used to manage long seizures within the emergency setting.
- Phenytoin is best taken at approximately the same time of day, preferably with food or following meals.
- Chewable tablets may be swallowed whole, chewed or crushed before swallowing.
- Suspension needs to be shaken well before use. Measure dose accurately with syringe or measuring spoon.
- If this drug is given through a feeding tube, if possible, stop tube feeding 2 hours before giving this drug and delay feed for 2 hours after giving the drug. Please discuss this with your doctor if continuous feed is necessary.
Side effects
All drugs may cause side effects. However, many people have no side effects or only have minor side effects.
Patients of Han Chinese ancestry may have a genetic marker which can increase the risk of severe skin reactions. Please discuss with your doctor and a blood test can be done to screen for this gene before starting this medication.
Possible side effects include:
- Loss of appetite, nausea or vomiting
- Drowsiness or dizziness, feeling nervous or excitable
- Trouble sleeping
- Change in taste
- Blurred vision or double vision – usually seen if the medication levels are too high
- Slurred speech, confusion or unsteadiness – usually if the medication levels are too high
- Excess hair growth – usually with prolonged use
- Coarsening of facial features – usually with prolonged use
- Swollen, tender gums – usually with prolonged use.
More medically serious side effects include:
- Difficulties with balance and coordination – usually with prolonged use
- Weak bones (osteopenia) – usually with prolonged use
- Suicidal thoughts or actions or other changes in mood or behaviour
- Heart problems, like slow heart beat – usually when medication given through the vein
- Increase in the number of seizures – may occur in some types of epilepsy (Eg: Absence, Myoclonic, Dravet Syndrome)
- An allergic reaction (e.g. Stevens Johnsons Syndrome), like red, swollen, blistered or peeling skin; red or irritated eyes; or sores in your mouth, throat, nose or eyes; with or without fever – seek urgent medical help if this occurs.
These are not all the side effects that may occur. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away.
Interactions
- There are many drugs including other anti-epileptics that interact with phenytoin and can alter its levels in the blood.
- Phenytoin can also change the level of other medications in the blood so always tell your doctor that your child is taking phenytoin. This is also important if you are giving your child herbal or complementary medicines. The doctor can check to make sure they are compatible.
Need-to-know
Monitoring and medication levels
- Levels of phenytoin can be unpredictable and need to be monitored in the blood, especially when the medication is started and with any changes in dose. Phenytoin levels are usually taken before the medication is due (trough level), and as advised by your doctor.
Pregnancy and contraception
- If a pregnancy is planned, a discussion with your neurologist is recommended. For further information, refer to the Contraception and Pregnancy section of the PENNSW website.
Disclaimer
The information provided in this handout is limited and does not replace the need for a medical consultation. It is very important you speak to your doctor about all aspects of your medication including side effects when medication is first prescribed. Report any concerns to your doctor promptly.
Information last reviewed: 09/06/2023.