Phenytoin and epilepsy - your simple overview

  • January 16, 2024
  • 4
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Phenytoin is one of the oldest and most widely-used anti-seizure medications - well over 1 million people take it in the United States. If you’ve recently started taking phenytoin, you’ll likely have lots of questions about this medication, how it works, and if there are any phenytoin side effects that you need to know about. 

If you’re unsure about taking phenytoin, speak with your doctor or pharmacist. There should also be a leaflet that comes in the package that will give you additional information too. 

But here are the essential things to know about phenytoin. 

What is phenytoin?

Phenytoin is an anticonvulsant medication. This means that it’s mainly used to treat epileptic seizures. It was first approved by the FDA in 1939, and has been used by millions of people around the world since then. Due to certain phenytoin side effects (more below) it’s rarely prescribed as a first-line epilepsy treatment - you’ll usually only be given phenytoin after trying another seizure medicine first. 

Phenytoin is usually taken by mouth, and can come as a pill you swallow, a chewable tablet, capsules or as a liquid. The main phenytoin brand names in the US are Dilantin and Phenytek. 

Phenytoin is used to help people with certain kinds of seizures:

Phenytoin is also used to treat trigeminal neuralgia, which is when people feel sharp pain in their faces. 

Fosphenytoin vs phenytoin

You might have heard of fosphenytoin. It is a similar  medicine to phenytoin, but it is designed for intravenous usage (injecting into your bloodstream), rather than being swallowed. Fosphenytoin is used for treating status epilepticus, while phenytoin is used as an everyday medicine to prevent seizures from starting in the first place. 

How does phenytoin help prevent seizures?

A seizure is when there is a sudden increase in electrical activity in your brain. Phenytoin works by blocking certain channels in your brain that are involved in rapidly sending electrical signals. That means your seizures are either prevented from starting, or stop faster once they’ve begun. 

Many studies have looked into how effective phenytoin is, and the results indicate that over half of people who take it achieve seizure-freedom after a few months or years. That said, epilepsy medication doesn’t help everyone get in control of their seizures. Fortunately, there are alternative treatment pathways available

Phenytoin side effects

Like all medicines, phenytoin can cause unwanted side effects. Many people don't experience any phenytoin side effects at all. But it’s important to be aware of them so you can recognize them if they do happen to you. 

Mild phenytoin side effects

Some of the milder phenytoin side effects are fairly common. These include:

  • Having headaches
  • Tiredness
  • Feeling dizzy
  • Feeling unsteady, nervous or shaky
  • Having constipation
  • Painful, sore or swollen gums

You may experience these side effects in the first few weeks after you start taking phenytoin as your body gets used to the medication. They often go away by themselves. But talk to your physician or pharmacist if they are bothering you or don’t seem to be ‘shifting’. 

Learn more: Overview of seizure medication side effects

Serious phenytoin side effects

There are some serious side effects of phenytoin which it’s important to watch out for. These include:

  • A very high temperature or skin rash
  • The whites of your eyes going yellow
  • Unexpected bleeding or bruising
  • A severe rash
  • Difficulty swallowing or breathing

If you experience these side effects, seek medical help urgently. 

The leaflet inside your medication will contain more details about severe side effects. If you notice anything unusual, contact your doctor or a healthcare specialist as soon as possible. 

Phenytoin and pregnancy

Phenytoin has been linked to problems in pregnancy and development issues for babies whose mothers took the medicine. If you find out you are pregnant or are planning to get pregnant while taking phenytoin, speak with your doctor as soon as possible for advice. 

Phenytoin toxicity

It is possible to overdose with phenytoin and experience phenytoin toxicity. If you take phenytoin for epilepsy, the most common signs of an overdose are slurred speech, losing your sense of balance, and confusion. It’s important to get medical treatment if you (or someone you know) appears to have overdosed on phenytoin, because it can cause serious illness - and could even be fatal. 

Phenytoin toxicity may happen because of accidentally overdosing. But it can also happen if you take it at the same time as some other medication and drugs - including alcohol. These other drugs may mean the phenytoin stays in your body for longer, so your levels increase each time you take the medication. 

When you begin taking phenytoin, tell your doctor about any other medications you take, so they can check for possible interactions. In the first few weeks of taking this medication, your doctor may ask you to do some blood tests, to check you have a normal phenytoin level. 

Remembering to take your phenytoin

Most people need to take phenytoin once or twice per day - but it’s easy to forget to take your medication. Epsy is a seizure diary that helps to remind you to take your medication and lets you note down any side effects you have to share with your doctor. Try Epsy today.

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