Phenytoin

Phenytoin is a medication that is used for the treatment of certain kinds of seizures in people with epilepsy. While the drug cannot prevent epileptic seizures from occurring, it can help control seizures. Phenytoin, which is available by prescription, comes in several different forms, including chewable tablets, extended-release capsules, and an oral suspension. Side effects may include confusion, muscle coordination problems, and slurred speech.

 

What Is Phenytoin?

Phenytoin (Dilantin®) is a prescription medication used to treat certain types of seizures in people with epilepsy. There are several different phenytoin products: Dilantin Kapseals® (phenytoin sodium extended-release capsules), Dilantin Infatabs® (phenytoin chewable tablets) and Dilantin-125® (phenytoin oral suspension, or liquid). Specifically, phenytoin is approved to control the following types of seizures:
 
  • Complex partial seizures -- complex partial seizures involve decreased consciousness ("complex") and affect only one part of the brain ("partial")
     
  • Generalized tonic-clonic seizures -- these seizures, which are also known as "grand mal" seizures, affect the whole brain ("generalized"), and involve muscle rigidity and contractions ("tonic-clonic")
     
  • Seizures during brain surgery.
     
(Click What Is Phenytoin Used For? for more information on the uses of this medication, including possible off-label uses.)
 

Who Makes Phenytoin?

It is made by Pfizer.
 

How Does It Work?

Epilepsy is a brain disorder that occurs when there are recurring, brief changes in how the brain's electrical system works. These changes in brain activity can lead to a seizure (see Epilepsy Symptoms).
 
Phenytoin works by affecting sodium channels in the brain. It does not prevent abnormal brain activity from starting; instead, it prevents the abnormal activity from spreading to other parts of the brain. This action helps control seizures.
 

When and How to Take Phenytoin

Some general considerations for when and how to take the medication include:
 
  • Phenytoin comes in extended-release capsules, chewable tablets, and an oral suspension. These products are not interchangeable.

 

  • Phenytoin can be taken with or without food. If it upsets your stomach, try taking it with food. It is important that you take it consistently the same way (either with food or without food).

 

  • For phenytoin suspension, make sure to shake the medication thoroughly before each dose.

 

  • Chewable Dilantin Infatabs (tablets) can also be swallowed whole.

 

  • Do not chew, crush, or open Dilantin Kapseals (capsules), as they are extended-release products.

 

  • Phenytoin should be taken at the same times each day to maintain even levels of the drug in your blood.

 

  • For the medication to work properly, it must be taken as prescribed. It will not work if you stop taking it.

 

  • Do not stop taking phenytoin without first discussing it with your healthcare provider (see Dilantin Withdrawal).
     

Dosing Information

The dosage that your healthcare provider recommends will vary depending on a number of factors, including:
 
  • The particular phenytoin product
  • Your age and weight
  • The amount of phenytoin in your blood (measured using a blood test)
  • Other medications you may be taking
  • Other medical conditions you may have.
     
As with any medication, do not adjust your dose unless your healthcare provider specifically instructs you to do so.
 
(Click Phenytoin Dosing for more information.)
 

Side Effects

As with any medicine, side effects are possible with phenytoin. However, not everyone who takes the drug will experience side effects. In fact, most people tolerate it quite well. If side effects do occur, in most cases they are minor and either require no treatment or can easily be treated by you or your healthcare provider. Serious side effects are less common.
 
Common side effects of phenytoin include, but are not limited to:
 
  • Unusual eye movements
  • Muscle coordination problems
  • Slurred speech
  • Confusion.
     
(Click Side Effects of Phenytoin to learn more, including potentially serious side effects that you should report immediately to your healthcare provider.)
 

Drug Interactions

Phenytoin can potentially interact with many other medicines (see Drug Interactions With Phenytoin).
 

What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking this medication if you have:
 
  • Porphyria
  • Swollen lymph nodes
  • Diabetes
  • Liver disease, such as liver failure or cirrhosis
  • Any allergies, including allergies to food, dyes, or preservatives.
     
Also let your healthcare provider know if you:
 
You should also make sure to tell your healthcare provider about all other medicines you are currently taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.
 
(Click Precautions and Warnings With Phenytoin to learn more, including information on who should not take the drug.)
 

What If I Overdose on Phenytoin?

People who take too much phenytoin may have overdose symptoms that could include:
 
  • Unusual eye movements
  • Coordination problems
  • Joint pain
  • Shakiness (tremors)
  • Overactive reflexes
  • Lethargy
  • Slurred speech
  • Nausea and vomiting
  • Coma
  • Low blood pressure
  • Loss of life.
     
If you happen to overdose, seek medical attention immediately.
 
(Click Dilantin Overdose for more information.)
 

How Should It Be Stored?

The medication should be stored at room temperature, away from moisture and heat. It should be stored in an airtight container.
 
Keep phenytoin and all other medications out of the reach of children.
 

What Should I Do If I Miss a Dose?

If you do not take your phenytoin as scheduled, take your missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose. Be sure to tell your healthcare provider if you miss any of your phenytoin doses, as this information may be helpful for adjusting your dosage.
 

Alternatives to Phenytoin

There are several alternatives to phenytoin for controlling seizures. These alternatives can include other seizure medications (see Epilepsy Medication), surgery (see Epilepsy Surgery), or even -- in some cases -- a special diet (see Epilepsy Diet).
 
While phenytoin is often effective and many people tolerate it well, it does not work for everyone. It may also cause side effects. With so many different treatment options for epilepsy, people should not settle for treatment that is not effective enough for them or that causes bothersome side effects.
 
(Click Dilantin Alternatives for more information.)
 

Strengths 

Extended-release phenytoin capsules (Dilantin Kapseals) are available in two strengths:
 
  • Phenytoin 30 mg capsules
  • Phenytoin 100 mg capsules.
     
Additional strengths of extended-release phenytoin sodium capsules are available under a different name (made by a different company):
 
  • Phenytek® 100 mg capsules
  • Phenytek 200 mg capsules
  • Phenytek 300 mg capsules.
     
Chewable phenytoin tablets come in one strength -- Dilantin 50 mg Infatabs. Liquid phenytoin also comes in one strength – Dilantin-125 suspension, containing 125 mg per 5 mL (125 mg per teaspoonful).
 
Phenytoin injection is also available, although it is rarely used. In fact, it is used so rarely that the brand-name version of phenytoin injection is no longer being made (although generic versions are still available).
 

Is There a Generic Version of Phenytoin?

Currently, some phenytoin products are available in generic versions, while others are not (see Generic Dilantin).
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Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD;