What is the most important information I should know about phenytoin?

• Do not stop taking phenytoin even if you feel better. It is important to continue taking the medication to prevent seizures from recurring.
  
  
• Do not change brands of phenytoin without first talking to your doctor or pharmacist. Some brands of phenytoin are interchangeable while others are not. Your doctor and/or pharmacist know which brand/generic formulations may be substituted for another.
  
  
• Do not crush, chew, or break the capsules. Swallow them whole. They are specially formulated to release the drug slowly into the body.
  
  
• Carry or wear a medical identification tag to let others know that you are taking this medicine in the case of an emergency.

What is phenytoin?

• Phenytoin is an anti-epileptic. It works by slowing down impulses in the brain that cause seizures.
  
  
• Phenytoin is used to control seizures.
  
  
• Phenytoin may also be used for purposes other than those listed in this medication guide.

What should I discuss with my healthcare provider before taking phenytoin?

• Before taking this medication, tell your doctor if you have, or ever have had, liver disease. You may not be able to take phenytoin, or you may require a lower dose or special monitoring during treatment.
  
  
• Phenytoin may increase blood sugar. If you are a diabetic and are taking phenytoin, watch for changes in blood sugar levels that may be caused by this medication.
  
  
• It is not known whether phenytoin will be harmful to an unborn baby. Do not take phenytoin without first talking to your doctor if you are pregnant or could become pregnant during treatment.
  
  
• Phenytoin passes into breast milk and may affect a nursing infant. Do not take phenytoin without first talking to your doctor if you are breast-feeding a baby.

How should I take phenytoin?

• Take phenytoin exactly as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
  
  
• Take each dose of phenytoin with a full glass of water.
  
  
• Take phenytoin with food to lessen stomach upset.
  
  
• Do not crush, chew, or break the capsules. Swallow them whole. They are specially formulated to release the drug slowly into the body.
  
  
• Chew the chewable tablets thoroughly or break them into small pieces before swallowing.
  
  
• Shake the liquid form of phenytoin well before use. To ensure that you measure a correct dose, measure the suspension with a special dose-measuring spoon or a cup, not with a regular tablespoon. If you do not have a dose-measuring device, ask your pharmacist where you can get one.
  
  
• Do not take any capsule, tablet, or suspension that is discolored.
  
  
• Do not change brands of phenytoin without first talking to your doctor or pharmacist. Some brands of phenytoin are interchangeable while others are not. Your doctor and/or pharmacist know which brand/generic formulations may be substituted for another.
  
  
• It is important to take phenytoin regularly to get the most benefit.
  
  
• Do not stop taking phenytoin even if you feel better. It is important to continue taking the medication to prevent seizures from recurring.
  
  
• Your doctor may want you to have blood tests or other medical evaluations during treatment with phenytoin to monitor progress and side effects.
  
  
• Brush and floss your teeth as directed to reduce the risk of gum disease while taking phenytoin.
  
  
• Carry or wear a medical identification tag to let others know that you are taking this medicine in the case of an emergency.
  
  
• Store phenytoin at room temperature away from moisture, light, and heat.

What happens if I miss a dose?

• Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the dose you missed and take only the next regularly scheduled dose. Do not take a double dose of this medication.

What happens if I overdose?

• Seek emergency medical treatment if an overdose is suspected.
  
  
• Symptoms of a phenytoin overdose include back-and-forth eye movements, slurred speech, stumbling or staggering walk, imbalance, drowsiness, unconsciousness, nausea, vomiting, tremor, low blood pressure, and slow breathing.

What should I avoid while taking phenytoin?

• Do not drink alcohol while taking this medication. Alcohol can cause deep sedation or sleepiness. It may also increase the risk of seizures.
  
  
• Use caution when driving, operating machinery, or performing other hazardous activities. Phenytoin may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.
  
  
• Brush and floss your teeth as directed to reduce the risk of gum disease while taking phenytoin.

What are the possible side effects of phenytoin?

• If you experience any of the following serious side effects, stop taking phenytoin and seek emergency medical attention or contact your doctor immediately:
  
  
  
  • an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);
    
    
  • hallucinations;
    
    
  • slurred speech or staggering walk;
    
    
  • a rash;
    
    
  • changes in vision;
    
    
  • agitation;
    
    
  • low blood pressure;
    
    
  • slow or irregular heartbeats;
    
    
  • abdominal pain, dark urine, light colored stools, or jaundice (yellow skin or eyes);
    
    
  • easy bruising or bleeding; or
    
    
  • swollen or tender gums.
  
  
• Other, less serious side effects may be more likely to occur. Continue to take phenytoin and talk to your doctor if you experience
  
  
  • nausea, vomiting, constipation, or diarrhea;
    
    
  • mild dizziness or drowsiness;
    
    
  • tender or swollen glands;
    
    
  • swollen or painful gums;
    
    
  • headache;
    
    
  • muscle twitches;
    
    
  • increased facial hair;
    
    
  • swelling of breasts, or
    
    
  • insomnia.
  
  
• Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect phenytoin?

• The following drugs can increase the level of phenytoin in the blood which may cause dangerous side effects:
  
  
  
  • alcohol (with occasional use);
    
    
  • other seizure medicines such as ethosuximide (Zarontin) or methsuximide (Celontin Kapseals);
    
    
  • the stomach medicines cimetidine (Tagamet, Tagamet HB) or ranitidine (Zantac, Zantac 75);
    
    
  • the anxiety and insomnia medicines chlordiazepoxide (Librium, Librax) and diazepam (Valium);
    
    
  • estrogens such as conjugated estrogens (Premarin, Premphase, Prempro), estradiol (Estrace), esterified estrogens (Estratab, Menest), estropipate (Ogen), and estrogen patches (Estraderm, Vivelle, Climara);
    
    
  • the heart medicine amiodarone (Cordarone);
    
    
  • salicylates such as aspirin, magnesium salicylate (Magan), choline salicylate (Arthropan), and choline and magnesium salicylate (Trilisate);
    
    
  • anti-infective medicines such as isoniazid (Nydrazid) and sulfonamides such as sulfamethoxazole (Septra, Bactrim);
    
    
  • methylphenidate (Ritalin, Concerta, Metadate, Methylin);
    
    
  • tolbutamide;
    
    
  • trazodone (Desyrel); and
    
    
  • disulfiram (Antabuse).
  
  
• Other drugs may decrease the amount of phenytoin in the blood. This can decrease the effects of phenytoin and result in seizures. The following drugs may have this effect:
  
  
  
  • alcohol (when used regularly);
    
    
  • carbamazepine (Tegretol, Epitol, Carbatrol);
    
    
  • reserpine;
    
    
  • sucralfate (Carafate); and
    
    
  • molindone (Moban).
  
  
• Other seizure medicines may interact unpredictably with phenytoin and either increase or decrease its effects. These drugs include
  
  
  
  • valproic acid (Depakene) and divalproex sodium (Depakote); and
    
    
  • phenobarbital (Luminal).
  
  
• It may be necessary for your doctor to adjust your phenytoin dosage if you are taking any of the medicines listed above.
  
  
• Phenytoin may also decrease the activity of other medicines, including
  
  
  
  • steroid medicines such as prednisone (Deltasone), hydrocortisone (Cortef), betamethasone (Celestone), dexamethasone (Decadron), methylprednisolone (Medrol), and others;
    
    
  • warfarin (Coumadin);
    
    
  • quinidine (Quinidex, Quinaglute, others);
    
    
  • birth control pills;
    
    
  • estrogens such as Premarin, Ogen, Menest, Estratest, Estraderm, Vivelle, Climara, and others;
    
    
  • the anti-infective medicines rifampin (Rimactane, Rifadin) and doxycycline (Doryx, Vibramycin, Doxy, Monodox, Adoxa, others);
    
    
  • furosemide (Lasix); and
    
    
  • theophylline (Theo-Dur, Theochron, Theo-Bid, Theolair, Aerolate, others).
  
  
• Drugs other than those listed here may also interact with phenytoin. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including herbal products.

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The materials contained on the Epilepsy Newfoundland and Labrador website are to provide general information about epilepsy to the public. The information presented is not intended as medical or legal advice. Epilepsy Newfoundland and Labrador, its employees, board members, medical advisors, volunteers, agents and sponsors do not assume responsibility for inaccuracies or omissions or for the consequences from the use of the information obtained over this site or any links accessed through this site. Epilepsy Newfoundland and Labrador is not liable for any outcome or damages resulting from information in either a direct or indirect form. We recognize that each individual's experience of epilepsy is different. Consult your physician and/or neurologist with any questions you have.