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Phenytoin

Canadian Brand Names

Side Effects

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

More common

  • Decreased coordination
  • Mental confusion
  • Nervousness
  • Slurred speech
  • Trouble with breathing, speaking, or swallowing
  • Unsteadiness, trembling, or other problems with muscle control or coordination

Rare

  • Inability to move the eyes
  • Increased blinking or spasms of the eyelid
  • Shakiness and unsteady walk shakiness in the legs, arms, hands, or feet
  • Sticking out of the tongue
  • Trembling or shaking of the hands or feet
  • Twitching, twisting, or uncontrolled repetitive movements of the tongue, lips, face, arms, or legs
  • Uncontrolled twisting movements of the neck, trunk, arms, or legs
  • Unusual facial expressions

Incidence not known

  • Abdominal or stomach pain
  • Bleeding gums
  • Blistering, peeling, or loosening of the skin
  • Blisters, hives, or itching
  • Bloating of the abdomen or stomach
  • Blood in the urine or stools
  • Bloody, black, or tarry stools
  • Chest pain
  • Chills
  • Cough or hoarseness
  • Dark urine
  • Diarrhea
  • Difficulty with moving
  • Fainting spells
  • Fever with or without chills
  • General feeling of discomfort or illness
  • General feeling of tiredness or weakness
  • Hair loss
  • Headache
  • High fever
  • Irregular heartbeat
  • Irritation in the mouth
  • Joint or muscle pain
  • Light-colored stools
  • Lower back or side pain
  • Muscle stiffness
  • Nausea or vomiting
  • Numbness, tingling, or pain in the hands or feet
  • Painful or difficult urination
  • Pale skin
  • Pinpoint red spots on the skin
  • Red skin lesions, often with a purple center
  • Red, irritated eyes
  • Redness and swelling of the gums
  • Shortness of breath or troubled breathing
  • Skin blisters
  • Skin rash
  • Sore throat
  • Sores, ulcers, or white spots on the lips or in the mouth
  • Swollen glands
  • Swollen, painful, or tender lymph glands in the neck, armpit, or groin
  • Unexplained bleeding or bruising
  • Unusual bleeding or bruising
  • Unusual tiredness
  • Upper right abdominal pain
  • Weakness
  • Weight loss
  • Yellow eyes or skin

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Sleeplessness
  • Trouble with sleeping
  • Unable to sleep
  • Uncontrolled eye movements

Incidence not known

  • Difficulty having a bowel movement (stool)
  • Enlarged lips
  • Increased hair growth on the forehead, back, arms, or legs
  • Pain of penis on erection

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Precautions

It is very important that your doctor check your progress at regular visits while you are using this medicine to see if it is working properly and to allow for a change in the dose. Blood tests may be needed to check for any unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away. Your doctor may want you to join a pregnancy registry for patients taking a seizure medicine.

Lymph node problems may occur while using this medicine. Check with your doctor right away if you have swollen, painful, or tender lymph glands in your neck, armpit, or groin.

Do not stop taking this medicine without first checking with your doctor. Your doctor may want you to gradually reduce the amount you are using before stopping completely.

If you develop a skin rash, hives, or any allergic reaction to this medicine, stop taking the medicine and check with your doctor as soon as possible.

This medicine may affect blood sugar levels. If you notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.

This medicine may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you, your child, or your caregiver notice any of these side effects, tell your doctor or your child’s doctor right away.

In some patients (usually younger patients), tenderness, swelling, or bleeding of the gums (gingival hyperplasia) may appear soon after phenytoin treatment is started. To help prevent this, brush and floss your teeth carefully and regularly and massage your gums. Also, see your dentist every 6 months to have your teeth cleaned. If you have any questions about how to take care of your teeth and gums, or if you notice any tenderness, swelling, or bleeding of your gums, check with your doctor or dentist.

Before you have any medical tests, tell the medical doctor in charge that you are taking this medicine. The results of some tests may be affected by this medicine.

Avoid drinking alcohol while you are receiving this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Proper Use

Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.

This medicine may be used with other seizure medicines. Keep using all of your seizure medicines unless your doctor tells you to stop.

Do not change brands or dosage forms of phenytoin without first checking with your doctor. Different products may not work the same way. If you refill your medicine and it looks different, check with your pharmacist.

Swallow the tablet whole or chew it thoroughly before being swallowed together with a glass of water.

Measure the oral suspension with a marked measuring spoon, oral syringe, or medicine cup. Rinse the dosing spoon or cup with water after each use.

If you are receiving tube feeding preparations, it is best to take this medicine before or after a feeding.

Dosing

The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For seizures:
    • For oral dosage form (extended-release capsules):
      • Adults—At first, 100 milligrams (mg) three times a day or 300 mg once a day. Your doctor may increase your dose as needed. For patients in the clinic or hospital (except with a history of liver or kidney disease), a loading dose of 1000 mg is divided into three doses (400 mg, 300 mg, 300 mg) and given every two hours. Then, normal maintenance dose may be started 24 hours after the loading dose.
      • Teenagers and children above 6 years of age—300 mg per day. Your doctor may increase your dose as needed.
      • Children 6 years of age and below—Dose is based on body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in two or three divided doses per day. The doctor may adjust the dose as needed.
    • For oral dosage form (suspension):
      • Adults—At first, 5 milliliters (mL) or 125 milligrams (mg) three times a day. Your doctor may increase your dose as needed.
      • Teenagers and children above 6 years of age—300 milligrams (mg) per day. Your doctor may increase your dose as needed.
      • Children 6 years of age and below—Dose is based on age and body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in two or three divided doses per day. Your doctor may adjust your dose as needed.
    • For oral dosage form (tablets):
      • Adults—At first, 100 milligrams (mg) three times a day. Your doctor may increase your dose as needed.
      • Teenagers and children above 6 years of age—300 milligrams (mg) per day, given in two or three divided doses per day. Your doctor may increase your dose as needed.
      • Children 6 years of age and below—Dose is based on age and body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in two or three divided doses per day. The doctor may adjust the dose as needed.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Before Using

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of phenytoin in children.

Geriatric

No information is available on the relationship of age to the effects of phenytoin in geriatric patients. However, elderly patients are more likely to have age-related liver, kidney, or heart problems, which may require an adjustment in the dose for patients receiving phenytoin.

Pregnancy

Pregnancy Category Explanation
All Trimesters D Studies in pregnant women have demonstrated a risk to the fetus. However, the benefits of therapy in a life threatening situation or a serious disease, may outweigh the potential risk.

Breastfeeding

Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Drug Interactions

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

  • Boceprevir
  • Nifedipine
  • Praziquantel
  • Ranolazine
  • Rilpivirine

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Abiraterone
  • Apazone
  • Beclamide
  • Cabazitaxel
  • Crizotinib
  • Dasatinib
  • Delavirdine
  • Dronedarone
  • Erlotinib
  • Etravirine
  • Everolimus
  • Ezogabine
  • Imatinib
  • Infliximab
  • Irinotecan
  • Ixabepilone
  • Ketorolac
  • Lapatinib
  • Lidocaine
  • Linagliptin
  • Lopinavir
  • Maraviroc
  • Methotrexate
  • Naproxen
  • Nilotinib
  • Posaconazole
  • Rivaroxaban
  • Roflumilast
  • Romidepsin
  • St John’s Wort
  • Sunitinib
  • Tacrolimus
  • Temsirolimus
  • Ticagrelor
  • Tolvaptan
  • Vandetanib
  • Vemurafenib
  • Voriconazole

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Acetaminophen
  • Acetazolamide
  • Acyclovir
  • Amiodarone
  • Amitriptyline
  • Amprenavir
  • Aprepitant
  • Atorvastatin
  • Betamethasone
  • Bexarotene
  • Bleomycin
  • Busulfan
  • Capecitabine
  • Carbamazepine
  • Carboplatin
  • Caspofungin
  • Chloramphenicol
  • Cimetidine
  • Ciprofloxacin
  • Cisplatin
  • Clarithromycin
  • Clobazam
  • Clofazimine
  • Clopidogrel
  • Clozapine
  • Colesevelam
  • Cortisone
  • Cyclosporine
  • Desogestrel
  • Dexamethasone
  • Diazepam
  • Dicumarol
  • Dienogest
  • Digitoxin
  • Diltiazem
  • Disopyramide
  • Disulfiram
  • Doxepin
  • Doxorubicin Hydrochloride
  • Drospirenone
  • Estradiol Cypionate
  • Estradiol Valerate
  • Ethinyl Estradiol
  • Ethosuximide
  • Ethynodiol Diacetate
  • Etonogestrel
  • Felbamate
  • Fentanyl
  • Fluconazole
  • Fludrocortisone
  • Fluorouracil
  • Fluoxetine
  • Fluvoxamine
  • Folic Acid
  • Fosamprenavir
  • Gefitinib
  • Ginkgo
  • Ibuprofen
  • Imipramine
  • Isoniazid
  • Itraconazole
  • Levodopa
  • Levomethadyl
  • Levonorgestrel
  • Levothyroxine
  • Medroxyprogesterone Acetate
  • Mestranol
  • Methoxsalen
  • Methsuximide
  • Miconazole
  • Midazolam
  • Nafimidone
  • Nelfinavir
  • Nilutamide
  • Nisoldipine
  • Norelgestromin
  • Norethindrone
  • Norgestimate
  • Norgestrel
  • Oxcarbazepine
  • Paclitaxel
  • Pancuronium
  • Paroxetine
  • Phenprocoumon
  • Piperine
  • Prednisolone
  • Prednisone
  • Progabide
  • Quetiapine
  • Quinidine
  • Quinine
  • Remacemide
  • Rifampin
  • Rifapentine
  • Risperidone
  • Ritonavir
  • Rufinamide
  • Sabeluzole
  • Sertraline
  • Shankhapulshpi
  • Simvastatin
  • Sirolimus
  • Sulfamethizole
  • Sulfaphenazole
  • Sulthiame
  • Telithromycin
  • Tenidap
  • Theophylline
  • Tiagabine
  • Ticlopidine
  • Ticrynafen
  • Tirilazad
  • Tizanidine
  • Tolbutamide
  • Topiramate
  • Trazodone
  • Triamcinolone
  • Trimethoprim
  • Tubocurarine
  • Valproic Acid
  • Vecuronium
  • Verapamil
  • Vigabatrin
  • Viloxazine

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Enteral Nutrition
  • Ethanol

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Bone problems (e.g., osteomalacia) or
  • Depression, history of or
  • Diabetes or
  • Lymphadenopathy (lymph node problems) or
  • Porphyria (an enzyme problem)—Use with caution. May make these conditions worse.
  • Kidney disease or
  • Liver disease—Use with caution. The effects may be increased because of slower removal from the body.

Description

Phenytoin is used to control seizures (convulsions) in the treatment of epilepsy. It is also used to prevent and treat seizures that occur during brain surgery. This medicine is an anticonvulsant that works in the brain tissue to stop seizures.

This medicine is available only with your doctor’s prescription.