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Phenytoin, Oral FEN-i-toyn

What are other names for this medicine?

Type of medicine: hydantoin antiseizure

Generic and brand names: phenytoin, oral; Dilantin; Dilantin-125; Phenytek; Dilantin 50mg Chewables; Dilantin Infatabs

What is this medicine used for?

This medicine is used to control seizures caused by certain types of epilepsy.

It may be used for other conditions as determined by your healthcare provider.

What should my healthcare provider know before I take this medicine?

Before taking this medicine, tell your healthcare provider if you have ever had:

  • an allergic reaction to any medicine
  • a blood disorder
  • diabetes
  • a vitamin D deficiency or any other problem that causes thinning of the bones
  • heart disease or an irregular heartbeat
  • liver or kidney disease
  • lupus
  • porphyria (nerve pain or sensitivity to sunlight)
  • problems with alcohol abuse

If you are of Asian ancestry, you may be at high risk of a serious skin reaction. You may need a blood test before you start taking the medicine. Talk with your provider about this.

Females of childbearing age: This medicine is not usually given to pregnant women because it can harm the baby. If you are pregnant, tell your healthcare provider. Do not become pregnant during treatment with this medicine. If you become pregnant, contact your healthcare provider right away. Do not breast-feed while you are receiving this medicine.

How do I use it?

Read the Medication Guide that comes in the medicine package when you start taking this medicine and each time you get a refill.

Check the label on the medicine for directions about your specific dose. Take this medicine exactly as your healthcare provider prescribes. This medicine must be taken regularly every day to control seizures. Do not stop taking this medicine without your healthcare provider's approval. You may have to gradually reduce your dosage. If you stop taking the medicine too quickly, your seizures may increase.

You may take this medicine with or without food. Taking it with meals may lessen the chance the drug will upset your stomach.

This medicine comes in long-acting capsules, chewable tablets, and liquid forms. If you have long-acting capsules, do not break, crush, or chew them. Swallow them whole. If you have the liquid form, shake the bottle well before using. Use a specially marked dosing spoon or measuring cup to measure the dose accurately. If you are taking the chewable tablet you may crush or chew the tablets or swallow them whole.

Do not take capsules that are discolored.

If you are taking tube feedings, you should hold the feedings 1 to 2 hours before and after taking this medicine. Talk with your healthcare provider about this.

What if I miss a dose?

Do not miss a dose. If you miss a dose, take it as soon as you remember unless it is almost time for the next scheduled dose. In that case, skip the missed dose and take the next one as directed. Do not take double doses. If you are not sure of what to do if you miss a dose, or if you miss more than one dose, contact your healthcare provider.

What if I overdose?

If you or anyone else has intentionally taken too much of this medicine, call 911 or go to the emergency room right away. If you pass out, have seizures, weakness or confusion, or have trouble breathing, call 911. If you think that you or anyone else may have taken too much of this medicine, call the poison control center. Do this even if there are no signs of discomfort or poisoning. The poison control center number is 800-222-1222.

Symptoms of an acute overdose may include: twitching eye movements, slurred speech, loss of balance, tremors, muscle stiffness, weakness, nausea, vomiting, lightheadedness, fainting, slow or shallow breathing.

What should I watch out for?

Antiseizure medicines may increase suicidal thoughts or actions in some people. Call your healthcare provider right away if you have new or increased thoughts of suicide.

This medicine may make you drowsy or dizzy. Do not drive or operate machinery unless you are fully alert.

Your healthcare provider will want to check your progress regularly and adjust your dosage. Keep all appointments.

If you need emergency care, surgery, or dental work, tell the healthcare provider or dentist you are taking this medicine.

Carry some form of ID stating that you have seizures and are taking an antiseizure medicine.

This medicine may increase the effects of alcohol and other drugs that slow down your nervous system. Do not drink alcohol or take other medicines unless your healthcare provider approves.

This medicine may cause swelling and irritation of your gums. Ask your healthcare provider or dentist about proper dental care.

Do not start or stop taking any other medicine without your healthcare providers advice. Other medicine may affect how this medicine works.

Contraceptives (birth control medicines), may not work properly while taking this medicine. Talk to your healthcare provider about other forms of birth control.

Diabetics: This medicine may affect your blood sugar level and change the amount of insulin or other diabetes medicines you may need. Talk to your healthcare provider about this.

What are the possible side effects?

Along with its needed effects, your medicine may cause some unwanted side effects. Some side effects may be very serious. Some side effects may go away as your body adjusts to the medicine. Tell your healthcare provider if you have any side effects that continue or get worse.

Life-threatening (Report these to your healthcare provider right away). If you cannot reach your healthcare provider right away, get emergency medical care or call 911 for help): Allergic reaction (hives; itching; rash; trouble breathing; chest pain or tightness in your chest; swelling of your lips, tongue, and throat).

Serious (report these to your healthcare provider right away): Nausea or vomiting; confusion; mood changes; depression; thoughts of suicide; vision problems; lightheadedness; uncontrollable eye or muscle twitches; slurred speech; increased seizures; pounding heartbeat; skin rash; chest pain; strange feelings in your hands or feet; trembling; trouble breathing; severe dizziness; dark urine; mouth sores; sore throat; fever; unusual bruising or bleeding; yellowish skin or eyes; swollen glands.

Other: Slight drowsiness or dizziness, trouble sleeping, loss of appetite, clumsiness, mild nausea or vomiting, constipation, diarrhea.

What products might interact with this medicine?

When you take this medicine with other medicines, it can change the way this or any of the other medicines work. Nonprescription medicines, vitamins, natural remedies, and certain foods may also interact. Using these products together might cause harmful side effects. Talk to your healthcare provider if you are taking:

  • acetaminophen (Tylenol)
  • alcohol
  • antidepressants such as amitriptyline, doxepin, fluoxetine (Prozac), fluvoxamine (Luvox), imipramine (Tofranil), nortriptyline (Pamelor), sertraline (Zoloft), and trazodone
  • antihistamines such as chlorpheniramine (Chlor-Trimeton) and diphenhydramine (Benadryl)
  • amphetamines such as dextroamphetamine (Dexedrine) and methamphetamine (Desoxyn)
  • antibiotics such as chloramphenicol, ciprofloxacin (Cipro), clarithromycin (Biaxin), doxycycline (Adoxa, Doryx, Monodox, Vibramycin), erythromycin (Ery-Tabs, E.E.S.), isoniazid (INH), rifampin (Rifadin), and sulfamethoxazole/trimethoprim (Bactrim, Septra)
  • antifungals such as fluconazole (Diflucan), itraconazole (Sporanox), ketoconazole (Nizoral), miconazole (Monistat), and voriconazole (Vfend)
  • anti-HIV medicines such as delavirdine (Rescriptor), indinavir (Crixivan), ritonavir (Norvir), and saquinavir (Invirase)
  • antipsychotic medicines such as chlorpromazine, clozapine (Clozaril), fluphenazine, perphenazine, thioridazine, and trifluoperazine
  • cancer medicines such as gefitinib (Iressa) and imatinib (Gleevec)
  • calcium supplements
  • cholesterol-lowering medicines such as atorvastatin (Lipitor), colesevelam (WelChol), fluvastatin (Lescol), and simvastatin (Zocor)
  • diuretics such as bumetanide, furosemide (Lasix), and torsemide (Demadex)
  • disulfiram (Antabuse)
  • hormonal birth control such as pills, implants, shots, patches, or vaginal rings; or conjugated estrogen (Premarin, Premphase, Prempro), estradiol (Estrace), esterified estrogen (Estratab, Menest), estropipate (Ogen), and estrogen patches (Estraderm, Vivelle, Climara)
  • fluorouracil (Carac, Efudex, Fluoroplex, Adrucil)
  • immunosuppressant medicines such as cyclosporine (Neoral, Gengraf, Sandimmune), sirolimus (Rapamune), and tacrolimus (Prograf)
  • lithium (Lithobid)
  • medicines to treat heart problems such as amiodarone (Cordarone, Pacerone), amlodipine (Norvasc), diltiazem (Cardizem, Cartia XT; Dilacor XR, Tiazac), felodipine, nifedipine (Procardia), quinidine, and verapamil (Calan, Isoptin, Covera, Verelan)
  • oral medicines for diabetes such as acarbose (Precose), glipizide (Glucotrol), glyburide (DiaBeta, Glynase), metformin (Glucophage), nateglinide (Starlix), pioglitazone (Actos), repaglinide (Prandin), and rosiglitazone (Avandia)
  • muscle relaxants such as baclofen (Lioresal), carisoprodol (Soma), cyclobenzaprine (Flexeril), dantrolene (Dantrium), methocarbamol (Robaxin), and tizanidine (Zanaflex)
  • narcotic analgesics (painkillers) such as codeine, fentanyl (Duragesic, Actiq), hydrocodone (Vicodin, Lortab), hydromorphone (Dilaudid), meperidine (Demerol), methadone (Dolophine), morphine (Kadian, MS Contin), oxycodone (OxyContin, Roxicodone), oxycodone/acetaminophen (Percocet, Tylox), and pentazocine (Talwin)
  • natural remedies such as evening primrose, gotu kola, kava, St. John's wort, and valerian
  • other antiseizure medicines such as carbamazepine (Tegretol), ethosuximide (Zarontin), methsuximide (Celontin Kapseals), tiagabine (Gabitril), and valproic acid (Depakote, Depakene)
  • sedatives such as butabarbital (Butisol), pentobarbital, phenobarbital, zaleplon (Sonata), and zolpidem (Ambien)
  • steroid medicines such as betamethasone (Celestone), dexamethasone, methylprednisolone (Medrol), hydrocortisone (Cortef), and prednisone
  • tranquilizers such as chlordiazepoxide (Librium), clonazepam (Klonopin), diazepam (Valium), estazolam (ProSom), flurazepam, and temazepam (Restoril)
  • stimulant medicine such as dexmethylphenidate (Focalin, Focalin XR) and methylphenidate (Concerta, Metadate CD, Metadate ER, Ritalin)
  • stomach medicines such as cimetidine (Tagamet), omeprazole (Prilosec), ranitidine (Zantac), sucralfate (Carafate), and antacids
  • theophylline
  • thyroid medicines such as levothyroxine (Synthroid), liotrix (Euthroid, Thyrolar), and liothyronine (Cytomel)
  • warfarin (Coumadin)

If you are not sure if your medicines might interact, ask your pharmacist or healthcare provider. Keep a list of all your medicines with you. List all the prescription medicines, nonprescription medicines, supplements, natural remedies, and vitamins that you take. Be sure that you tell all healthcare providers who treat you about all the products you are taking.

How should I store this medicine?

Store this medicine at room temperature. Do not refrigerate. Do not let it freeze. Keep the container tightly closed. Protect it from heat, high humidity, and bright light.


This advisory includes selected information only and may not include all side effects of this medicine or interactions with other medicines. Ask your healthcare provider or pharmacist for more information or if you have any questions.

Ask your pharmacist for the best way to dispose of outdated medicine or medicine you have not used. Do not throw medicine in the trash.

Keep all medicines out of the reach of children.

Do not share medicines with other people.


Developed by RelayHealth.
Medication Advisor 2012.1 published by RelayHealth.
Last modified: 2011-12-15
Last reviewed: 2010-03-09
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2012 RelayHealth and/or its affiliates. All rights reserved.
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