Phenytoin: What is it? How does it work? Warnings, Dosage, Toxicity, Side Effects and Interactions

It is an anticonvulsant that is used to treat most types of seizure disorders and epileptic states, with the exception of seizure attacks.

This medicine is also used to prevent seizures after brain surgery.

Generic name: Phenytoin sodium capsules – oral.

Brand: Dilantin is the phenytoin drug brand.

How does it work?

This medicine belongs to a class of medications known as anticonvulsants. It works by decreasing and stabilizing the abnormal electrical activity in the brain, which prevents seizures from occurring.

Dilantin was originally approved for use in seizures by the Food and Drug Administration (FDA). Phenytoin is a commonly used medication.

Phenytoin is also prescribed as a treatment for severe burning pains or pangs in the face, a nerve pain called trigeminal neuralgia . This is because you can modify some types of pain.

If you have been given phenytoin for this reason, tell your doctor if you have questions about your treatment.


Phenytoin does not treat all types of seizures, and your doctor will determine if it is the right medication for you.

You should not take Dilantin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin, ethotoin (Peganone) fosphenytoin, (Cerebyx) or mephenytoin (Mesantoin).

This medicine can change your mental health in unexpected ways. Some people who take Dilantin become suicidal. You or your caregiver should tell your doctor right away if you have any of the following symptoms:

  • Thinking or talking about suicide.
  • Agitation or restlessness
  • Irritability.
  • Depression .
  • Anxiety .
  • Panic attacks .
  • Violent behavior.
  • Withdraw from friends and family.
  • Mania (an abnormally excited mood).

Dilantin can increase your blood sugar levels. You should talk with your doctor about the symptoms of high blood sugar levels and what to do if you experience them.

This medicine may also increase your risk of developing osteomalacia (weakening and softening of the bones) and Hodgkin’s lymphoma (cancer that starts in the lymph nodes).

You may also experience swollen lymph nodes while taking Dilantin. You should discuss these risks with your doctor.

Dilantin can also cause swelling and bleeding of the gums and may increase the risk of gum damage. You should talk about the proper ways to take care of your teeth and gums while taking this medication.

Before taking this medication, you must inform your doctor if you have or have ever had:

  • Diabetes.
  • Lupus.
  • A deficiency of folate or vitamin B-12.
  • Porphyria (a rare hereditary condition that affects the functioning of blood hemoglobin).
  • Kidney disease
  • Liver disease

You should also tell your doctor if you are an alcoholic or have ever consumed large amounts of alcohol.

In case of an emergency, you may want to use a medical alert label or identification card that says you take Dilantin, so healthcare providers know it.

Tell your doctor that you are taking Dilantin before having any type of surgery, including dental procedures.

Several clinical and anecdotal reports have linked anticonvulsants such as Dilantin with Stevens-Johnson syndrome , a rare but serious disorder of the skin and mucous membranes.

Symptoms of Stevens-Johnson syndrome include hives , swelling of the face and tongue, rash, irritation and scaling of the skin and blisters.

Toxicity of Phenytoin

Severe toxicity can occur in people who take the drug Phenytoin. This is more likely to occur when doses are increased or other medications are started or stopped.

Signs and symptoms of phenytoin toxicity generally correspond to the serum level and progress from occasional mild nystagmus to 10-20 mcg / ml (therapeutic range) to coma and seizures at levels greater than 50 mcg / ml.

Common symptoms of Dilantin toxicity include dizziness, drowsiness, coordination problems, rapid eye movements and extreme fatigue.


Dilantin is a category D drug in pregnancy, which means it can harm an unborn baby. However, having a seizure during pregnancy could also harm the baby and his mother.

You should not start taking Dilantin if you are pregnant unless your doctor tells you to. If you become pregnant while taking Dilantin, do not stop taking the medication without first consulting your doctor.

This medicine can also make some contraceptive methods less effective. You should talk with your doctor about the use of non-hormonal contraceptive options to prevent pregnancy while taking Dilantin.

Dilantin can pass into breast milk and can harm a nursing baby. You should not breast-feed while taking this medication.

Side effects of phenytoin

The unwanted effects often improve as your body adjusts to the new medication, but talk to your doctor or pharmacist if any of the following continues or becomes bothersome.

Common side effects

  • Uncontrollable eye movements or abnormal body movements.
  • Difficulty falling asleep or falling asleep
  • Confusion or slow thinking.
  • Loss of coordination.
  • Dizziness.
  • Headache.
  • Nausea, vomiting or constipation .
  • Lip extension
  • Overgrowth of the gums.
  • Unwanted hair growth.
  • Facial changes
  • Pain or curvature of the penis.
  • Skin rash.

Serious side effects

You should call your doctor immediately if you experience any of the following serious side effects:

  • Fever.
  • Blisters or rash
  • Swollen glands
  • Pain in the joints.
  • Yellowing of the eyes or skin.
  • Pain in the upper right part of the stomach.
  • Excessive fatigue
  • Symptoms similar to the flu.
  • Sore throat.
  • Severe skin rash
  • Ulcers in the mouth.
  • Hematomas or unexplained hemorrhages.


There are many drugs that can interact with Dilantin. Before you start, tell your doctor about all the prescription, non-prescription, illegal, recreational, herbal, nutritional or dietary medications you are taking, especially:

  • Antacids that contain calcium (Maalox, Mylanta, Tums, others).
  • Amiodarone (Cordarone, Pacerone).
  • Anticoagulants such as  warfarin (Coumadin).
  • Antidepresivos como amitriptilina (Elavil), amoxapina (Asendin), clomipramina (Anafranil), desipramina (Norpramin), doxepina (Sinequan), imipramina (Tofranil), maprotilina, nortriptilina (Pamelor), protriptilina (Vivactil) y trimipramina (Surmontil).
  • Chloramphenicol .
  • Clordiazepóxido (Librium).
  • Diazepam (Valium).
  • Digoxina (Lanoxin).
  • Disulfiram (Antabuse).
  • Doxycycline (Doryx, Monodox, Vibramycin, others).
  • Fluoxetina (Prozac, Sarafem, en Symbyax).
  • Furosemide (Lasix).
  • Antagonistas H2 como cimetidina (Tagamet), famotidina (Pepcid), nizatidina (Axid) y ranitidina (Zantac).
  • Hormonal contraceptives such as birth control pills, patches, rings or injections.
  • Hormone replacement therapy (HRT).
  • Isoniacida (in Rifamate, in Rifater).

Drugs for mental illness and nausea

Other medications for seizures
  • Carbamazepine (Carbatrol, Equetro, Tegretol), ethosuximide (Zarontin), methsuximide (Celontin) and phenobarbital.
  • Acido valproico (Depacon, Depakene, Stavzor).
  • Methylphenidate (Daytrana, Concerta, Metadate, Ritalin).
  • Molindone (Moban).
  • Oral steroids such as dexamethasone (Decadron, Dexone), methylprednisolone (Medrol), prednisolone and prednisone (Deltasone).
  • Paroxetine (Paxil, Pexeva).
  • Quinidina.
  • Reserpina (Serpalan).
  • Rifampin (Rimactane, a Rifamate, a Rifater).
  • Analgesics with salicylate such as aspirin, magnesium trisalicylate and choline, choline salicylate (Arthropan).
  • Diflunisal (Dolobid), magnesium salicylate (Doan’s, others) and salsalate (Argesic, Disalcid, Salgesic).
  • Sucralfato (Carafate).
  • Sulfa antibiotics.
  • Teofilina (Theo-Dur).
  • Ticlopidina (Ticlid).
  • Tolbutamida.
  • Trazodone.
  • Vitamina D.

Dilantin and alcohol consumption

Alcohol can interfere with Dilantin. You should talk to your doctor about the amount of alcohol and types that are safe to consume while taking this medication.

Dilantin and other interactions

Dilantin may cause dizziness and coordination problems. Avoid performing jobs that require total attention such as driving cars and operating cars while not knowing how you will react to Phenytoin.

Phenytoin dosage

Dilantin comes as a chewable tablet, a prolonged-release tablet and a liquid to take orally.

The recommended dose for adults is typically 100 milligrams (mg), two to four times per day. The dose can be increased as required by each patient.

Liquid and chewable tablets are usually taken two or three times a day; and in some cases up to four times if they are capsules.

Swallow the extended-release capsules whole. Do not crush, chew or split. Also, do not take the capsules if they are discolored.

You can chew or swallow chewable tablets.

Shake the liquid form of this medicine well before each dose.

Your doctor will probably start with a low dose of Dilantin and gradually increase it.

Try to take this medicine at about the same time every day. Follow the instructions carefully on the label of your recipe. Do not take more or less of this medication than prescribed.


It must not exceed the indicated doses of Phenytoin.

If you suspect an overdose, you should immediately contact a poison control center or the emergency room.

If there is a missed dose

If you miss a dose of the medication, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and continue your regular dosing schedule. Do not double the doses to make up for a loss.

How to store Phenytoin

  • Keep all medications out of the reach and sight of children.
  • Store in a cool, dry place, away from heat and direct light.