• Basic Info
• Top Questions
• Clinical Info
• Interactions

Drugs that can increase phenytoin levels in your blood include:

• stomach acid reducers such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), or nizatidine (Axid);

• certain sedatives (such as Librium or Valium) or antidepressants (such as Prozac);

• estrogen hormone replacement;

• chlorpromazine (Thorazine), prochlorperazine (Compazine), thioridazine (Mellaril) and other phenothiazines;

• disulfiram (Antabuse);

• methylphenidate (Ritalin, Concerta, Daytrana); and

• sulfa drugs such as Septra or Bactrim.

Drugs that can make phenytoin less effective in controlling seizures include:

• carbamazepine (Tegretol, Epitol, Carbatrol);

• sucralfate (Carafate); and

• molindone (Moban).

Other drugs that can interact with phenytoin include:

• valproic acid (Depakene) or divalproex sodium (Depakote);

• phenobarbital (Luminal, Solfoton);

• steroid medicines (prednisone and others);

• antidepressants such as amitriptyline (Elavil), clomipramine (Anafranil), imipramine (Janimine, Tofranil), paroxetine (Paxil), and others;

• antibiotics such as rifampin (Rimactane, Rifadin, Rifamate) or doxycycline (Doryx, Vibramycin, Adoxa, and others);

• digitoxin (digitalis, Lanoxin);

• furosemide (Lasix); and

• theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl).

This list is not complete and there are many other medicines that can interact with phenytoin. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor. Keep a list with you of all the medicines you use and show this list to any doctor or other healthcare provider who treats you.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have any of these serious side effects:

• swollen glands;

• fever, sore throat, and headache with a severe blistering, peeling, and red skin rash;

• confusion, hallucinations, unusual thoughts or behavior;

• slurred speech, loss of balance or coordination;

• restless muscle movements in your eyes, tongue, jaw, or neck;

• tremor (uncontrolled shaking);

• extreme thirst or hunger, urinating more than usual;

• nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);

• easy bruising or bleeding;

• swollen or tender gums; or

• changes in the shape of your face or lips.

Less serious side effects may include:

• mild skin rash or itching;

• dizziness, nervousness, sleep problems (insomnia);

• twitching;

• nausea, vomiting, constipation;

• headache; or

• joint pain.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.