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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.

Where can I get more information?

• Your pharmacist has additional information about phenytoin written for health professionals that you may read.
• Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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Although we have made considerable efforts to ensure that the information provided here is accurate, up-to-date, and complete, MedLibrary.org makes no guarantee to that effect. Drug information contained herein may be time sensitive. This medication information does not endorse drugs, diagnose patients or recommend any specific pharmacotherapy. This is an educational resource only -- intended to supplement but not to replace the expertise, skill, knowledge and judgment of medically qualified healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, please check with your doctor, nurse or local pharmacist. MedLibrary.org does not assume any responsibility for any aspect of healthcare administered with the aid of information provided here.

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Version: 5.01. Revision date: 5/13/03.