PRECAUTIONS: Before taking phenytoin, tell your doctor or pharmacist if you are allergic to it; or to other anti-seizure medications (e.g., ethotoin, phenobarbital, ethosuximide, trimethadione); or if you have any other allergies. Before using this medication, tell your doctor or pharmacist your medical history, especially of: alcohol use, certain blood conditions (porphyria), diabetes, liver disease, lupus, folate or vitamin B-12 deficiency (megaloblastic anemia). This drug may make you dizzy or drowsy; use caution engaging in activities requiring alertness such as driving or using machinery. Limit alcoholic beverages because they may increase the risk of side effects. Alcohol may also affect your blood levels of this drug. Tell your doctor you are using phenytoin prior to surgery or any procedure that makes you unable to take it by mouth. If you have diabetes, this drug may increase your blood sugar levels. Check your blood (or urine) glucose level frequently, as directed by your doctor. Promptly report any abnormal results as directed. Your medicine, exercise plan, or diet may need to be adjusted. Vitamin D supplements may be necessary to prevent weakening of the bones (osteomalacia). Discuss this with your doctor. This medication is not recommended for use during pregnancy due to the possible risk of birth defects and fetal harm. Consult your doctor for more details. Phenytoin passes into breast milk. Therefore, breast-feeding while using this medication is not recommended. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: See also How to Use section. This drug should not be used with the following medications because very serious interactions may occur: azapropazone, delavirdine, dofetilide, telithromycin. If you are currently using any of these medications, tell your doctor or pharmacist before starting phenytoin. Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: certain azole antifungals (e.g., fluconazole, itraconazole), "blood thinners" (e.g., warfarin), caspofungin, chloramphenicol, chlordiazepoxide, cimetidine, corticosteroids (e.g., prednisone), cyclosporine, diazepam, diazoxide, digoxin, disulfiram, doxycycline, drugs that affect heart rhythm (e.g., amiodarone, disopyramide, quinidine), drugs to treat cancer (e.g., capecitabine, irinotecan, imatinib), estrogens, felodipine, fluoxetine, folic acid, furosemide, isoniazid, levodopa, methadone, methylphenidate, metyrapone, molindone, phenylbutazone, pyrimethamine, quetiapine, quinolone antibiotics (e.g., ciprofloxacin, levofloxacin), reserpine, rifamycins (e.g., rifabutin, rifampin), salicylates, other drugs to treat seizures (e.g., carbamazepine, phenobarbital, valproic acid), St. John's wort, sucralfate, sulfa drugs, theophylline, tirilazad, tolbutamide, trimethoprim, trazodone, vitamin D. Report the use of drugs which might increase seizure risk (decrease seizure threshold) such as: phenothiazines (e.g., thioridazine) or tricyclic antidepressants (e.g., amitriptyline) among others. Consult your doctor or pharmacist for details. Phenytoin may decrease the effectiveness of birth control pills, patches, implants or injections. This can result in pregnancy. You may need to use an additional form of reliable birth control while using this medication. Consult your doctor or pharmacist for details. This product can affect the results of certain lab tests. Make sure laboratory personnel and your doctors know you use this drug. Do not start or stop any medicine without doctor or pharmacist approval.