Before taking phenytoin, tell your doctor or pharmacist if you are allergic to it; or to other anti-seizure medications (e.g., carbamazepine, ethotoin, phenobarbital, ethosuximide, trimethadione); or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
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. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely. Limit alcoholic beverages. 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.
During pregnancy, this medication should be used only when clearly needed. It may harm an unborn baby. However, since untreated seizures are a serious condition that can harm both a pregnant woman and her unborn baby, do not stop taking this medication unless directed by your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, immediately talk to your doctor about the benefits and risks of using this medication during pregnancy. Since birth control pills, patches, implants, and injections may not work if taken with this medication (see also Drug Interactions section), discuss reliable forms of birth control with your doctor.
Phenytoin passes into breast milk. Consult your doctor before breast-feeding.
See also How to Use section.
Some products that may interact with this drug include: azapropazone, darunavir, delavirdine, dofetilide, etravirine, nisoldipine, rilpivirine, colesevelam, molindone, pyridoxine (vitamin B6), sucralfate, sulfa drugs, telithromycin.
Other medications can affect the removal of phenytoin from your body, which may affect how phenytoin works. Examples include amiodarone, azole antifungals (such as itraconazole), cimetidine, macrolide antibiotics (such as erythromycin), estrogens, isoniazid, rifamycins (such as rifabutin), St. John’s wort, other anti-seizure medicines (such as carbamazepine, phenobarbital, valproic acid), among others.
Phenytoin can speed up the removal of other medications from your body, which may affect how they work. Examples of affected drugs include some drugs to treat cancer (such as imatinib, irinotecan), cobicistat, corticosteroids (such as prednisone), cyclosporine, felodipine, quetiapine, quinidine, suvorexant, theophylline, vitamin D, warfarin, among others.
Also 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.
This medication may decrease the effectiveness of hormonal birth control such as pills, patch, or ring. This could cause pregnancy. Discuss with your doctor or pharmacist if you should use additional reliable birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well.
This product can affect the results of certain lab tests. Make sure laboratory personnel and your doctors know you use this drug.