See also How to Use section.
Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.
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.