Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.
Many drugs can interact with phenytoin. Not all possible interactions are listed here. TELL YOUR DOCTOR ABOUT ALL OTHER MEDICINES YOU USE, and any you start or stop using during treatment with Dilantin. This includes prescription and over-the-counter medicines, vitamins, and herbal products.
 Dilantin drug interactions (more detail)
