Any time a doctor suggests a new prescription, be sure to talk about what other medicines, supplements, herbs, and vitamins are already being taken. Sometimes one kind of medicine changes the way another kind of medicine works in the body. If two kinds of medicine affect each other, the doctor may prescribe something else or change the amount to be taken.

This is true not only for prescription medicines, but also for medicines you just pick up off the shelf at the store. For instance, aspirin (ASA) is generally safe to take with Dilantin at the usual doses, but if more than 1500 mg per day is taken, the level of Dilantin in the blood will be increased.

Interactions like this can also occur with herbal products, vitamins, a few kinds of food (like grapefruit juice), and even cigarettes!

Some substances that are safe to use in small amounts with Dilantin can be a problem if larger amounts are used. For instance, one or two drinks of alcohol will seldom affect the level of Dilantin in any important way, but if a person who does not often consume alcohol has several drinks within a short time, the level of Dilantin in the blood may be significantly increased, causing problems with side effects. On the other hand, a person who continually abuses alcohol may have lower levels of Dilantin and be more likely to have seizures.

Medicines that contain calcium, including some antacids, can prevent the body from absorbing Dilantin. They can be used, but not near the time of a dose of Dilantin. They should not be taken for a couple of hours after the Dilantin. This limitation does not apply to foods such as dairy products, which also contain calcium.

How does Dilantin affect other medicines?
Dilantin makes birth control pills less effective, so the chances of becoming pregnant are greater. Women who use pills for birth control should talk to the doctor who prescribed them right away if they start taking Dilantin. The same is true for some other forms of birth control such as Depo-Provera or implants. Dilantin does not affect barrier types of birth control, like condoms, IUDs, and diaphragms.

Dilantin also affects the way the body handles many other medicines. For instance, it reduces the levels of other seizure medicines:

• carbamazepine (Tegretol, Carbatrol)
• felbamate (Felbatol)
• lamotrigine (Lamictal)
• tiagabine (Gabitril)
• topiramate (Topamax)
• valproate (Depakote)
• zonisamide (Zonegran)

It also lowers the levels of many other types of medicine, reducing their effectiveness. Check with the doctor or pharmacist.

How do other medicines affect Dilantin?
Some other medicines do affect the level of Dilantin in the body, either raising it or lowering it. Many of these interactions vary from person to person, however, or may even vary from time to time for the same person. Make sure that your doctor is aware of all the medicines being used.