The only people who definitely should not take Phenytek (extended-release phenytoin) are those who are allergic to phenytoin or to other medicines in the same family, called hydantoins.

People who have liver disease or who must take certain other types of medicines may need to be extra cautious about taking Phenytek, however. Interactions occur with many other medicines. It is very important to make sure the doctor knows about any liver disease and about every kind of medicine that is being taken. Most people can take both Phenytek and other medicines successfully by working with the doctor to determine the correct amount to take.